Cloud Condensation Nuclei Particle Counter (CCN) Instrument Handbook

DOE Office of Scientific and Technical Information (OSTI.GOV)

Uin, Janek

2016-04-01

The Cloud Condensation Nuclei Counter—CCN (Figure 1) is a U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Climate Research Facility instrument for measuring the concentration of aerosol particles that can act as cloud condensation nuclei [1, 2]. The CCN draws the sample aerosol through a column with thermodynamically unstable supersaturated water vapor that can condense onto aerosol particles. Particles that are activated, i.e., grown larger in this process, are counted (and sized) by an Optical Particle Counter (OPC). Thus, activated ambient aerosol particle number concentration as a function of supersaturation is measured. Models CCN-100 and CCN-200 differ only inmore » the number of humidifier columns and related subsystems: CCN-100 has one column and CCN-200 has two columns along with dual flow systems and electronics.« less

Online single particle analysis of ice particle residuals from mountain-top mixed-phase clouds using laboratory derived particle type assignment

NASA Astrophysics Data System (ADS)

Schmidt, Susan; Schneider, Johannes; Klimach, Thomas; Mertes, Stephan; Schenk, Ludwig Paul; Kupiszewski, Piotr; Curtius, Joachim; Borrmann, Stephan

2017-01-01

In situ single particle analysis of ice particle residuals (IPRs) and out-of-cloud aerosol particles was conducted by means of laser ablation mass spectrometry during the intensive INUIT-JFJ/CLACE campaign at the high alpine research station Jungfraujoch (3580 m a.s.l.) in January-February 2013. During the 4-week campaign more than 70 000 out-of-cloud aerosol particles and 595 IPRs were analyzed covering a particle size diameter range from 100 nm to 3 µm. The IPRs were sampled during 273 h while the station was covered by mixed-phase clouds at ambient temperatures between -27 and -6 °C. The identification of particle types is based on laboratory studies of different types of biological, mineral and anthropogenic aerosol particles. The outcome of these laboratory studies was characteristic marker peaks for each investigated particle type. These marker peaks were applied to the field data. In the sampled IPRs we identified a larger number fraction of primary aerosol particles, like soil dust (13 ± 5 %) and minerals (11 ± 5 %), in comparison to out-of-cloud aerosol particles (2.4 ± 0.4 and 0.4 ± 0.1 %, respectively). Additionally, anthropogenic aerosol particles, such as particles from industrial emissions and lead-containing particles, were found to be more abundant in the IPRs than in the out-of-cloud aerosol. In the out-of-cloud aerosol we identified a large fraction of aged particles (31 ± 5 %), including organic material and secondary inorganics, whereas this particle type was much less abundant (2.7 ± 1.3 %) in the IPRs. In a selected subset of the data where a direct comparison between out-of-cloud aerosol particles and IPRs in air masses with similar origin was possible, a pronounced enhancement of biological particles was found in the IPRs.

Warming ancient Mars with water clouds

NASA Astrophysics Data System (ADS)

Hartwick, V.; Toon, B.

2017-12-01

High clouds in the present day Mars atmosphere nucleate on interplanetary dust particles (IDPs) that burn up on entry into the Mars atmosphere. Clouds form when superstaturated water vapor condenses on suspended aerosols. Radiatively active water ice clouds may play a crucial role in warming the early Mars climate. Urata and Toon (2011) simulate a stable warm paleo-climate for Mars if clouds form high in the atmosphere and if particles are sufficiently large (r > 10 μm). The annual fluence of micrometeoroids at Mars was larger early on in the evolution of our solar system. Additionally, the water vapor budget throughout the middle and high atmosphere was likely heightened . Both factors should contribute to enhanced nucleation and growth of water ice cloud particles at high altitudes. Here, we use the MarsCAM-CARMA general circulation model (GCM) to examine the radiative impact of high altitude water ice clouds on the early Mars climate and as a possible solution to the faint young sun problem for Mars.

An experimental study of the role of particle diffusive convection on the residence time of volcanic ash clouds

NASA Astrophysics Data System (ADS)

Deal, E.; Carazzo, G.; Jellinek, M.

2013-12-01

The longevity of volcanic ash clouds generated by explosive volcanic plumes is difficult to predict. Diffusive convective instabilities leading to the production of internal layering are known to affect the stability and longevity of these clouds, but the detailed mechanisms controlling particle dynamics and sedimentation are poorly understood. We present results from a series of analog experiments reproducing diffusive convection in a 2D (Hele-Shaw) geometry, which allow us to constrain conditions for layer formation, sedimentation regime and cloud residence time as a function of only the source conditions. We inject a turbulent particle-laden jet sideways into a tank containing a basal layer of salt water and an upper layer of fresh water, which ultimately spreads as a gravity current. After the injection is stopped, particles in suspension settle through the cloud to form particle boundary layers (PBL) at the cloud base. We vary the initial particle concentration of the plume and the injection velocity over a wide range of conditions to identify and characterize distinct regimes of sedimentation. Our experiments show that convective instabilities driven as a result of differing diffusivities of salt and particles lead to periodic layering over a wide range of conditions expected in nature. The flux of particles from layered clouds and the thicknesses of the layers are understood using classical theory for double diffusive convection adjusted for the hydrodynamic diffusion of particles. Although diffusive convection increases sedimentation rates for the smallest particles (<30 μm) its overall effect is to extend the cloud residence time to several hours by maintaining larger particles in suspension within the layers, which is several orders of magnitude longer than expected when considering individual settling rates.

The Cloud Ice Mountain Experiment (CIME) 1998: experiment overview and modelling of the microphysical processes during the seeding by isentropic gas expansion

NASA Astrophysics Data System (ADS)

Wobrock, Wolfram; Flossmann, Andrea I.; Monier, Marie; Pichon, Jean-Marc; Cortez, Laurent; Fournol, Jean-François; Schwarzenböck, Alfons; Mertes, Stephan; Heintzenberg, Jost; Laj, Paolo; Orsi, Giordano; Ricci, Loretta; Fuzzi, Sandro; Brink, Harry Ten; Jongejan, Piet; Otjes, René

The second field campaign of the Cloud Ice Mountain Experiment (CIME) project took place in February 1998 on the mountain Puy de Dôme in the centre of France. The content of residual aerosol particles, of H 2O 2 and NH 3 in cloud droplets was evaluated by evaporating the drops larger than 5 μm in a Counterflow Virtual Impactor (CVI) and by measuring the residual particle concentration and the released gas content. The same trace species were studied behind a round jet impactor for the complementary interstitial aerosol particles smaller than 5 μm diameter. In a second step of experiments, the ambient supercooled cloud was converted to a mixed phase cloud by seeding the cloud with ice particles by the gas release from pressurised gas bottles. A comparison between the physical and chemical characteristics of liquid drops and ice particles allows a study of the fate of the trace constituents during the presence of ice crystals in the cloud. In the present paper, an overview is given of the CIME 98 experiment and the instrumentation deployed. The meteorological situation during the experiment was analysed with the help of a cloud scale model. The microphysics processes and the behaviour of the scavenged aerosol particles before and during seeding are analysed with the detailed microphysical model ExMix. The simulation results agreed well with the observations and confirmed the assumption that the Bergeron-Findeisen process was dominating during seeding and was influencing the partitioning of aerosol particles between drops and ice crystals. The results of the CIME 98 experiment give an insight on microphysical changes, redistribution of aerosol particles and cloud chemistry during the Bergeron-Findeisen process when acting also in natural clouds.

Aerosol-cloud feedbacks in a turbulent environment: Laboratory measurements representative of conditions in boundary layer clouds

NASA Astrophysics Data System (ADS)

Cantrell, W. H.; Chandrakar, K. K.; Karki, S.; Kinney, G.; Shaw, R.

2017-12-01

Many of the climate impacts of boundary layer clouds are modulated by aerosol particles. As two examples, their interactions with incoming solar and upwelling terrestrial radiation and their propensity for precipitation are both governed by the population of aerosol particles upon which the cloud droplets formed. In turn, clouds are the primary removal mechanism for aerosol particles smaller than a few micrometers and larger than a few nanometers. Aspects of these interconnected phenomena are known in exquisite detail (e.g. Köhler theory), but other parts have not been as amenable to study in the laboratory (e.g. scavenging of aerosol particles by cloud droplets). As a complicating factor, boundary layer clouds are ubiquitously turbulent, which introduces fluctuations in the water vapor concentration and temperature, which govern the saturation ratio which mediates aerosol-cloud interactions. We have performed laboratory measurements of aerosol-cloud coupling and feedbacks, using Michigan Tech's Pi Chamber (Chang et al., 2016). In conditions representative of boundary layer clouds, our data suggest that the lifetime of most interstitial particles in the accumulation mode is governed by cloud activation - particles are removed from the Pi Chamber when they activate and settle out of the chamber as cloud droplets. As cloud droplets are removed, these interstitial particles activate until the initially polluted cloud cleans itself and all particulates are removed from the chamber. At that point, the cloud collapses. Our data also indicate that smaller particles, Dp < ˜ 20 nm are not activated, but are instead removed through diffusion, enhanced by the fact that droplets are moving relative to the suspended aerosol. I will discuss results from both warm (i.e. liquid water only) and mixed phase clouds, showing that cloud and aerosol properties are coupled through fluctuations in the supersaturation, and that threshold behaviors can be defined through the use of the Dämkohler number, the ratio of the characteristic turbulence timescale to the cloud's microphysical response time. Chang, K., et al., 2016. A laboratory facility to study gas-aerosol-cloud interactions in a turbulent environment: The Π Chamber. Bull. Amer. Meteor. Soc., doi:10.1175/BAMS-D-15-00203.1

Simulations of the Vertical Redistribution of HNO3 by NAT or NAD PSCs: The Sensitivity to the Number of Cloud Particles Formed and the Cloud Lifetime

NASA Technical Reports Server (NTRS)

Jensen, Eric J.; Tabazadeh, Azadeh; Drdla, Katja; Toon, Owen B.; Gore, Warren J. (Technical Monitor)

2000-01-01

Recent satellite and in situ measurements have indicated that limited denitrification can occur in the Arctic stratosphere. In situ measurements from the SOLVE campaign indicate polar stratospheric clouds (PSCs) composed of small numbers (about 3 x 10^ -4 cm^-3) of 10-20 micron particles (probably NAT or NAD). These observations raise the issue of whether low number density NAT PSCs can substantially denitrify the air with reasonable cloud lifetimes. In this study, we use a one dimensional cloud model to investigate the verticle redistribution of HNO3 by NAT/NAD PSCs. The cloud formation is driven by a temperature oscillation which drops the temperature below the NAT/NAD formation threshold (about 195 K) for a few days. We assume that a small fraction of the available aerosols act as NAT nuclei when the saturation ratio of HNO3 over NAT(NAD) exceeds 10(l.5). The result is a cloud between about 16 and 20 km in the model, with NAT/NAD particle effective radii as large as about 10 microns (in agreement with the SOLVE data). We find that for typical cloud lifetimes of 2-3 days or less, the net depletion of HNO3 is no more than 1-2 ppbv, regardless of the NAT or NAD particle number density. Repeated passes of the air column through the cold pool build up the denitrification to 3-4 ppbv, and the cloud altitude steadily decreases due to the downward transport of nitric acid. Increasing the cloud lifetime results in considerably more effective denitrification, even with very low cloud particle number densities. As expected, the degree of denitrification by NAT clouds is much larger than that by NAD Clouds. Significant denitrification by NAD Clouds is only possible if the cloud lifetime is several days or more. The clouds also cause a local maximum HNO3 mixing ratio at cloud base where the cloud particles sublimate.

Airborne observations of the microphysical structure of two contrasting cirrus clouds

NASA Astrophysics Data System (ADS)

O'Shea, S. J.; Choularton, T. W.; Lloyd, G.; Crosier, J.; Bower, K. N.; Gallagher, M.; Abel, S. J.; Cotton, R. J.; Brown, P. R. A.; Fugal, J. P.; Schlenczek, O.; Borrmann, S.; Pickering, J. C.

2016-11-01

We present detailed airborne in situ measurements of cloud microphysics in two midlatitude cirrus clouds, collected as part of the Cirrus Coupled Cloud-Radiation Experiment. A new habit recognition algorithm for sorting cloud particle images using a neural network is introduced. Both flights observed clouds that were related to frontal systems, but one was actively developing while the other dissipated as it was sampled. The two clouds showed distinct differences in particle number, habit, and size. However, a number of common features were observed in the 2-D stereo data set, including a distinct bimodal size distribution within the higher-temperature regions of the clouds. This may result from a combination of local heterogeneous nucleation and large particles sedimenting from aloft. Both clouds had small ice crystals (<100 µm) present at all levels However, this small ice mode is not present in observations from a holographic probe. This raises the possibility that the small ice observed by optical array probes may at least be in part an instrument artifact due to the counting of out-of-focus large particles as small ice. The concentrations of ice crystals were a factor 10 higher in the actively growing cloud with the stronger updrafts, with a mean concentration of 261 L-1 compared to 29 L-1 in the decaying case. Particles larger than 700 µm were largely absent from the decaying cirrus case. A comparison with ice-nucleating particle parameterizations suggests that for the developing case the ice concentrations at the lowest temperatures are best explained by homogenous nucleation.

Cloud residues and interstitial aerosols from non-precipitating clouds over an industrial and urban area in northern China

NASA Astrophysics Data System (ADS)

Li, Weijun; Li, Peiren; Sun, Guode; Zhou, Shengzhen; Yuan, Qi; Wang, Wenxing

2011-05-01

Most studies of aerosol-cloud interactions have been conducted in remote locations; few have investigated the characterization of cloud condensation nuclei (CCN) over highly polluted urban and industrial areas. The present work, based on samples collected at Mt. Tai, a site in northern China affected by nearby urban and industrial air pollutant emissions, illuminates CCN properties in a polluted atmosphere. High-resolution transmission electron microscopy (TEM) was used to obtain the size, composition, and mixing state of individual cloud residues and interstitial aerosols. Most of the cloud residues displayed distinct rims which were found to consist of soluble organic matter (OM). Nearly all (91.7%) cloud residues were attributed to sulfate-related salts (the remainder was mostly coarse crustal dust particles with nitrate coatings). Half the salt particles were internally mixed with two or more refractory particles (e.g., soot, fly ash, crustal dust, CaSO 4, and OM). A comparison between cloud residues and interstitial particles shows that the former contained more salts and were of larger particle size than the latter. In addition, a somewhat high number scavenging ratio of 0.54 was observed during cloud formation. Therefore, the mixtures of salts with OMs account for most of the cloud-nucleating ability of the entire aerosol population in the polluted air of northern China. We advocate that both size and composition - the two influential, controlling factors for aerosol activation - should be built into all regional climate models of China.

Formation of highly porous aerosol particles by atmospheric freeze-drying in ice clouds

PubMed Central

Adler, Gabriela; Koop, Thomas; Haspel, Carynelisa; Taraniuk, Ilya; Moise, Tamar; Koren, Ilan; Heiblum, Reuven H.; Rudich, Yinon

2013-01-01

The cycling of atmospheric aerosols through clouds can change their chemical and physical properties and thus modify how aerosols affect cloud microphysics and, subsequently, precipitation and climate. Current knowledge about aerosol processing by clouds is rather limited to chemical reactions within water droplets in warm low-altitude clouds. However, in cold high-altitude cirrus clouds and anvils of high convective clouds in the tropics and midlatitudes, humidified aerosols freeze to form ice, which upon exposure to subsaturation conditions with respect to ice can sublimate, leaving behind residual modified aerosols. This freeze-drying process can occur in various types of clouds. Here we simulate an atmospheric freeze-drying cycle of aerosols in laboratory experiments using proxies for atmospheric aerosols. We find that aerosols that contain organic material that undergo such a process can form highly porous aerosol particles with a larger diameter and a lower density than the initial homogeneous aerosol. We attribute this morphology change to phase separation upon freezing followed by a glass transition of the organic material that can preserve a porous structure after ice sublimation. A porous structure may explain the previously observed enhancement in ice nucleation efficiency of glassy organic particles. We find that highly porous aerosol particles scatter solar light less efficiently than nonporous aerosol particles. Using a combination of satellite and radiosonde data, we show that highly porous aerosol formation can readily occur in highly convective clouds, which are widespread in the tropics and midlatitudes. These observations may have implications for subsequent cloud formation cycles and aerosol albedo near cloud edges. PMID:24297908

Formation of highly porous aerosol particles by atmospheric freeze-drying in ice clouds.

PubMed

Adler, Gabriela; Koop, Thomas; Haspel, Carynelisa; Taraniuk, Ilya; Moise, Tamar; Koren, Ilan; Heiblum, Reuven H; Rudich, Yinon

2013-12-17

The cycling of atmospheric aerosols through clouds can change their chemical and physical properties and thus modify how aerosols affect cloud microphysics and, subsequently, precipitation and climate. Current knowledge about aerosol processing by clouds is rather limited to chemical reactions within water droplets in warm low-altitude clouds. However, in cold high-altitude cirrus clouds and anvils of high convective clouds in the tropics and midlatitudes, humidified aerosols freeze to form ice, which upon exposure to subsaturation conditions with respect to ice can sublimate, leaving behind residual modified aerosols. This freeze-drying process can occur in various types of clouds. Here we simulate an atmospheric freeze-drying cycle of aerosols in laboratory experiments using proxies for atmospheric aerosols. We find that aerosols that contain organic material that undergo such a process can form highly porous aerosol particles with a larger diameter and a lower density than the initial homogeneous aerosol. We attribute this morphology change to phase separation upon freezing followed by a glass transition of the organic material that can preserve a porous structure after ice sublimation. A porous structure may explain the previously observed enhancement in ice nucleation efficiency of glassy organic particles. We find that highly porous aerosol particles scatter solar light less efficiently than nonporous aerosol particles. Using a combination of satellite and radiosonde data, we show that highly porous aerosol formation can readily occur in highly convective clouds, which are widespread in the tropics and midlatitudes. These observations may have implications for subsequent cloud formation cycles and aerosol albedo near cloud edges.

Light scattering by nonspherical particles: Remote sensing and climatic implications

NASA Astrophysics Data System (ADS)

Liou, K. N.; Takano, Y.

Calculations of the scattering and adsorption properties of ice crystals and aerosols, which are usually nonspherical, require specific methodologies. There is no unique theoretical solution for the scattering by nonspherical particles. Practically, all the numerical solutions for the scattering of nonspherical particles, including the exact wave equation approach, integral equation method, and discrete-dipole approximation, are applicable only to size parameters less than about 20. Thus, these methods are useful for the study of radiation problems involving nonspherical aerosols and small ice crystals in the thermal infrared wavelengths. The geometric optics approximation has been used to evaluate the scattering, absorption and polarization properties of hexagonal ice crystals whose sizes are much larger than the incident wavelength. This approximation is generally valid for hexagonal ice crystals with size parameters larger than about 30. From existing laboratory data and theoretical results, we illustrate that nonspherical particles absorb less and have a smaller asymmetry factor than the equal-projected area/volume spherical counterparts. In particular, we show that hexagonal ice crystals exhibit numerous halo and arc features that cannot be obtained from spherical particles; and that ice crystals scatter more light in the 60° to 140° scattering angle regions than the spherical counterparts. Satellite remote sensing of the optical depth and height of cirrus clouds using visible and IR channels must use appropriate phase functions for ice crystals. Use of an equivalent sphere model would lead to a significant overestimation and underestimation of the cirrus optical depth and height, respectively. Interpretation of the measurements for polarization reflected from sunlight involving cirrus clouds cannot be made without an appropriate ice crystal model. Large deviations exist for the polarization patterns between spheres and hexagonal ice crystals. Interpretation of lidar backscattering and depolarization signals must also utilize the scattering characteristics of hexagonal ice crystals. Equivalent spherical models substantially underestimate the broadband solar albedos of ice crystal clouds because of stronger forward scattering and larger absorption by spherical particles than hexagonal ice crystals. We illustrate that the net cloud radiative forcing at the top of the atmosphere involving most cirrus clouds is positive, implying that the IR greenhouse effect outweighs the solar albedo effect. If the radiative properties of equivalent spheres are used, a significant increase in cloud radiative forcing occurs. Using a one-dimensional cloud and climate model, we further demonstrate that there is sufficient model sensitivity, in terms of temperature increase, to the use of ice crystal models in radiation calculations.

Performance of laminar-flow leading-edge test articles in cloud encounters

NASA Technical Reports Server (NTRS)

Davis, Richard E.; Maddalon, Dal V.; Wagner, Richard D.

1987-01-01

An extensive data bank of concurrent measurements of laminar flow (LF), particle concentration, and aircraft charging state was gathered for the first time. From this data bank, 13 flights in the simulated airline service (SAS) portion were analyzed to date. A total of 6.86 hours of data at one-second resolution were analyzed. An extensive statistical analysis, for both leading-edge test articles, shows that there is a significant effect of cloud and haze particles on the extent of laminar flow obtained. Approximately 93 percent of data points simulating LFC flight were obtained in clear air conditions; approximately 7 percent were obtained in cloud and haze. These percentages are consistent with earlier USAF and NASA estimates and results. The Hall laminar flow loss criteria was verified qualitatively. Larger particles and higher particle concentrations have a more marked effect on LF than do small particles. A particle spectrometer of a charging patch are both acceptable as diagnostic indicators of the presence of particles detrimental to laminar flow.

The mechanisms of fine particle generation and electrification during Mount St. Helens volcanic eruption

NASA Technical Reports Server (NTRS)

Cheng, R. J.

1982-01-01

Microscopical investigation of volcanic ash collected from ground stations during Mount St. Helens eruptions reveal a distinctive bimodel size distribution with high concentrations of particle ranges at (1) 200-100 microns and (2) 20-0.1 microns. Close examination of individual particles shows that most larger ones are solidified magma particles of porous pumice with numerous gas bubbles in the interior and the smaller ones are all glassy fragments without any detectable gas bubbles. Elemental analysis demonstrates that the fine fragments all have a composition similar to that of the larger pumice particles. Laboratory experiments suggest that the formation of the fine fragments is by bursting of glassy bubbles from a partially solidified surface of a crystallizing molten magma particle. The production of gas bubbles is due to the release of absorbed gases in molten magma particles when solubility decreases during phase transition. Diffusion cloud chamber experiments strongly indicate that sub-micron volcanic fragments are highly hygroscopic and extremely active as cloud condensation nuclei. Ice crystals also are evidently formed on those fragments in a supercooled (-20 C) cloud chamber. It has been reported that charge generation from ocean volcanic eruptions is due to contact of molten lava with sea water. This seems to be insufficient to explain the observed rapid and intense lightning activities over Mount St. Helens eruptions. Therefore, a hypothesis is presented here that highly electrically charged fine solid fragments are ejected by bursting of gas bubbles from the surface of a crystallizing molten magma particles.

Properties of Arctic Aerosol Particles and Residuals of Warm Clouds: Cloud Activation Efficiency and the Aerosol Indirect Effect

NASA Astrophysics Data System (ADS)

Zelenyuk, A.; Imre, D. G.; Leaitch, R.; Ovchinnikov, M.; Liu, P.; Macdonald, A.; Strapp, W.; Ghan, S. J.; Earle, M. E.

2012-12-01

Single particle mass spectrometer, SPLAT II, was used to characterize the size, composition, number concentration, density, and shape of individual Arctic spring aerosol. Background particles, particles above and below the cloud, cloud droplet residuals, and interstitial particles were characterized with goal to identify the properties that separate cloud condensation nuclei (CCN) from background aerosol particles. The analysis offers a comparison between warm clouds formed on clean and polluted days, with clean days having maximum particle concentrations (Na) lower than ~250 cm-3, as compared with polluted days, in which maximum concentration was tenfold higher. On clean days, particles were composed of organics, organics mixed with sulfates, biomass burning (BB), sea salt (SS), and few soot and dust particles. On polluted days, BB, organics associated with BB, and their mixtures with sulfate dominated particle compositions. Based on the measured compositions and size distributions of cloud droplet residuals, background aerosols, and interstitial particles, we conclude that these three particle types had virtually the same compositions, which means that cloud activation probabilities were surprisingly nearly composition independent. Moreover, these conclusions hold in cases in which less than 20% or more than 90% of background particles got activated. We concluded that for the warm clouds interrogated in this study particle size played a more important factor on aerosol CCN activity. Comparative analysis of all studied clouds reveals that aerosol activation efficiency strongly depends on the aerosol concentrations, such that at Na <200 cm-3, nearly all particles activate, and at higher concentrations the activation efficiency is lower. For example, when Na was greater than 1500 cm-3, less than ~30% of particles activated. The data suggest that as the number of nucleated droplets increases, condensation on existing droplets effectively competes with particle activation, limiting maximum droplet concentrations Nd = 525 ± 50 cm-3, which is lower than the 750 cm-3 limit found by Leaitch et al. (1986) for mid-latitude continental cloud that had generally larger updraft speeds than the clouds interrogated in Arctic. These findings are important for the aerosol indirect effect, in which increase in aerosol particle number concentrations is expected to result in increase in Nd and decrease in droplet size, leading to increased cloud albedo and potentially lifetimes. Our conclusions point to limited susceptibility to changes in ambient aerosol concentrations, providing simple explanation for the finding of weaker than expected indirect effect. In summary, the data presented here show that Nd increases as the cloud base particle number concentration increases; however, they also show a limit on Nd that is in the range of 500-600 cm-3.

Effect of the Inhomogeneity of Ice Crystals on Retrieving Ice Cloud Optical Thickness and Effective Particle Size

NASA Technical Reports Server (NTRS)

Xie, Yu; Minnis, Patrick; Hu, Yong X.; Kattawar, George W.; Yang, Ping

2008-01-01

Spherical or spheroidal air bubbles are generally trapped in the formation of rapidly growing ice crystals. In this study the single-scattering properties of inhomogeneous ice crystals containing air bubbles are investigated. Specifically, a computational model based on an improved geometric-optics method (IGOM) has been developed to simulate the scattering of light by randomly oriented hexagonal ice crystals containing spherical or spheroidal air bubbles. A combination of the ray-tracing technique and the Monte Carlo method is used. The effect of the air bubbles within ice crystals is to smooth the phase functions, diminish the 22deg and 46deg halo peaks, and substantially reduce the backscatter relative to bubble-free particles. These features vary with the number, sizes, locations and shapes of the air bubbles within ice crystals. Moreover, the asymmetry factors of inhomogeneous ice crystals decrease as the volume of air bubbles increases. Cloud reflectance lookup tables were generated at wavelengths 0.65 m and 2.13 m with different air-bubble conditions to examine the impact of the bubbles on retrieving ice cloud optical thickness and effective particle size. The reflectances simulated for inhomogeneous ice crystals are slightly larger than those computed for homogenous ice crystals at a wavelength of 0.65 microns. Thus, the retrieved cloud optical thicknesses are reduced by employing inhomogeneous ice cloud models. At a wavelength of 2.13 microns, including air bubbles in ice cloud models may also increase the reflectance. This effect implies that the retrieved effective particle sizes for inhomogeneous ice crystals are larger than those retrieved for homogeneous ice crystals, particularly, in the case of large air bubbles.

Influence of cloud fraction and snow cover to the variation of surface UV radiation at King Sejong station, Antarctica

NASA Astrophysics Data System (ADS)

Lee, Yun Gon; Koo, Ja-Ho; Kim, Jhoon

2015-10-01

This study investigated how cloud fraction and snow cover affect the variation of surface ultraviolet (UV) radiation by using surface Erythemal UV (EUV) and Near UV (NUV) observed at the King Sejong Station, Antarctica. First the Radiative Amplification Factor (RAF), the relative change of surface EUV according to the total-column ozone amount, is compared for different cloud fractions and solar zenith angles (SZAs). Generally, all cloudy conditions show that the increase of RAF as SZA becomes larger, showing the larger effects of vertical columnar ozone. For given SZA cases, the EUV transmission through mean cloud layer gradually decreases as cloud fraction increases, but sometimes the maximum of surface EUV appears under partly cloudy conditions. The high surface EUV transmittance under broken cloud conditions seems due to the re-radiation of scattered EUV by cloud particles. NUV transmission through mean cloud layer also decreases as cloud amount increases but the sensitivity to the cloud fraction is larger than EUV. Both EUV and NUV radiations at the surface are also enhanced by the snow cover, and their enhancement becomes higher as SZA increases implying the diurnal variation of surface albedo. This effect of snow cover seems large under the overcast sky because of the stronger interaction between snow surface and cloudy sky.

Mars aerosol studies with the MGS TES emission phase function observations: Optical depths, particle sizes, and ice cloud types versus latitude and solar longitude

NASA Astrophysics Data System (ADS)

Clancy, R. Todd; Wolff, Michael J.; Christensen, Philip R.

2003-09-01

Emission phase function (EPF) observations taken in 1999-2001 by Mars Global Surveyor Thermal Emission Spectrometer (MGS TES) support the broadest study of Martian aerosol properties to date. TES solar band and infrared (IR) spectral EPF sequences are analyzed to obtain first-time seasonal/latitudinal distributions of visible optical depths, particle sizes, and single scattering phase functions. This combined angular and wavelength coverage enables identification of two distinct ice cloud types over 45°S-45°N. Type 1 ice clouds exhibit small particle sizes (reff = 1-2 μm) and a distinctive backscattering increase. They are most prevalent in the southern hemisphere during aphelion, but also appear more widely distributed in season and latitude as topographic and high-altitude (>=20 km) ice hazes. Type 2 ice clouds exhibit larger particle sizes (reff = 3-4 μm), a distinct side-scattering minimum at 90-100° phase angles (characteristic of a change in particle shape relative to the type 1), and appear most prominently in the northern subtropical aphelion cloud belt. The majority of retrieved dust visible-to-IR optical depth ratios are indicative of reff = 1.5 +/- 0.1 μm, consistent with Pathfinder and Viking/Mariner 9 reanalyses. However, increased ratios (2.7 versus 1.7) appear frequently in the northern hemisphere over LS = 50-200°, indicating substantially smaller dust particles sizes (reff = 1.0 +/- 0.2 μm) at this time. In addition, larger (reff = 1.8-2.5 μm) dust particles were observed locally in the southern hemisphere during the peak of the 2001 global dust storm. Detailed spectral modeling of the TES visible band pass indicates agreement of EPF-derived dust single scattering albedos (0.92-0.94) with the spectrally resolved results from Pathfinder observations.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Erfani, Ehsan; Mitchell, David L.

Here, ice particle mass- and projected area-dimension ( m- D and A- D) power laws are commonly used in the treatment of ice cloud microphysical and optical properties and the remote sensing of ice cloud properties. Although there has long been evidence that a single m- D or A- D power law is often not valid over all ice particle sizes, few studies have addressed this fact. This study develops self-consistent m- D and A- D expressions that are not power laws but can easily be reduced to power laws for the ice particle size (maximum dimension or D) rangemore » of interest, and they are valid over a much larger D range than power laws. This was done by combining ground measurements of individual ice particle m and D formed at temperature T < –20 °C during a cloud seeding field campaign with 2-D stereo (2D-S) and cloud particle imager (CPI) probe measurements of D and A, and estimates of m, in synoptic and anvil ice clouds at similar temperatures. The resulting m- D and A- D expressions are functions of temperature and cloud type (synoptic vs. anvil), and are in good agreement with m- D power laws developed from recent field studies considering the same temperature range (–60 °C < T < –20 °C).« less

Agglomeration of dust in convective clouds initialized by nuclear bursts

NASA Astrophysics Data System (ADS)

Bacon, D. P.; Sarma, R. A.

Convective clouds initialized by nuclear bursts are modeled using a two-dimensional axisymmetric cloud model. Dust transport through the atmosphere is studied using five different sizes ranging from 1 to 10,000 μm in diameter. Dust is transported in the model domain by advection and sedimentation. Water is allowed to condense onto dust particles in regions of supersaturation in the cloud. The agglomeration of dust particles resulting from the collision of different size dust particles is modeled. The evolution of the dust mass spectrum due to agglomeration is modeled using a numerical scheme which is mass conserving and has low implicit diffusion. Agglomeration moves mass from the small particles with very small fall velocity to the larger sizes which fall to the ground more readily. Results indicate that the dust fallout can be increased significantly due to this process. In preliminary runs using stable and unstable environmental soundings, at 30 min after detonation the total dust in the domain was 11 and 30%, respectively, less than a control case without agglomeration.

Developing and bounding ice particle mass- and area-dimension expressions for use in atmospheric models and remote sensing

DOE PAGES

Erfani, Ehsan; Mitchell, David L.

2016-04-07

Here, ice particle mass- and projected area-dimension ( m- D and A- D) power laws are commonly used in the treatment of ice cloud microphysical and optical properties and the remote sensing of ice cloud properties. Although there has long been evidence that a single m- D or A- D power law is often not valid over all ice particle sizes, few studies have addressed this fact. This study develops self-consistent m- D and A- D expressions that are not power laws but can easily be reduced to power laws for the ice particle size (maximum dimension or D) rangemore » of interest, and they are valid over a much larger D range than power laws. This was done by combining ground measurements of individual ice particle m and D formed at temperature T < –20 °C during a cloud seeding field campaign with 2-D stereo (2D-S) and cloud particle imager (CPI) probe measurements of D and A, and estimates of m, in synoptic and anvil ice clouds at similar temperatures. The resulting m- D and A- D expressions are functions of temperature and cloud type (synoptic vs. anvil), and are in good agreement with m- D power laws developed from recent field studies considering the same temperature range (–60 °C < T < –20 °C).« less

Core/Shell Microstructure Induced Synergistic Effect for Efficient Water-Droplet Formation and Cloud-Seeding Application.

PubMed

Tai, Yanlong; Liang, Haoran; Zaki, Abdelali; El Hadri, Nabil; Abshaev, Ali M; Huchunaev, Buzgigit M; Griffiths, Steve; Jouiad, Mustapha; Zou, Linda

2017-12-26

Cloud-seeding materials as a promising water-augmentation technology have drawn more attention recently. We designed and synthesized a type of core/shell NaCl/TiO 2 (CSNT) particle with controlled particle size, which successfully adsorbed more water vapor (∼295 times at low relative humidity, 20% RH) than that of pure NaCl, deliquesced at a lower environmental RH of 62-66% than the hygroscopic point (h g.p ., 75% RH) of NaCl, and formed larger water droplets ∼6-10 times its original measured size area, whereas the pure NaCl still remained as a crystal at the same conditions. The enhanced performance was attributed to the synergistic effect of the hydrophilic TiO 2 shell and hygroscopic NaCl core microstructure, which attracted a large amount of water vapor and turned it into a liquid faster. Moreover, the critical particle size of the CSNT particles (0.4-10 μm) as cloud-seeding materials was predicted via the classical Kelvin equation based on their surface hydrophilicity. Finally, the benefits of CSNT particles for cloud-seeding applications were determined visually through in situ observation under an environmental scanning electron microscope on the microscale and cloud chamber experiments on the macroscale, respectively. These excellent and consistent performances positively confirmed that CSNT particles could be promising cloud-seeding materials.

Saharan dust, convective lofting, aerosol enhancement zones, and potential impacts on ice nucleation in the tropical upper troposphere

NASA Astrophysics Data System (ADS)

Twohy, C. H.; Anderson, B. E.; Ferrare, R. A.; Sauter, K. E.; L'Ecuyer, T. S.; van den Heever, S. C.; Heymsfield, A. J.; Ismail, S.; Diskin, G. S.

2017-08-01

Dry aerosol size distributions and scattering coefficients were measured on 10 flights in 32 clear-air regions adjacent to tropical storm anvils over the eastern Atlantic Ocean. Aerosol properties in these regions were compared with those from background air in the upper troposphere at least 40 km from clouds. Median values for aerosol scattering coefficient and particle number concentration >0.3 μm diameter were higher at the anvil edges than in background air, showing that convective clouds loft particles from the lower troposphere to the upper troposphere. These differences are statistically significant. The aerosol enhancement zones extended 10-15 km horizontally and 0.25 km vertically below anvil cloud edges but were not due to hygroscopic growth since particles were measured under dry conditions. Number concentrations of particles >0.3 μm diameter were enhanced more for the cases where Saharan dust layers were identified below the clouds with airborne lidar. Median number concentrations in this size range increased from 100 l-1 in background air to 400 l-1 adjacent to cloud edges with dust below, with larger enhancements for stronger storm systems. Integration with satellite cloud frequency data indicates that this transfer of large particles from low to high altitudes by convection has little impact on dust concentrations within the Saharan Air Layer itself. However, it can lead to substantial enhancement in large dust particles and, therefore, heterogeneous ice nuclei in the upper troposphere over the Atlantic. This may induce a cloud/aerosol feedback effect that could impact cloud properties in the region and downwind.

Cloud Condensation Nuclei in FIRE III

NASA Technical Reports Server (NTRS)

Hudson, James G.; Delnore, Victor E. (Technical Monitor)

2002-01-01

Yum and Hudson showed that the springtime Arctic aerosol is probably a result of long-range transport at high altitudes. Scavenging of particles by clouds reduces the low level concentrations by a factor of 3. This produces a vertical gradient in particle concentrations when low-level clouds are present. Concentrations are uniform with height when clouds are not present. Low-level CCN (cloud condensation nuclei) spectra are similar to those in other maritime areas as found by previous projects including FIRE 1 and ASTEX, which were also supported on earlier NASA-FIRE grants. Wylie and Hudson carried this work much further by comparing the CCN spectra observed during ACE with back trajectories of air masses and satellite photographs. This showed that cloud scavenging reduces CCN concentrations at all altitudes over the springtime Arctic, with liquid clouds being more efficient scavengers than frozen clouds. The small size of the Arctic Ocean seems to make it more susceptible to continental and thus anthropogenic aerosol influences than any of the other larger oceans.

Aerosol processing in stratiform clouds in ECHAM6-HAM

NASA Astrophysics Data System (ADS)

Neubauer, David; Lohmann, Ulrike; Hoose, Corinna

2013-04-01

Aerosol processing in stratiform clouds by uptake into cloud particles, collision-coalescence, chemical processing inside the cloud particles and release back into the atmosphere has important effects on aerosol concentration, size distribution, chemical composition and mixing state. Aerosol particles can act as cloud condensation nuclei. Cloud droplets can take up further aerosol particles by collisions. Atmospheric gases may also be transferred into the cloud droplets and undergo chemical reactions, e.g. the production of atmospheric sulphate. Aerosol particles are also processed in ice crystals. They may be taken up by homogeneous freezing of cloud droplets below -38° C or by heterogeneous freezing above -38° C. This includes immersion freezing of already immersed aerosol particles in the droplets and contact freezing of particles colliding with a droplet. Many clouds do not form precipitation and also much of the precipitation evaporates before it reaches the ground. The water soluble part of the aerosol particles concentrates in the hydrometeors and together with the insoluble part forms a single, mixed, larger particle, which is released. We have implemented aerosol processing into the current version of the general circulation model ECHAM6 (Stevens et al., 2013) coupled to the aerosol module HAM (Stier et al., 2005). ECHAM6-HAM solves prognostic equations for the cloud droplet number and ice crystal number concentrations. In the standard version of HAM, seven modes are used to describe the total aerosol. The modes are divided into soluble/mixed and insoluble modes and the number concentrations and masses of different chemical components (sulphate, black carbon, organic carbon, sea salt and mineral dust) are prognostic variables. We extended this by an explicit representation of aerosol particles in cloud droplets and ice crystals in stratiform clouds similar to Hoose et al. (2008a,b). Aerosol particles in cloud droplets are represented by 5 tracers for the chemical components as well as 5 tracers for aerosol particles in ice crystals. This allows simulations of aerosol processing in warm, mixed-phase (e.g. through the Bergeron-Findeisen process) and ice clouds. The fixed scavenging ratios used for wet deposition in clouds in standard HAM are replaced by an explicit treatment of collision of cloud droplets/ice crystals with interstitial aerosol particles. Nucleation scavenging of aerosol particles by acting as cloud condensation nuclei or ice nuclei, freezing and evaporation of cloud droplets and melting and sublimation of ice crystals are treated explicitly. In extension to previous studies, aerosol particles from evaporating precipitation are released to modes which correspond to their size. Cloud processing of aerosol particles changes their size distribution and hence influences cloud droplet and ice crystal number concentrations as well as precipitation rate, which in turn affects aerosol concentrations. Results will be presented at the conference. Hoose et al., JGR, 2008a, doi: 10.1029/2007JD009251 Hoose et al., ACP, 2008b, doi: 10.5194/acp-8-6939-2008 Stevens et al., 2013, submitted Stier et al., ACP, 2005, doi: 10.5194/acp-5-1125-2005

Inference of Ice Cloud Properties from High-spectral Resolution Infrared Observations. Appendix 4

NASA Technical Reports Server (NTRS)

Huang, Hung-Lung; Yang, Ping; Wei, Heli; Baum, Bryan A.; Hu, Yongxiang; Antonelli, Paolo; Ackerman, Steven A.

2005-01-01

The theoretical basis is explored for inferring the microphysical properties of ice crystal from high-spectral resolution infrared observations. A radiative transfer model is employed to simulate spectral radiances to address relevant issues. The extinction and absorption efficiencies of individual ice crystals, assumed as hexagonal columns for large particles and droxtals for small particles, are computed from a combination of the finite- difference time-domain (FDTD) technique and a composite method. The corresponding phase functions are computed from a combination of FDTD and an improved geometric optics method (IGOM). Bulk scattering properties are derived by averaging the single- scattering properties of individual particles for 30 particle size distributions developed from in situ measurements and for additional four analytical Gamma size distributions for small particles. The non-sphericity of ice crystals is shown to have a significant impact on the radiative signatures in the infrared (IR) spectrum; the spherical particle approximation for inferring ice cloud properties may result in an overest&ation of the optical thickness and an inaccurate retrieval of effective particle size. Furthermore, we show that the error associated with the use of the Henyey-Greenstein phase function can be as larger as 1 K in terms of brightness temperature for larger particle effective size at some strong scattering wavenumbers. For small particles, the difference between the two phase functions is much less, with brightness temperatures generally differing by less than 0.4 K. The simulations undertaken in this study show that the slope of the IR brightness temperature spectrum between 790-960/cm is sensitive to the effective particle size. Furthermore, a strong sensitivity of IR brightness temperature to cloud optical thickness is noted within the l050-1250/cm region. Based on this spectral feature, a technique is presented for the simultaneous retrieval of the visible optical thickness and effective particle size from high spectral resolution infrared data under ice cloudy con&tion. The error analysis shows that the uncertainty of the retrieved optical thickness and effective particle size has a small range of variation. The error for retrieving particle size in conjunction with an uncertainty of 5 K in cloud'temperature, or a surface temperature uncertainty of 2.5 K, is less than 15%. The corresponding e m r in the uncertainty of optical thickness is within 5-2096, depending on the value of cloud optical thickness. The applicability of the technique is demonstrated using the aircraft-based High- resolution Interferometer Sounder (HIS) data from the Subsonic Aircraft: Contrail and Cloud Effects Special Study (SUCCESS) in 1996 and the First ISCCP Regional Experiment - Arctic Clouds Experiment (FIRE-ACE) in 1998.

Comparisons of Mixed-Phase Icing Cloud Simulations with Experiments Conducted at the NASA Propulsion Systems Laboratory

NASA Technical Reports Server (NTRS)

Bartkus, Tadas P.; Struk, Peter M.; Tsao, Jen-Ching

2017-01-01

This paper builds on previous work that compares numerical simulations of mixed-phase icing clouds with experimental data. The model couples the thermal interaction between ice particles and water droplets of the icing cloud with the flowing air of an icing wind tunnel for simulation of NASA Glenn Research Centers (GRC) Propulsion Systems Laboratory (PSL). Measurements were taken during the Fundamentals of Ice Crystal Icing Physics Tests at the PSL tunnel in March 2016. The tests simulated ice-crystal and mixed-phase icing that relate to ice accretions within turbofan engines. Experimentally measured air temperature, humidity, total water content, liquid and ice water content, as well as cloud particle size, are compared with model predictions. The model showed good trend agreement with experimentally measured values, but often over-predicted aero-thermodynamic changes. This discrepancy is likely attributed to radial variations that this one-dimensional model does not address. One of the key findings of this work is that greater aero-thermodynamic changes occur when humidity conditions are low. In addition a range of mixed-phase clouds can be achieved by varying only the tunnel humidity conditions, but the range of humidities to generate a mixed-phase cloud becomes smaller when clouds are composed of smaller particles. In general, the model predicted melt fraction well, in particular with clouds composed of larger particle sizes.

Approach for measuring the chemistry of individual particles in the size range critical for cloud formation.

PubMed

Zauscher, Melanie D; Moore, Meagan J K; Lewis, Gregory S; Hering, Susanne V; Prather, Kimberly A

2011-03-15

Aerosol particles, especially those ranging from 50 to 200 nm, strongly impact climate by serving as nuclei upon which water condenses and cloud droplets form. However, the small number of analytical methods capable of measuring the composition of particles in this size range, particularly at the individual particle level, has limited our knowledge of cloud condensation nuclei (CCN) composition and hence our understanding of aerosols effect on climate. To obtain more insight into particles in this size range, we developed a method which couples a growth tube (GT) to an ultrafine aerosol time-of-flight mass spectrometer (UF-ATOFMS), a combination that allows in situ measurements of the composition of individual particles as small as 38 nm. The growth tube uses water to grow particles to larger sizes so they can be optically detected by the UF-ATOFMS, extending the size range to below 100 nm with no discernible changes in particle composition. To gain further insight into the temporal variability of aerosol chemistry and sources, the GT-UF-ATOFMS was used for online continuous measurements over a period of 3 days.

Calculations of the variability of ice cloud radiative properties at selected solar wavelengths

NASA Technical Reports Server (NTRS)

Welch, R. M.; Zdunkowski, W. G.; Cox, S. K.

1980-01-01

This study shows that there is surprising little difference in values of reflectance, absorptance, and transmittance for many of the intermediate-size particle spectra. Particle size distributions with mode radii ranging from approximately 50 to 300 microns, irrespective of particle shape and nearly independent of the choice of size distribution representation, give relatively similar flux values. The very small particle sizes, however, have significantly larger values of reflectance and transmittance with corresponding smaller values of absorptance than do the larger particle sizes. The very large particle modes produce very small values of reflectance and transmittance along with very large values of absorptance. Such variations are particularly noticeable when plotted as a function of wavelength.

Potential climatic impact of organic haze on early Earth.

PubMed

Hasenkopf, Christa A; Freedman, Miriam A; Beaver, Melinda R; Toon, Owen B; Tolbert, Margaret A

2011-03-01

We have explored the direct and indirect radiative effects on climate of organic particles likely to have been present on early Earth by measuring their hygroscopicity and cloud nucleating ability. The early Earth analog aerosol particles were generated via ultraviolet photolysis of an early Earth analog gas mixture, which was designed to mimic possible atmospheric conditions before the rise of oxygen. An analog aerosol for the present-day atmosphere of Saturn's moon Titan was tested for comparison. We exposed the early Earth aerosol to a range of relative humidities (RHs). Water uptake onto the aerosol was observed to occur over the entire RH range tested (RH=80-87%). To translate our measurements of hygroscopicity over a specific range of RHs into their water uptake ability at any RH < 100% and into their ability to act as cloud condensation nuclei (CCN) at RH > 100%, we relied on the hygroscopicity parameter κ, developed by Petters and Kreidenweis. We retrieved κ=0.22 ±0.12 for the early Earth aerosol, which indicates that the humidified aerosol (RH < 100 %) could have contributed to a larger antigreenhouse effect on the early Earth atmosphere than previously modeled with dry aerosol. Such effects would have been of significance in regions where the humidity was larger than 50%, because such high humidities are needed for significant amounts of water to be on the aerosol. Additionally, Earth organic aerosol particles could have activated into CCN at reasonable-and even low-water-vapor supersaturations (RH > 100%). In regions where the haze was dominant, it is expected that low particle concentrations, once activated into cloud droplets, would have created short-lived, optically thin clouds. Such clouds, if predominant on early Earth, would have had a lower albedo than clouds today, thereby warming the planet relative to current-day clouds. © Mary Ann Liebert, Inc.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Fan; Ovchinnikov, Mikhail; Shaw, Raymond A.

Lagrangian ice particle tracking is applied in both a 3-D time dependent velocity field produced by a Large Eddy Simulation cloud model and in a 2-D idealized field. It is found that more than 10% of ice particles have lifetimes longer than 1.5 hours, much longer than the large eddy turnover time or the time for a crystal to fall through the depth of a non-turbulent cloud. An analysis of trajectories in a 2-D idealized field shows that there are two types of long lifetime ice particles: quasi-steady and recycled growth. For quasi-steady growth, ice particles are suspended in themore » updraft velocity region for a long time. For recycled growth, ice particles are trapped in the large-eddy structures, and whether ice particles grow or evaporate depends on the ice relative humidity profile within the boundary layer. Some ice particles can grow after each cycle in the trapping region, until they are too large to be trapped, and thus have long lifetimes. The relative contribution of the recycled ice particles to the cloud mean ice water content depends on both the dynamic and thermodynamic properties of the mixing layer. In particular, the total ice water content of a mixed phase cloud in a decoupled boundary layer can be much larger than that in a fully coupled boundary layer.« less

Coagulation of grains in static and collapsing protostellar clouds

NASA Technical Reports Server (NTRS)

Weidenschilling, S. J.; Ruzmaikina, T. V.

1993-01-01

The wavelength dependence of extinction in the diffuse interstellar medium implies that it is produced by particles of dominant size of approximately 10(exp -5) cm. There is some indication that in the cores of dense molecular clouds, sub-micron grains can coagulate to form larger particles; this process is probably driven by turbulence. The most primitive meteorites (carbonaceous chondrites) are composed of particles with a bimodal size distribution with peaks near 1 micron (matrix) and 1 mm (chondrules). Models for chondrule formation that involve processing of presolar material by chemical reactions or through an accretion shock during infall assume that aggregates of the requisite mass could form before or during collapse. The effectiveness of coagulation during collapse has been disputed; it appears to depend on specific assumptions. The first results of detailed numerical modeling of spatial and temporal variations of particle sizes in presolar clouds, both static and collapsing, is reported in this article.

Fog and Cloud Induced Aerosol Modification Observed by AERONET

NASA Technical Reports Server (NTRS)

Eck, T. F.; Holben, B. N.; Reid, J. S.; Giles, D. M.; Rivas, M. A.; Singh, R. P.; Tripathi, S. N.; Bruegge, C. J.; Platnick, S. E.; Arnold, G. T.;

Evaluating the impact of aerosol particles above cloud on cloud optical depth retrievals from MODIS

NASA Astrophysics Data System (ADS)

Alfaro-Contreras, Ricardo; Zhang, Jianglong; Campbell, James R.; Holz, Robert E.; Reid, Jeffrey S.

2014-05-01

Using two different operational Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) cloud optical depth (COD) retrievals (0.86 versus 1.6 µm), we evaluate the impact of above-cloud smoke aerosol particles on near-IR (0.86 µm) COD retrievals. Aerosol Index (AI) from the collocated Ozone Monitoring Instrument (OMI) are used to identify above-cloud aerosol particle loading over the southern Atlantic Ocean, including both smoke and dust from the African subcontinent. Collocated Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation data constrain cloud phase and provide contextual above-cloud aerosol optical depth. The frequency of occurrence of above-cloud aerosol events is depicted on a global scale for the spring and summer seasons from OMI and Cloud Aerosol Lidar with Orthogonal Polarization. Seasonal frequencies for smoke-over-cloud off the southwestern Africa coastline reach 20-50% in boreal summer. We find a corresponding low COD bias of 10-20% for standard MODIS COD retrievals when averaged OMI AI are larger than 1. No such bias is found over the Saharan dust outflow region off northern Africa, since both MODIS 0.86 and 1.6 µm channels are vulnerable to radiance attenuation due to dust particles. A similar result is found for a smaller domain, in the Gulf of Tonkin region, from smoke advection over marine stratocumulus clouds and outflow into the northern South China Sea in spring. This study shows the necessity of accounting for the above-cloud aerosol events for future studies using standard MODIS cloud products in biomass burning outflow regions, through the use of collocated OMI AI and supplementary MODIS 1.6 µm COD products.

Cloud droplet size distribution broadening during diffusional growth: ripening amplified by deactivation and reactivation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Fan; Kollias, Pavlos; Shaw, Raymond A.

Cloud droplet size distributions (CDSDs), which are related to cloud albedo and lifetime, are usually broader in warm clouds than predicted from adiabatic parcel calculations. We investigate a mechanism for the CDSD broadening using a Lagrangian bin-microphysics cloud parcel model that considers the condensational growth of cloud droplets formed on polydisperse, sub-micrometer aerosols in an adiabatic cloud parcel that undergoes vertical oscillations, such as those due to cloud circulations or turbulence. Results show that the CDSD can be broadened during condensational growth as a result of Ostwald ripening amplified by droplet deactivation and reactivation, which is consistent with Korolev (1995).more » The relative roles of the solute effect, curvature effect, deactivation and reactivation on CDSD broadening are investigated. Deactivation of smaller cloud droplets, which is due to the combination of curvature and solute effects in the downdraft region, enhances the growth of larger cloud droplets and thus contributes particles to the larger size end of the CDSD. Droplet reactivation, which occurs in the updraft region, contributes particles to the smaller size end of the CDSD. In addition, we find that growth of the largest cloud droplets strongly depends on the residence time of cloud droplet in the cloud rather than the magnitude of local variability in the supersaturation fluctuation. This is because the environmental saturation ratio is strongly buffered by smaller cloud droplets. Two necessary conditions for this CDSD broadening, which generally occur in the atmosphere, are: (1) droplets form on polydisperse aerosols of varying hygroscopicity and (2) the cloud parcel experiences upwards and downwards motions. Therefore we expect that this mechanism for CDSD broadening is possible in real clouds. Our results also suggest it is important to consider both curvature and solute effects before and after cloud droplet activation in a cloud model. The importance of this mechanism compared with other mechanisms on cloud properties should be investigated through in-situ measurements and 3-D dynamic models.« less

Cloud droplet size distribution broadening during diffusional growth: ripening amplified by deactivation and reactivation

DOE PAGES

Yang, Fan; Kollias, Pavlos; Shaw, Raymond A.; ...

2017-12-06

Cloud droplet size distributions (CDSDs), which are related to cloud albedo and lifetime, are usually broader in warm clouds than predicted from adiabatic parcel calculations. We investigate a mechanism for the CDSD broadening using a Lagrangian bin-microphysics cloud parcel model that considers the condensational growth of cloud droplets formed on polydisperse, sub-micrometer aerosols in an adiabatic cloud parcel that undergoes vertical oscillations, such as those due to cloud circulations or turbulence. Results show that the CDSD can be broadened during condensational growth as a result of Ostwald ripening amplified by droplet deactivation and reactivation, which is consistent with Korolev (1995).more » The relative roles of the solute effect, curvature effect, deactivation and reactivation on CDSD broadening are investigated. Deactivation of smaller cloud droplets, which is due to the combination of curvature and solute effects in the downdraft region, enhances the growth of larger cloud droplets and thus contributes particles to the larger size end of the CDSD. Droplet reactivation, which occurs in the updraft region, contributes particles to the smaller size end of the CDSD. In addition, we find that growth of the largest cloud droplets strongly depends on the residence time of cloud droplet in the cloud rather than the magnitude of local variability in the supersaturation fluctuation. This is because the environmental saturation ratio is strongly buffered by smaller cloud droplets. Two necessary conditions for this CDSD broadening, which generally occur in the atmosphere, are: (1) droplets form on polydisperse aerosols of varying hygroscopicity and (2) the cloud parcel experiences upwards and downwards motions. Therefore we expect that this mechanism for CDSD broadening is possible in real clouds. Our results also suggest it is important to consider both curvature and solute effects before and after cloud droplet activation in a cloud model. The importance of this mechanism compared with other mechanisms on cloud properties should be investigated through in-situ measurements and 3-D dynamic models.« less

Cloud droplet size distribution broadening during diffusional growth: ripening amplified by deactivation and reactivation

NASA Astrophysics Data System (ADS)

Yang, Fan; Kollias, Pavlos; Shaw, Raymond A.; Vogelmann, Andrew M.

2018-05-01

Cloud droplet size distributions (CDSDs), which are related to cloud albedo and rain formation, are usually broader in warm clouds than predicted from adiabatic parcel calculations. We investigate a mechanism for the CDSD broadening using a moving-size-grid cloud parcel model that considers the condensational growth of cloud droplets formed on polydisperse, submicrometer aerosols in an adiabatic cloud parcel that undergoes vertical oscillations, such as those due to cloud circulations or turbulence. Results show that the CDSD can be broadened during condensational growth as a result of Ostwald ripening amplified by droplet deactivation and reactivation, which is consistent with early work. The relative roles of the solute effect, curvature effect, deactivation and reactivation on CDSD broadening are investigated. Deactivation of smaller cloud droplets, which is due to the combination of curvature and solute effects in the downdraft region, enhances the growth of larger cloud droplets and thus contributes particles to the larger size end of the CDSD. Droplet reactivation, which occurs in the updraft region, contributes particles to the smaller size end of the CDSD. In addition, we find that growth of the largest cloud droplets strongly depends on the residence time of cloud droplet in the cloud rather than the magnitude of local variability in the supersaturation fluctuation. This is because the environmental saturation ratio is strongly buffered by numerous smaller cloud droplets. Two necessary conditions for this CDSD broadening, which generally occur in the atmosphere, are as follows: (1) droplets form on aerosols of different sizes, and (2) the cloud parcel experiences upwards and downwards motions. Therefore we expect that this mechanism for CDSD broadening is possible in real clouds. Our results also suggest it is important to consider both curvature and solute effects before and after cloud droplet activation in a cloud model. The importance of this mechanism compared with other mechanisms on cloud properties should be investigated through in situ measurements and 3-D dynamic models.

Optical, physical, and chemical properties of springtime aerosol over Barrow Alaska in 2008

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shantz, Nicole C.; Gultepe, Ismail; Andrews, Elisabeth

2014-03-06

Airborne observations from four flights during the 2008 Indirect and Semi-Direct Aerosol Campaign (ISDAC) are used to examine some cloud-free optical, physical, and chemical properties of aerosol particles in the springtime Arctic troposphere. The number concentrations of particles larger than 0.12 μm (Na>120), important for light extinction and cloud droplet formation, ranged from 15 to 2260 cm -3, with the higher Na>120 cases dominated by measurements from two flights of long-range transported biomass burning (BB) aerosols. The two other flights examined here document a relatively clean aerosol and an Arctic Haze aerosol impacted by larger particles largely composed of dust.more » For observations from the cleaner case and the BB cases, the particle light scattering coefficients at low relative humidity (RH<20%) increased nonlinearly with increasing Na>120, driven mostly by an increase in mean sizes of particles with increasing Na>120 (BB cases). For those three cases, particle light absorption coefficients also increased nonlinearly with increasing Na>120 and linearly with increasing submicron particle volume concentration. In addition to black carbon, brown carbon was estimated to have increased light absorption coefficients by 27% (450 nm wavelength) and 14% (550 nm) in the BB cases. For the case with strong dust influence, the absorption relative to submicron particle volume was small compared with the other cases. There was a slight gradient of Passive Cavity Aerosol Spectrometer Probe (PCASP) mean volume diameter (MVD) towards smaller sizes with increasing height, which suggests more scavenging of the more elevated particles, consistent with a typically longer lifetime of particles higher in the atmosphere. However, in approximately 10% of the cases, the MVD increased (>0.4 μm) with increasing altitude, suggesting transport of larger fine particle mass (possibly coarse particle mass) at high levels over the Arctic. This may be because of transport of larger particles at higher elevations and relatively slow deposition to the surface.« less

Near-Cloud Aerosol Properties from the 1 Km Resolution MODIS Ocean Product

NASA Technical Reports Server (NTRS)

Varnai, Tamas; Marshak, Alexander

2014-01-01

This study examines aerosol properties in the vicinity of clouds by analyzing high-resolution atmospheric correction parameters provided in the MODIS (Moderate Resolution Imaging Spectroradiometer) ocean color product. The study analyzes data from a 2 week long period of September in 10 years, covering a large area in the northeast Atlantic Ocean. The results indicate that on the one hand, the Quality Assessment (QA) flags of the ocean color product successfully eliminate cloud-related uncertainties in ocean parameters such as chlorophyll content, but on the other hand, using the flags introduces a sampling bias in atmospheric products such as aerosol optical thickness (AOT) and Angstrom exponent. Therefore, researchers need to select QA flags by balancing the risks of increased retrieval uncertainties and sampling biases. Using an optimal set of QA flags, the results reveal substantial increases in optical thickness near clouds-on average the increase is 50% for the roughly half of pixels within 5 km from clouds and is accompanied by a roughly matching increase in particle size. Theoretical simulations show that the 50% increase in 550nm AOT changes instantaneous direct aerosol radiative forcing by up to 8W/m2 and that the radiative impact is significantly larger if observed near-cloud changes are attributed to aerosol particles as opposed to undetected cloud particles. These results underline that accounting for near-cloud areas and understanding the causes of near-cloud particle changes are critical for accurate calculations of direct aerosol radiative forcing.

Detecting Aerosol Effect on Deep Precipitation Systems: A Modeling Study

NASA Astrophysics Data System (ADS)

Li, X.; Tao, W.; Khain, A.; Kummerow, C.; Simpson, J.

2006-05-01

Urban cities produce high concentrations of anthropogenic aerosols. These aerosols are generally hygroscopic and may serve as Cloud Condensation Nuclei (CCN). This study focuses on the aerosol indirect effect on the deep convective systems over the land. These deep convective systems contribute to the majority of the summer time rainfall and are important for local hydrological cycle and weather forecast. In a companion presentation (Tao et al.) in this session, the mechanisms of aerosol-cloud-precipitation interactions in deep convective systems are explored using cloud-resolving model simulations. Here these model results will be analyzed to provide guidance to the detection of the impact of aerosols as CCN on summer time, deep convections using the currently available observation methods. The two-dimensional Goddard Cumulus Ensemble (GCE) model with an explicit microphysical scheme has been used to simulate the aerosol effect on deep precipitation systems. This model simulates the size distributions of aerosol particles, as well as cloud, rain, ice crystals, snow, graupel, and hail explicitly. Two case studies are analyzed: a midlatitude summer time squall in Oklahoma, and a sea breeze convection in Florida. It is shown that increasing the CCN number concentration does not affect the rainfall structure and rain duration in these two cases. The total surface rainfall rate is reduced in the squall case, but remains essentially the same in the sea breeze case. For the long-lived squall system with a significant portion of the stratiform rain, the surface rainfall PDF (probability density function) distribution is more sensitive to the change of the initial CCN concentrations compared with the total surface rainfall. The possibility of detecting the aerosol indirect effect in deep precipitation systems from the space is also studied in this presentation. The hydrometeors fields from the GCE model simulations are used as inputs to a microwave radiative transfer model. It is found that Tb at higher frequencies (35 GHz and 85 GHz) are quite sensitive to the CCN concentration variations. This is because the higher frequency brightness temperatures are sensitive to large, ice-phase particles. In a clean environment, the deep convections produce larger cloud particles. When these cloud particles are transported above the freezing level by strong updrafts, they form larger precipitable ice particles (snow, graupel and hail) compared with dirty environment simulations. These larger ice particles result in significantly colder brightness temperatures at high frequencies in the clean scenario simulations.

Importance of aggregation and small ice crystals in cirrus clouds, based on observations and an ice particle growth model

NASA Technical Reports Server (NTRS)

Mitchell, David L.; Chai, Steven K.; Dong, Yayi; Arnott, W. Patrick; Hallett, John

1993-01-01

The 1 November 1986 FIRE I case study was used to test an ice particle growth model which predicts bimodal size spectra in cirrus clouds. The model was developed from an analytically based model which predicts the height evolution of monomodal ice particle size spectra from the measured ice water content (IWC). Size spectra from the monomodal model are represented by a gamma distribution, N(D) = N(sub o)D(exp nu)exp(-lambda D), where D = ice particle maximum dimension. The slope parameter, lambda, and the parameter N(sub o) are predicted from the IWC through the growth processes of vapor diffusion and aggregation. The model formulation is analytical, computationally efficient, and well suited for incorporation into larger models. The monomodal model has been validated against two other cirrus cloud case studies. From the monomodal size spectra, the size distributions which determine concentrations of ice particles less than about 150 mu m are predicted.

Infrared radiative properties of tropical cirrus clouds inferred with aircraft measurements

NASA Technical Reports Server (NTRS)

Griffith, K. T.; Cox, S. K.; Knollenberg, R. G.

1980-01-01

Longwave emissivities and the vertical profile of cooling rates of tropical cirrus clouds are determined using broadband hemispheric irradiance data. Additionally, a broadband mass absorption coefficient is defined and used to relate emissivity to water content. The data used were collected by the National Center for Atmospheric Research (NCAR) Sabreliner during the GARP Atlantic Tropical Experiment (GATE) in the summer of 1974. Three case studies are analyzed showing that these tropical cirrus clouds approached an emissivity of 1.0 within a vertical distance of 1.0 km. Broadband mass absorption coefficients ranging from 0.076 to 0.096 sq m per g are derived. A comparison of these results with other work suggests that tropical cirrus cloud emissivities may be significantly larger than heretofore believed. Ice water content of the clouds were deduced from data collected by a one-dimensional particle spectrometer. Analyses of the ice water content and the observed particle size distributions are presented.

Constraints on the Longevity of the 2010 Eyjaföll Eruption Cloud From Analog Experiments and Modeling

NASA Astrophysics Data System (ADS)

Carazzo, G.; Jellinek, M.

2010-12-01

The prolonged disruption of global air travel as a result of the 2010 Eyjafjöll eruption in Iceland underscores the value of discerning the dynamics of volcanic ash-clouds in the atmosphere. Understanding the longevity of these clouds is a particularly long standing problem that bears not only on volcanic hazards to humans but also on the nature and time scale of volcanic forcings on climate change. Since early work on the subject, the common practice to tackle the problem of cloud longevity has been to account for the dynamics of sedimentation by individual particle settling. We use 1D modeling and analog experiments of a turbulent particle-laden umbrella cloud to show that this classical view can be misleading and that the residence times of these ash-clouds in the atmosphere depends strongly on the collective behavior of the solid fraction. Diffusive convection driven by the differential diffusion of constituents altering the cloud density (ash, temperature, sulfur dioxide) may enhance particle scavenging and extend the cloud longevity over time scales orders of magnitude longer than currently expected (i.e., years rather than days for powerful eruptions). Records of this behavior can be found in real-time measurements of stratospheric post-volcanic aerosols following the 1974 Fuego, the 1982 El Chichon, the 1991 Hudson and Pinatubo events, and more recently, from the 14 April 2010 Eyjafjöll eruption. The importance of diffusive convection in volcanic ash-clouds depends strongly on particle size distribution and concentration. For the 2010 Eyjafjöll eruption, we predict that particles larger than 10 microns should settle individually as commonly assumed, but particles smaller than 1 micron should diffuse slowly in layers extending the cloud longevity to several weeks rather than days. These predictions are found to be in good agreement with a number of satellite and ground-based lidar data on ash size and mass estimates performed at different locations across Europe.

Tight coupling of particle size and composition in atmospheric cloud droplet activation

NASA Astrophysics Data System (ADS)

Topping, D.; McFiggans, G.

2011-09-01

The substantial uncertainty in the indirect effect on radiative forcing in large part arises from the influences of atmospheric aerosol particles on (i) the brightness of clouds, exerting significant shortwave cooling with no appreciable compensation in the longwave, and on (ii) their ability to precipitate, with implications for cloud cover and lifetime. Predicting the ambient conditions at which aerosol particles may become cloud droplets is largely reliant on an equilibrium relationship derived in 1936. However, the theoretical basis of the relationship restricts its application to particles solely comprising involatile compounds and water, whereas a substantial fraction of particles in the real atmosphere will contain potentially thousands of semi-volatile organic compounds in addition to containing semi-volatile inorganic components such as ammonium nitrate. We show that equilibration of atmospherically reasonable concentrations of organic compounds with a growing particle as the ambient humidity increases has larger implications on cloud droplet formation than any other equilibrium compositional dependence, owing to inextricable linkage between the aerosol composition and a particles size under ambient conditions. Whilst previous attempts to account for co-condensation of gases other than water vapour have been restricted to one inorganic condensate, our method demonstrates that accounting for the co-condensation of any number of organic compounds substantially decreases the saturation ratio of water vapour required for droplet activation. This effect is far greater than any other compositional dependence; moreso even than the unphysical effect of surface tension reduction in aqueous organic mixtures, ignoring differences in bulk and surface surfactant concentrations.

Measurements of the light-absorbing material inside cloud droplets and its effect on cloud albedo

NASA Technical Reports Server (NTRS)

Twohy, C. H.; Clarke, A. D.; Warren, Stephen G.; Radke, L. F.; Charleson, R. J.

1990-01-01

Most of the measurements of light-absorbing aerosol particles made previously have been in non-cloudy air and therefore provide no insight into aerosol effects on cloud properties. Here, researchers describe an experiment designed to measure light absorption exclusively due to substances inside cloud droplets, compare the results to related light absorption measurements, and evaluate possible effects on the albedo of clouds. The results of this study validate those of Twomey and Cocks and show that the measured levels of light-absorbing material are negligible for the radiative properties of realistic clouds. For the measured clouds, which appear to have been moderately polluted, the amount of elemental carbon (EC) present was insufficient to affect albedo. Much higher contaminant levels or much larger droplets than those measured would be necessary to significantly alter the radiative properties. The effect of the concentrations of EC actually measured on the albedo of snow, however, would be much more pronounced since, in contrast to clouds, snowpacks are usually optically semi-infinite and have large particle sizes.

An interfacial mechanism for cloud droplet formation on organic aerosols

DOE PAGES

Ruehl, C. R.; Davies, J. F.; Wilson, K. R.

2016-03-25

Accurate predictions of aerosol/cloud interactions require simple, physically accurate parameterizations of the cloud condensation nuclei (CCN) activity of aerosols. Current models assume that organic aerosol species contribute to CCN activity by lowering water activity. We measured droplet diameters at the point of CCN activation for particles composed of dicarboxylic acids or secondary organic aerosol and ammonium sulfate. Droplet activation diameters were 40 to 60% larger than predicted if the organic was assumed to be dissolved within the bulk droplet, suggesting that a new mechanism is needed to explain cloud droplet formation. A compressed film model explains how surface tension depressionmore » by interfacial organic molecules can alter the relationship between water vapor supersaturation and droplet size (i.e., the Köhler curve), leading to the larger diameters observed at activation.« less

An interfacial mechanism for cloud droplet formation on organic aerosols

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ruehl, C. R.; Davies, J. F.; Wilson, K. R.

Accurate predictions of aerosol/cloud interactions require simple, physically accurate parameterizations of the cloud condensation nuclei (CCN) activity of aerosols. Current models assume that organic aerosol species contribute to CCN activity by lowering water activity. We measured droplet diameters at the point of CCN activation for particles composed of dicarboxylic acids or secondary organic aerosol and ammonium sulfate. Droplet activation diameters were 40 to 60% larger than predicted if the organic was assumed to be dissolved within the bulk droplet, suggesting that a new mechanism is needed to explain cloud droplet formation. A compressed film model explains how surface tension depressionmore » by interfacial organic molecules can alter the relationship between water vapor supersaturation and droplet size (i.e., the Köhler curve), leading to the larger diameters observed at activation.« less

An interfacial mechanism for cloud droplet formation on organic aerosols.

PubMed

Ruehl, Christopher R; Davies, James F; Wilson, Kevin R

2016-03-25

Accurate predictions of aerosol/cloud interactions require simple, physically accurate parameterizations of the cloud condensation nuclei (CCN) activity of aerosols. Current models assume that organic aerosol species contribute to CCN activity by lowering water activity. We measured droplet diameters at the point of CCN activation for particles composed of dicarboxylic acids or secondary organic aerosol and ammonium sulfate. Droplet activation diameters were 40 to 60% larger than predicted if the organic was assumed to be dissolved within the bulk droplet, suggesting that a new mechanism is needed to explain cloud droplet formation. A compressed film model explains how surface tension depression by interfacial organic molecules can alter the relationship between water vapor supersaturation and droplet size (i.e., the Köhler curve), leading to the larger diameters observed at activation. Copyright © 2016, American Association for the Advancement of Science.

Summertime observations of elevated levels of ultrafine particles in the high Arctic marine boundary layer

NASA Astrophysics Data System (ADS)

Burkart, Julia; Willis, Megan D.; Bozem, Heiko; Thomas, Jennie L.; Law, Kathy; Hoor, Peter; Aliabadi, Amir A.; Köllner, Franziska; Schneider, Johannes; Herber, Andreas; Abbatt, Jonathan P. D.; Leaitch, W. Richard

2017-05-01

Motivated by increasing levels of open ocean in the Arctic summer and the lack of prior altitude-resolved studies, extensive aerosol measurements were made during 11 flights of the NETCARE July 2014 airborne campaign from Resolute Bay, Nunavut. Flights included vertical profiles (60 to 3000 m above ground level) over open ocean, fast ice, and boundary layer clouds and fogs. A general conclusion, from observations of particle numbers between 5 and 20 nm in diameter (N5 - 20), is that ultrafine particle formation occurs readily in the Canadian high Arctic marine boundary layer, especially just above ocean and clouds, reaching values of a few thousand particles cm-3. By contrast, ultrafine particle concentrations are much lower in the free troposphere. Elevated levels of larger particles (for example, from 20 to 40 nm in size, N20 - 40) are sometimes associated with high N5 - 20, especially over low clouds, suggestive of aerosol growth. The number densities of particles greater than 40 nm in diameter (N > 40) are relatively depleted at the lowest altitudes, indicative of depositional processes that will lower the condensation sink and promote new particle formation. The number of cloud condensation nuclei (CCN; measured at 0.6 % supersaturation) are positively correlated with the numbers of small particles (down to roughly 30 nm), indicating that some fraction of these newly formed particles are capable of being involved in cloud activation. Given that the summertime marine Arctic is a biologically active region, it is important to better establish the links between emissions from the ocean and the formation and growth of ultrafine particles within this rapidly changing environment.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zardecki, A.

The effect of multiple scattering on the validity of the Beer-Lambert law is discussed for a wide range of particle-size parameters and optical depths. To predict the amount of received radiant power, appropriate correction terms are introduced. For particles larger than or comparable to the wavelength of radiation, the small-angle approximation is adequate; whereas for small densely packed particles, the diffusion theory is advantageously employed. These two approaches are used in the context of the problem of laser-beam propagation in a dense aerosol medium. In addition, preliminary results obtained by using a two-dimensional finite-element discrete-ordinates transport code are described. Multiple-scatteringmore » effects for laser propagation in fog, cloud, rain, and aerosol cloud are modeled.« less

Sedimentation Efficiency of Condensation Clouds in Substellar Atmospheres

NASA Astrophysics Data System (ADS)

Gao, Peter; Marley, Mark S.; Ackerman, Andrew S.

2018-03-01

Condensation clouds in substellar atmospheres have been widely inferred from spectra and photometric variability. Up until now, their horizontally averaged vertical distribution and mean particle size have been largely characterized using models, one of which is the eddy diffusion–sedimentation model from Ackerman and Marley that relies on a sedimentation efficiency parameter, f sed, to determine the vertical extent of clouds in the atmosphere. However, the physical processes controlling the vertical structure of clouds in substellar atmospheres are not well understood. In this work, we derive trends in f sed across a large range of eddy diffusivities (K zz ), gravities, material properties, and cloud formation pathways by fitting cloud distributions calculated by a more detailed cloud microphysics model. We find that f sed is dependent on K zz , but not gravity, when K zz is held constant. f sed is most sensitive to the nucleation rate of cloud particles, as determined by material properties like surface energy and molecular weight. High surface energy materials form fewer, larger cloud particles, leading to large f sed (>1), and vice versa for materials with low surface energy. For cloud formation via heterogeneous nucleation, f sed is sensitive to the condensation nuclei flux and radius, connecting cloud formation in substellar atmospheres to the objects’ formation environments and other atmospheric aerosols. These insights could lead to improved cloud models that help us better understand substellar atmospheres. For example, we demonstrate that f sed could increase with increasing cloud base depth in an atmosphere, shedding light on the nature of the brown dwarf L/T transition.

Sensitivity of simulated snow cloud properties to mass-diameter parameterizations.

NASA Astrophysics Data System (ADS)

Duffy, G.; Nesbitt, S. W.; McFarquhar, G. M.

2015-12-01

Mass to diameter (m-D) relationships are used in model parameterization schemes to represent ice cloud microphysics and in retrievals of bulk cloud properties from remote sensing instruments. One of the most common relationships, used in the current Global Precipitation Measurement retrieval algorithm for example, assigns the density of snow as a constant tenth of the density of ice (0.1g/m^3). This assumption stands in contrast to the results of derived m-D relationships of snow particles, which imply decreasing particle densities at larger sizes and result in particle masses orders of magnitude below the constant density relationship. In this study, forward simulations of bulk cloud properties (e.g., total water content, radar reflectivity and precipitation rate) derived from measured size distributions using several historical m-D relationships are presented. This expands upon previous studies that mainly focused on smaller ice particles because of the examination of precipitation-sized particles here. In situ and remote sensing data from the GPM Cold season Experiment (GCPEx) and Canadian CloudSAT/Calypso Validation Program (C3VP), both synoptic snowstorm field experiments in southern Ontario, Canada, are used to evaluate the forward simulations against total water content measured by the Nevzorov and Cloud Spectrometer and Impactor (CSI) probe, radar reflectivity measured by a C band ground based radar and a nadir pointing Ku/Ka dual frequency airborne radar, and precipitation rate measured by a 2D video disdrometer. There are differences between the bulk cloud properties derived using varying m-D relations, with constant density assumptions producing results differing substantially from the bulk measured quantities. The variability in bulk cloud properties derived using different m-D relations is compared against the natural variability in those parameters seen in the GCPEx and C3VP field experiments.

Evaluating the impact of above-cloud aerosols on cloud optical depth retrievals from MODIS

NASA Astrophysics Data System (ADS)

Alfaro, Ricardo

Using two different operational Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) cloud optical depth (COD) retrievals (visible and shortwave infrared), the impacts of above-cloud absorbing aerosols on the standard COD retrievals are evaluated. For fine-mode aerosol particles, aerosol optical depth (AOD) values diminish sharply from the visible to the shortwave infrared channels. Thus, a suppressed above-cloud particle radiance aliasing effect occurs for COD retrievals using shortwave infrared channels. Aerosol Index (AI) from the spatially and temporally collocated Ozone Monitoring Instrument (OMI) are used to identify above-cloud aerosol particle loading over the southern Atlantic Ocean, including both smoke and dust from the African sub-continent. MODIS and OMI Collocated Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) data are used to constrain cloud phase and provide contextual above-cloud AOD values. The frequency of occurrence of above-cloud aerosols is depicted on a global scale for the spring and summer seasons from OMI and CALIOP, thus indicating the significance of the problem. Seasonal frequencies for smoke-over-cloud off the southwestern Africa coastline reach 20--50% in boreal summer. We find a corresponding low COD bias of 10--20% for standard MODIS COD retrievals when averaged OMI AI are larger than 1.0. No such bias is found over the Saharan dust outflow region off northern Africa, since both MODIS visible and shortwave in channels are vulnerable to dust particle aliasing, and thus a COD impact cannot be isolated with this method. A similar result is found for a smaller domain, in the Gulf of Tonkin region, from smoke advection over marine stratocumulus clouds and outflow into the northern South China Sea in spring. This study shows the necessity of accounting for the above-cloud aerosol events for future studies using standard MODIS cloud products in biomass burning outflow regions, through the use of collocated OMI AI and supplementary MODIS shortwave infrared COD products.

Space Weather Connections to Clouds and Climate

NASA Astrophysics Data System (ADS)

Tinsley, B. A.

2004-12-01

There is now a considerable amount of observational data and theoretical work pointing to a link between space weather and atmospheric electricity, and then between atmospheric electricity and cloud cover and precipitation, which ultimately affect climate and the biosphere. Studies so far have been largely confined to the Earth, but may be applicable to all planets with clouds in their atmospheres. The current density Jz, that is the return current flowing downward through clouds in the global circuit, is modulated by the galactic cosmic ray flux; by solar energetic particles; by the dawn-dusk polar cap potential difference; and by the precipitation of relativistic electrons from the radiation belts. The flow of Jz through clouds generates unipolar space charge, which is positive at cloud tops and negative at cloud base. This charge attaches to aerosol particles, and affects their interaction with other particles and droplets. Ultrafine aerosol particles are formed around ions and are preserved from scavenging on background aerosols, and preserved for growth by vapor deposition, by space charge at the bases and tops of layer clouds. There is electro-preservation of both ultrafines and of existing CCN that leads to increases in CCN concentration, and increases in cloud cover and reduction in both droplet size and precipitation by the `indirect aerosol effect'. For cold clouds and larger aerosol particles that act as ice forming nuclei, the rate of scavenging of the IFN by large supercooled droplets varies with space charge. Changes in space weather affect both ion production and Jz in planetary atmospheres. In addition, changes in cosmic ray flux affect conductivity within thunderclouds and may affect the output of the thundercloud generators in the global circuit. Thus all four processes, (a) ion-induced nucleation, (b) electro-preservation of leading to increases in CCN concentration and the indirect aerosol effect, (c) contact ice nucleation affecting the production of ices, (d) cosmic ray effects on the generators of the global circuit, are potential links between space weather and life on planets.

Observations of Aircraft Dissipation Trails from GOES

NASA Technical Reports Server (NTRS)

Duda, David P.; Minnis, Patrick

2002-01-01

Two cases of distrails (aircraft dissipation trails) with associated fall streak clouds were analyzed using multispectral geostationary satellite data. One distrail was observed on 23 July 2000 in a single cloud layer over southeastern Virginia and the Chesapeake Bay. Another set of trails developed on 6 January 2000 at the top of multilayer clouds off the coasts of Georgia and South Carolina. The distrails on both days formed in optically thin, midlevel stratified clouds with cloud-top heights between 7.6 and 9.1 km. The distrail features remained intact and easily visible from satellite images for 1-2 h in spite of winds near 50 km at cloud level. The width of the distrails spread as far as 20 km within 90 min or less. Differences between the optical properties of the clouds surrounding the trails and those of the fall streak particles inside the distrails allowed for easy identification of the fall streak clouds in either the 3.9-micrometer brightness temperature imagery, or the 10.7-micrometer - 12.0-micrometer brightness temperature difference. Although the three-channel infrared retrieval was better at retrieving cloud properties in the multilayer cloud case, two independent remote sensing retrievals of both distrail cases showed that the fall streaks had larger particle sizes than the clouds outside of the trails.

Microwave Polarized Signatures Generated within Cloud Systems: SSM/I Observations Interpreted with Radiative Transfer Simulations

NASA Technical Reports Server (NTRS)

Prigent, Catherine; Pardo, Juan R.; Mishchenko, Michael I.; Rossow, Willaim B.; Hansen, James E. (Technical Monitor)

2001-01-01

Special Sensor Microwave /Imager (SSM/I) observations in cloud systems are studied over the tropics. Over optically thick cloud systems, presence of polarized signatures at 37 and 85 GHz is evidenced and analyzed with the help of cloud top temperature and optical thickness extracted from visible and IR satellite observations. Scattering signatures at 85 GHz (TbV(85) less than or = 250 K) are associated with polarization differences greater than or = 6 K, approx. 50%, of the time over ocean and approx. 40% over land. In addition. over thick clouds the polarization difference at 37 GHz is rarely negligible. The polarization differences at 37 and 85 GHz do not stem from the surface but are generated in regions of relatively homogeneous clouds having high liquid water content. To interpret the observations, a radiative transfer model that includes the scattering by non-spherical particles is developed. based on the T-matrix approach and using the doubling and adding method. In addition to handling randomly and perfectly oriented particles, this model can also simulate the effect of partial orientation of the hydrometeors. Microwave brightness temperatures are simulated at SSM/I frequencies and are compared with the observations. Polarization differences of approx. 2 K can be simulated at 37 GHz over a rain layer, even using spherical drops. The polarization difference is larger for oriented non-spherical particles. The 85 GHz simulations are very sensitive to the ice phase of the cloud. Simulations with spherical particles or with randomly oriented non-spherical ice particles cannot replicate the observed polarization differences. However, with partially oriented non-spherical particles, the observed polarized signatures at 85 GHz are explained, and the sensitivity of the scattering characteristics to the particle size, asphericity, and orientation is analyzed. Implications on rain and ice retrievals are discussed.

Experimental studies of aerosol- cloud droplet interactions at the puy de Dome observatory (France)

NASA Astrophysics Data System (ADS)

Laj, P.; Dupuy, R.; Sellegri, K.; Pichon, J.; Fournol, J.; Cortes, L.; Preunkert, S.; Legrand, M.

2001-05-01

The interactions between aerosol particles, gases and cloud droplets were studied at the puy de Dome cloud station (France, 1465 a.s.l.) during winter 2000. The partitioning of gas and aerosol species between interstitial and condensed phases is achieved using a series of instrumentation including a newly developed dual counter-flow virtual impactor (CVI)/ Round jet impactor (RJI) system. The RJI/CVI system, coupled with measurement of cloud microphysical properties, provided direct observation of number and mass partitioning of aerosols under different air mass conditions. Preliminary results from this field experiment allowed for the characterization of size segregated chemical composition of CCNs and of interstitial aerosols by means of gravimetric analysis and ion chromatography. It appears that CCNs are clearly enriched in soluble species as respect to interstitial aerosols. We found evidences of limited growth of Ca2+ - rich coarse particles (>1 μm) that did not form droplets larger than the 5 μm CVI cut-off. The number partitioning of aerosol particles between interstitial and condensed phases clearly depends upon cloud microphysics and aerosol properties and therefore undergoes different behaviour according to air mass origin. However, results cannot be fully explained by diffusion growth alone, in particular for high cloud LWC.

Influence of particle size distribution on reflected and transmitted light from clouds.

PubMed

Kattawar, G W; Plass, G N

1968-05-01

The light reflected and transmitted from clouds with various drop size distributions is calculated by a Monte Carlo technique. Six different models are used for the drop size distribution: isotropic, Rayleigh, haze continental, haze maritime, cumulus, and nimbostratus. The scattering function for each model is calculated from the Mie theory. In general, the reflected and transmitted radiances for the isotropic and Rayleigh models tend to be similar, as are those for the various haze and cloud models. The reflected radiance is less for the haze and cloud models than for the isotropic and Rayleigh models/except for an angle of incidence near the horizon when it is larger around the incident beam direction. The transmitted radiance is always much larger for the haze and cloud models near the incident direction; at distant angles it is less for small and moderate optical thicknesses and greater for large optical thicknesses (all comparisons to isotropic and Rayleigh models). The downward flux, cloud albedo, and ean optical path are discussed. The angular spread of the beam as a function of optical thickness is shown for the nimbostratus model.

Lidar inelastic multiple-scattering parameters of cirrus particle ensembles determined with geometrical-optics crystal phase functions.

PubMed

Reichardt, J; Hess, M; Macke, A

2000-04-20

Multiple-scattering correction factors for cirrus particle extinction coefficients measured with Raman and high spectral resolution lidars are calculated with a radiative-transfer model. Cirrus particle-ensemble phase functions are computed from single-crystal phase functions derived in a geometrical-optics approximation. Seven crystal types are considered. In cirrus clouds with height-independent particle extinction coefficients the general pattern of the multiple-scattering parameters has a steep onset at cloud base with values of 0.5-0.7 followed by a gradual and monotonic decrease to 0.1-0.2 at cloud top. The larger the scattering particles are, the more gradual is the rate of decrease. Multiple-scattering parameters of complex crystals and of imperfect hexagonal columns and plates can be well approximated by those of projected-area equivalent ice spheres, whereas perfect hexagonal crystals show values as much as 70% higher than those of spheres. The dependencies of the multiple-scattering parameters on cirrus particle spectrum, base height, and geometric depth and on the lidar parameters laser wavelength and receiver field of view, are discussed, and a set of multiple-scattering parameter profiles for the correction of extinction measurements in homogeneous cirrus is provided.

Aerosol characteristics and particle production in the upper troposphere over the Amazon Basin

NASA Astrophysics Data System (ADS)

Andreae, Meinrat O.; Afchine, Armin; Albrecht, Rachel; Amorim Holanda, Bruna; Artaxo, Paulo; Barbosa, Henrique M. J.; Borrmann, Stephan; Cecchini, Micael A.; Costa, Anja; Dollner, Maximilian; Fütterer, Daniel; Järvinen, Emma; Jurkat, Tina; Klimach, Thomas; Konemann, Tobias; Knote, Christoph; Krämer, Martina; Krisna, Trismono; Machado, Luiz A. T.; Mertes, Stephan; Minikin, Andreas; Pöhlker, Christopher; Pöhlker, Mira L.; Pöschl, Ulrich; Rosenfeld, Daniel; Sauer, Daniel; Schlager, Hans; Schnaiter, Martin; Schneider, Johannes; Schulz, Christiane; Spanu, Antonio; Sperling, Vinicius B.; Voigt, Christiane; Walser, Adrian; Wang, Jian; Weinzierl, Bernadett; Wendisch, Manfred; Ziereis, Helmut

2018-01-01

Airborne observations over the Amazon Basin showed high aerosol particle concentrations in the upper troposphere (UT) between 8 and 15 km altitude, with number densities (normalized to standard temperature and pressure) often exceeding those in the planetary boundary layer (PBL) by 1 or 2 orders of magnitude. The measurements were made during the German-Brazilian cooperative aircraft campaign ACRIDICON-CHUVA, where ACRIDICON stands for Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems and CHUVA is the acronym for Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (global precipitation measurement), on the German High Altitude and Long Range Research Aircraft (HALO). The campaign took place in September-October 2014, with the objective of studying tropical deep convective clouds over the Amazon rainforest and their interactions with atmospheric trace gases, aerosol particles, and atmospheric radiation. Aerosol enhancements were observed consistently on all flights during which the UT was probed, using several aerosol metrics, including condensation nuclei (CN) and cloud condensation nuclei (CCN) number concentrations and chemical species mass concentrations. The UT particles differed sharply in their chemical composition and size distribution from those in the PBL, ruling out convective transport of combustion-derived particles from the boundary layer (BL) as a source. The air in the immediate outflow of deep convective clouds was depleted of aerosol particles, whereas strongly enhanced number concentrations of small particles (< 90 nm diameter) were found in UT regions that had experienced outflow from deep convection in the preceding 5-72 h. We also found elevated concentrations of larger (> 90 nm) particles in the UT, which consisted mostly of organic matter and nitrate and were very effective CCN. Our findings suggest a conceptual model, where production of new aerosol particles takes place in the continental UT from biogenic volatile organic material brought up by deep convection and converted to condensable species in the UT. Subsequently, downward mixing and transport of upper tropospheric aerosol can be a source of particles to the PBL, where they increase in size by the condensation of biogenic volatile organic compound (BVOC) oxidation products. This may be an important source of aerosol particles for the Amazonian PBL, where aerosol nucleation and new particle formation have not been observed. We propose that this may have been the dominant process supplying secondary aerosol particles in the pristine atmosphere, making clouds the dominant control of both removal and production of atmospheric particles.

Aerosol characteristics and particle production in the upper troposphere over the Amazon Basin

DOE PAGES

Andreae, Meinrat O.; Afchine, Armin; Albrecht, Rachel; ...

2018-01-25

Airborne observations over the Amazon Basin showed high aerosol particle concentrations in the upper troposphere (UT) between 8 and 15 km altitude, with number densities (normalized to standard temperature and pressure) often exceeding those in the planetary boundary layer (PBL) by 1 or 2 orders of magnitude. The measurements were made during the German–Brazilian cooperative aircraft campaign ACRIDICON–CHUVA, where ACRIDICON stands for Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems and CHUVA is the acronym for Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (globalmore » precipitation measurement), on the German High Altitude and Long Range Research Aircraft (HALO). The campaign took place in September–October 2014, with the objective of studying tropical deep convective clouds over the Amazon rainforest and their interactions with atmospheric trace gases, aerosol particles, and atmospheric radiation. Aerosol enhancements were observed consistently on all flights during which the UT was probed, using several aerosol metrics, including condensation nuclei (CN) and cloud condensation nuclei (CCN) number concentrations and chemical species mass concentrations. The UT particles differed sharply in their chemical composition and size distribution from those in the PBL, ruling out convective transport of combustion-derived particles from the boundary layer (BL) as a source. The air in the immediate outflow of deep convective clouds was depleted of aerosol particles, whereas strongly enhanced number concentrations of small particles (< 90 nm diameter) were found in UT regions that had experienced outflow from deep convection in the preceding 5–72 h. We also found elevated concentrations of larger (> 90 nm) particles in the UT, which consisted mostly of organic matter and nitrate and were very effective CCN. Our findings suggest a conceptual model, where production of new aerosol particles takes place in the continental UT from biogenic volatile organic material brought up by deep convection and converted to condensable species in the UT. Subsequently, downward mixing and transport of upper tropospheric aerosol can be a source of particles to the PBL, where they increase in size by the condensation of biogenic volatile organic compound (BVOC) oxidation products. This may be an important source of aerosol particles for the Amazonian PBL, where aerosol nucleation and new particle formation have not been observed. We propose that this may have been the dominant process supplying secondary aerosol particles in the pristine atmosphere, making clouds the dominant control of both removal and production of atmospheric particles.« less

Aerosol characteristics and particle production in the upper troposphere over the Amazon Basin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andreae, Meinrat O.; Afchine, Armin; Albrecht, Rachel

Airborne observations over the Amazon Basin showed high aerosol particle concentrations in the upper troposphere (UT) between 8 and 15 km altitude, with number densities (normalized to standard temperature and pressure) often exceeding those in the planetary boundary layer (PBL) by 1 or 2 orders of magnitude. The measurements were made during the German–Brazilian cooperative aircraft campaign ACRIDICON–CHUVA, where ACRIDICON stands for Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems and CHUVA is the acronym for Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (globalmore » precipitation measurement), on the German High Altitude and Long Range Research Aircraft (HALO). The campaign took place in September–October 2014, with the objective of studying tropical deep convective clouds over the Amazon rainforest and their interactions with atmospheric trace gases, aerosol particles, and atmospheric radiation. Aerosol enhancements were observed consistently on all flights during which the UT was probed, using several aerosol metrics, including condensation nuclei (CN) and cloud condensation nuclei (CCN) number concentrations and chemical species mass concentrations. The UT particles differed sharply in their chemical composition and size distribution from those in the PBL, ruling out convective transport of combustion-derived particles from the boundary layer (BL) as a source. The air in the immediate outflow of deep convective clouds was depleted of aerosol particles, whereas strongly enhanced number concentrations of small particles (< 90 nm diameter) were found in UT regions that had experienced outflow from deep convection in the preceding 5–72 h. We also found elevated concentrations of larger (> 90 nm) particles in the UT, which consisted mostly of organic matter and nitrate and were very effective CCN. Our findings suggest a conceptual model, where production of new aerosol particles takes place in the continental UT from biogenic volatile organic material brought up by deep convection and converted to condensable species in the UT. Subsequently, downward mixing and transport of upper tropospheric aerosol can be a source of particles to the PBL, where they increase in size by the condensation of biogenic volatile organic compound (BVOC) oxidation products. This may be an important source of aerosol particles for the Amazonian PBL, where aerosol nucleation and new particle formation have not been observed. We propose that this may have been the dominant process supplying secondary aerosol particles in the pristine atmosphere, making clouds the dominant control of both removal and production of atmospheric particles.« less

Unveiling aerosol-cloud interactions - Part 1: Cloud contamination in satellite products enhances the aerosol indirect forcing estimate

NASA Astrophysics Data System (ADS)

Christensen, Matthew W.; Neubauer, David; Poulsen, Caroline A.; Thomas, Gareth E.; McGarragh, Gregory R.; Povey, Adam C.; Proud, Simon R.; Grainger, Roy G.

2017-11-01

Increased concentrations of aerosol can enhance the albedo of warm low-level cloud. Accurately quantifying this relationship from space is challenging due in part to contamination of aerosol statistics near clouds. Aerosol retrievals near clouds can be influenced by stray cloud particles in areas assumed to be cloud-free, particle swelling by humidification, shadows and enhanced scattering into the aerosol field from (3-D radiative transfer) clouds. To screen for this contamination we have developed a new cloud-aerosol pairing algorithm (CAPA) to link cloud observations to the nearest aerosol retrieval within the satellite image. The distance between each aerosol retrieval and nearest cloud is also computed in CAPA. Results from two independent satellite imagers, the Advanced Along-Track Scanning Radiometer (AATSR) and Moderate Resolution Imaging Spectroradiometer (MODIS), show a marked reduction in the strength of the intrinsic aerosol indirect radiative forcing when selecting aerosol pairs that are located farther away from the clouds (-0.28±0.26 W m-2) compared to those including pairs that are within 15 km of the nearest cloud (-0.49±0.18 W m-2). The larger aerosol optical depths in closer proximity to cloud artificially enhance the relationship between aerosol-loading, cloud albedo, and cloud fraction. These results suggest that previous satellite-based radiative forcing estimates represented in key climate reports may be exaggerated due to the inclusion of retrieval artefacts in the aerosol located near clouds.

The Apparent Bluing of Aerosols Near Clouds

NASA Technical Reports Server (NTRS)

Marshak, Alexander

2008-01-01

Numerous studies based on satellite observations have reported that aerosol optical depths increase with increasing cloud cover. Part of the increase comes from the humidification and consequent growth of aerosol particles in the moist cloud environment, but part comes from 3D cloud-radiative transfer effects on the retrieved aerosol properties. Often, discerning whether the observed increases in aerosol optical depths are artifacts or real proves difficult. I describe a simple model that quantifies the enhanced illumination of cloud-free columns in the vicinity of clouds that are used in the aerosol retrievals. This model is based on the assumption that the enhancement in the cloud-free column radiance comes from enhanced Rayleigh scattering that results from the presence of the nearby clouds. This assumption leads to a larger increase of AOT for shorter wavelengths, or to a "bluing" of aerosols near clouds. Examples from the MODIS observations that illustrate the apparent bluing of aerosols near clouds will be discussed.

Large Eddy Simulation of Cirrus Clouds

NASA Technical Reports Server (NTRS)

Wu, Ting; Cotton, William R.

1999-01-01

The Regional Atmospheric Modeling System (RAMS) with mesoscale interactive nested-grids and a Large-Eddy Simulation (LES) version of RAMS, coupled to two-moment microphysics and a new two-stream radiative code were used to investigate the dynamic, microphysical, and radiative aspects of the November 26, 1991 cirrus event. Wu (1998) describes the results of that research in full detail and is enclosed as Appendix 1. The mesoscale nested grid simulation successfully reproduced the large scale circulation as compared to the Mesoscale Analysis and Prediction System's (MAPS) analyses and other observations. Three cloud bands which match nicely to the three cloud lines identified in an observational study (Mace et al., 1995) are predicted on Grid #2 of the nested grids, even though the mesoscale simulation predicts a larger west-east cloud width than what was observed. Large-eddy simulations (LES) were performed to study the dynamical, microphysical, and radiative processes in the 26 November 1991 FIRE 11 cirrus event. The LES model is based on the RAMS version 3b developed at Colorado State University. It includes a new radiation scheme developed by Harrington (1997) and a new subgrid scale model developed by Kosovic (1996). The LES model simulated a single cloud layer for Case 1 and a two-layer cloud structure for Case 2. The simulations demonstrated that latent heat release can play a significant role in the formation and development of cirrus clouds. For the thin cirrus in Case 1, the latent heat release was insufficient for the cirrus clouds to become positively buoyant. However, in some special cases such as Case 2, positively buoyant cells can be embedded within the cirrus layers. These cells were so active that the rising updraft induced its own pressure perturbations that affected the cloud evolution. Vertical profiles of the total radiative and latent heating rates indicated that for well developed, deep, and active cirrus clouds, radiative cooling and latent heating could be comparable in magnitude in the cloudy layer. This implies that latent heating cannot be neglected in the construction of a cirrus cloud model. The probability density function (PDF) of w was analyzed to assist in the parameterization of cloud-scale velocities in large-scale models. For the more radiatively-driven, thin cirrus case, the PDFs are approximately Gaussian. However, in the interior of the deep, convectively unstable case, the PDFs of w are multi-modal and very broad, indicating that parameterizing cloud-scale motions for such clouds can be very challenging. The results of this research are described in detail in a paper submitted to the Journal of Atmospheric Science (Wu and Cotton, 1999), which is enclosed as Appendix 2. Using soundings extracted from a mesoscale simulation of the November 26, 1991 cirrus event, the radiative effects on vapor deposition/sublimation of ice crystals was studied using a two-dimensional cloud-resolving model (CRM) version of RAMS, coupled to an explicit bin-resolving microphysics. The CRM simulations of the November 26, 1991 cirrus event demonstrate that the radiative impact on the diffusional growth (or sublimation) of ice crystals is significant. In this case, the ice particles experienced radiative warming. Model results show that radiative feedbacks in the diffusional growth of ice particles can be very complex. Radiative warming of an ice particle will restrict the particle's diffusional growth. In the case of radiative warming, ice particles larger than a certain size will experience so much radiative warming that surface ice saturation vapor pressures become large enough to cause sublimation of the larger crystals, while smaller crystals are growing by vapor deposition. However, ice mass production can be enhanced in the case of radiative cooling of an ice particle. For the November 26, 1991 cirrus event, radiative feedback results in significant reduction in the total ice mass, especially in the production of large ice crystals, and consequently, both radiative and dynamic properties of the cirrus cloud are significantly affected. A complete description of this research has been submitted as a paper to the Journal of Atmospheric Science (Wu et al., 1999), and included as Appendix 3.

Redistribution of ice nuclei between cloud and rain droplets: Parameterization and application to deep convective clouds

NASA Astrophysics Data System (ADS)

Paukert, M.; Hoose, C.; Simmel, M.

2017-03-01

In model studies of aerosol-dependent immersion freezing in clouds, a common assumption is that each ice nucleating aerosol particle corresponds to exactly one cloud droplet. In contrast, the immersion freezing of larger drops—"rain"—is usually represented by a liquid volume-dependent approach, making the parameterizations of rain freezing independent of specific aerosol types and concentrations. This may lead to inconsistencies when aerosol effects on clouds and precipitation shall be investigated, since raindrops consist of the cloud droplets—and corresponding aerosol particles—that have been involved in drop-drop-collisions. Here we introduce an extension to a two-moment microphysical scheme in order to account explicitly for particle accumulation in raindrops by tracking the rates of selfcollection, autoconversion, and accretion. This provides a direct link between ice nuclei and the primary formation of large precipitating ice particles. A new parameterization scheme of drop freezing is presented to consider multiple ice nuclei within one drop and effective drop cooling rates. In our test cases of deep convective clouds, we find that at altitudes which are most relevant for immersion freezing, the majority of potential ice nuclei have been converted from cloud droplets into raindrops. Compared to the standard treatment of freezing in our model, the less efficient mineral dust-based freezing results in higher rainwater contents in the convective core, affecting both rain and hail precipitation. The aerosol-dependent treatment of rain freezing can reverse the signs of simulated precipitation sensitivities to ice nuclei perturbations.

A Closure Study of Total Scattering Using Airborne In Situ Measurements from the Winter Phase of TCAP

DOE PAGES

Kassianov, Evgueni; Berg, Larry; Pekour, Mikhail; ...

2018-06-12

We examine the performance of our approach for calculating the total scattering coefficient of both non-absorbing and absorbing aerosol at ambient conditions from aircraft data. Our extended examination involves airborne in situ data collected by the U.S. Department of Energy’s (DOE) Gulf Stream 1 aircraft during winter over Cape Cod and the western North Atlantic Ocean as part of the Two-Column Aerosol Project (TCAP). The particle population represented by the winter dataset, in contrast with its summer counterpart, contains more hygroscopic particles and particles with an enhanced ability to absorb sunlight due to the larger fraction of black carbon. Moreover,more » the winter observations are characterized by more frequent clouds and a larger fraction of super-micron particles. We calculate model total scattering coefficient at ambient conditions using size spectra measured by optical particle counters (OPCs) and ambient complex refractive index (RI) estimated from measured chemical composition and relative humidity (RH). We demonstrate that reasonable agreement (~20% on average) between the observed and calculated scattering can be obtained under subsaturated ambient conditions (RH < 80%) by applying both screening for clouds and chemical composition data for the RI-based correction of the OPC-derived size spectra.« less

A Closure Study of Total Scattering Using Airborne In Situ Measurements from the Winter Phase of TCAP

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kassianov, Evgueni; Berg, Larry; Pekour, Mikhail

We examine the performance of our approach for calculating the total scattering coefficient of both non-absorbing and absorbing aerosol at ambient conditions from aircraft data. Our extended examination involves airborne in situ data collected by the U.S. Department of Energy’s (DOE) Gulf Stream 1 aircraft during winter over Cape Cod and the western North Atlantic Ocean as part of the Two-Column Aerosol Project (TCAP). The particle population represented by the winter dataset, in contrast with its summer counterpart, contains more hygroscopic particles and particles with an enhanced ability to absorb sunlight due to the larger fraction of black carbon. Moreover,more » the winter observations are characterized by more frequent clouds and a larger fraction of super-micron particles. We calculate model total scattering coefficient at ambient conditions using size spectra measured by optical particle counters (OPCs) and ambient complex refractive index (RI) estimated from measured chemical composition and relative humidity (RH). We demonstrate that reasonable agreement (~20% on average) between the observed and calculated scattering can be obtained under subsaturated ambient conditions (RH < 80%) by applying both screening for clouds and chemical composition data for the RI-based correction of the OPC-derived size spectra.« less

Radar observations of individual rain drops in the free atmosphere

PubMed Central

Schmidt, Jerome M.; Flatau, Piotr J.; Harasti, Paul R.; Yates, Robert D.; Littleton, Ricky; Pritchard, Michael S.; Fischer, Jody M.; Fischer, Erin J.; Kohri, William J.; Vetter, Jerome R.; Richman, Scott; Baranowski, Dariusz B.; Anderson, Mark J.; Fletcher, Ed; Lando, David W.

2012-01-01

Atmospheric remote sensing has played a pivotal role in the increasingly sophisticated representation of clouds in the numerical models used to assess global and regional climate change. This has been accomplished because the underlying bulk cloud properties can be derived from a statistical analysis of the returned microwave signals scattered by a diverse ensemble comprised of numerous cloud hydrometeors. A new Doppler radar, previously used to track small debris particles shed from the NASA space shuttle during launch, is shown to also have the capacity to detect individual cloud hydrometeors in the free atmosphere. Similar to the traces left behind on film by subatomic particles, larger cloud particles were observed to leave a well-defined radar signature (or streak), which could be analyzed to infer the underlying particle properties. We examine the unique radar and environmental conditions leading to the formation of the radar streaks and develop a theoretical framework which reveals the regulating role of the background radar reflectivity on their observed characteristics. This main expectation from theory is examined through an analysis of the drop properties inferred from radar and in situ aircraft measurements obtained in two contrasting regions of an observed multicellular storm system. The observations are placed in context of the parent storm circulation through the use of the radar’s unique high-resolution waveforms, which allow the bulk and individual hydrometeor properties to be inferred at the same time. PMID:22652569

Radar observations of individual rain drops in the free atmosphere.

PubMed

Schmidt, Jerome M; Flatau, Piotr J; Harasti, Paul R; Yates, Robert D; Littleton, Ricky; Pritchard, Michael S; Fischer, Jody M; Fischer, Erin J; Kohri, William J; Vetter, Jerome R; Richman, Scott; Baranowski, Dariusz B; Anderson, Mark J; Fletcher, Ed; Lando, David W

2012-06-12

Atmospheric remote sensing has played a pivotal role in the increasingly sophisticated representation of clouds in the numerical models used to assess global and regional climate change. This has been accomplished because the underlying bulk cloud properties can be derived from a statistical analysis of the returned microwave signals scattered by a diverse ensemble comprised of numerous cloud hydrometeors. A new Doppler radar, previously used to track small debris particles shed from the NASA space shuttle during launch, is shown to also have the capacity to detect individual cloud hydrometeors in the free atmosphere. Similar to the traces left behind on film by subatomic particles, larger cloud particles were observed to leave a well-defined radar signature (or streak), which could be analyzed to infer the underlying particle properties. We examine the unique radar and environmental conditions leading to the formation of the radar streaks and develop a theoretical framework which reveals the regulating role of the background radar reflectivity on their observed characteristics. This main expectation from theory is examined through an analysis of the drop properties inferred from radar and in situ aircraft measurements obtained in two contrasting regions of an observed multicellular storm system. The observations are placed in context of the parent storm circulation through the use of the radar's unique high-resolution waveforms, which allow the bulk and individual hydrometeor properties to be inferred at the same time.

Organic Aerosols as Cloud Condensation Nuclei

NASA Astrophysics Data System (ADS)

Hudson, J. G.

2002-05-01

The large organic component of the atmospheric aerosol contributes to both natural and anthropogenic cloud condensation nuclei (CCN). Moreover, some organic substances may reduce droplet surface tension (Facchini et al. 1999), while others may be partially soluble (Laaksonen et al. 1998), and others may inhibit water condensation. The interaction of organics with water need to be understood in order to better understand the indirect aerosol effect. Therefore, laboratory CCN spectral measurements of organic aerosols are presented. These are measurements of the critical supersaturation (Sc), the supersaturation needed to produce an activated cloud droplet, as a function of the size of the organic particles. Substances include sodium lauryl (dodecyl) sulfate, oxalic, adipic, pinonic, hexadecanedioic, glutaric, stearic, succinic, phthalic, and benzoic acids. These size-Sc relationships are compared with theoretical and measured size-Sc relationships of common inorganic compounds (e.g., NaCl, KI, ammonium and calcium sulfate). Unlike most inorganics some organics display variations in solubility per unit mass as a function of particle size. Those showing relatively greater solubility at smaller sizes may be attributable to surface tension reduction, which is greater for less water dilution, as is the case for smaller particles, which are less diluted at the critical sizes. This was the case for sodium dodecyl sulfate, which does reduce surface tension. Relatively greater solubility for larger particles may be caused by greater dissolution at the higher dilutions that occur with larger particles; this is partial solubility. Measurements are also presented of internal mixtures of various organic and inorganic substances. These measurements were done with two CCN spectrometers (Hudson 1989) operating simultaneously. These two instruments usually displayed similar results in spite of the fact that they have different flow rates and supersaturation profiles. The degree of agreement between these cloud chambers then tests and defines the limits of possible alterations of conventional Kohler theory (e.g., Kulmala et al. 1993).

Stratospheric ion and aerosol chemistry and possible links with cirrus cloud microphysics - A critical assessment

NASA Technical Reports Server (NTRS)

Mohnen, Volker A.

1990-01-01

Aspects of stratospheric ion chemistry and physics are assessed as they relate to aerosol formation and the transport of aerosols to upper tropospheric regions to create conditions favorable for cirrus cloud formation. It is found that ion-induced nucleation and other known phase transitions involving ions and sulfuric acid vapor are probably not efficient processes for stratospheric aerosol formation, and cannot compete with condensation of sulfuric acid on preexisting particles of volcanic or meteoritic origin which are larger than about 0.15 micron in radius. Thus, galactic cosmic rays cannot have a significant impact on stratospheric aerosol population. Changes in the stratospheric aerosol burden due to volcanos are up to two orders of magnitude larger than changes in ion densities. Thus, volcanic activity may modulate the radiative properties of cirrus clouds.

Climate impact of anthropogenic aerosols on cirrus clouds

NASA Astrophysics Data System (ADS)

Penner, J.; Zhou, C.

2017-12-01

Cirrus clouds have a net warming effect on the atmosphere and cover about 30% of the Earth's area. Aerosol particles initiate ice formation in the upper troposphere through modes of action that include homogeneous freezing of solution droplets, heterogeneous nucleation on solid particles immersed in a solution, and deposition nucleation of vapor onto solid particles. However, the efficacy with which particles act to form cirrus particles in a model depends on the representation of updrafts. Here, we use a representation of updrafts based on observations of gravity waves, and follow ice formation/evaporation during both updrafts and downdrafts. We examine the possible change in ice number concentration from anthropogenic soot originating from surface sources of fossil fuel and biomass burning and from aircraft particles that have previously formed ice in contrails. Results show that fossil fuel and biomass burning soot aerosols with this version exert a radiative forcing of -0.15±0.02 Wm-2 while aircraft aerosols that have been pre-activated within contrails exert a forcing of -0.20±0.06 Wm-2, but it is possible to decrease these estimates of forcing if a larger fraction of dust particles act as heterogeneous ice nuclei. In addition aircraft aerosols may warm the climate if a large fraction of these particles act as ice nuclei. The magnitude of the forcing in cirrus clouds can be comparable to the forcing exerted by anthropogenic aerosols on warm clouds. This assessment could therefore support climate models with high sensitivity to greenhouse gas forcing, while still allowing the models to fit the overall historical temperature change.

Parameterization of Cirrus Cloud Vertical Profiles and Geometrical Thickness Using CALIPSO and CloudSat Data

NASA Astrophysics Data System (ADS)

Khatri, P.; Iwabuchi, H.; Saito, M.

2017-12-01

High-level cirrus clouds, which normally occur over more than 20% of the globe, are known to have profound impacts on energy budget and climate change. The scientific knowledge regarding the vertical structure of such high-level cirrus clouds and their geometrical thickness are relatively poorer compared to low-level water clouds. Knowledge regarding cloud vertical structure is especially important in passive remote sensing of cloud properties using infrared channels or channels strongly influenced by gaseous absorption when clouds are geometrically thick and optically thin. Such information is also very useful for validating cloud resolving numerical models. This study analyzes global scale data of ice clouds identified by Cloud profiling Radar (CPR) onboard CloudSat and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard CALIPSO to parameterize (i) vertical profiles of ice water content (IWC), cloud-particle effective radius (CER), and ice-particle number concentration for varying ice water path (IWP) values and (ii) the relation of cloud geometrical thickness (CGT) with IWP and CER for varying cloud top temperature (CTT) values. It is found that the maxima in IWC and CER profile shifts towards cloud base with the increase of IWP. Similarly, if the cloud properties remain same, CGT shows an increasing trend with the decrease of CTT. The implementation of such cloud vertical inhomogeneity parameterization in the forward model used in the Integrated Cloud Analysis System ICAS (Iwabuchi et al., 2016) generally shows increase of brightness temperatures in infrared channels compared to vertically homogeneous cloud assumption. The cloud vertical inhomogeneity is found to bring noticeable changes in retrieved cloud properties. Retrieved CER and cloud top height become larger for optically thick cloud. We will show results of comparison of cloud properties retrieved from infrared measurements and active remote sensing.

Mars Aerosol Studies with the MGS TES Emission Phase Function Observations: Opacities, Particle Sizes, and Ice Cloud Types

NASA Astrophysics Data System (ADS)

Wolff, M. J.; Clancy, R. T.; Pitman, K. M.; Christensen, P. R.; Whitney, B. A.

2001-11-01

A full Mars year (1999-2001) of emission phase function (EPF) observations from Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) provide the most complete study of Mars dust and ice aerosol properties to date. TES visible (solar band average) and infrared spectral EPF sequences are analyzed self-consistently with detailed multiple scattering radiative transfer codes. As a consequence of the combined angular and wavelength coverage, we are able to define two distinct ice cloud types at 45\\arcdeg S-45\\arcdeg N latitudes on Mars. Type I ice clouds exhibit small particle sizes (1-2 \\micron\\ radii), as well as a broad, deep minimum in side-scattering that are potentially indicative of aligned ice grains. Type I ice aerosols are most prevalent in the southern hemisphere during Mars aphelion, but also appear more widely distributed in season and latitude as topographic and high altitude (>20 km) ice hazes. Type II ice clouds exhibit larger particle sizes (3-5 \\micron) and a much narrower side-scattering minimum, indicative of poorer grain alignment or a change in particle shape relative to the type I ice clouds. Type II ice clouds appear most prominently in the northern subtropical aphelion cloud belt, where relatively low altitudes water vapor saturation (10 km) coincide with strong advective transport. Retrieved dust particle radii of 1.5-1.8 \\micron\\ are consistent with Pathfinder and recent Viking/Mariner 9 reanalyses. Our analyses also find EPF-derived dust single scattering albedos (ssa) in agreement with those from Pathfinder. Spatial and seasonal changes in the dust ssa (0.92-0.95, solar band average) and phase functions suggest possible dust property variations, but may also be a consequence of variable high altitude ice hazes. The annual variations of both dust and ice clouds at 45S-45N latitudes are predominately orbital rather than seasonal in character and have shown remarkable repeatability during the portions of two Mars years observed by MGS.

Vertical Cloud Climatology During TC4 Derived from High-Altitude Aircraft Merged Lidar and Radar Profiles

NASA Technical Reports Server (NTRS)

Hlavka, Dennis; Tian, Lin; Hart, William; Li, Lihua; McGill, Matthew; Heymsfield, Gerald

2009-01-01

Aircraft lidar works by shooting laser pulses toward the earth and recording the return time and intensity of any of the light returning to the aircraft after scattering off atmospheric particles and/or the Earth s surface. The scattered light signatures can be analyzed to tell the exact location of cloud and aerosol layers and, with the aid of a few optical assumptions, can be analyzed to retrieve estimates of optical properties such as atmospheric transparency. Radar works in a similar fashion except it sends pulses toward earth at a much larger wavelength than lidar. Radar records the return time and intensity of cloud or rain reflection returning to the aircraft. Lidar can measure scatter from optically thin cirrus and aerosol layers whose particles are too small for the radar to detect. Radar can provide reflection profiles through thick cloud layers of larger particles that lidar cannot penetrate. Only after merging the two instrument products can accurate measurements of the locations of all layers in the full atmospheric column be achieved. Accurate knowledge of the vertical distribution of clouds is important information for understanding the Earth/atmosphere radiative balance and for improving weather/climate forecast models. This paper describes one such merged data set developed from the Tropical Composition, Cloud and Climate Coupling (TC4) experiment based in Costa Rica in July-August 2007 using the nadir viewing Cloud Physics Lidar (CPL) and the Cloud Radar System (CRS) on board the NASA ER-2 aircraft. Statistics were developed concerning cloud probability through the atmospheric column and frequency of the number of cloud layers. These statistics were calculated for the full study area, four sub-regions, and over land compared to over ocean across all available flights. The results are valid for the TC4 experiment only, as preferred cloud patterns took priority during mission planning. The TC4 Study Area was a very cloudy region, with cloudy profiles occurring 94 percent of the time during the ER-2 flights. One to three cloud layers were common, with the average calculated at 2.03 layers per profile. The upper troposphere had a cloud frequency generally over 30%, reaching 42 percent near 13 km during the study. There were regional differences. The Caribbean was much clearer than the Pacific regions. Land had a much higher frequency of high clouds than ocean areas. One region just south and west of Panama had a high probability of clouds below 15 km altitude with the frequency never dropping below 25% and reaching a maximum of 60% at 11-13 km altitude. These cloud statistics will help characterize the cloud volume for TC4 scientists as they try to understand the complexities of the tropical atmosphere.

Further evidence for CCN aerosol concentrations determining the height of warm rain and ice initiation in convective clouds over the Amazon basin

NASA Astrophysics Data System (ADS)

Campos Braga, Ramon; Rosenfeld, Daniel; Weigel, Ralf; Jurkat, Tina; Andreae, Meinrat O.; Wendisch, Manfred; Pöschl, Ulrich; Voigt, Christiane; Mahnke, Christoph; Borrmann, Stephan; Albrecht, Rachel I.; Molleker, Sergej; Vila, Daniel A.; Machado, Luiz A. T.; Grulich, Lucas

2017-12-01

We have investigated how aerosols affect the height above cloud base of rain and ice hydrometeor initiation and the subsequent vertical evolution of cloud droplet size and number concentrations in growing convective cumulus. For this purpose we used in situ data of hydrometeor size distributions measured with instruments mounted on HALO aircraft during the ACRIDICON-CHUVA campaign over the Amazon during September 2014. The results show that the height of rain initiation by collision and coalescence processes (Dr, in units of meters above cloud base) is linearly correlated with the number concentration of droplets (Nd in cm-3) nucleated at cloud base (Dr ≈ 5 ṡ Nd). Additional cloud processes associated with Dr, such as GCCN, cloud, and mixing with ambient air and other processes, produce deviations of ˜ 21 % in the linear relationship, but it does not mask the clear relationship between Dr and Nd, which was also found at different regions around the globe (e.g., Israel and India). When Nd exceeded values of about 1000 cm-3, Dr became greater than 5000 m, and the first observed precipitation particles were ice hydrometeors. Therefore, no liquid water raindrops were observed within growing convective cumulus during polluted conditions. Furthermore, the formation of ice particles also took place at higher altitudes in the clouds in polluted conditions because the resulting smaller cloud droplets froze at colder temperatures compared to the larger drops in the unpolluted cases. The measured vertical profiles of droplet effective radius (re) were close to those estimated by assuming adiabatic conditions (rea), supporting the hypothesis that the entrainment and mixing of air into convective clouds is nearly inhomogeneous. Additional CCN activation on aerosol particles from biomass burning and air pollution reduced re below rea, which further inhibited the formation of raindrops and ice particles and resulted in even higher altitudes for rain and ice initiation.

Microphysical effects determine macrophysical response for aerosol impacts on deep convective clouds

NASA Astrophysics Data System (ADS)

Fan, Jiwen; Leung, L. Ruby; Rosenfeld, Daniel; Chen, Qian; Li, Zhanqing; Zhang, Jinqiang; Yan, Hongru

2013-11-01

Deep convective clouds (DCCs) play a crucial role in the general circulation, energy, and hydrological cycle of our climate system. Aerosol particles can influence DCCs by altering cloud properties, precipitation regimes, and radiation balance. Previous studies reported both invigoration and suppression of DCCs by aerosols, but few were concerned with the whole life cycle of DCC. By conducting multiple monthlong cloud-resolving simulations with spectral-bin cloud microphysics that capture the observed macrophysical and microphysical properties of summer convective clouds and precipitation in the tropics and midlatitudes, this study provides a comprehensive view of how aerosols affect cloud cover, cloud top height, and radiative forcing. We found that although the widely accepted theory of DCC invigoration due to aerosol's thermodynamic effect (additional latent heat release from freezing of greater amount of cloud water) may work during the growing stage, it is microphysical effect influenced by aerosols that drives the dramatic increase in cloud cover, cloud top height, and cloud thickness at the mature and dissipation stages by inducing larger amounts of smaller but longer-lasting ice particles in the stratiform/anvils of DCCs, even when thermodynamic invigoration of convection is absent. The thermodynamic invigoration effect contributes up to ∼27% of total increase in cloud cover. The overall aerosol indirect effect is an atmospheric radiative warming (3-5 Wṡm-2) and a surface cooling (-5 to -8 Wṡm-2). The modeling findings are confirmed by the analyses of ample measurements made at three sites of distinctly different environments.

Microphysical effects determine macrophysical response for aerosol impacts on deep convective clouds.

PubMed

Fan, Jiwen; Leung, L Ruby; Rosenfeld, Daniel; Chen, Qian; Li, Zhanqing; Zhang, Jinqiang; Yan, Hongru

2013-11-26

Deep convective clouds (DCCs) play a crucial role in the general circulation, energy, and hydrological cycle of our climate system. Aerosol particles can influence DCCs by altering cloud properties, precipitation regimes, and radiation balance. Previous studies reported both invigoration and suppression of DCCs by aerosols, but few were concerned with the whole life cycle of DCC. By conducting multiple monthlong cloud-resolving simulations with spectral-bin cloud microphysics that capture the observed macrophysical and microphysical properties of summer convective clouds and precipitation in the tropics and midlatitudes, this study provides a comprehensive view of how aerosols affect cloud cover, cloud top height, and radiative forcing. We found that although the widely accepted theory of DCC invigoration due to aerosol's thermodynamic effect (additional latent heat release from freezing of greater amount of cloud water) may work during the growing stage, it is microphysical effect influenced by aerosols that drives the dramatic increase in cloud cover, cloud top height, and cloud thickness at the mature and dissipation stages by inducing larger amounts of smaller but longer-lasting ice particles in the stratiform/anvils of DCCs, even when thermodynamic invigoration of convection is absent. The thermodynamic invigoration effect contributes up to ~27% of total increase in cloud cover. The overall aerosol indirect effect is an atmospheric radiative warming (3-5 W m(-2)) and a surface cooling (-5 to -8 W m(-2)). The modeling findings are confirmed by the analyses of ample measurements made at three sites of distinctly different environments.

Effect of ship-stack effluents on cloud reflectivity

NASA Technical Reports Server (NTRS)

Coakley, James A., Jr.; Bernstein, Robert L.; Durkee, Philip A.

1987-01-01

Under stable meteorological conditions the effect of ship-stack exhaust on overlying clouds was detected in daytime satellite images as an enhancement in cloud reflectivity at 3.7 micrometers. The exhaust is a source of cloud-condensation nuclei that increases the number of cloud droplets while reducing droplet size. This reduction in droplet size causes the reflectivity at 3.7 micrometers to be greater than the levels for nearby noncontaminated clouds of similar physical characteristics. The increase in droplet number causes the reflectivity at 0.63 micrometer to be significantly higher for the contaminated clouds despite the likelihood that the exhaust is a source of particles that absorb at visible wavelengths. The effect of aerosols on cloud reflectivity is expected to have a larger influence on the earth's albedo than that due to the direct scattering and absorption of sunlight by the aerosols alone.

CloudSat First Image of a Warm Front Storm Over the Norwegian Sea

NASA Technical Reports Server (NTRS)

2006-01-01

[figure removed for brevity, see original site] Figure 1

CloudSat's first image, of a warm front storm over the Norwegian Sea, was obtained on May 20, 2006. In this horizontal cross-section of clouds, warm air is seen rising over colder air as the satellite travels from right to left. The red colors are indicative of highly reflective particles such as water droplets (or rain) or larger ice crystals (or snow), while the blue indicates thinner clouds (such as cirrus). The flat green/blue lines across the bottom represent the ground signal. The vertical scale on the CloudSat Cloud Profiling Radar image is approximately 30 kilometers (19 miles). The blue line below the Cloud Profiling Radar image indicates that the data were taken over water. The inset image shows the CloudSat track relative to a Moderate Resolution Imaging Spectroradiometer (MODIS) infrared image taken at nearly the same time.

Observations of fluorescent aerosol-cloud interactions in the free troposphere at the Sphinx high Alpine research station, Jungfraujoch

NASA Astrophysics Data System (ADS)

Crawford, I.; Lloyd, G.; Bower, K. N.; Connolly, P. J.; Flynn, M. J.; Kaye, P. H.; Choularton, T. W.; Gallagher, M. W.

2015-09-01

The fluorescent nature of aerosol at a high Alpine site was studied using a wide-band integrated bioaerosol (WIBS-4) single particle multi-channel ultra violet-light induced fluorescence (UV-LIF) spectrometer. This was supported by comprehensive cloud microphysics and meteorological measurements with the aims of cataloguing concentrations of bio-fluorescent aerosols at this high altitude site and also investigating possible influences of UV-fluorescent particle types on cloud-aerosol processes. Analysis of background free tropospheric air masses, using a total aerosol inlet, showed there to be a minor but statistically insignificant increase in the fluorescent aerosol fraction during in-cloud cases compared to out of cloud cases. The size dependence of the fluorescent aerosol fraction showed the larger aerosol to be more likely to be fluorescent with 80 % of 10 μm particles being fluorescent. Whilst the fluorescent particles were in the minority (NFl/NAll = 0.27±0.19), a new hierarchical agglomerative cluster analysis approach, Crawford et al. (2015) revealed the majority of the fluorescent aerosol were likely to be representative of fluorescent mineral dust. A minor episodic contribution from a cluster likely to be representative of primary biological aerosol particles (PBAP) was also observed with a wintertime baseline concentration of 0.1±0.4 L-1. Given the low concentration of this cluster and the typically low ice active fraction of studied PBAP (e.g. pseudomonas syringae) we suggest that the contribution to the observed ice crystal concentration at this location is not significant during the wintertime.

A New Look into the Effect of Large Drops on Radiative Transfer Process

NASA Technical Reports Server (NTRS)

Marshak, Alexander

2003-01-01

Recent studies indicate that a cloudy atmosphere absorbs more solar radiation than any current 1D or 3D radiation model can predict. The excess absorption is not large, perhaps 10-15 W/sq m or less, but any such systematic bias is of concern since radiative transfer models are assumed to be sufficiently accurate for remote sensing applications and climate modeling. The most natural explanation would be that models do not capture real 3D cloud structure and, as a consequence, their photon path lengths are too short. However, extensive calculations, using increasingly realistic 3D cloud structures, failed to produce photon paths long enough to explain the excess absorption. Other possible explanations have also been unsuccessful so, at this point, conventional models seem to offer no solution to this puzzle. The weakest link in conventional models is the way a size distribution of cloud particles is mathematically handled. Basically, real particles are replaced with a single average particle. This "ensemble assumption" assumes that all particle sizes are well represented in any given elementary volume. But the concentration of larger particles can be so low that this assumption is significantly violated. We show how a different mathematical route, using the concept of a cumulative distribution, avoids the ensemble assumption. The cumulative distribution has jumps, or steps, corresponding to the rarer sizes. These jumps result in an additional term, a kind of Green's function, in the solution of the radiative transfer equation. Solving the cloud radiative transfer equation with the measured particle distributions, described in a cumulative rather than an ensemble fashion, may lead to increased cloud absorption of the magnitude observed.

Redistribution of ice nuclei between cloud and rain droplets: Parameterization and application to deep convective clouds: ICE NUCLEI IN RAIN DROPLETS

DOE PAGES

Paukert, M.; Hoose, C.; Simmel, M.

2017-02-21

In model studies of aerosol-dependent immersion freezing in clouds, a common assumption is that each ice nucleating aerosol particle corresponds to exactly one cloud droplet. Conversely, the immersion freezing of larger drops—“rain”—is usually represented by a liquid volume-dependent approach, making the parameterizations of rain freezing independent of specific aerosol types and concentrations. This may lead to inconsistencies when aerosol effects on clouds and precipitation shall be investigated, since raindrops consist of the cloud droplets—and corresponding aerosol particles—that have been involved in drop-drop-collisions. We introduce an extension to a two-moment microphysical scheme in order to account explicitly for particle accumulation inmore » raindrops by tracking the rates of selfcollection, autoconversion, and accretion. This also provides a direct link between ice nuclei and the primary formation of large precipitating ice particles. A new parameterization scheme of drop freezing is presented to consider multiple ice nuclei within one drop and effective drop cooling rates. In our test cases of deep convective clouds, we find that at altitudes which are most relevant for immersion freezing, the majority of potential ice nuclei have been converted from cloud droplets into raindrops. Compared to the standard treatment of freezing in our model, the less efficient mineral dust-based freezing results in higher rainwater contents in the convective core, affecting both rain and hail precipitation. The aerosol-dependent treatment of rain freezing can reverse the signs of simulated precipitation sensitivities to ice nuclei perturbations.« less

Redistribution of ice nuclei between cloud and rain droplets: Parameterization and application to deep convective clouds: ICE NUCLEI IN RAIN DROPLETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paukert, M.; Hoose, C.; Simmel, M.

In model studies of aerosol-dependent immersion freezing in clouds, a common assumption is that each ice nucleating aerosol particle corresponds to exactly one cloud droplet. Conversely, the immersion freezing of larger drops—“rain”—is usually represented by a liquid volume-dependent approach, making the parameterizations of rain freezing independent of specific aerosol types and concentrations. This may lead to inconsistencies when aerosol effects on clouds and precipitation shall be investigated, since raindrops consist of the cloud droplets—and corresponding aerosol particles—that have been involved in drop-drop-collisions. We introduce an extension to a two-moment microphysical scheme in order to account explicitly for particle accumulation inmore » raindrops by tracking the rates of selfcollection, autoconversion, and accretion. This also provides a direct link between ice nuclei and the primary formation of large precipitating ice particles. A new parameterization scheme of drop freezing is presented to consider multiple ice nuclei within one drop and effective drop cooling rates. In our test cases of deep convective clouds, we find that at altitudes which are most relevant for immersion freezing, the majority of potential ice nuclei have been converted from cloud droplets into raindrops. Compared to the standard treatment of freezing in our model, the less efficient mineral dust-based freezing results in higher rainwater contents in the convective core, affecting both rain and hail precipitation. The aerosol-dependent treatment of rain freezing can reverse the signs of simulated precipitation sensitivities to ice nuclei perturbations.« less

Effect of Small-Scale Gravity Waves on Polar Mesospheric Clouds Observed From CIPS/AIM

NASA Astrophysics Data System (ADS)

Gao, Haiyang; Li, Licheng; Bu, Lingbing; Zhang, Qilin; Tang, Yuanhe; Wang, Zhen

2018-05-01

Data from the Cloud Imaging and Particle Size experiment on the Aeronomy of Ice in the Mesosphere (AIM) satellite are employed to study the impact of small-scale gravity wave (GW) on albedo, ice water content (IWC), and particle radius (PR) of polar mesospheric clouds. Overall, 23,987 eligible GW events, with a horizontal wavelength of 20-150 km are eventually extracted from Cloud Imaging and Particle Size level 2 orbit albedo maps during 2007-2011. The overall statistical results show that when small-scale GWs travel horizontally in polar mesospheric clouds, they can amplify the albedo and IWC by a rate of 10.0-22.6%, while reducing the PR by as much as -7.01%. Owing to the strong temporal and spatial dependences, the albedo and IWC variations are larger on an average during the core of the season, while they decrease during the initial and final periods of the season. The obvious zonal asymmetries are also found. The albedo variations show a positive linear relation with the GW amplitudes in albedo, as opposed to a negative linear relation with GW horizontal wavelengths. In most of the GW events, the periodic variation in the trend of albedo exhibits an anticorrelation with that of PR. Combining previous research studies with our results, we deduce that the rapid change in particle concentration and the upward movement of water vapor by GWs may be very important aspects for explaining the influence mechanism.

Impact of Long-Range Transported African Dust Events on Cloud Composition and Physical Properties at a Caribbean Tropical Montane Cloud Forest

NASA Astrophysics Data System (ADS)

Valle-Diaz, C. J.; Torres-Delgado, E.; Lee, T.; Collett, J. L.; Cuadra-Rodriguez, L. A.; Prather, K. A.; Spiegel, J.; Eugster, W.

2012-12-01

We studied the impact of long-range transported African Dust (LRTAD) on cloud composition and properties at the Caribbean tropical montane cloud forest (TMCF) of Pico del Este (PE), as part of the Puerto Rico African Dust and Clouds Study (PRADACS). Here we present results from measurements performed in July 2011. Bulk chemical analysis of cloud water and rainwater showed pH and conductivity higher in the presence of dust. pH and conductivity were also higher for larger cloud droplets (size cut of 17 μm at 50% efficiency) suggesting a higher content of dust in this fraction. The concentration of the water-soluble ions in rainwater was found to be lower than for cloud water. This in turn translates to higher pH and lower conductivity. African dust influence at PE was confirmed by the presence of nss-Ca, Fe, Mg, Na, and Al in cloud/rain water, and inferred by HYSPLIT trajectories and the satellite images from the Saharan Air Layer (SAL). Interstitial single-particle size and chemistry measured using aerosol time-of-flight mass spectrometry revealed mostly sea-salt particles (Na, Cl, Ca) and dust particles (Fe, Ti, Mg, nss-Ca). Anthropogenic influence detected as the presence of EC, a tracer for combustion processes, was found to be fairly small according to ATOFMS measurements. An increase of total organic carbon, total nitrogen, and dissolved organic carbon was observed during LRTAD events. Cloud droplet distributions revealed that LRTAD can lead to more numerous, but smaller cloud droplets (around 8 μm in average) at PE. However, total liquid water content appeared to be unaffected by this shift of droplet sizes. Overall, differences in the studied physicochemical properties of aerosols and clouds during dust and non-dust events were observed. Our results show that during LRTAD events, aerosol-cloud-precipitation interactions are altered at PE. Detailed results will be presented at the meeting.

Aerosol Production and Growth in the Upper Troposphere over the Amazon Forest Observed during ACRIDICON-CHUVA

NASA Astrophysics Data System (ADS)

Andreae, M. O.; Afchine, A.; Albrecht, R. I.; Artaxo, P.; Borrmann, S.; Cecchini, M. A.; Costa, A.; Fütterer, D.; Järvinen, E.; Klimach, T.; Konemann, T.; Kraemer, M.; Machado, L.; Mertes, S.; Pöhlker, C.; Pöhlker, M. L.; Poeschl, U.; Sauer, D. N.; Schnaiter, M.; Schneider, J.; Schulz, C.; Spanu, A.; Walser, A.; Wang, J.; Weinzierl, B.; Wendisch, M.

2016-12-01

Observations during ACRIDICON-CHUVA showed high aerosol concentrations in the upper troposphere (UT) over the Amazon Basin, with aerosol number concentrations after normalization to STP often exceeding those in the boundary layer (BL) by one or two orders of magnitude. The measurements were made during the German-Brazilian cooperative aircraft campaign ACRIDICON-CHUVA (Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems) on the German research aircraft HALO. The campaign took place over the Amazon Basin in September/October 2014, with the objective of studying tropical deep convective clouds over the Amazon rainforest and their interactions with trace gases, aerosol particles, and atmospheric radiation. Aerosol enhancements were consistently observed on all flights, using several aerosol metrics, including condensation nuclei (CN), cloud condensation nuclei (CCN), and chemical species mass concentrations. These UT aerosols were different in their composition and size distribution from the aerosol in the BL, making convective transport of particles unlikely as a source. The regions in the immediate outflow of deep convective clouds were depleted in aerosol particles, whereas dramatically enhanced small (<90 nm diameter) aerosol number concentrations were found in UT regions that had experienced outflow from deep convection in the preceding 24-48 hours. We also found elevated concentrations of larger (>90 nm) particles in the UT, which consisted mostly of organic matter and nitrate and were very effective CCN. Our findings suggest that aerosol production takes place in the UT from volatile material brought up by deep convection, which is converted to condensable species in the UT. Subsequently, downward mixing and transport of upper tropospheric aerosol may be a source of particles to the BL, where they increase in size by the condensation of biogenic volatile organic carbon (BVOC) oxidation products. This may be an important source of aerosol particles in the Amazonian BL, where aerosol nucleation and new particle formation has not been observed. We propose that this may have been the dominant process supplying secondary aerosols in the pristine atmosphere, making clouds the dominant control of both removal and production of atmospheric particles.

Premixed flame propagation in combustible particle cloud mixtures

NASA Technical Reports Server (NTRS)

Seshadri, K.; Yang, B.

1993-01-01

The structures of premixed flames propagating in combustible systems, containing uniformly distributed volatile fuel particles, in an oxidizing gas mixtures is analyzed. The experimental results show that steady flame propagation occurs even if the initial equivalence ratio of the combustible mixture based on the gaseous fuel available in the particles, phi(u) is substantially larger than unity. A model is developed to explain these experimental observations. In the model it is presumed that the fuel particles vaporize first to yield a gaseous fuel of known chemical composition which then reacts with oxygen in a one-step overall process. It is shown that the interplay of vaporization kinetics and oxidation process, can result in steady flame propagation in combustible mixtures where the value of phi(u) is substantially larger than unity. This prediction is in agreement with experimental observations.

Evidence of Chemical Cloud Processing from In Situ Measurements in the Polluted Marine Environment

NASA Astrophysics Data System (ADS)

Hudson, J. G.; Noble, S. R., Jr.

2017-12-01

Chemical cloud processing alters activated cloud condensation nuclei (CCN). Aqueous oxidation of trace gases dissolved within cloud droplets adds soluble material. As most cloud droplets evaporate, the residual material produces CCN that are larger and with a different hygroscopicity (κ). This improves the CCN, lowering the critical supersaturation (Sc), making it more easily activated. This process separates the processed (accumulation) and unprocessed (Aitken) modes creating bimodal CCN distributions (Hudson et al., 2015). Various measurements made during the MArine Stratus/stratocumulus Experiment (MASE), including CCN, exhibited aqueous processing signals. Particle size distributions; measured by a differential mobility analyzer; were compared with CCN distributions; measured by the Desert Research Institute CCN spectrometer; by converting size to Sc using κ to overlay concurrent distributions. By tuning each mode to the best agreement, κ for each mode is determined; processed κ (κp), unprocessed κ (κu). In MASE, 59% of bimodal distributions had different κ for the two modes indicating dominance of chemical processing via aqueous oxidation. This is consistent with Hudson et al. (2015). Figure 1A also indicates chemical processing with larger κp between 0.35-0.75. Processed CCN had an influx of soluble material from aqueous oxidation which increased κp versus κu. Above 0.75 κp is lower than κu (Fig. 1A). When κu is high and sulfate material is added, κp tends towards κ of the added material. Thus, κp is reduced by additional material that is less soluble than the original material. Chemistry measurements in MASE also indicate in-cloud aqueous oxidation (Fig. 1B and 1C). Higher fraction of CCN concentrations in the processed mode are also associated with larger amounts of sulfates (Fig. 1B, red) and nitrates (Fig. 1C, orange) while SO2 (Fig. 1B, black) and O3 (Fig. 1C, blue) have lower amounts. This larger amount of sulfate is at the expense of SO2, indicating aqueous oxidation within cloud as associated with larger concentrations in the processed mode. Thus, in situ measurements indicate that chemical cloud processing alters size, Sc and κ of activated CCN. Hudson et al. (2015), JGRA, 120, 3436-3452.

Retrieval of Aerosol Absorption Properties from Satellite Observations

NASA Technical Reports Server (NTRS)

Torres, Omar; Bhartia, Pawan K.; Jethva, H.; Ahn, Chang-Woo

2012-01-01

The Angstrom Absorption Exponent (AAE) is a parameter commonly used to characterize the wavelength-dependence of aerosol absorption optical depth (AAOD). It is closely related to aerosol composition. Black carbon (BC) containing aerosols yield AAE values near unity whereas Organic carbon (OC) aerosol particles are associated with values larger than 2. Even larger AAE values have been reported for desert dust aerosol particles. Knowledge of spectral AAOD is necessary for the calculation of direct radiative forcing effect of aerosols and for inferring aerosol composition. We have developed a satellitebased method of determining the spectral AAOD of absorbing aerosols. The technique uses multi-spectral measurements of upwelling radiation from scenes where absorbing aerosols lie above clouds as indicated by the UV Aerosol Index. For those conditions, the satellite measurement can be explained, using an approximations of Beer's Law (BL), as the upwelling reflectance at the cloud top attenuated by the absorption effects of the overlying aerosol layer. The upwelling reflectance at the cloud-top in an aerosol-free atmospheric column is mainly a function of cloud optical depth (COD). In the proposed method of AAE derivation, the first step is determining COD which is retrieved using a previously developed color-ratio based approach. In the second step, corrections for molecular scattering effects are applied to both the observed ad the calculated cloud reflectance terms, and the spectral AAOD is then derived by an inversion of the BL approximation. The proposed technique will be discussed in detail and application results making use of OMI multi-spectral measurements in the UV-Vis. will be presented.

Reduced anthropogenic aerosol radiative forcing caused by biogenic new particle formation

PubMed Central

Sengupta, Kamalika; Duplissy, Jonathan; Frege, Carla; Williamson, Christina; Heinritzi, Martin; Simon, Mario; Yan, Chao; Almeida, João; Tröstl, Jasmin; Nieminen, Tuomo; Ortega, Ismael K.; Wagner, Robert; Dunne, Eimear M.; Adamov, Alexey; Amorim, Antonio; Bernhammer, Anne-Kathrin; Bianchi, Federico; Breitenlechner, Martin; Brilke, Sophia; Chen, Xuemeng; Craven, Jill S.; Dias, Antonio; Ehrhart, Sebastian; Fischer, Lukas; Flagan, Richard C.; Franchin, Alessandro; Fuchs, Claudia; Guida, Roberto; Hakala, Jani; Hoyle, Christopher R.; Jokinen, Tuija; Junninen, Heikki; Kangasluoma, Juha; Kim, Jaeseok; Krapf, Manuel; Kürten, Andreas; Laaksonen, Ari; Lehtipalo, Katrianne; Makhmutov, Vladimir; Mathot, Serge; Molteni, Ugo; Monks, Sarah A.; Onnela, Antti; Peräkylä, Otso; Piel, Felix; Petäjä, Tuukka; Praplan, Arnaud P.; Pringle, Kirsty J.; Richards, Nigel A. D.; Rissanen, Matti P.; Rondo, Linda; Sarnela, Nina; Scott, Catherine E.; Seinfeld, John H.; Sharma, Sangeeta; Sipilä, Mikko; Steiner, Gerhard; Stozhkov, Yuri; Stratmann, Frank; Tomé, Antonio; Virtanen, Annele; Vogel, Alexander Lucas; Wagner, Andrea C.; Wagner, Paul E.; Weingartner, Ernest; Wimmer, Daniela; Winkler, Paul M.; Ye, Penglin; Zhang, Xuan; Hansel, Armin; Worsnop, Douglas R.; Baltensperger, Urs; Kulmala, Markku; Curtius, Joachim

2016-01-01

The magnitude of aerosol radiative forcing caused by anthropogenic emissions depends on the baseline state of the atmosphere under pristine preindustrial conditions. Measurements show that particle formation in atmospheric conditions can occur solely from biogenic vapors. Here, we evaluate the potential effect of this source of particles on preindustrial cloud condensation nuclei (CCN) concentrations and aerosol–cloud radiative forcing over the industrial period. Model simulations show that the pure biogenic particle formation mechanism has a much larger relative effect on CCN concentrations in the preindustrial atmosphere than in the present atmosphere because of the lower aerosol concentrations. Consequently, preindustrial cloud albedo is increased more than under present day conditions, and therefore the cooling forcing of anthropogenic aerosols is reduced. The mechanism increases CCN concentrations by 20–100% over a large fraction of the preindustrial lower atmosphere, and the magnitude of annual global mean radiative forcing caused by changes of cloud albedo since 1750 is reduced by 0.22 W m−2 (27%) to −0.60 W m−2. Model uncertainties, relatively slow formation rates, and limited available ambient measurements make it difficult to establish the significance of a mechanism that has its dominant effect under preindustrial conditions. Our simulations predict more particle formation in the Amazon than is observed. However, the first observation of pure organic nucleation has now been reported for the free troposphere. Given the potentially significant effect on anthropogenic forcing, effort should be made to better understand such naturally driven aerosol processes. PMID:27790989

Reduced anthropogenic aerosol radiative forcing caused by biogenic new particle formation

NASA Astrophysics Data System (ADS)

Gordon, Hamish; Sengupta, Kamalika; Rap, Alexandru; Duplissy, Jonathan; Frege, Carla; Williamson, Christina; Heinritzi, Martin; Simon, Mario; Yan, Chao; Almeida, João; Tröstl, Jasmin; Nieminen, Tuomo; Ortega, Ismael K.; Wagner, Robert; Dunne, Eimear M.; Adamov, Alexey; Amorim, Antonio; Bernhammer, Anne-Kathrin; Bianchi, Federico; Breitenlechner, Martin; Brilke, Sophia; Chen, Xuemeng; Craven, Jill S.; Dias, Antonio; Ehrhart, Sebastian; Fischer, Lukas; Flagan, Richard C.; Franchin, Alessandro; Fuchs, Claudia; Guida, Roberto; Hakala, Jani; Hoyle, Christopher R.; Jokinen, Tuija; Junninen, Heikki; Kangasluoma, Juha; Kim, Jaeseok; Kirkby, Jasper; Krapf, Manuel; Kürten, Andreas; Laaksonen, Ari; Lehtipalo, Katrianne; Makhmutov, Vladimir; Mathot, Serge; Molteni, Ugo; Monks, Sarah A.; Onnela, Antti; Peräkylä, Otso; Piel, Felix; Petäjä, Tuukka; Praplan, Arnaud P.; Pringle, Kirsty J.; Richards, Nigel A. D.; Rissanen, Matti P.; Rondo, Linda; Sarnela, Nina; Schobesberger, Siegfried; Scott, Catherine E.; Seinfeld, John H.; Sharma, Sangeeta; Sipilä, Mikko; Steiner, Gerhard; Stozhkov, Yuri; Stratmann, Frank; Tomé, Antonio; Virtanen, Annele; Vogel, Alexander Lucas; Wagner, Andrea C.; Wagner, Paul E.; Weingartner, Ernest; Wimmer, Daniela; Winkler, Paul M.; Ye, Penglin; Zhang, Xuan; Hansel, Armin; Dommen, Josef; Donahue, Neil M.; Worsnop, Douglas R.; Baltensperger, Urs; Kulmala, Markku; Curtius, Joachim; Carslaw, Kenneth S.

2016-10-01

The magnitude of aerosol radiative forcing caused by anthropogenic emissions depends on the baseline state of the atmosphere under pristine preindustrial conditions. Measurements show that particle formation in atmospheric conditions can occur solely from biogenic vapors. Here, we evaluate the potential effect of this source of particles on preindustrial cloud condensation nuclei (CCN) concentrations and aerosol-cloud radiative forcing over the industrial period. Model simulations show that the pure biogenic particle formation mechanism has a much larger relative effect on CCN concentrations in the preindustrial atmosphere than in the present atmosphere because of the lower aerosol concentrations. Consequently, preindustrial cloud albedo is increased more than under present day conditions, and therefore the cooling forcing of anthropogenic aerosols is reduced. The mechanism increases CCN concentrations by 20-100% over a large fraction of the preindustrial lower atmosphere, and the magnitude of annual global mean radiative forcing caused by changes of cloud albedo since 1750 is reduced by 0.22 W m-2 (27%) to -0.60 W m-2. Model uncertainties, relatively slow formation rates, and limited available ambient measurements make it difficult to establish the significance of a mechanism that has its dominant effect under preindustrial conditions. Our simulations predict more particle formation in the Amazon than is observed. However, the first observation of pure organic nucleation has now been reported for the free troposphere. Given the potentially significant effect on anthropogenic forcing, effort should be made to better understand such naturally driven aerosol processes.

Microphysical effects determine macrophysical response for aerosol impacts on deep convective clouds

PubMed Central

Fan, Jiwen; Leung, L. Ruby; Rosenfeld, Daniel; Chen, Qian; Li, Zhanqing; Zhang, Jinqiang; Yan, Hongru

2013-01-01

Deep convective clouds (DCCs) play a crucial role in the general circulation, energy, and hydrological cycle of our climate system. Aerosol particles can influence DCCs by altering cloud properties, precipitation regimes, and radiation balance. Previous studies reported both invigoration and suppression of DCCs by aerosols, but few were concerned with the whole life cycle of DCC. By conducting multiple monthlong cloud-resolving simulations with spectral-bin cloud microphysics that capture the observed macrophysical and microphysical properties of summer convective clouds and precipitation in the tropics and midlatitudes, this study provides a comprehensive view of how aerosols affect cloud cover, cloud top height, and radiative forcing. We found that although the widely accepted theory of DCC invigoration due to aerosol’s thermodynamic effect (additional latent heat release from freezing of greater amount of cloud water) may work during the growing stage, it is microphysical effect influenced by aerosols that drives the dramatic increase in cloud cover, cloud top height, and cloud thickness at the mature and dissipation stages by inducing larger amounts of smaller but longer-lasting ice particles in the stratiform/anvils of DCCs, even when thermodynamic invigoration of convection is absent. The thermodynamic invigoration effect contributes up to ∼27% of total increase in cloud cover. The overall aerosol indirect effect is an atmospheric radiative warming (3–5 W⋅m−2) and a surface cooling (−5 to −8 W⋅m−2). The modeling findings are confirmed by the analyses of ample measurements made at three sites of distinctly different environments. PMID:24218569

Particle-in-cell simulations of the critical ionization velocity effect in finite size clouds

NASA Technical Reports Server (NTRS)

Moghaddam-Taaheri, E.; Lu, G.; Goertz, C. K.; Nishikawa, K. - I.

1994-01-01

The critical ionization velocity (CIV) mechanism in a finite size cloud is studied with a series of electrostatic particle-in-cell simulations. It is observed that an initial seed ionization, produced by non-CIV mechanisms, generates a cross-field ion beam which excites a modified beam-plasma instability (MBPI) with frequency in the range of the lower hybrid frequency. The excited waves accelerate electrons along the magnetic field up to the ion drift energy that exceeds the ionization energy of the neutral atoms. The heated electrons in turn enhance the ion beam by electron-neutral impact ionization, which establishes a positive feedback loop in maintaining the CIV process. It is also found that the efficiency of the CIV mechanism depends on the finite size of the gas cloud in the following ways: (1) Along the ambient magnetic field the finite size of the cloud, L (sub parallel), restricts the growth of the fastest growing mode, with a wavelength lambda (sub m parallel), of the MBPI. The parallel electron heating at wave saturation scales approximately as (L (sub parallel)/lambda (sub m parallel)) (exp 1/2); (2) Momentum coupling between the cloud and the ambient plasma via the Alfven waves occurs as a result of the finite size of the cloud in the direction perpendicular to both the ambient magnetic field and the neutral drift. This reduces exponentially with time the relative drift between the ambient plasma and the neutrals. The timescale is inversely proportional to the Alfven velocity. (3) The transvers e charge separation field across the cloud was found to result in the modulation of the beam velocity which reduces the parallel heating of electrons and increases the transverse acceleration of electrons. (4) Some energetic electrons are lost from the cloud along the magnetic field at a rate characterized by the acoustic velocity, instead of the electron thermal velocity. The loss of energetic electrons from the cloud seems to be larger in the direction of plasma drift relative to the neutrals, where the loss rate is characterized by the neutral drift velocity. It is also shown that a factor of 4 increase in the ambient plasma density, increases the CIV ionization yield by almost 2 orders of magnitude at the end of a typical run. It is concluded that a larger ambient plasma density can result in a larger CIV yield because of (1) larger seed ion production by non-CIV mechanisms, (2) smaller Alfven velocity and hence weak momentum coupling, and (3) smaller ratio of the ion beam density to the ambient ion density, and therefore a weaker modulation of the beam velocity. The simulation results are used to interpret various chemical release experiments in space.

New particle dependant parameterizations of heterogeneous freezing processes.

NASA Astrophysics Data System (ADS)

Diehl, Karoline; Mitra, Subir K.

2014-05-01

For detailed investigations of cloud microphysical processes an adiabatic air parcel model with entrainment is used. It represents a spectral bin model which explicitly solves the microphysical equations. The initiation of the ice phase is parameterized and describes the effects of different types of ice nuclei (mineral dust, soot, biological particles) in immersion, contact, and deposition modes. As part of the research group INUIT (Ice Nuclei research UnIT), existing parameterizations have been modified for the present studies and new parameterizations have been developed mainly on the basis of the outcome of INUIT experiments. Deposition freezing in the model is dependant on the presence of dry particles and on ice supersaturation. The description of contact freezing combines the collision kernel of dry particles with the fraction of frozen drops as function of temperature and particle size. A new parameterization of immersion freezing has been coupled to the mass of insoluble particles contained in the drops using measured numbers of ice active sites per unit mass. Sensitivity studies have been performed with a convective temperature and dew point profile and with two dry aerosol particle number size distributions. Single and coupled freezing processes are studied with different types of ice nuclei (e.g., bacteria, illite, kaolinite, feldspar). The strength of convection is varied so that the simulated cloud reaches different levels of temperature. As a parameter to evaluate the results the ice water fraction is selected which is defined as the relation of the ice water content to the total water content. Ice water fractions between 0.1 and 0.9 represent mixed-phase clouds, larger than 0.9 ice clouds. The results indicate the sensitive parameters for the formation of mixed-phase and ice clouds are: 1. broad particle number size distribution with high number of small particles, 2. temperatures below -25°C, 3. specific mineral dust particles as ice nuclei such as illite or montmorillonite. Coupled cases of deposition and contact freezing show that they are hardly in competition because of differences in the preferred particle sizes. In the contact mode, small particles are less efficient for collisions as well as less efficient as ice nuclei so that these are available for deposition freezing. On the other hand, immersion freezing is the dominant process when it is coupled with deposition freezing. As it is initiated earlier the formed ice particles consume water vapor for growing. The competition of combined contact and immersion freezing leads to lower ice water contents because more ice particles are formed via the immersion mode. In general, ice clouds and mixed-phase clouds with high ice water fractions are not directly the result of primary ice formation but of secondary ice formation and growth of ice particles at the expense of liquid drops.

Long-term observation of aerosol cloud relationships in the Mid-Atlantic region

NASA Astrophysics Data System (ADS)

Li, S.; Joseph, E.; Min, Q.; Yin, B.

2013-12-01

Long-term ground-based observations of aerosol and cloud properties derived from measurements of Multifilter Rotating Shadow Band Radiometer and microwave radiometer at an atmospheric measurement field station in the Baltimore-Washington corridor operated by Howard University are used to examine the temporal variation of aerosol and cloud properties and moreover aerosol indirect effect on clouds. Through statistical analysis of five years (from 2006 to 2010) of these observations, the proportion of polluted cases is found larger in 2006 and 2007 and the proportion of optically thick clouds cases is also larger in 2006 and 2007 than that in 2008, 2009 and 2010. Both the mean aerosol optical depth (AOD) and cloud optical depth (COD) are observed decreasing from 2006 to 2010 but there is no obvious trend observed on cloud liquid water path (LWP). Because of the limit of AOD retrievals under cloudy conditions surface measurements of fine particle particulate matter 2.5 (PM2.5) were used for assessing aerosol indirect effect. A positive relationship between LWP and cloud droplets effective radius (Re) and a negative relationship between PM2.5 and Re are observed based on a stringent case selection method which is used to reduce the uncertainties from retrieval and meteorological impacts. The total 5 years summer time observations are segregated according to the value of PM2.5. Examination of distributions of COD, cloud condensation nuclei (CCN), cloud droplets effective radius and LWP under polluted and pristine conditions further confirm that the high aerosol loading decreases cloud droplets effective radius and increases cloud optical depth.

Powerful Hurricane Irma Seen in 3D by NASA's CloudSat

NASA Image and Video Library

2017-09-08

NASA's CloudSat satellite flew over Hurricane Irma on Sept. 6, 2017 at 1:45 p.m. EDT (17:45 UTC) as the storm was approaching Puerto Rico in the Atlantic Ocean. Hurricane Irma contained estimated maximum sustained winds of 185 miles per hour (160 knots) with a minimum pressure of 918 millibars. CloudSat transected the eastern edge of Hurricane Irma's eyewall, revealing details of the storm's cloud structure beneath its thick canopy of cirrus clouds. The CloudSat Cloud Profiling Radar excels in detecting the organization and placement of cloud layers beneath a storm's cirrus canopy, which are not readily detected by other satellite sensors. The CloudSat overpass reveals the inner details beneath the cloud tops of this large system; intense areas of convection with moderate to heavy rainfall (deep red and pink colors), cloud-free areas (moats) in between the inner and outer cloud bands of Hurricane Irma and cloud top heights averaging around 9 to 10 miles (15 to 16 kilometers). Lower values of reflectivity (areas of green and blue) denote smaller-sized ice and water particle sizes typically located at the top of a storm system (in the anvil area). The Cloud Profiling Radar loses signal at around 3 miles (5 kilometers) in height (in the melting layer) due to water (ice) particles larger than 0.12 inches (3 millimeters) in diameter. Moderate to heavy rainfall occurs in these areas where signal weakening is detectable. Smaller cumulus and cumulonimbus cloud types are evident as CloudSat moves farther south, beneath the thick cirrus canopy. An animation is available at https://photojournal.jpl.nasa.gov/catalog/PIA21947

Retrieval of Venus' cloud parameters from VIRTIS nightside spectra in the latitude band 25°-55°N

NASA Astrophysics Data System (ADS)

Magurno, Davide; Maestri, Tiziano; Grassi, Davide; Piccioni, Giuseppe; Sindoni, Giuseppe

2017-09-01

Two years of data from the M-channel of the Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS), on board the European Space Agency mission Venus Express operating around the planet Venus, are analysed. Nocturnal data from a nadir viewpoint in the latitude band 25°N-55°N are selected for their configuration advantages and maximisation of the scene homogeneity. A reference model, and radiance spectrum, is defined based on average accepted values of the Venus main atmospheric and cloud parameters found in the literature. Extensive radiative transfer simulations are performed to provide a synthetic database of more than 10 000 VIRTIS radiances representing the natural variability of the system parameters (atmospheric temperature profile, cloud H2Osbnd H2SO4 solution concentration and vertical distribution, particle size distribution density and modal radius). A simulated-observed fitting algorithm of spectral radiances in window channels, based on a weighting procedure accounting for the latitudinal observed radiance variations, is used to derive the best atmosphere-cloud configuration for each observation. Results show that the reference Venus model does not adequately reproduce the observed VIRTIS spectra. In particular, the model accounting for a constant sulphuric acid concentration along the vertical extent of the clouds is never selected as a best fit. The 75%/96% and 84%/96% concentrations (the first values refer to the upper cloud layers and the second values to the lower ones) are the most commonly retrieved models representing more than 85% of the retrieved cases for any latitudinal band considered. It is shown that the assumption of stratified concentration of aqueous sulphuric acid allows to adequately fit the observed radiance, in particular the peak at 1.74 μm and around 4 μm. The analysis of the results concerning the microphysics suggests larger radii for the upper cloud layers in conjunction with a large reduction of their number density with respect to the reference standard. Considerable variation of the particle concentration in the Venus' atmosphere is retrieved for altitudes between 60 and 70 km. The retrieved models also suggest that lower cloud layers have smaller particle radii and larger number density than expected from the reference model. Latitudinal variations of microphysical and chemical parameters are also analysed.

Analysis of aerosol effects on warm clouds over the Yangtze River Delta from multi-sensor satellite observations

NASA Astrophysics Data System (ADS)

Liu, Yuqin; de Leeuw, Gerrit; Kerminen, Veli-Matti; Zhang, Jiahua; Zhou, Putian; Nie, Wei; Qi, Ximeng; Hong, Juan; Wang, Yonghong; Ding, Aijun; Guo, Huadong; Krüger, Olaf; Kulmala, Markku; Petäjä, Tuukka

2017-05-01

Aerosol effects on low warm clouds over the Yangtze River Delta (YRD, eastern China) are examined using co-located MODIS, CALIOP and CloudSat observations. By taking the vertical locations of aerosol and cloud layers into account, we use simultaneously observed aerosol and cloud data to investigate relationships between cloud properties and the amount of aerosol particles (using aerosol optical depth, AOD, as a proxy). Also, we investigate the impact of aerosol types on the variation of cloud properties with AOD. Finally, we explore how meteorological conditions affect these relationships using ERA-Interim reanalysis data. This study shows that the relation between cloud properties and AOD depends on the aerosol abundance, with a different behaviour for low and high AOD (i.e. AOD < 0.35 and AOD > 0.35). This applies to cloud droplet effective radius (CDR) and cloud fraction (CF), but not to cloud optical thickness (COT) and cloud top pressure (CTP). COT is found to decrease when AOD increases, which may be due to radiative effects and retrieval artefacts caused by absorbing aerosol. Conversely, CTP tends to increase with elevated AOD, indicating that the aerosol is not always prone to expand the vertical extension. It also shows that the COT-CDR and CWP (cloud liquid water path)-CDR relationships are not unique, but affected by atmospheric aerosol loading. Furthermore, separation of cases with either polluted dust or smoke aerosol shows that aerosol-cloud interaction (ACI) is stronger for clouds mixed with smoke aerosol than for clouds mixed with dust, which is ascribed to the higher absorption efficiency of smoke than dust. The variation of cloud properties with AOD is analysed for various relative humidity and boundary layer thermodynamic and dynamic conditions, showing that high relative humidity favours larger cloud droplet particles and increases cloud formation, irrespective of vertical or horizontal level. Stable atmospheric conditions enhance cloud cover horizontally. However, unstable atmospheric conditions favour thicker and higher clouds. Dynamically, upward motion of air parcels can also facilitate the formation of thicker and higher clouds. Overall, the present study provides an understanding of the impact of aerosols on cloud properties over the YRD. In addition to the amount of aerosol particles (or AOD), evidence is provided that aerosol types and ambient environmental conditions need to be considered to understand the observed relationships between cloud properties and AOD.

Trace metal characterization of aerosol particles and cloud water during HCCT 2010

NASA Astrophysics Data System (ADS)

Fomba, K. W.; van Pinxteren, D.; Müller, K.; Iinuma, Y.; Lee, T.; Collett, J. L., Jr.; Herrmann, H.

2015-08-01

Trace metal characterization of bulk and size-resolved aerosol and cloud water samples were performed during the Hill Cap Cloud Thuringia (HCCT) campaign. Cloud water was collected at the top of Mt. Schmücke while aerosol samples were collected at two stations upwind and downwind of Mt. Schmücke. Fourteen trace metals including Ti, V, Fe, Mn, Co, Zn, Ni, Cu, As, Sr, Rb, Pb, Cr, and Se were investigated during four full cloud events (FCEs) that fulfilled the conditions of a continuous air mass flow through the three stations. Aerosol particle trace metal concentrations were found to be lower than those observed in the same region during previous field experiments but were within a similar range to those observed in other rural regions in Europe. Fe and Zn were the most abundant elements with concentration ranges of 0.2-111.6 and 1.1-32.1 ng m-3, respectively. Fe, Mn, and Ti were mainly found in coarse mode aerosols while Zn, Pb, and As were mostly found in the fine mode. Correlation and enrichment factor analysis of trace metals revealed that trace metals such as Ti and Rb were mostly of crustal origin while trace metals such as Zn, Pb, As, Cr, Ni, V, and Cu were of anthropogenic origin. Trace metals such as Fe and Mn were of mixed origins including crustal and combustion sources. Trace metal cloud water concentration decreased from Ti, Mn, Cr, to Co with average concentrations of 9.18, 5.59, 5.54, and 0.46 μg L-1, respectively. A non-uniform distribution of soluble Fe, Cu, and Mn was observed across the cloud drop sizes. Soluble Fe and Cu were found mainly in cloud droplets with diameters between 16 and 22 μm, while Mn was found mostly in larger drops greater than 22 μm. Fe(III) was the main form of soluble Fe especially in the small and larger drops with concentrations ranging from 2.2 to 37.1 μg L-1. In contrast to other studies, Fe(II) was observed mainly in the evening hours, implying its presence was not directly related to photochemical processes. Aerosol-cloud interaction did not lead to a marked increase in soluble trace metal concentrations; rather it led to differences in the chemical composition of the aerosol due to preferential loss of aerosol particles through physical processes including cloud drop deposition to vegetative surfaces.

Trace metal characterization of aerosol particles and cloud water during HCCT 2010

NASA Astrophysics Data System (ADS)

Fomba, K. W.; van Pinxteren, D.; Müller, K.; Iinuma, Y.; Lee, T.; Collet, J., Jr.; Herrmann, H.

2015-04-01

Trace metal characterization of bulk and size resolved aerosol and cloud water samples were performed during the Hill Cap Cloud Thuringia (HCCT) campaign. Cloud water was collected at the top of Mt. Schmücke while aerosol samples were collected at two stations upwind and downwind of Mt. Schmücke. Fourteen trace metals including Ti, V, Fe, Mn, Co, Zn, Ni, Cu, As, Sr, Rb, Pb, Cr, and Se were investigated during four full cloud events (FCE) that fulfilled the conditions of a continuous air mass flow through the three stations. Aerosol particle trace metal concentrations were found to be lower than those observed in the same region during previous field experiments but were within a similar range to those observed in other rural regions in Europe. Fe and Zn were the most abundant elements with concentration ranges of 0.2-111.6 and 1.1-32.1 ng m-3, respectively. Fe, Mn and Ti were mainly found in coarse mode aerosols while Zn, Pb and As were mostly found in the fine mode. Correlation and enrichment factor analysis of trace metals revealed that trace metals such as Ti and Rb were mostly of crustal origin while trace metals such as Zn, Pb, As, Cr, Ni, V, and Cu were of anthropogenic origin. Trace metals such as Fe, Mn, were of mixed origins including crustal and combustion sources. Trace metal cloud water concentration decreased from Ti, Mn, Cr, to Co with average concentrations of 9.18, 5.59, 5.54, and 0.46 μg L-1, respectively. A non-uniform distribution of soluble Fe, Cu and Mn was observed across the cloud drop sizes. Soluble Fe and Cu were found mainly in cloud droplets with diameters between 16 and 22 μm while Mn was found mostly in larger drops greater than 22 μm. Fe (III) was the main form of soluble Fe especially in the small and larger drops with concentrations ranging from 2.2 to 37.1 μg L-1. In contrast to other studies, Fe (II) was observed mainly in the evening hours, implying its presence was not directly related to photochemical processes. Aerosol cloud interaction did not lead to a mark increase in soluble trace metal concentrations, but led to differences in the chemical composition of the aerosol due to preferential loss of aerosol particles through physical processes including cloud drop deposition to vegetative surfaces.

Modeling Dust in the Magellanic Clouds

NASA Astrophysics Data System (ADS)

Zonca, Alberto; Casu, Silvia; Mulas, Giacomo; Aresu, Giambattista; Cecchi-Pestellini, Cesare

2015-09-01

We model the extinction profiles observed in the Small and Large Magellanic clouds with a synthetic population of dust grains consisting of core-mantle particles and a collection of free-flying polycyclic aromatic hydrocarbons (PAHs). All different flavors of the extinction curves observed in the Magellanic Clouds (MCs) can be described by the present model, which has been previously (successfully) applied to a large sample of diffuse and translucent lines of sight in the Milky Way. We find that in the MCs the extinction produced by classical grains is generally larger than absorption by PAHs. Within this model, the nonlinear far-UV rise is accounted for by PAHs, whose presence in turn is always associated with a gap in the size distribution of classical particles. This hints either at a physical connection between (e.g., a common cause for) PAHs and the absence of middle-sized dust particles or the need for an additional component in the model that can account for the nonlinear far-UV rise without contributing to the UV bump at ∼217 nm such as, e.g., nanodiamonds.

The Impact of Aerosol Sources and Aging on CCN Formation in the Houston-Galveston-Gulf of Mexico Region

NASA Astrophysics Data System (ADS)

Quinn, P.; Bates, T.; Coffman, D.; Covert, D.

2007-12-01

The impact of anthropogenic aerosol on cloud properties, cloud lifetime, and precipitation processes is one of the largest uncertainties in our current understanding of climate change. Aerosols affect cloud properties by serving as cloud condensation nuclei (CCN) thereby leading to the formation of cloud droplets. The process of cloud drop activation is a function of both the size and chemistry of the aerosol particles which, in turn, depend on the source of the aerosol and transformations that occur downwind. In situ field measurements that can lead to an improved understanding of the process of cloud drop formation and simplifying parameterizations for improving the accuracy of climate models are highly desirable. During the Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS), the NOAA RV Ronald H. Brown encountered a wide variety of aerosol types ranging from marine near the Florida panhandle to urban and industrial in the Houston-Galveston area. These varied sources provided an opportunity to investigate the role of aerosol sources, aging, chemistry, and size in the activation of particles to form cloud droplets. Here, we use the correlation between variability in critical diameter for activation (determined empirically from measured CCN concentrations and the number size distribution) and aerosol composition to quantify the impact of composition on particle activation. Variability in aerosol composition is parameterized by the mass fraction of Hydrocarbon-like Organic Aerosol (HOA) for particle diameters less than 200 nm (vacuum aerodynamic). The HOA mass fraction in this size range is lowest for marine aerosol and higher for aerosol impacted by anthropogenic emissions. Combining all data collected at 0.44 percent supersaturation (SS) reveals that composition (defined in this way) explains 40 percent of the variance in the critical diameter. As expected, the dependence of activation on composition is strongest at lower SS. At the same time, correlations between HOA mass fraction and aerosol mean diameter show that these two parameters are essentially independent of one another for this data set. We conclude that, based on the variability of the HOA mass fraction observed during GoMACCS, composition plays a dominant role in determining the fraction of particles that are activated to form cloud droplets. Using Kohler theory, we estimate the error that results in calculated CCN concentrations if the organic fraction of the aerosol is neglected (i.e., a fully soluble composition of ammonium sulfate is assumed) for the range of organic mass fractions and mean diameters observed during GoMACCS. We then relate this error to the source and age of the aerosol. At 0.22 and 0.44 percent SS, the error is considerable for anthropogenic aerosol sampled near the source region as this aerosol has, on average, a high POM mass fraction and smaller particle mean diameter. The error is lower for more aged aerosol as it has a lower POM mass fraction and larger mean particle diameter. Hence, the percent error in calculated CCN concentration is expected to be larger for younger, organic- rich aerosol and smaller for aged, sulfate rich aerosol and for marine aerosol. We extend this analysis to continental and marine data sets recently reported by Dusek et al. [Science, 312, 1375, 2006] and Hudson [Geophys. Res., Lett., 34, L08801, 2007].

Cloud condensation nuclei closure study on summer arctic aerosol

NASA Astrophysics Data System (ADS)

Martin, M.; Chang, R. Y.-W.; Sierau, B.; Sjogren, S.; Swietlicki, E.; Abbatt, J. P. D.; Leck, C.; Lohmann, U.

2011-03-01

We present an aerosol - cloud condensation nuclei CCN) closure study on summer high Arctic aerosol based on measurements that were carried out in summer 2008 during the Arctic Summer Cloud Ocean Study (ASCOS) on board the Swedish ice breaker Oden. The data presented here were collected during a three-week time period in the pack ice (>85° N) when the icebreaker Oden was moored to an ice floe and drifted passively during the most biological active period into autumn freeze up conditions. CCN number concentrations were obtained using two CCN counters measuring at different supersaturations. The directly measured CCN number concentration is then compared with a CCN number concentration calculated using both bulk aerosol mass composition data from an aerosol mass spectrometer and aerosol number size distributions obtained from a differential mobility particle sizer, assuming κ-Köhler theory and an internally mixed aerosol. For the two highest measured supersaturations, 0.73 and 0.41%, closure could not be achieved with the investigated settings concerning hygroscopicity and density. The calculated CCN number concentration was always higher than the measured one. One possible explanation is that the smaller particles that activate at these supersaturations have a relative larger insoluble organic mass fraction and thus are less good CCN than the larger particles. At 0.20, 0.15 and 0.10% supersaturation, the measured CCN number can be represented with different parameters for the hygroscopicity and density of the particles. For the best agreement of the calculated CCNnumber concentration with the measured one the organic fraction of the aerosol needs to be nearly insoluble (қorg=0.02). However, this is not unambigious and қorg=0.2 is found as an upper limit at 0.1% supersaturation.

Vertical distribution of microphysical properties of Arctic springtime low-level mixed-phase clouds over the Greenland and Norwegian seas

NASA Astrophysics Data System (ADS)

Mioche, Guillaume; Jourdan, Olivier; Delanoë, Julien; Gourbeyre, Christophe; Febvre, Guy; Dupuy, Régis; Monier, Marie; Szczap, Frédéric; Schwarzenboeck, Alfons; Gayet, Jean-François

2017-10-01

This study aims to characterize the microphysical and optical properties of ice crystals and supercooled liquid droplets within low-level Arctic mixed-phase clouds (MPCs). We compiled and analyzed cloud in situ measurements from four airborne spring campaigns (representing 18 flights and 71 vertical profiles in MPCs) over the Greenland and Norwegian seas mainly in the vicinity of the Svalbard archipelago. Cloud phase discrimination and representative vertical profiles of the number, size, mass and shape of ice crystals and liquid droplets are established. The results show that the liquid phase dominates the upper part of the MPCs. High concentrations (120 cm-3 on average) of small droplets (mean values of 15 µm), with an averaged liquid water content (LWC) of 0.2 g m-3 are measured at cloud top. The ice phase dominates the microphysical properties in the lower part of the cloud and beneath it in the precipitation region (mean values of 100 µm, 3 L-1 and 0.025 g m-3 for diameter, particle concentration and ice water content (IWC), respectively). The analysis of the ice crystal morphology shows that the majority of ice particles are irregularly shaped or rimed particles; the prevailing regular habits found are stellars and plates. We hypothesize that riming and diffusional growth processes, including the Wegener-Bergeron-Findeisen (WBF) mechanism, are the main growth mechanisms involved in the observed MPCs. The impact of larger-scale meteorological conditions on the vertical profiles of MPC properties was also investigated. Large values of LWC and high concentration of smaller droplets are possibly linked to polluted situations and air mass origins from the south, which can lead to very low values of ice crystal size and IWC. On the contrary, clean situations with low temperatures exhibit larger values of ice crystal size and IWC. Several parameterizations relevant for remote sensing or modeling studies are also determined, such as IWC (and LWC) - extinction relationship, ice and liquid integrated water paths, ice concentration and liquid water fraction according to temperature.

The role of jet and film drops in controlling the mixing state of submicron sea spray aerosol particles

NASA Astrophysics Data System (ADS)

Wang, Xiaofei; Deane, Grant B.; Moore, Kathryn A.; Ryder, Olivia S.; Stokes, M. Dale; Beall, Charlotte M.; Collins, Douglas B.; Santander, Mitchell V.; Burrows, Susannah M.; Sultana, Camille M.; Prather, Kimberly A.

2017-07-01

The oceans represent a significant global source of atmospheric aerosols. Sea spray aerosol (SSA) particles comprise sea salts and organic species in varying proportions. In addition to size, the overall composition of SSA particles determines how effectively they can form cloud droplets and ice crystals. Thus, understanding the factors controlling SSA composition is critical to predicting aerosol impacts on clouds and climate. It is often assumed that submicrometer SSAs are mainly formed by film drops produced from bursting bubble-cap films, which become enriched with hydrophobic organic species contained within the sea surface microlayer. In contrast, jet drops formed from the base of bursting bubbles are postulated to mainly produce larger supermicrometer particles from bulk seawater, which comprises largely salts and water-soluble organic species. However, here we demonstrate that jet drops produce up to 43% of total submicrometer SSA number concentrations, and that the fraction of SSA produced by jet drops can be modulated by marine biological activity. We show that the chemical composition, organic volume fraction, and ice nucleating ability of submicrometer particles from jet drops differ from those formed from film drops. Thus, the chemical composition of a substantial fraction of submicrometer particles will not be controlled by the composition of the sea surface microlayer, a major assumption in previous studies. This finding has significant ramifications for understanding the factors controlling the mixing state of submicrometer SSA particles and must be taken into consideration when predicting SSA impacts on clouds and climate.

The role of jet and film drops in controlling the mixing state of submicron sea spray aerosol particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Xiaofei; Deane, Grant B.; Moore, Kathryn A.

Covering 71% of the Earth’s surface, oceans represent a significant global source of atmospheric aerosols. The size and composition of sea spray aerosols (SSA) affect their ability to serve as cloud seeds and thus understanding the factors controlling their composition is critical to predicting their impact on clouds and climate. SSA particles have been shown to be an external mixture of particles with different compositions. Film and jet drop production mechanisms ultimately determine the individual particle compositions which are comprised of an array of salt/organic mixtures ranging from pure sea salt to nearly pure organic particles. It is often assumedmore » that the majority of submicron SSA are formed by film drops produced from bursting hydrophobic organic-rich bubble film caps at the sea surface, and in contrast, jet drops are postulated to produce larger supermicron particles from underlying seawater comprised largely of salts and water soluble organic species. However, here we show that jet drops produced by bursting sub-100 m bubbles account for up to 40 % of all submicron particles. They have distinct chemical compositions, organic volume fractions and ice nucleating activities from submicron film drops. Thus a substantial fraction of submicron particles will not necessarily be controlled by the composition of the sea surface microlayer as has been assumed in many studies. This finding has significant ramifications for the size-resolved mixing states of SSA particles which must be taken into consideration when accessing SSA impacts on clouds.« less

The role of jet and film drops in controlling the mixing state of submicron sea spray aerosol particles

DOE PAGES

Wang, Xiaofei; Deane, Grant B.; Moore, Kathryn A.; ...

2017-06-19

Covering 71% of the Earth’s surface, oceans represent a significant global source of atmospheric aerosols. The size and composition of sea spray aerosols (SSA) affect their ability to serve as cloud seeds and thus understanding the factors controlling their composition is critical to predicting their impact on clouds and climate. SSA particles have been shown to be an external mixture of particles with different compositions. Film and jet drop production mechanisms ultimately determine the individual particle compositions which are comprised of an array of salt/organic mixtures ranging from pure sea salt to nearly pure organic particles. It is often assumedmore » that the majority of submicron SSA are formed by film drops produced from bursting hydrophobic organic-rich bubble film caps at the sea surface, and in contrast, jet drops are postulated to produce larger supermicron particles from underlying seawater comprised largely of salts and water soluble organic species. However, here we show that jet drops produced by bursting sub-100 m bubbles account for up to 40 % of all submicron particles. They have distinct chemical compositions, organic volume fractions and ice nucleating activities from submicron film drops. Thus a substantial fraction of submicron particles will not necessarily be controlled by the composition of the sea surface microlayer as has been assumed in many studies. This finding has significant ramifications for the size-resolved mixing states of SSA particles which must be taken into consideration when accessing SSA impacts on clouds.« less

Thin cirrus clouds - Seasonal distribution over oceans deduced from Nimbus-4 IRIS

NASA Technical Reports Server (NTRS)

Prabhakara, C.; Fraser, R. S.; Dalu, G.; Wu, Man-Li C.; Curran, R. J.

1988-01-01

Spectral differences in the extinction of the 10.8- and 12.6-micron bands of the IR window region, due to optically thin clouds, were found in the measurements made by both an airborne broadband IR radiometer and the IR interferometer spectrometer (IRIS) aboard the Nimbus-4 satellite; the extinction at 12.6 microns was significantly larger than that at 10.8 microns; both water and ice particles in the clouds can account for such spectral difference in extinction. Multiple scattering radiative transfer calculations of IRIS data revealed this spectral feature about 100 to 20 km away from the high-altitude cold clouds; it is assumed that this feature is related to the spreading of cirrus clouds. Based on this assumption, mean seasonal maps of the distribution of thin cirrus clouds over the oceans were deduced from the IRIS data. The maps show that such clouds are often present over the convectively active areas, such as ITCZ, SPCZ, and the Bay of Bengal during the summer monsoon.

Emissions from Ships with respect to Their Effects on Clouds.

NASA Astrophysics Data System (ADS)

Hobbs, Peter V.; Garrett, Timothy J.; Ferek, Ronald J.; Strader, Scott R.; Hegg, Dean A.; Frick, Glendon M.; Hoppel, William A.; Gasparovic, Richard F.; Russell, Lynn M.; Johnson, Douglas W.; O'Dowd, Colin; Durkee, Philip A.; Nielsen, Kurt E.; Innis, George

2000-08-01

Emissions of particles, gases, heat, and water vapor from ships are discussed with respect to their potential for changing the microstructure of marine stratiform clouds and producing the phenomenon known as `ship tracks.' Airborne measurements are used to derive emission factors of SO2 and NO from diesel-powered and steam turbine-powered ships, burning low-grade marine fuel oil (MFO); they were 15-89 and 2-25 g kg1 of fuel burned, respectively. By contrast a steam turbine-powered ship burning high-grade navy distillate fuel had an SO2 emission factor of 6 g kg1.Various types of ships, burning both MFO and navy distillate fuel, emitted from 4 × 1015 to 2 × 1016 total particles per kilogram of fuel burned (4 × 1015-1.5 × 1016 particles per second). However, diesel-powered ships burning MFO emitted particles with a larger mode radius (0.03-0.05 m) and larger maximum sizes than those powered by steam turbines burning navy distillate fuel (mode radius 0.02 m). Consequently, if the particles have similar chemical compositions, those emitted by diesel ships burning MFO will serve as cloud condensation nuclei (CCN) at lower supersaturations (and will therefore be more likely to produce ship tracks) than the particles emitted by steam turbine ships burning distillate fuel. Since steam turbine-powered ships fueled by MFO emit particles with a mode radius similar to that of diesel-powered ships fueled by MFO, it appears that, for given ambient conditions, the type of fuel burned by a ship is more important than the type of ship engine in determining whether or not a ship will produce a ship track. However, more measurements are needed to test this hypothesis.The particles emitted from ships appear to be primarily organics, possibly combined with sulfuric acid produced by gas-to-particle conversion of SO2. Comparison of model results with measurements in ship tracks suggests that the particles from ships contain only about 10% water-soluble materials. Measurements of the total particles entering marine stratiform clouds from diesel-powered ships fueled by MFO, and increases in droplet concentrations produced by these particles, show that only about 12% of the particles serve as CCN.The fluxes of heat and water vapor from ships are estimated to be 2-22 MW and 0.5-1.5 kg s1, respectively. These emissions rarely produced measurable temperature perturbations, and never produced detectable perturbations in water vapor, in the plumes from ships. Nuclear-powered ships, which emit heat but negligible particles, do not produce ship tracks. Therefore, it is concluded that heat and water vapor emissions do not play a significant role in ship track formation and that particle emissions, particularly from those burning low-grade fuel oil, are responsible for ship track formation. Subsequent papers in this special issue discuss and test these hypotheses.

Added value of far-infrared radiometry for remote sensing of ice clouds

NASA Astrophysics Data System (ADS)

Libois, Quentin; Blanchet, Jean-Pierre

2017-06-01

Several cloud retrieval algorithms based on satellite observations in the infrared have been developed in the last decades. However, these observations only cover the midinfrared (MIR, λ < 15 μm) part of the spectrum, and none are available in the far-infrared (FIR, λ≥ 15 μm). Using the optimal estimation method, we show that adding a few FIR channels to existing spaceborne radiometers would significantly improve their ability to retrieve ice cloud radiative properties. For clouds encountered in the polar regions and the upper troposphere, where the atmosphere is sufficiently transparent in the FIR, using FIR channels would reduce by more than 50% the uncertainties on retrieved values of optical thickness, effective particle diameter, and cloud top altitude. Notably, this would extend the range of applicability of current retrieval methods to the polar regions and to clouds with large optical thickness, where MIR algorithms perform poorly. The high performance of solar reflection-based algorithms would thus be reached in nighttime conditions. Since the sensitivity of ice cloud thermal emission to effective particle diameter is approximately 5 times larger in the FIR than in the MIR, using FIR observations is a promising venue for studying ice cloud microphysics and precipitation processes. This is highly relevant for cirrus clouds and convective towers. This is also essential to study precipitation in the driest regions of the atmosphere, where strong feedbacks are at play between clouds and water vapor. The deployment in the near future of a FIR spaceborne radiometer is technologically feasible and should be strongly supported.

On the size and composition of particles in polar stratospheric clouds

NASA Technical Reports Server (NTRS)

Kinne, Stefan; Toon, Owen B.; Toon, Goeff C.; Farmer, Crofton B.; Browell, Edward V.

1988-01-01

Attenuation measurements of the solar radiation between 1.5 and 15 micron wavelengths were performed with the airborne (DC-8) JPL MARK 4 interferometer during the 1987 Antarctic Expedition. The opacities not only provide information about the abundance of stratospheric gases but also about the optical depths of polar stratospheric clouds (PSCs) at wavelengths of negligible gas absorption (windows). The optical depth of PSCs can be determined for each window once the background attenuation, due to air-molecules and aerosol has been filtered out with a simple extinction law. The ratio of optical thicknesses at different wavelengths reveals information about particle size and particle composition. Among the almost 700 measured spectra only a few PSC cases exist. PSC events are identified by sudden reductions in the spectrally integrated intensity value and are also verified with backscattering data from an upward directed lidar instrument, that was mounted on the DC-8. For the selected case on September 21st at 14.40 GMT, lidar data indicate an optically thin cloud at 18k and later an additional optically thick cloud at 15 km altitude. All results still suffer from: (1) often arbitrary definitions of a clear case, that often already may have contained PSC particles and (2) noise problems that restrict the calculations of optical depths to values larger than 0.001. Once these problems are handled, this instrument may become a valuable tool towards a better understanding of the role PSCs play in the Antarctic stratosphere.

Disintegration of Dust Aggregates in Interstellar Shocks and the Lifetime of Dust Grains in the ISM

NASA Technical Reports Server (NTRS)

Dominik, C.; Jones, A. P.; Tielens, A. G. G. M.; Cuzzi, Jeff (Technical Monitor)

1994-01-01

Interstellar grains are destroyed by shock waves moving through the ISM. In fact, the destruction of grains may be so effective that it is difficult to explain the observed abundance of dust in the ISM as a steady state between input of grains from stellar sources and destruction of grains in shocks. This is especially a problem for the larger grains. Therefore, the dust grains must be protected in some way. Jones et al. have already considered coatings and the increased post-shock drag effects for low density grains. In molecular clouds and dense clouds, coagulation of grains is an important process, and the largest interstellar grains may indeed be aggregates of smaller grains rather than homogeneous particles. This may provide a means to protect the larger grains, in that, in moderate velocity grain-grain collisions in a shock the aggregates may disintegrate rather than be vaporized. The released small particles are more resilient to shock destruction (except in fast shocks) and may reform larger grains later, recovering the observed size distribution. We have developed a model for the binding forces in grain aggregates and apply this model to the collisions between an aggregate and fast small grains. We discuss the results in the light of statistical collision probabilities and grain life times.

Impact of natural and anthropogenic aerosols on stratocumulus and precipitation in the Southeast Pacific: a regional modelling study using WRF-Chem

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Q.; Gustafson, W. I.; Fast, J. D.

2012-09-28

Cloud-system resolving simulations with the chemistry version of the Weather Research and Forecasting (WRF-Chem) model are used to quantify the relative impacts of regional anthropogenic and oceanic emissions on changes in aerosol properties, cloud macro- and microphysics, and cloud radiative forcing over the Southeast Pacific (SEP) during the VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) (15 October–16 November 2008). Two distinct regions are identified. The near-coast polluted region is characterized by low surface precipitation rates, the strong suppression of non-sea-salt particle activation due to sea-salt particles, a predominant albedo effect in aerosol indirect effects, and limited impact of aerosols associated withmore » anthropogenic emissions on clouds. Opposite sensitivities to natural marine and anthropogenic aerosol perturbations are seen in cloud properties (e.g., cloud optical depth and cloud-top and cloud-base heights), precipitation, and the top-of-atmosphere and surface shortwave fluxes over this region. The relatively clean remote region is characterized by large contributions of aerosols from non-regional sources (lateral boundaries) and much stronger drizzle at the surface. Under a scenario of five-fold increase in regional anthropogenic emissions, this relatively clean region shows large cloud responses, for example, a 13% increase in cloud-top height and a 9% increase in albedo in response to a moderate increase (25% of the reference case) in cloud condensation nuclei (CCN) concentration. The reduction of precipitation due to this increase in anthropogenic aerosols more than doubles the aerosol lifetime in the clean marine boundary layer. Therefore, the aerosol impacts on precipitation are amplified by the positive feedback of precipitation on aerosol, which ultimately alters the cloud micro- and macro-physical properties, leading to strong aerosol-cloud-precipitation interactions. The high sensitivity is also related to an increase in cloud-top entrainment rate (by 16% at night) due to the increased anthropogenic aerosols. The simulated aerosol-cloud-precipitation interactions due to the increased anthropogenic aerosols have a stronger diurnal cycle over the clean region compared to the near-coast region with stronger interactions at night. During the day, solar heating results in more frequent decoupling of the cloud and sub-cloud layers, thinner clouds, reduced precipitation, and reduced sensitivity to the increase in anthropogenic emissions. This study shows the importance of natural aerosols in accurately quantifying anthropogenic forcing within a regional modeling framework. Finally, the results of this study also imply that the energy balance perturbations from increased anthropogenic emissions are larger in the more susceptible clean environment than in already polluted environment and are larger than possible from the first indirect effect alone.« less

Ice in Volcanic Clouds

NASA Astrophysics Data System (ADS)

Few, A. A.

2010-12-01

It is widely recognized that lightning activity in thunderstorm clouds is associated with ice in the clouds. In volcanic plumes the lower electrical discharges near the vent are clearly not associated with ice; however, the electrical discharges from the upper volcanic clouds very likely are associated with ice. There is ample water in volcanic plumes and clouds. The explosive volcanic eruption is produced by volatile components in the rising magma. Researchers estimate that the water content of the volatiles is up to 99% by mole; other gases are mainly sulfur and chlorine species. These volatiles carry with them a wide range of hot magma melts and solids, importantly silicate particles and tephra. The more massive components fall out near the vent carrying with them much of the heat from the plume; these large components are not in thermodynamic equilibrium with the gases, ash, and lapilli; thus the heat removed does not lower the temperature of the materials carried aloft in the plume. Upward motion is initially provided by the thrust from the volcanic eruption, then by buoyancy of the hot plume. The rising plume is cooled by entrainment of environmental air, which contains water, and by adiabatic expansion; the plume transitions into a volcanic cloud. Further lifting and cooling produces supercooled water droplets (T ~ -5 C) in a limited zone (z ~ 9 km) before the fast updraft (~ 60 m/s) rapidly transforms them into ice. Computer models of volcanic clouds that include water and ice microphysics indicate that the latent heat of condensation is not significant in cloud dynamics because it occurs in a region where buoyancy is provided by the original hot plume material. The latent heat of ice formation occurs at higher and colder levels and seems to contribute to the final lifting of the cloud top by ~1.5km. Laboratory results indicate that the fine silicate ash particles, which are abundant, are good ice nuclei, IN. Because of the abundance of the silicate ash, modelers conclude that there are many small ice particles in a volcanic clouds compared to thunderstorm clouds where the scarcity of IN produce fewer but larger ice particles. Another microphysical difference is that in the water phase (drops or ice surface) adsorption of sulfur and chlorine gases is enhanced and the freezing temperature lowered. During diffusion growth of ice particles sulfur dioxide can be incorporated in the ice. The sulfur dioxide sequestered by the ice can be converted to sulfate and transported into the stratosphere and released when the ice sublimates. Do these microphysical differences significantly alter the electrical charging mechanisms that exist in thunderstorm clouds? Observations of the lightning discharges associated with the upper regions of volcanic clouds seem to indicate that the charging mechanisms are essentially the same.

FLASHFlux Info

Atmospheric Science Data Center

2013-05-20

... Surface Emissivity Cloud Area Fraction Cloud Effective Pressure Cloud Effective Temperature Cloud Effective Height Cloud Top Pressure Cloud Base Pressure Cloud Particle Phase Liquid Water Path Ice Water Path Water Particle Radius Ice Particle ...

Phase-partitioning in mixed-phase clouds - An approach to characterize the entire vertical column

NASA Astrophysics Data System (ADS)

Kalesse, H.; Luke, E. P.; Seifert, P.

2017-12-01

The characterization of the entire vertical profile of phase-partitioning in mixed-phase clouds is a challenge which can be addressed by synergistic profiling measurements with ground-based polarization lidars and cloud radars. While lidars are sensitive to small particles and can thus detect supercooled liquid (SCL) layers, cloud radar returns are dominated by larger particles (like ice crystals). The maximum lidar observation height is determined by complete signal attenuation at a penetrated optical depth of about three. In contrast, cloud radars are able to penetrate multiple liquid layers and can thus be used to expand the identification of cloud phase to the entire vertical column beyond the lidar extinction height, if morphological features in the radar Doppler spectrum can be related to the existence of SCL. Relevant spectral signatures such as bimodalities and spectral skewness can be related to cloud phase by training a neural network appropriately in a supervised learning scheme, with lidar measurements functioning as supervisor. The neural network output (prediction of SCL location) derived using cloud radar Doppler spectra can be evaluated with several parameters such as liquid water path (LWP) detected by microwave radiometer (MWR) and (liquid) cloud base detected by ceilometer or Raman lidar. The technique has been previously tested on data from Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) instruments in Barrow, Alaska and is in this study utilized for observations from the Leipzig Aerosol and Cloud Remote Observations System (LACROS) during the Analysis of the Composition of Clouds with Extended Polarization Techniques (ACCEPT) field experiment in Cabauw, Netherlands in Fall 2014. Comparisons to supercooled-liquid layers as classified by CLOUDNET are provided.

CERES-MISR Info

Atmospheric Science Data Center

2013-05-20

... Surface Albedo Cloud Area Fraction Cloud Effective Pressure Cloud Effective Temperature Cloud Effective Height Cloud Top Pressure Cloud Base Pressure Cloud Particle Phase Liquid Water Path Ice Water Path Water Particle Radius Ice Particle ...

CERES CRS Info

Atmospheric Science Data Center

2013-05-17

... Flux - Down Cloud Area Fraction Cloud Effective Pressure Cloud Effective Temperature Cloud Effective Height Cloud Top Pressure Cloud Base Pressure Cloud Particle Phase Liquid Water Path Ice Water Path Water Particle Radius Ice Particle ...

CERES SSF Current Info

Atmospheric Science Data Center

2013-05-17

... Surface Albedo Cloud Area Fraction Cloud Effective Pressure Cloud Effective Temperature Cloud Effective Height Cloud Top Pressure Cloud Base Pressure Cloud Particle Phase Liquid Water Path Ice Water Path Water Particle Radius Ice Particle ...

The first observed cloud echoes and microphysical parameter retrievals by China's 94-GHz cloud radar

NASA Astrophysics Data System (ADS)

Wu, Juxiu; Wei, Ming; Hang, Xin; Zhou, Jie; Zhang, Peichang; Li, Nan

2014-06-01

By using the cloud echoes first successfully observed by China's indigenous 94-GHz SKY cloud radar, the macrostructure and microphysical properties of drizzling stratocumulus clouds in Anhui Province on 8 June 2013 are analyzed, and the detection capability of this cloud radar is discussed. The results are as follows. (1) The cloud radar is able to observe the time-varying macroscopic and microphysical parameters of clouds, and it can reveal the microscopic structure and small-scale changes of clouds. (2) The velocity spectral width of cloud droplets is small, but the spectral width of the cloud containing both cloud droplets and drizzle is large. When the spectral width is more than 0.4 m s-1, the radar reflectivity factor is larger (over -10 dBZ). (3) The radar's sensitivity is comparatively higher because the minimum radar reflectivity factor is about -35 dBZ in this experiment, which exceeds the threshold for detecting the linear depolarized ratio (LDR) of stratocumulus (commonly -11 to -14 dBZ; decreases with increasing turbulence). (4) After distinguishing of cloud droplets from drizzle, cloud liquid water content and particle effective radius are retrieved. The liquid water content of drizzle is lower than that of cloud droplets at the same radar reflectivity factor.

Global cloud top height retrieval using SCIAMACHY limb spectra: model studies and first results

NASA Astrophysics Data System (ADS)

Eichmann, Kai-Uwe; Lelli, Luca; von Savigny, Christian; Sembhi, Harjinder; Burrows, John P.

2016-03-01

Cloud top heights (CTHs) are retrieved for the period 1 January 2003 to 7 April 2012 using height-resolved limb spectra measured with the SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY (SCIAMACHY) on board ENVISAT (ENVIronmental SATellite). In this study, we present the retrieval code SCODA (SCIAMACHY cloud detection algorithm) based on a colour index method and test the accuracy of the retrieved CTHs in comparison to other methods. Sensitivity studies using the radiative transfer model SCIATRAN show that the method is capable of detecting cloud tops down to about 5 km and very thin cirrus clouds up to the tropopause. Volcanic particles can be detected that occasionally reach the lower stratosphere. Upper tropospheric ice clouds are observable for a nadir cloud optical thickness (COT) ≥ 0.01, which is in the subvisual range. This detection sensitivity decreases towards the lowermost troposphere. The COT detection limit for a water cloud top height of 5 km is roughly 0.1. This value is much lower than thresholds reported for passive cloud detection methods in nadir-viewing direction. Low clouds at 2 to 3 km can only be retrieved under very clean atmospheric conditions, as light scattering of aerosol particles interferes with the cloud particle scattering. We compare co-located SCIAMACHY limb and nadir cloud parameters that are retrieved with the Semi-Analytical CloUd Retrieval Algorithm (SACURA). Only opaque clouds (τN,c > 5) are detected with the nadir passive retrieval technique in the UV-visible and infrared wavelength ranges. Thus, due to the frequent occurrence of thin clouds and subvisual cirrus clouds in the tropics, larger CTH deviations are detected between both viewing geometries. Zonal mean CTH differences can be as high as 4 km in the tropics. The agreement in global cloud fields is sufficiently good. However, the land-sea contrast, as seen in nadir cloud occurrence frequency distributions, is not observed in limb geometry. Co-located cloud top height measurements of the limb-viewing Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on ENVISAT are compared for the period from January 2008 to March 2012. The global CTH agreement of about 1 km is observed, which is smaller than the vertical field of view of both instruments. Lower stratospheric aerosols from volcanic eruptions occasionally interfere with the cloud retrieval and inhibit the detection of tropospheric clouds. The aerosol impact on cloud retrievals was studied for the volcanoes Kasatochi (August 2008), Sarychev Peak (June 2009), and Nabro (June 2011). Long-lasting aerosol scattering is detected after these events in the Northern Hemisphere for heights above 12.5 km in tropical and polar latitudes. Aerosol top heights up to about 22 km are found in 2009 and the enhanced lower stratospheric aerosol layer persisted for about 7 months. In August 2009 about 82 % of the lower stratosphere between 30 and 70° N was filled with scattering particles and nearly 50 % in October 2008.

The role of jet and film drops in controlling the mixing state of submicron sea spray aerosol particles

PubMed Central

Wang, Xiaofei; Deane, Grant B.; Moore, Kathryn A.; Ryder, Olivia S.; Stokes, M. Dale; Beall, Charlotte M.; Santander, Mitchell V.; Burrows, Susannah M.; Sultana, Camille M.; Prather, Kimberly A.

2017-01-01

The oceans represent a significant global source of atmospheric aerosols. Sea spray aerosol (SSA) particles comprise sea salts and organic species in varying proportions. In addition to size, the overall composition of SSA particles determines how effectively they can form cloud droplets and ice crystals. Thus, understanding the factors controlling SSA composition is critical to predicting aerosol impacts on clouds and climate. It is often assumed that submicrometer SSAs are mainly formed by film drops produced from bursting bubble-cap films, which become enriched with hydrophobic organic species contained within the sea surface microlayer. In contrast, jet drops formed from the base of bursting bubbles are postulated to mainly produce larger supermicrometer particles from bulk seawater, which comprises largely salts and water-soluble organic species. However, here we demonstrate that jet drops produce up to 43% of total submicrometer SSA number concentrations, and that the fraction of SSA produced by jet drops can be modulated by marine biological activity. We show that the chemical composition, organic volume fraction, and ice nucleating ability of submicrometer particles from jet drops differ from those formed from film drops. Thus, the chemical composition of a substantial fraction of submicrometer particles will not be controlled by the composition of the sea surface microlayer, a major assumption in previous studies. This finding has significant ramifications for understanding the factors controlling the mixing state of submicrometer SSA particles and must be taken into consideration when predicting SSA impacts on clouds and climate. PMID:28630346

Bimodality and variability of particle size distributions in high Ice Water Content regions and their implications for microphysical models

NASA Astrophysics Data System (ADS)

Zhu, S.; McFarquhar, G. M.; Leroy, D.; Korolev, A.; Schwarzenboeck, A.; Wu, W.; Strapp, J. W.

2016-12-01

Aviation records since the 1990s indicate that aircraft engines are facing a threat of occasional power loss due to ice ingestion over tropical oceanic convective clouds. The typical absence of radar echoes greater than 30 dBZ during such incidents suggests the existence of large amounts of small ice particles. The industrial aviation safety concerns inspired the High Altitude Ice Crystals / High Ice Water Content (HAIC/HIWC) campaign, whose Phase I was conducted between January and March 2014. A 2-D Stereo (2DS) probe, Precipitation Imaging Probe (PIP) and Isokinetic Evaporator Probe were installed on the French Falcon 20 making in-situ observations off the coast of Darwin, Australia. Composite particle size distributions (PSDs) using 2DS and PIP data were derived for each 5 second period in cloud. Using an automated technique to identify multiple modes in PSDs and an Incomplete Gamma Fit technique, the intercept (N0), slope (λ) and shape parameter (μ) of each mode of a gamma distribution were determined. The variation of PSDs and fit parameters for Ice Water Contents (IWCs) > 1.5 g m-3 with cloud and environmental parameters and their differences from PSDs measured outside of high IWC conditions are summarized here. Two types of HIWC conditions were observed, according to whether the median mass diameters (MMD) were positively or negatively correlated with IWC. The principal findings about high IWC regions are as follows: 1) larger μ and N0 are found in high IWC regions while λ tends to remain unchanged; 2) PSDs are more likely to be bimodal at lower temperatures. 3) Positive MMD-IWC correlations are associated with larger μ and smaller N0; 4) Bimodal distributions are more frequent for positive MMD-IWC correlations; and 5) Positive MMD-IWC correlations are usually associated with longer-aged clouds, but there are exceptions, showing other factors affect the occurrence of frequent small particles in high IWC regions. Implications for modeling of high IWC events are discussed.

Comparing airborne and satellite retrievals of cloud optical thickness and particle effective radius using a spectral radiance ratio technique: two case studies for cirrus and deep convective clouds

NASA Astrophysics Data System (ADS)

Krisna, Trismono C.; Wendisch, Manfred; Ehrlich, André; Jäkel, Evelyn; Werner, Frank; Weigel, Ralf; Borrmann, Stephan; Mahnke, Christoph; Pöschl, Ulrich; Andreae, Meinrat O.; Voigt, Christiane; Machado, Luiz A. T.

2018-04-01

Solar radiation reflected by cirrus and deep convective clouds (DCCs) was measured by the Spectral Modular Airborne Radiation Measurement System (SMART) installed on the German High Altitude and Long Range Research Aircraft (HALO) during the Mid-Latitude Cirrus (ML-CIRRUS) and the Aerosol, Cloud, Precipitation, and Radiation Interaction and Dynamic of Convective Clouds System - Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modelling and to the Global Precipitation Measurement (ACRIDICON-CHUVA) campaigns. On particular flights, HALO performed measurements closely collocated with overpasses of the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Aqua satellite. A cirrus cloud located above liquid water clouds and a DCC topped by an anvil cirrus are analyzed in this paper. Based on the nadir spectral upward radiance measured above the two clouds, the optical thickness τ and particle effective radius reff of the cirrus and DCC are retrieved using a radiance ratio technique, which considers the cloud thermodynamic phase, the vertical profile of cloud microphysical properties, the presence of multilayer clouds, and the heterogeneity of the surface albedo. For the cirrus case, the comparison of τ and reff retrieved on the basis of SMART and MODIS measurements yields a normalized mean absolute deviation of up to 1.2 % for τ and 2.1 % for reff. For the DCC case, deviations of up to 3.6 % for τ and 6.2 % for reff are obtained. The larger deviations in the DCC case are mainly attributed to the fast cloud evolution and three-dimensional (3-D) radiative effects. Measurements of spectral upward radiance at near-infrared wavelengths are employed to investigate the vertical profile of reff in the cirrus. The retrieved values of reff are compared with corresponding in situ measurements using a vertical weighting method. Compared to the MODIS observations, measurements of SMART provide more information on the vertical distribution of particle sizes, which allow reconstructing the profile of reff close to the cloud top. The comparison between retrieved and in situ reff yields a normalized mean absolute deviation, which ranges between 1.5 and 10.3 %, and a robust correlation coefficient of 0.82.

On the Chemical Characterization of Organic Matter in Rain at Mexico City.

NASA Astrophysics Data System (ADS)

Montero-Martinez, G.; Andraca-Ayala, G. L.; Hernández-Nagay, D. P.; Mendoza-Trejo, A.; Rivera-Arellano, J.; Rosado-Abon, A.; Roy, P. D.

2016-12-01

The chemical composition of the aerosol plays a central role in atmospheric processes and has influence on the hydrological cycle. Clouds form through the nucleation of water vapor on certain atmospheric aerosol particles, called cloud condensation nuclei (CCN). Also, precipitating particles scavenge some other aerosol particles on their way to the surface. Atmospheric particles are a mixture of organic and inorganic materials, both soluble and insoluble in water. Aerosol chemical characterization indicates a larger variety of compounds in urban areas respect to other regions. Thus, chemical composition of rainwater may represent an important aspect for estimating atmospheric air pollution. It has been recognized that organic species present in aerosol particles are important in the formation of cloud droplets. Therefore, the information about the organic compounds in precipitation samples may be helpful to understand their effects on the formation of clouds and rain, as well as their sources. Organic acids are ubiquitous components of aerosols and have been identified in precipitation water. In this work, preliminary results of the content of soluble organic (neutral and acidic) matter in rainwater samples collected in Mexico City during 2015 will be presented. The organic compounds content was performed by using an ionic chromatographic methodology with gradient elution; so the total amount was evaluated as the sum of four fractions: neutral/basic, mono-, bi-, and poly-acid compounds. The outcomes suggest that most of the amount of organic substances soluble in water is contained by the neutral/basic and mono-acid fractions. Regarding the total amount of water soluble organic compounds, the rain samples collected in Mexico City are in agreement with some others reported for large urban areas.

Importance of including ammonium sulfate ((NH4)2SO4) aerosols for ice cloud parameterization in GCMs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhattacharjee, P. S.; Sud, Yogesh C.; Liu, Xiaohong

2010-02-22

A common deficiency of many cloud-physics parameterizations including the NASA’s microphysics of clouds with aerosol- cloud interactions (hereafter called McRAS-AC) is that they simulate less (larger) than the observed ice cloud particle number (size). A single column model (SCM) of McRAS-AC and Global Circulation Model (GCM) physics together with an adiabatic parcel model (APM) for ice-cloud nucleation (IN) of aerosols were used to systematically examine the influence of ammonium sulfate ((NH4)2SO4) aerosols, not included in the present formulations of McRAS-AC. Specifically, the influence of (NH4)2SO4 aerosols on the optical properties of both liquid and ice clouds were analyzed. First anmore » (NH4)2SO4 parameterization was included in the APM to assess its effect vis-à-vis that of the other aerosols. Subsequently, several evaluation tests were conducted over the ARM-SGP and thirteen other locations (sorted into pristine and polluted conditions) distributed over marine and continental sites with the SCM. The statistics of the simulated cloud climatology were evaluated against the available ground and satellite data. The results showed that inclusion of (NH4)2SO4 in the SCM made a remarkable improvement in the simulated effective radius of ice clouds. However, the corresponding ice-cloud optical thickness increased more than is observed. This can be caused by lack of cloud advection and evaporation. We argue that this deficiency can be mitigated by adjusting the other tunable parameters of McRAS-AC such as precipitation efficiency. Inclusion of ice cloud particle splintering introduced through well- established empirical equations is found to further improve the results. Preliminary tests show that these changes make a substantial improvement in simulating the cloud optical properties in the GCM, particularly by simulating a far more realistic cloud distribution over the ITCZ.« less

Comets: Dirty snowballs or icy dirtballs

NASA Astrophysics Data System (ADS)

Keller, H. U.

1989-12-01

The observations of comet Halley show that the non-volatile (dust) component of the cometary nucleus has become more dominant if compared to the perception based on the icy conglomerate nucleus. The in-situ observations on the Giotto spacecraft revealed an excess of large dust particles that dominate the mass distribution. Even larger particles were derived from the attitude changes of the spacecraft bridging the gap to the cloud of particles observed by radar techniques. A dust to gas ratio larger than one was derived for comet Halley. The importance of dust for the structure of the nucleus is corroborated by the amount of particles and their lifetime in meteor streams. Fireballs show that large (meter size) objects separate from the nucleus and are stable enough to survive hundreds of orbital periods. From the various lines of evidence it is concluded that the structure of cometary nuclei is determined by the non-volatile component rather than by ice or snow. Laboratory models based on icy agglomerations do not seem realistic as nucleus analogs.

Particle nonuniformity effects on particle cloud flames in low gravity

NASA Technical Reports Server (NTRS)

Berlad, A. L.; Tangirala, V.; Seshadri, K.; Facca, L. T.; Ogrin, J.; Ross, H.

1991-01-01

Experimental and analytical studies of particle cloud combustion at reduced gravity reveal the substantial roles that particle cloud nonuniformities may play in particle cloud combustion. Macroscopically uniform, quiescent particle cloud systems (at very low gravitational levels and above) sustain processes which can render them nonuniform on both macroscopic and microscopic scales. It is found that a given macroscopically uniform, quiescent particle cloud flame system can display a range of microscopically nonuniform features which lead to a range of combustion features. Microscopically nonuniform particle cloud distributions are difficult experimentally to detect and characterize. A uniformly distributed lycopodium cloud of particle-enriched microscopic nonuniformities in reduced gravity displays a range of burning velocities for any given overall stoichiometry. The range of observed and calculated burning velocities corresponds to the range of particle enriched concentrations within a characteristic microscopic nonuniformity. Sedimentation effects (even in reduced gravity) are also examined.

Physical and Optical/Radiative Characteristics of Aerosol and Cloud Particles in Tropical Cirrus: Importance in Radiation Balance

NASA Technical Reports Server (NTRS)

Pueschel, R. F.; Howard, S. D.; Foster, T. C.; Hallett, J.; Arnott, W. P.; Condon, Estelle P. (Technical Monitor)

1996-01-01

Whether cirrus clouds heat or cool the Earth-atmosphere system depends on the relative importance of the cloud shortwave albedo effect and the cloud thermal greenhouse effect. Both are determined by the distribution of ice condensate with cloud particle size. The microphysics instrument package flown aboard the NASA DC-8 in TOGA/COARE included an ice crystal replicator, a 2D Greyscale Cloud Particle Probe and a Forward Scattering Spectrometer Aerosol Probe. In combination, the electro-optical instruments permitted particle size measurements between 0.5 micrometer and 2.6 millimeter diameter. Ice crystal replicas were used to validate signals from the electrooptical instruments. Both optical and scanning electron microscopy were utilized to analyze aerosol and ice particle replicas between 0.1 micrometer and several 100 micrometer diameter. In first approximation, the combined aerosol-cloud particle spectrum in several clouds followed a power law N alpha D(sup -2.5). Thus, large cloud particles carried most of the condensate mass, while small cloud and aerosol particles determined the surface area. The mechanism of formation of small particles is growth of (hygroscopic, possibly ocean-derived) aerosol particles along the Kohler curves. The concentration of small particles is higher and less variable in space and time, and their tropospheric residence time is longer, than those of large cloud particles because of lower sedimentation velocities. Small particles shift effective cloud particle radii to sizes much smaller than the mean diameter of the cloud particles. This causes an increase in shortwave reflectivity and IR emissivity, and a decrease in transmissivity. Occasionally, the cloud reflectivity increased with altitude (decreasing temperature) stronger than did cloud emissivity, yielding enhanced radiative cooling at higher altitudes. Thus, cirrus produced by deep convection in the tropics may be critical in controlling processes whereby energy from warm tropical oceans is injected to different levels in the atmosphere to subsequently influence not only tropical but mid-latitude climate.

Aerosol properties, source identification, and cloud processing in orographic clouds measured by single particle mass spectrometry on a central European mountain site during HCCT-2010

NASA Astrophysics Data System (ADS)

Roth, A.; Schneider, J.; Klimach, T.; Mertes, S.; van Pinxteren, D.; Herrmann, H.; Borrmann, S.

2016-01-01

Cloud residues and out-of-cloud aerosol particles with diameters between 150 and 900 nm were analysed by online single particle aerosol mass spectrometry during the 6-week study Hill Cap Cloud Thuringia (HCCT)-2010 in September-October 2010. The measurement location was the mountain Schmücke (937 m a.s.l.) in central Germany. More than 160 000 bipolar mass spectra from out-of-cloud aerosol particles and more than 13 000 bipolar mass spectra from cloud residual particles were obtained and were classified using a fuzzy c-means clustering algorithm. Analysis of the uncertainty of the sorting algorithm was conducted on a subset of the data by comparing the clustering output with particle-by-particle inspection and classification by the operator. This analysis yielded a false classification probability between 13 and 48 %. Additionally, particle types were identified by specific marker ions. The results from the ambient aerosol analysis show that 63 % of the analysed particles belong to clusters having a diurnal variation, suggesting that local or regional sources dominate the aerosol, especially for particles containing soot and biomass burning particles. In the cloud residues, the relative percentage of large soot-containing particles and particles containing amines was found to be increased compared to the out-of-cloud aerosol, while, in general, organic particles were less abundant in the cloud residues. In the case of amines, this can be explained by the high solubility of the amines, while the large soot-containing particles were found to be internally mixed with inorganics, which explains their activation as cloud condensation nuclei. Furthermore, the results show that during cloud processing, both sulfate and nitrate are added to the residual particles, thereby changing the mixing state and increasing the fraction of particles with nitrate and/or sulfate. This is expected to lead to higher hygroscopicity after cloud evaporation, and therefore to an increase of the particles' ability to act as cloud condensation nuclei after their cloud passage.

The Effect of Asian Dust Aerosols on Cloud Properties and Radiative Forcing from MODIS and CERES

NASA Technical Reports Server (NTRS)

Huang, Jianping; Minnis, Patrick; Lin, Bing; Wang, Tianhe; Yi, Yuhong; Hu, Yongxiang; Sun-Mack, Sunny; Ayers, Kirk

2005-01-01

The effects of dust storms on cloud properties and radiative forcing are analyzed over northwestern China from April 2001 to June 2004 using data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) and Clouds and the Earth's Radiant Energy System (CERES) instruments on the Aqua and Terra satellites. On average, ice cloud effective particle diameter, optical depth and ice water path of the cirrus clouds under dust polluted conditions are 11%, 32.8%, and 42% less, respectively, than those derived from ice clouds in dust-free atmospheric environments. The humidity differences are larger in the dusty region than in the dust-free region, and may be caused by removal of moisture by wet dust precipitation. Due to changes in cloud microphysics, the instantaneous net radiative forcing is reduced from -71.2 W/m2 for dust contaminated clouds to -182.7 W/m2 for dust-free clouds. The reduced cooling effects of dusts may lead to a net warming of 1 W/m2, which, if confirmed, would be the strongest aerosol forcing during later winter and early spring dust storm seasons over the studied region.

Coagulation of grains in static and collapsing protostellar clouds

NASA Technical Reports Server (NTRS)

Weidenschilling, S. J.; Ruzmaikina, T. V.

1994-01-01

We simulate collisional evolution of grains in dense turbulent molecular cloud cores (or Bok globules) in static equilibrium and free-fall collapse, assuming spherical symmetry. Relative velocities are due to thermal motions, differential settling, and turbulence, with the latter dominant for sonic turbulence with an assumed Kolmogorov spectrum. Realistic criteria are used to determine outcomes of collisions (coagulation vs. destruction) as functions of particle size and velocity. Results are presented for a variety of cloud parameters (radial density profile, turbulent velocity) and particle properties (density, impact strength). Results are sensitive to the assumed mechanical properties (density and impact strength) of grain aggregates. Particle growth is enhanced if aggregates have low density or fractal structures. On a timescale of a few Myr, an initial population of 0.1 micrometers grains may produce dense compact particles approximately 1 micrometer in size, or fluffy aggregates approximately 100 micrometers. For impact strengths less than or equal to 10(exp 6) ergs/g, a steady state is reached between coagulation of small grains and collisional disruption of larger aggregates. Formation of macroscopic aggregates requires high mechanical strengths and low aggregate densities. We assume sonic turbulence during collapse, with varied eddy size scales determining the dissipation rate or turbulence strength. The degree of collisional evolution during collapse is sensitive to the assumed small-scale structure (inner sc ale) of the turbulence. Weak turbulence results in few collisions and preserves the precollapse particle size distribution with little change. Strong turbulence tends to produce net destruction, rather than particle growth, during infall, unless inpact strengths are greater than 10(exp 6)ergs/g.

Individual aerosol particles in and below clouds along a Mt. Fuji slope: Modification of sea-salt-containing particles by in-cloud processing

NASA Astrophysics Data System (ADS)

Ueda, S.; Hirose, Y.; Miura, K.; Okochi, H.

2014-02-01

Sizes and compositions of atmospheric aerosol particles can be altered by in-cloud processing by absorption/adsorption of gaseous and particulate materials and drying of aerosol particles that were formerly activated as cloud condensation nuclei. To elucidate differences of aerosol particles before and after in-cloud processing, aerosols were observed along a slope of Mt. Fuji, Japan (3776 m a.s.l.) during the summer in 2011 and 2012 using a portable laser particle counter (LPC) and an aerosol sampler. Aerosol samples for analyses of elemental compositions were obtained using a cascade impactor at top-of-cloud, in-cloud, and below-cloud altitudes. To investigate composition changes via in-cloud processing, individual particles (0.5-2 μm diameter) of samples from five cases (days) collected at different altitudes under similar backward air mass trajectory conditions were analyzed using a transmission electron microscope (TEM) equipped with an energy dispersive X-ray analyzer. For most cases (four cases), most particles at all altitudes mainly comprised sea salts: mainly Na with some S and/or Cl. Of those, in two cases, sea-salt-containing particles with Cl were found in below-cloud samples, although sea-salt-containing particles in top-of-cloud samples did not contain Cl. This result suggests that Cl in the sea salt was displaced by other cloud components. In the other two cases, sea-salt-containing particles on samples at all altitudes were without Cl. However, molar ratios of S to Na (S/Na) of the sea-salt-containing particles of top-of-cloud samples were higher than those of below-cloud samples, suggesting that sulfuric acid or sulfate was added to sea-salt-containing particles after complete displacement of Cl by absorption of SO2 or coagulation with sulfate. The additional volume of sulfuric acid in clouds for the two cases was estimated using the observed S/Na values of sea-salt-containing particles. The estimation revealed that size changes by in-cloud processing from below-cloud to top-of-cloud altitudes were less than 6% for sizes of 0.5-2 μm diameter. The obtained results will be useful to evaluate the aging effect and transition of aerosol particles through in-cloud processing.

CCN production by new particle formation in the free troposphere

NASA Astrophysics Data System (ADS)

Rose, Clémence; Sellegri, Karine; Moreno, Isabel; Velarde, Fernando; Ramonet, Michel; Weinhold, Kay; Krejci, Radovan; Andrade, Marcos; Wiedensohler, Alfred; Ginot, Patrick; Laj, Paolo

2017-01-01

Global models predict that new particle formation (NPF) is, in some environments, responsible for a substantial fraction of the total atmospheric particle number concentration and subsequently contributes significantly to cloud condensation nuclei (CCN) concentrations. NPF events were frequently observed at the highest atmospheric observatory in the world, on Chacaltaya (5240 m a.s.l.), Bolivia. The present study focuses on the impact of NPF on CCN population. Neutral cluster and Air Ion Spectrometer and mobility particle size spectrometer measurements were simultaneously used to follow the growth of particles from cluster sizes down to ˜ 2 nm up to CCN threshold sizes set to 50, 80 and 100 nm. Using measurements performed between 1 January and 31 December 2012, we found that 61 % of the 94 analysed events showed a clear particle growth and significant enhancement of the CCN-relevant particle number concentration. We evaluated the contribution of NPF, relative to the transport and growth of pre-existing particles, to CCN size. The averaged production of 50 nm particles during those events was 5072, and 1481 cm-3 for 100 nm particles, with a larger contribution of NPF compared to transport, especially during the wet season. The data set was further segregated into boundary layer (BL) and free troposphere (FT) conditions at the site. The NPF frequency of occurrence was higher in the BL (48 %) compared to the FT (39 %). Particle condensational growth was more frequently observed for events initiated in the FT, but on average faster for those initiated in the BL, when the amount of condensable species was most probably larger. As a result, the potential to form new CCN was higher for events initiated in the BL (67 % against 53 % in the FT). In contrast, higher CCN number concentration increases were found when the NPF process initially occurred in the FT, under less polluted conditions. This work highlights the competition between particle growth and the removal of freshly nucleated particles by coagulation processes. The results support model predictions which suggest that NPF is an effective source of CCN in some environments, and thus may influence regional climate through cloud-related radiative processes.

Biomass-burning impact on CCN number, hygroscopicity and cloud formation during summertime in the eastern Mediterranean

NASA Astrophysics Data System (ADS)

Bougiatioti, Aikaterini; Bezantakos, Spiros; Stavroulas, Iasonas; Kalivitis, Nikos; Kokkalis, Panagiotis; Biskos, George; Mihalopoulos, Nikolaos; Papayannis, Alexandros; Nenes, Athanasios

2016-06-01

This study investigates the concentration, cloud condensation nuclei (CCN) activity and hygroscopic properties of particles influenced by biomass burning in the eastern Mediterranean and their impacts on cloud droplet formation. Air masses sampled were subject to a range of atmospheric processing (several hours up to 3 days). Values of the hygroscopicity parameter, κ, were derived from CCN measurements and a Hygroscopic Tandem Differential Mobility Analyzer (HTDMA). An Aerosol Chemical Speciation Monitor (ACSM) was also used to determine the chemical composition and mass concentration of non-refractory components of the submicron aerosol fraction. During fire events, the increased organic content (and lower inorganic fraction) of the aerosol decreases the values of κ, for all particle sizes. Particle sizes smaller than 80 nm exhibited considerable chemical dispersion (where hygroscopicity varied up to 100 % for particles of same size); larger particles, however, exhibited considerably less dispersion owing to the effects of condensational growth and cloud processing. ACSM measurements indicate that the bulk composition reflects the hygroscopicity and chemical nature of the largest particles (having a diameter of ˜ 100 nm at dry conditions) sampled. Based on positive matrix factorization (PMF) analysis of the organic ACSM spectra, CCN concentrations follow a similar trend as the biomass-burning organic aerosol (BBOA) component, with the former being enhanced between 65 and 150 % (for supersaturations ranging between 0.2 and 0.7 %) with the arrival of the smoke plumes. Using multilinear regression of the PMF factors (BBOA, OOA-BB and OOA) and the observed hygroscopicity parameter, the inferred hygroscopicity of the oxygenated organic aerosol components is determined. We find that the transformation of freshly emitted biomass burning (BBOA) to more oxidized organic aerosol (OOA-BB) can result in a 2-fold increase of the inferred organic hygroscopicity; about 10 % of the total aerosol hygroscopicity is related to the two biomass-burning components (BBOA and OOA-BB), which in turn contribute almost 35 % to the fine-particle organic water of the aerosol. Observation-derived calculations of the cloud droplet concentrations that develop for typical boundary layer cloud conditions suggest that biomass burning increases droplet number, on average by 8.5 %. The strongly sublinear response of clouds to biomass-burning (BB) influences is a result of strong competition of CCN for water vapor, which results in very low maximum supersaturation (0.08 % on average). Attributing droplet number variations to the total aerosol number and the chemical composition variations shows that the importance of chemical composition increases with distance, contributing up to 25 % of the total droplet variability. Therefore, although BB may strongly elevate CCN numbers, the impact on droplet number is limited by water vapor availability and depends on the aerosol particle concentration levels associated with the background.

Small particle cirrus observed by the Atmospheric Infrared Sounder

NASA Astrophysics Data System (ADS)

Kahn, B. H.; Eldering, A.; Fishbein, E. F.

2003-04-01

The high-resolution spectra of the Atmospheric Infrared Sounder (AIRS) have provided an opportunity to globally observe small particle-dominated cirrus clouds. The shape of the radiance spectra in the atmospheric windows is uniquely influenced by small ice crystals with an effective radius (reff) of a few 10s of microns and smaller. In some rare instances, minima in the AIRS brightness temperature (BT) spectra between 800 to 850 cm-1 are seen, consistent with the existence of ice particles with an reff smaller than 3 microns. Much more frequent occurences of small ice particle clouds with reff larger than 3 microns are observed through the large 998 to 811 cm-1 BT differences without minima. The small particle events are occasionally found in orographic cirrus clouds, in and around cumulonimbus towers, and in cirrus bands far removed from convection and orography. Several cases spanning the variety of small particle-dominated cirrus events will be presented. AIRS, located on the EOS-Aqua platform, is a high-resolution grating spectrometer that scans at angles 49.5 degrees on either side of nadir view, at both visible and infrared wavelengths. The surface footprint is 13.5 km at the nadir view, and coverage in the infrared is in three bandpasses (649-1136, 1265-1629, and 2169-2674 cm-1). Comparisons of observed spectra are made with simulated spectra generated by a plane-parallel scattering radiative transfer model using ice particle shapes and sizes calculated by the T-matrix method. These comparisons yield information on small particle cirrus cloud reff and optical depth. Aumann, H.H., and R.J. Pagano, Atmospheric Infrared Sounder on the Earth Observing System. Opt. Eng. 33, 776-784, 1994. Mishchenko, M.I., and L.D. Travis, Capabilities and limitations of a current Fortran implementation of the T-matrix method for randomly oriented, rotationally symmetric scatterers. J. Quant. Spectrosc. Radiat. Transfer, 60, 309-324, 1998. Moncet, J.L., and S.A. Clough, Accelerated monochromatic radiative transfer for scattering atmospheres: Application of a new model to spectral radiance observations. J. Geophys. Res., 102, 21,853-21,866, 1997. Rathke, C., and J. Fischer, Retrieval of cloud microphysical properties from thermal infrared observations by a fast iterative radiance fitting method, J. Atmos. Ocean. Tech., 17, 1509-1524, 2000. Smith, W.L., S. Ackerman, H. Revercomb, H. Huang, D.H. DeSlover, W. Feltz, L. Gumley, and A. Collard, Infrared spectral absorption of nearly invisible cirrus clouds. Geophys. Res. Lett., 25, 1137-1140, 1998. Strabala, K.I., S.A. Ackerman, and W.P. Menzel, Cloud properties inferred from 8-12 micron data. J. Appl. Meteor., 33, 212-229, 1994.

Importance of the mixing state for ice nucleating capabilities of individual aerosol particles

NASA Astrophysics Data System (ADS)

Ebert, Martin; Worringen, Annette; Benker, Nathalie; Weinbruch, Stephan

2010-05-01

The effects of aerosol particles on heterogeneous ice formation are currently insufficiently understood. Modelling studies have shown that the type and quantity of atmospheric aerosol particles acting as ice nuclei (IN) can influence ice cloud microphysical and radiative properties as well as their precipitation efficiency. Therefore, the physicochemical identification of IN and a quantitative description of the ice nucleation processes are crucial for a better understanding of formation, life cycles, and the optical properties of clouds as well as for numerical precipitation forecast. During the CLACE 5 campaign in 2006 at the high alpine research station Jungfraujoch (3580 m asl), Switzerland, the physicochemical parameters of IN within mixed-phase clouds were studied. By the use of special Ice-Counterflow Virtual Impactor, residual particles of small ice nuclei (IN) and the interstitial aerosol fraction were sampled seperately within mixed-phase clouds. The size, morphology, elemental composition and mixing state of more than 7000 particles of selected IN- and interstitial-samples were analyzed by scanning electron microscopy (SEM) combined with energy-dispersive X-ray analysis (EDX). For selected particles, the mineralogical phase composition was determined by transmission electron microscopy. In order to receive detailed information about the mixing state (coatings, agglomerates, heterogeneous inclusions) of the IN- and interstitial-samples, the complete individual particle analysis was performed operator controlled. Four different particle types were identified to act as IN. 1) Carbonaceous particles, which were identified to be a complex mixture of soot (main component), sulfate and nitrate. 2) Complex mixtures of two or more diverse particle groups. In almost 75% of these particles silicates or metal oxides are the main-component. 3) Aluminium oxide particles, which were internally mixed with calcium and sulphate rich material and 4) Pb bearing particles. The high abundance of Pb-bearing particles in the IN-samples (up to 24% by number) was an unexpected finding. Besides a smaller content of larger PbO and PbCl2-particles the main component of the particles within this type are predominantly sea salt, soot or silicates, while Pb in these particles is only present as small (50 - 500 nm) heterogeneous Pb or PbS inclusions. In all 4 particle types identified as IN, the mixing state seems to play an essential role. Therefore it can be concluded that the determination of the main-component of a particle is not sufficient for the prediction of its IN-capability.

Observations and Parameterizations of Particle Size Distributions in Deep Tropical Cirrus and Stratiform Precipitation Clouds: Results from In-Situ Observations in TRMM Field Campaigns

NASA Technical Reports Server (NTRS)

Heymsfield, Andrew J.; Bansemer, Aaron; Field, Paul R.; Durden, Stephen L.; Stith, Jeffrey L.; Dye, James E.; Hall, William; Grainger, Cedric A.

2002-01-01

In this study, we report on the evolution of particle size distributions (PSDs) and habits as measured during slow, Lagrangian-type spiral descents through deep subtropical and tropical cloud layers in Florida, Brazil, and Kwajalein, Marshall Islands, most of which were precipitating. The objective of the flight patterns was to learn more about how the PSDs evolved in the vertical and to obtain information of the vertical structure of microphysical properties. New instrumentation yielding better information on the concentrations of particles in the size (D) range between 0.2 and 2 cm, as well as improved particle imagery, produced more comprehensive observations for tropical stratiform precipitation regions and anvils than have been available previously. Collocated radar observations provided additional information on the vertical structure of the cloud layers sampled. Most of the spirals began at cloud top, with temperatures (T) as low as -50 C, and ended at cloud base or below the melting layer (ML). The PSDs broadened from cloud top towards cloud base, with the largest particles increasing in size from several millimeters at cloud top to one centimeter or larger towards cloud base. Some continued growth was noted in the upper part of the ML. Concentrations of particles less than 1 mm in size decreased with decreasing height. The result was a consistent change in the PSDs in the vertical. Similarly, systematic changes in the size dependence of the particle cross-sectional area was noted with decreasing height. Aggregation-as ascertained from both the changes in the PSDs and evolution of particle habits as observed in high detail with the cloud particle imager (CPI) probe-was responsible for these trends. The PSDs were generally well-represented by gamma distributions of the form N = N0 gamma D microns e- lambda gamma D that were fitted to the PSDs over 1-km horizontal intervals throughout the spirals. The intercept (N0 gamma), slope (lambda gamma), and dispersion (microns) values were derived for each PSD. Exponential curves (N = N0e- lambdaD; micron = 0) were also fitted to the distributions. The lambda gamma values for given spirals varied systematically with temperature as did the values of lambda (exponential), and the data generally conformed to values found in previous studies involving exponential fits to size distributions in mid-latitude frontal and cirrus layers. Considerable variability often noted in the PSD properties during the loops of individual spirals was manifested primarily in large changes in N0 gamma and N0, but micron, lambda gamma and lambda remained fairly stable. Temperature is not found to be the sole factor controlling lambda gamma or lambda but is a primary one. Direct relationships were found between lambda gamma and N0 gamma or lambda gamma and micron for the gamma distributions and lambda and N0 for the exponential. The latter relationship was not found as distinctly in earlier studies; observed PSDs in this study had better fidelity with less scatter. The micron values changed monotonically with T over the range of temperatures and were directly related to N0 gamma or lambda gamma, thereby reducing the number of variables in the PSD functional equation to two. In the upper part of the ML, N0 and lambda continued to decrease, and in the lower part these values began to increase as the largest particles melted. We developed general expressions relating various bulk microphysical, radar, and radiative transfer-related variables to N0 gamma and lambda gamma, useful for both tropical and mid-latitude clouds. These relationships facilitate the specification of a number of bulk properties in cloud and climate models. The results presented in this paper apply best to temperatures between 0 and -40 C, for which the measured radar reflectivities fall in the range of 0 to 25 dBZe.

Landscape-precipitation feedback mediated by ice nuclei: an example from the Arctic

NASA Astrophysics Data System (ADS)

Stopelli, Emiliano; Conen, Franz; Zimmermann, Lukas; Morris, Cindy; Alewell, Christine

2016-04-01

The Arctic is one of the regions on Earth which are particularly sensitive to the effects of climate change. One of the largest uncertainties in describing climate and climate change is constituted by the characterisation of the behaviour of clouds. Specifically in the Arctic region there is a low abundance of cloud condensation nuclei (CCN) resulting in low droplet concentrations in clouds. Ice nucleating particles (INPs) in the atmosphere promote the aggregation of water molecules into ice, increasing the chance for precipitation. Therefore, a change in the absolute abundance of INPs and their relative presence compared to CCN is expected to have strong impacts on climate in the Arctic in terms of the radiative budget and of precipitation. In July 2015 we sampled particles from air at Haldde Observatory, Norway (69° 55'45" N, 22° 48'30" E, 905 m a.s.l.) on PM10 filters. We determined the number of INPs active at moderate supercooling temperatures (≥ -15 ° C, INPs-15) by immersion freezing. To identify potential sources of airborne INPs we also collected samples of soil from a highland and decaying leaf litter. Air masses passing over the land were enriched in INPs-15, with concentrations twice to three times larger than those found in air masses directly coming from the Barents Sea. Ice nucleation spectra suggest that it is mainly litter which accounts for this enrichment in INPs-15. This example helps elucidating the feedback linking landscapes and atmosphere mediated by INPs in the frame of climate change. While the snow coverage is progressively reducing in the Arctic, areas with decaying leaf litter and vegetation that are exposed to wind and grazing are expected to increase, resulting into a larger abundance of INPs in the local atmosphere. This increase in airborne INPs can promote a change in the freezing of clouds, with impact on the lifetime and on the radiative properties of clouds, and ultimately on the occurrence of precipitation in the Arctic region.

Partitioning CloudSat Ice Water Content for Comparison with Upper-Tropospheric Ice in Global Atmospheric Models

NASA Astrophysics Data System (ADS)

Chen, W. A.; Woods, C. P.; Li, J. F.; Waliser, D. E.; Chern, J.; Tao, W.; Jiang, J. H.; Tompkins, A. M.

2010-12-01

CloudSat provides important estimates of vertically resolved ice water content (IWC) on a global scale based on radar reflectivity. These estimates of IWC have proven beneficial in evaluating the representations of ice clouds in global models. An issue when performing model-data comparisons of IWC particularly germane to this investigation, is the question of which component(s) of the frozen water mass are represented by retrieval estimates and how they relate to what is represented in models. The present study developed and applied a new technique to partition CloudSat total IWC into small and large ice hydrometeors, based on the CloudSat-retrieved ice particle size distribution (PSD) parameters. The new method allows one to make relevant model-data comparisons and provides new insights into the model’s representation of atmospheric IWC. The partitioned CloudSat IWC suggests that the small ice particles contribute to 20-30% of the total IWC in the upper troposphere when a threshold size of 100 μm is used. Sensitivity measures with respect to the threshold size, the PSD parameters, and the retrieval algorithms are presented. The new dataset is compared to model estimates, pointing to areas for model improvement. Cloud ice analyses from the European Centre for Medium-Range Weather Forecasts model agree well with the small IWC from CloudSat. The finite-volume multi-scale modeling framework model underestimates total IWC at 147 and 215 hPa, while overestimating the fractional contribution from the small ice species. These results are discussed in terms of their applications to, and implications for, the evaluation of global atmospheric models, providing constraints on the representations of cloud feedback and precipitation in global models, which in turn can help reduce uncertainties associated with climate change projections. Figure 1. A sample lognormal ice number distribution (red curve), and the corresponding mass distribution (black curve). The dotted line represents the cutoff size for IWC partitioning (Dc = 100 µm as an example). The partial integrals of the mass distribution for particles smaller and larger than Dc correspond to IWC<100 (green area) and IWC>100 (blue area), respectively.

Chemical energy in cold-cloud aggregates - The origin of meteoritic chondrules

NASA Technical Reports Server (NTRS)

Clayton, D. D.

1980-01-01

If interstellar particles and molecules accumulate into larger particles during the collapse of a cold cloud, the resulting aggregates contain a large store of internal chemical energy. It is here proposed that subsequent warming of these accumulates leads to a thermal runaway when exothermic chemical reactions begin within the aggregate. These, after cooling, are the crystalline chondrules found so abundantly within chondritic meteorites. Chemical energy can also heat meteoritic parent bodies of any size, and both thermal metamorphism and certain molten meteorites are proposed to have occurred in this way. If this new theory is correct, (1) the model of chemical condensation in a hot gaseous solar system is eliminated, and (2) a new way of studying the chemical evolution of the interstellar medium has been found. A simple dust experiment on a comet flyby is proposed to test some features of this controversy.

Comparison of the mixing state of long-range transported Asian and African mineral dust

NASA Astrophysics Data System (ADS)

Fitzgerald, Elizabeth; Ault, Andrew P.; Zauscher, Melanie D.; Mayol-Bracero, Olga L.; Prather, Kimberly A.

2015-08-01

Mineral dust from arid regions represents the second largest global source of aerosols to the atmosphere. Dust strongly impacts the radiative balance of the earth's atmosphere by directly scattering solar radiation and acting as nuclei for the formation of liquid droplets and ice nuclei within clouds. The climate effects of mineral dust aerosols are poorly understood, however, due to their complex chemical and physical properties, which continuously evolve during atmospheric transport. This work focuses on characterizing atmospheric mineral dust from the two largest global dust sources: the Sahara Desert in Africa and the Gobi and Taklamakan Deserts in Asia. Measurements of individual aerosol particle size and chemical mixing state were made at El Yunque National Forest, Puerto Rico, downwind of the Sahara Desert, and Gosan, South Korea, downwind of the Gobi and Taklamakan Deserts. In general, the chemical characterization of the individual dust particles detected at these two sites reflected the dominant mineralogy of the source regions; aluminosilicate-rich dust was more common at El Yunque (∼91% of El Yunque dust particles vs. ∼69% of Gosan dust particles) and calcium-rich dust was more common at Gosan (∼22% of Gosan dust particles vs. ∼2% of El Yunque dust particles). Furthermore, dust particles from Africa and Asia were subjected to different transport conditions and atmospheric processing; African dust showed evidence of cloud processing, while Asian dust was modified via heterogeneous chemistry and direct condensation of secondary species. A larger fraction of dust detected at El Yunque contained the cloud-processing marker oxalate ion compared to dust detected at Gosan (∼20% vs ∼9%). Additionally, nearly 100% of dust detected at Gosan contained nitrate, showing it was aged via heterogeneous reactions with nitric acid, compared to only ∼60% of African dust. Information on the distinct differences in the chemical composition of mineral dust particles, as well as the mechanisms and extent of atmospheric processing, is critical for assessing its impacts on the earth's radiative budget through scattering, absorption, and nucleating cloud droplets and ice crystals.

Organic condensation: A vital link connecting aerosol formation to climate forcing (Invited)

NASA Astrophysics Data System (ADS)

Riipinen, I.; Pierce, J. R.; Yli-Juuti, T.; Nieminen, T.; Häkkinen, S.; Ehn, M.; Junninen, H.; Lehtipalo, K.; Petdjd, T. T.; Slowik, J. G.; Chang, R. Y.; Shantz, N. C.; Abbatt, J.; Leaitch, W. R.; Kerminen, V.; Worsnop, D. R.; Pandis, S. N.; Donahue, N. M.; Kulmala, M. T.

2010-12-01

Aerosol-cloud interactions represent the largest uncertainty in calculations of Earth’s radiative forcing. Number concentrations of atmospheric aerosol particles are in the core of this uncertainty, as they govern the numbers of cloud condensation nuclei (CCN) and influence the albedo and lifetime of clouds. Aerosols also impair air quality through their adverse effects on atmospheric visibility and human health. The ultrafine fraction (<100 nm) of atmospheric aerosol particles often dominates the total aerosol numbers, and nucleation of atmospheric vapours is one of the most important sources of these particles. To have climatic relevance, however, the freshly-nucleated particles need to grow in size, and consequently their climatic importance remains to be quantified (see Fig. 1). We combine observations from two continental sites (Egbert, Canada and Hyytiälä, Finland) to show that condensation of organic vapours is a crucial factor governing the lifetimes and climatic importance of the smallest atmospheric particles. We demonstrate that state-of-the-science organic gas-particle partitioning models fail to reproduce the observations; we propose a new modelling approach that is consistent with the measurements. Finally, we demonstrate the large sensitivity of climatic forcing of atmospheric aerosols to these interactions between organic vapours and the smallest atmospheric nanoparticles - highlighting the need for representing this process in global climate models. Figure 1. Organic emissions and the dynamic processes governing the climatic importance of ultrafine aerosol. Condensable vapours are produced upon oxidation of volatile organic compounds (VOCs) and can 1) nucleate to form new small particles; 2) grow freshly formed particles to larger sizes and increase their probability to serve as CCN; 3) condense on the background aerosol (> 100 nm) and enhance the loss of ultrafine particles. Primary organic aerosol (POA) contributes to the large end of the aerosol size distribution, enhancing the scavenging of the ultrafine particles.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sena, Elisa T.; McComiskey, Allison; Feingold, Graham

Empirical estimates of the microphysical response of cloud droplet size distribution to aerosol perturbations are commonly used to constrain aerosol–cloud interactions in climate models. Instead of empirical microphysical estimates, here macroscopic variables are analyzed to address the influence of aerosol particles and meteorological descriptors on instantaneous cloud albedo and the radiative effect of shallow liquid water clouds. Long-term ground-based measurements from the Atmospheric Radiation Measurement (ARM) program over the Southern Great Plains are used. A broad statistical analysis was performed on 14 years of coincident measurements of low clouds, aerosol, and meteorological properties. Here two cases representing conflicting results regardingmore » the relationship between the aerosol and the cloud radiative effect were selected and studied in greater detail. Microphysical estimates are shown to be very uncertain and to depend strongly on the methodology, retrieval technique and averaging scale. For this continental site, the results indicate that the influence of the aerosol on the shallow cloud radiative effect and albedo is weak and that macroscopic cloud properties and dynamics play a much larger role in determining the instantaneous cloud radiative effect compared to microphysical effects. On a daily basis, aerosol shows no correlation with cloud radiative properties (correlation = -0.01 ± 0.03), whereas the liquid water path shows a clear signal (correlation = 0.56 ± 0.02).« less

Statistical properties of the normalized ice particle size distribution

NASA Astrophysics Data System (ADS)

Delanoë, Julien; Protat, Alain; Testud, Jacques; Bouniol, Dominique; Heymsfield, A. J.; Bansemer, A.; Brown, P. R. A.; Forbes, R. M.

2005-05-01

Testud et al. (2001) have recently developed a formalism, known as the "normalized particle size distribution (PSD)", which consists in scaling the diameter and concentration axes in such a way that the normalized PSDs are independent of water content and mean volume-weighted diameter. In this paper we investigate the statistical properties of the normalized PSD for the particular case of ice clouds, which are known to play a crucial role in the Earth's radiation balance. To do so, an extensive database of airborne in situ microphysical measurements has been constructed. A remarkable stability in shape of the normalized PSD is obtained. The impact of using a single analytical shape to represent all PSDs in the database is estimated through an error analysis on the instrumental (radar reflectivity and attenuation) and cloud (ice water content, effective radius, terminal fall velocity of ice crystals, visible extinction) properties. This resulted in a roughly unbiased estimate of the instrumental and cloud parameters, with small standard deviations ranging from 5 to 12%. This error is found to be roughly independent of the temperature range. This stability in shape and its single analytical approximation implies that two parameters are now sufficient to describe any normalized PSD in ice clouds: the intercept parameter N*0 and the mean volume-weighted diameter Dm. Statistical relationships (parameterizations) between N*0 and Dm have then been evaluated in order to reduce again the number of unknowns. It has been shown that a parameterization of N*0 and Dm by temperature could not be envisaged to retrieve the cloud parameters. Nevertheless, Dm-T and mean maximum dimension diameter -T parameterizations have been derived and compared to the parameterization of Kristjánsson et al. (2000) currently used to characterize particle size in climate models. The new parameterization generally produces larger particle sizes at any temperature than the Kristjánsson et al. (2000) parameterization. These new parameterizations are believed to better represent particle size at global scale, owing to a better representativity of the in situ microphysical database used to derive it. We then evaluated the potential of a direct N*0-Dm relationship. While the model parameterized by temperature produces strong errors on the cloud parameters, the N*0-Dm model parameterized by radar reflectivity produces accurate cloud parameters (less than 3% bias and 16% standard deviation). This result implies that the cloud parameters can be estimated from the estimate of only one parameter of the normalized PSD (N*0 or Dm) and a radar reflectivity measurement.

Proceedings of Propulsion and Energetics Panel Symposium (71st) on Engine Condition Monitoring - Technology and Experience Held in Quebec City, Canada on 30 May-3 Jun 1988

DTIC Science & Technology

1988-06-03

S. This is 23.0030 US S per aircraft and year. A310/A300-600 Engine Condition Monitorig U 45000 a 4 37A 4a 4. - -n 2500 1.0 a F ig. 3 COSTS/SAVINGS...to correct for variations in the background caused by disturbances such as vapor clouds in the field of view creating scattering or obscuration...in the signal characteristics. Fine debris tends to travel with the airstream in a cloud , and larger flakes and particles become more dispersed because

Classification of Arctic, Mid-Latitude and Tropical Clouds in the Mixed-Phase Temperature Regime

NASA Astrophysics Data System (ADS)

Costa, Anja; Afchine, Armin; Luebke, Anna; Meyer, Jessica; Dorsey, James R.; Gallagher, Martin W.; Ehrlich, André; Wendisch, Manfred; Krämer, Martina

2016-04-01

The degree of glaciation and the sizes and habits of ice particles formed in mixed-phase clouds remain not fully understood. However, these properties define the mixed clouds' radiative impact on the Earth's climate and thus a correct representation of this cloud type in global climate models is of importance for an improved certainty of climate predictions. This study focuses on the occurrence and characteristics of two types of clouds in the mixed-phase temperature regime (238-275K): coexistence clouds (Coex), in which both liquid drops and ice crystals exist, and fully glaciated clouds that develop in the Wegener-Bergeron-Findeisen regime (WBF clouds). We present an extensive dataset obtained by the Cloud and Aerosol Particle Spectrometer NIXE-CAPS, covering Arctic, mid-latitude and tropical regions. In total, we spent 45.2 hours within clouds in the mixed-phase temperature regime during five field campaigns (Arctic: VERDI, 2012 and RACEPAC, 2014 - Northern Canada; mid-latitude: COALESC, 2011 - UK and ML-Cirrus, 2014 - central Europe; tropics: ACRIDICON, 2014 - Brazil). We show that WBF and Coex clouds can be identified via cloud particle size distributions. The classified datasets are used to analyse temperature dependences of both cloud types as well as range and frequencies of cloud particle concentrations and sizes. One result is that Coex clouds containing supercooled liquid drops are found down to temperatures of -40 deg C only in tropical mixed clouds, while in the Arctic and mid-latitudes no liquid drops are observed below about -20 deg C. In addition, we show that the cloud particles' aspherical fractions - derived from polarization signatures of particles with diameters between 20 and 50 micrometers - differ significantly between WBF and Coex clouds. In Coex clouds, the aspherical fraction of cloud particles is generally very low, but increases with decreasing temperature. In WBF clouds, where all cloud particles are ice, about 20-40% of the cloud particles are nevertheless classified as spherical for all temperatures, possibly indicating columnar ice crystals (see Järvinen et al, submitted to JAS 2016).

A simple model for the cloud adjacency effect and the apparent bluing of aerosols near clouds

NASA Astrophysics Data System (ADS)

Marshak, Alexander; Wen, Guoyong; Coakley, James A.; Remer, Lorraine A.; Loeb, Norman G.; Cahalan, Robert F.

2008-07-01

In determining aerosol-cloud interactions, the properties of aerosols must be characterized in the vicinity of clouds. Numerous studies based on satellite observations have reported that aerosol optical depths increase with increasing cloud cover. Part of the increase comes from the humidification and consequent growth of aerosol particles in the moist cloud environment, but part comes from 3-D cloud-radiative transfer effects on the retrieved aerosol properties. Often, discerning whether the observed increases in aerosol optical depths are artifacts or real proves difficult. The paper only addresses the cloud-clear sky radiative transfer interaction part. It provides a simple model that quantifies the enhanced illumination of cloud-free columns in the vicinity of clouds that are used in the aerosol retrievals. This model is based on the assumption that the enhancement in the cloud-free column radiance comes from enhanced Rayleigh scattering that results from the presence of the nearby clouds. This assumption leads to a larger increase of AOT for shorter wavelengths, or to a "bluing" of aerosols near clouds. The assumption that contribution from molecular scattering dominates over aerosol scattering and surface reflection is justified for the case of shorter wavelengths, dark surfaces, and an aerosol layer below the cloud tops. The enhancement in Rayleigh scattering is estimated using a stochastic cloud model to obtain the radiative flux reflected by broken clouds and comparing this flux with that obtained with the molecules in the atmosphere causing extinction, but no scattering.

Does Wilson's cloud chamber offer clues on lightning initiation in thunderclouds?

NASA Astrophysics Data System (ADS)

Cooray, V.; Rakov, V.

2007-12-01

The experimental evidence indicates that the large scale electric field in the cloud at the time of lightning initiation is about 100 kV/m [1], which is an order of magnitude lower than the expected conventional breakdown field. One important problem in atmospheric physics is to understand how lightning flashes are initiated in such low fields. Some scientists suggest that the electric field could reach higher values momentarily in small regions and this combined with the field enhancing action of hydrometeors in the cloud could provide trigger for lightning initiation [2, 3]. Others suggest that energetic electrons produced by cosmic rays could give rise to runaway electron avalanches generating the initial ionization necessary for lightning initiation [4]. Nguyen and Michnowski [2] suggested that in small cloud regions the electric field may exceed 200 to 400 kV/m and in these locations the discharges between hydrometeors could facilitate lightning initiation. This mechanism was further investigated by Cooray et al. [3] who showed that interaction between adjacent hydrometeors cannot produce a streamer discharge, a prerequisite for electric breakdown, unless the field exceeds about 830 kV/m. They also found that long chains of hydrometeors could initiate streamer discharges in relatively low electric fields. For example, in order to generate a streamer discharge in 100 kV/m electric field the length of the chain of hydrometeors of 0.1 mm radius should be about 65 mm with more than 100 particles constituting the chain. However, the question remains on how such long chains of hydrometeors can be produced in the cloud. We suggest the following possibility. Consider an energetic particle passing through the cloud producing ionization in its wake. The passage of such a particle will lead to a stream of positive ions and electrons with the latter being captured within a few tens of nanoseconds by oxygen molecules to form negative ions. If the water vapor in the region under consideration is supersaturated, water molecules will condense on the ions and the resulting droplets can grow to tens of micrometers in a fraction of a second. This is the mechanism utilized in Wilson's cloud chamber to visualize the tracks of ionizing particles. If the track of ionizing particle is aligned with the direction of the electric field in the cloud, the resultant drift of the oppositely charged particles in opposite directions will facilitate collisions among them leading to production of larger droplets. This process can potentially generate long chains of droplets in the cloud which may provide the trigger necessary for the initiation of lightning flashes. [1] Marshall, T. C., M. P. McCarthy and W. D. Rust, Electric field magnitudes and lightning initiation in thunderstorms, J. Geophys. Res., vol. 100, pp. 7097 - 7103, 1995. [2] Nguyen, M. D. and S. Michnowski, On the initiation of lightning discharges in a cloud, 2. The lightning initiation on precipitation particles, J. Geophys. Res., vol. 101, pp. 26 675 - 26 680, 1996. [3] Cooray, V., M. Berg, M. Akyuz and A. Larsson, Initiation of ground flashes: some microscopic electrical processes associated with precipitation particles, Proc. International Conference on Lightning Protection, Birmingham, UK, 2002. [4] Gurevich, A. V., G. M. Milikh and J. A. Valdivia, Model of X-ray emission and fast preconditioning during a thunderstorm, Phys. Lett., A 231, pp. 402 - 408, 1997.

Investigations of cloud microphysical response to mixing using digital holography

NASA Astrophysics Data System (ADS)

Beals, Matthew Jacob

Cloud edge mixing plays an important role in the life cycle and development of clouds. Entrainment of subsaturated air affects the cloud at the microscale, altering the number density and size distribution of its droplets. The resulting effect is determined by two timescales: the time required for the mixing event to complete, and the time required for the droplets to adjust to their new environment. If mixing is rapid, evaporation of droplets is uniform and said to be homogeneous in nature. In contrast, slow mixing (compared to the adjustment timescale) results in the droplets adjusting to the transient state of the mixture, producing an inhomogeneous result. Studying this process in real clouds involves the use of airborne optical instruments capable of measuring clouds at the 'single particle' level. Single particle resolution allows for direct measurement of the droplet size distribution. This is in contrast to other 'bulk' methods (i.e. hot-wire probes, lidar, radar) which measure a higher order moment of the distribution and require assumptions about the distribution shape to compute a size distribution. The sampling strategy of current optical instruments requires them to integrate over a path tens to hundreds of meters to form a single size distribution. This is much larger than typical mixing scales (which can extend down to the order of centimeters), resulting in difficulties resolving mixing signatures. The Holodec is an optical particle instrument that uses digital holography to record discrete, local volumes of droplets. This method allows for statistically significant size distributions to be calculated for centimeter scale volumes, allowing for full resolution at the scales important to the mixing process. The hologram also records the three dimensional position of all particles within the volume, allowing for the spatial structure of the cloud volume to be studied. Both of these features represent a new and unique view into the mixing problem. In this dissertation, holographic data recorded during two different field projects is analyzed to study the mixing structure of cumulus clouds. Using Holodec data, it is shown that mixing at cloud top can produce regions of clear but humid air that can subside down along the edge of the cloud as a narrow shell, or advect down shear as a 'humid halo'. This air is then entrained into the cloud at lower levels, producing mixing that appears to be very inhomogeneous. This inhomogeneous-like mixing is shown to be well correlated with regions containing elevated concentrations of large droplets. This is used to argue in favor of the hypothesis that dilution can lead to enhanced droplet growth rates. I also make observations on the microscale spatial structure of observed cloud volumes recorded by the Holodec.

Parameterizing Size Distribution in Ice Clouds

DOE Office of Scientific and Technical Information (OSTI.GOV)

DeSlover, Daniel; Mitchell, David L.

2009-09-25

PARAMETERIZING SIZE DISTRIBUTIONS IN ICE CLOUDS David L. Mitchell and Daniel H. DeSlover ABSTRACT An outstanding problem that contributes considerable uncertainty to Global Climate Model (GCM) predictions of future climate is the characterization of ice particle sizes in cirrus clouds. Recent parameterizations of ice cloud effective diameter differ by a factor of three, which, for overcast conditions, often translate to changes in outgoing longwave radiation (OLR) of 55 W m-2 or more. Much of this uncertainty in cirrus particle sizes is related to the problem of ice particle shattering during in situ sampling of the ice particle size distribution (PSD).more » Ice particles often shatter into many smaller ice fragments upon collision with the rim of the probe inlet tube. These small ice artifacts are counted as real ice crystals, resulting in anomalously high concentrations of small ice crystals (D < 100 µm) and underestimates of the mean and effective size of the PSD. Half of the cirrus cloud optical depth calculated from these in situ measurements can be due to this shattering phenomenon. Another challenge is the determination of ice and liquid water amounts in mixed phase clouds. Mixed phase clouds in the Arctic contain mostly liquid water, and the presence of ice is important for determining their lifecycle. Colder high clouds between -20 and -36 oC may also be mixed phase but in this case their condensate is mostly ice with low levels of liquid water. Rather than affecting their lifecycle, the presence of liquid dramatically affects the cloud optical properties, which affects cloud-climate feedback processes in GCMs. This project has made advancements in solving both of these problems. Regarding the first problem, PSD in ice clouds are uncertain due to the inability to reliably measure the concentrations of the smallest crystals (D < 100 µm), known as the “small mode”. Rather than using in situ probe measurements aboard aircraft, we employed a treatment of ice cloud optical properties formulated in terms of PSD parameters in combination with remote measurements of thermal radiances to characterize the small mode. This is possible since the absorption efficiency (Qabs) of small mode crystals is larger at 12 µm wavelength relative to 11 µm wavelength due to the process of wave resonance or photon tunneling more active at 12 µm. This makes the 12/11 µm absorption optical depth ratio (or equivalently the 12/11 µm Qabs ratio) a means for detecting the relative concentration of small ice particles in cirrus. Using this principle, this project tested and developed PSD schemes that can help characterize cirrus clouds at each of the three ARM sites: SGP, NSA and TWP. This was the main effort of this project. These PSD schemes and ice sedimentation velocities predicted from them have been used to test the new cirrus microphysics parameterization in the GCM known as the Community Climate Systems Model (CCSM) as part of an ongoing collaboration with NCAR. Regarding the second problem, we developed and did preliminary testing on a passive thermal method for retrieving the total water path (TWP) of Arctic mixed phase clouds where TWPs are often in the range of 20 to 130 g m-2 (difficult for microwave radiometers to accurately measure). We also developed a new radar method for retrieving the cloud ice water content (IWC), which can be vertically integrated to yield the ice water path (IWP). These techniques were combined to determine the IWP and liquid water path (LWP) in Arctic clouds, and hence the fraction of ice and liquid water. We have tested this approach using a case study from the ARM field campaign called M-PACE (Mixed-Phase Arctic Cloud Experiment). This research led to a new satellite remote sensing method that appears promising for detecting low levels of liquid water in high clouds typically between -20 and -36 oC. We hope to develop this method in future research.« less

In situ chemical composition measurement of individual cloud residue particles at a mountain site, southern China

NASA Astrophysics Data System (ADS)

Lin, Qinhao; Zhang, Guohua; Peng, Long; Bi, Xinhui; Wang, Xinming; Brechtel, Fred J.; Li, Mei; Chen, Duohong; Peng, Ping'an; Sheng, Guoying; Zhou, Zhen

2017-07-01

To investigate how atmospheric aerosol particles interact with chemical composition of cloud droplets, a ground-based counterflow virtual impactor (GCVI) coupled with a real-time single-particle aerosol mass spectrometer (SPAMS) was used to assess the chemical composition and mixing state of individual cloud residue particles in the Nanling Mountains (1690 m a. s. l. ), southern China, in January 2016. The cloud residues were classified into nine particle types: aged elemental carbon (EC), potassium-rich (K-rich), amine, dust, Pb, Fe, organic carbon (OC), sodium-rich (Na-rich) and Other. The largest fraction of the total cloud residues was the aged EC type (49.3 %), followed by the K-rich type (33.9 %). Abundant aged EC cloud residues that mixed internally with inorganic salts were found in air masses from northerly polluted areas. The number fraction (NF) of the K-rich cloud residues increased within southwesterly air masses from fire activities in Southeast Asia. When air masses changed from northerly polluted areas to southwesterly ocean and livestock areas, the amine particles increased from 0.2 to 15.1 % of the total cloud residues. The dust, Fe, Pb, Na-rich and OC particle types had a low contribution (0.5-4.1 %) to the total cloud residues. Higher fraction of nitrate (88-89 %) was found in the dust and Na-rich cloud residues relative to sulfate (41-42 %) and ammonium (15-23 %). Higher intensity of nitrate was found in the cloud residues relative to the ambient particles. Compared with nonactivated particles, nitrate intensity decreased in all cloud residues except for dust type. To our knowledge, this study is the first report on in situ observation of the chemical composition and mixing state of individual cloud residue particles in China.

Modeling the Impact of Drizzle and 3D Cloud Structure on Remote Sensing of Effective Radius

NASA Technical Reports Server (NTRS)

Platnick, Steven; Zinner, Tobias; Ackerman, S.

2008-01-01

Remote sensing of cloud particle size with passive sensors like MODIS is an important tool for cloud microphysical studies. As a measure of the radiatively relevant droplet size, effective radius can be retrieved with different combinations of visible through shortwave infrared channels. MODIS observations sometimes show significantly larger effective radii in marine boundary layer cloud fields derived from the 1.6 and 2.1 pm channel observations than for 3.7 pm retrievals. Possible explanations range from 3D radiative transport effects and sub-pixel cloud inhomogeneity to the impact of drizzle formation on the droplet distribution. To investigate the potential influence of these factors, we use LES boundary layer cloud simulations in combination with 3D Monte Carlo simulations of MODIS observations. LES simulations of warm cloud spectral microphysics for cases of marine stratus and broken stratocumulus, each for two different values of cloud condensation nuclei density, produce cloud structures comprising droplet size distributions with and without drizzle size drops. In this study, synthetic MODIS observations generated from 3D radiative transport simulations that consider the full droplet size distribution will be generated for each scene. The operational MODIS effective radius retrievals will then be applied to the simulated reflectances and the results compared with the LES microphysics.

Spontaneous deswelling of pNIPAM microgels at high concentrations

NASA Astrophysics Data System (ADS)

Gasser, Urs; Scotti, Andrea; Herman, Emily S.; Pelaez-Fernandez, Miguel; Han, Jun; Menzel, Andreas; Lyon, L. Andrew; Fernandez-Nieves, Alberto

Polydisperse suspensions of pNIPAM microgel particles show a unique, spontaneous particle deswelling behavior. Beyond a critical concentration, the largest microgels deswell and thereby reduce the polydispersity of the suspension. We have recently unraveled the mechanism of this spontaneous, selective deswelling. pNIPAM microgels carry charged sulfate groups originating from the ammonium persulfate starter used in particle synthesis. Most of the ammonium counterions are trapped close to the microgel surface, but a fraction of them escapes the electrostatic attraction and contributes to the osmotic pressure of the suspension. The counterion clouds of neighboring particles progressively overlap with increasing volume fraction, leading to an increase of free counterions and the osmotic pressure outside but not inside the microgel particles. We find particles to deswell when the resulting osmotic pressure difference between the inside and the outside becomes larger their bulk modulus. For pNIPAM microgels synthesized with the same protocol, the largest particles are the softest and deswell first.

OMMYDCLD: a New A-train Cloud Product that Co-locates OMI and MODIS Cloud and Radiance Parameters onto the OMI Footprint

NASA Technical Reports Server (NTRS)

Fisher, Brad; Joiner, Joanna; Vasilkov, Alexander; Veefkind, Pepijn; Platnick, Steven; Wind, Galina

2014-01-01

Clouds cover approximately 60% of the earth's surface. When obscuring the satellite's field of view (FOV), clouds complicate the retrieval of ozone, trace gases and aerosols from data collected by earth observing satellites. Cloud properties associated with optical thickness, cloud pressure, water phase, drop size distribution (DSD), cloud fraction, vertical and areal extent can also change significantly over short spatio-temporal scales. The radiative transfer models used to retrieve column estimates of atmospheric constituents typically do not account for all these properties and their variations. The OMI science team is preparing to release a new data product, OMMYDCLD, which combines the cloud information from sensors on board two earth observing satellites in the NASA A-Train: Aura/OMI and Aqua/MODIS. OMMYDCLD co-locates high resolution cloud and radiance information from MODIS onto the much larger OMI pixel and combines it with parameters derived from the two other OMI cloud products: OMCLDRR and OMCLDO2. The product includes histograms for MODIS scientific data sets (SDS) provided at 1 km resolution. The statistics of key data fields - such as effective particle radius, cloud optical thickness and cloud water path - are further separated into liquid and ice categories using the optical and IR phase information. OMMYDCLD offers users of OMI data cloud information that will be useful for carrying out OMI calibration work, multi-year studies of cloud vertical structure and in the identification and classification of multi-layer clouds.

The role of orbital dynamics and cloud-cloud collisions in the formation of giant molecular clouds in global spiral structures

NASA Technical Reports Server (NTRS)

Roberts, William W., Jr.; Stewart, Glen R.

1987-01-01

The role of orbit crowding and cloud-cloud collisions in the formation of GMCs and their organization in global spiral structure is investigated. Both N-body simulations of the cloud system and a detailed analysis of individual particle orbits are used to develop a conceptual understanding of how individual clouds participate in the collective density response. Detailed comparisons are made between a representative cloud-particle simulation in which the cloud particles collide inelastically with one another and give birth to and subsequently interact with young star associations and stripped down simulations in which the cloud particles are allowed to follow ballistic orbits in the absence of cloud-cloud collisions or any star formation processes. Orbit crowding is then related to the behavior of individual particle trajectories in the galactic potential field. The conceptual picture of how GMCs are formed in the clumpy ISMs of spiral galaxies is formulated, and the results are compared in detail with those published by other authors.

Water and organics in interplanetary dust particles

NASA Astrophysics Data System (ADS)

Bradley, John

Interplanetary dust particles (IDPs) and larger micrometeorites (MMs) impinge on the upper atmosphere where they decelerate at 90 km altitude and settle to the Earths surface. Comets and asteroids are the major sources and the flux, 30,000-40,000 tons/yr, is comparable to the mass of larger meteorites impacting the Earths surface. The sedimentary record suggests that the flux was much higher on the early Earth. The chondritic porous (CP) subset of IDPs together with their larger counterparts, ultracarbonaceous micrometeorites (UCMMs), appear to be unique among known meteoritic materials in that they are composed almost exclusively of anhydrous minerals, some of them contain >> 50% organic carbon by volume as well as the highest abundances of presolar silicate grains including GEMS. D/H and 15N abundances implicate the Oort Cloud or presolar molecular cloud as likely sources of the organic carbon. Prior to atmospheric entry, IDPs and MMs spend 104-105 year lifetimes in solar orbit where their surfaces develop amorphous space weathered rims from exposure to the solar wind (SW). Similar rims are observed on lunar soil grains and on asteroid Itokawa regolith grains. Using valence electron energy-loss spectroscopy (VEELS) we have detected radiolytic water in the rims on IDPs formed by the interaction of solar wind protons with oxygen in silicate minerals. Therefore, IDPs and MMs continuously deliver both water and organics to the earth and other terrestrial planets. The interaction of protons with oxygen-rich minerals to form water is a universal process.

The Impact of Aerosols on Cloud and Precipitation Processes: Cloud-Resolving Model Simulations

NASA Technical Reports Server (NTRS)

Tao, Wei-Kuo; Khain, A.; Simpson, S.; Johnson, D.; Li, X.; Remer, L.

2003-01-01

Cloud microphysics are inevitable affected by the smoke particle (CCN, cloud condensation nuclei) size distributions below the clouds. Therefore, size distribution parameterized as spectral bin microphysics are needed to explicitly study the effect of atmospheric aerosol concentration on cloud development, rainfall production, and rainfall rates convective clouds. Recently, two detailed spectral-bin microphysical schemes were implemented into the Goddard Cumulus Ensembel (GCE) model. The formulation for the explicit spectral-bim microphysical processes is based on solving stochastic kinetic equations for the size distribution functions of water droplets (i.e., cloud droplets and raindrops), and several types of ice particles [i.e., pristine ice crystals (columnar and plate-like), snow (dendrites and aggregates), groupel and frozen drops/hall] Each type is described by a special size distribution function containing many categories (i.e., 33 bins). Atmospheric aerosols are also described using number density size-distribution functions.A spectral-bin microphysical model is very expensive from a computational point of view and has only been implemented into the 2D version of the GCE at the present time. The model is tested by studying the evolution of deep cloud systems in the west Pacific warm pool region and in the mid-latitude using identical thermodynamic conditions but with different concentrations of CCN: a low "clean" concentration and a high "dirty" concentration. Besides the initial differences in aerosol concentration, preliminary results indicate that the low CCN concentration case produces rainfall at the surface sooner than the high CCN case but has less cloud water mass aloft. Because the spectral-bim model explicitly calculates and allows for the examination of both the mass and number concentration of cpecies in each size category, a detailed analysis of the instantaneous size spectrum can be obtained for the two cases. It is shown that since the low CCN case produces fever droplets, larger size develop due to greater condencational and collectional growth, leading to a broader size spectrum in comparison to the high CCN case.

The Impact of Aerosols on Cloud and Precipitation Processes: Cloud-Resolving Model Simulations

NASA Technical Reports Server (NTRS)

Tao, Wei-Kuo; Khain, A.; Simpson, S.; Johnson, D.; Li, X.; Remer, L.

2003-01-01

Cloud microphysics are inevitably affected by the smoke particle (CCN, cloud condensation nuclei) size distributions below the clouds. Therefore, size distributions parameterized as spectral bin microphysics are needed to explicitly study the effects of atmospheric aerosol concentration on cloud development, rainfall production, and rainfall rates for convective clouds. Recently, two detailed spectral-bin microphysical schemes were implemented into the Goddard Cumulus Ensemble (GCE) model. The formulation for the explicit spectral-bin microphysical processes is based on solving stochastic kinetic equations for the size distribution functions of water droplets (i.e., cloud droplets and raindrops), and several types of ice particles [i.e.,pristine ice crystals (columnar and plate-like), snow (dendrites and aggregates), graupel and frozen drops/hail]. Each type is described by a special size distribution function containing many categories (i.e. 33 bins). Atmospheric aerosols are also described using number density size-distribution functions.A spectral-bin microphysical model is very expensive from a from a computational point of view and has only been implemented into the 2D version of the GCE at the present time. The model is tested by studying the evolution of deep tropical clouds in the west Pacific warm pool region using identical thermodynamic conditions but with different concentrations of CCN: a low "clean" concentration and a high "dirty" concentration. Besides the initial differences in aerosol concentration, preliminary results indicate that the low CCN concentration case produces rainfall at the surface sooner than the high CCN case but has less cloud water mass aloft. Because the spectral-bin model explicitly calculates and allows for the examination of both the mass and number concentration of species in each size categor, a detailed analysis of the instantaneous size spectrum can be obtained for the two cases. It is shown that since the low CCN case produces fewer droplets, larger sized develop due to the greater condensational and collectional growth, leading to a broader size spectrum in comparison to the high CCN case.

Processes Controlling the Seasonal Cycle of Arctic Aerosol Number and Size Distributions

NASA Astrophysics Data System (ADS)

Wentworth, G.; Croft, B.; Martin, R.; Leaitch, W. R.; Tunved, P.; Breider, T. J.; D'Andrea, S.; Pierce, J. R.; Murphy, J. G.; Kodros, J.; Abbatt, J.

2015-12-01

Measurements at high-Arctic sites show a strong seasonal cycle in aerosol number and size. The number of aerosols with diameters larger than 20 nm exhibits a maximum in late spring associated with a dominant accumulation mode, and a second maximum in the summer associated with a dominant Aitken mode. Seasonal-mean aerosol effective diameter ranges from about 160 nm in summer to 250 nm in winter. This study interprets these seasonal cycles with the GEOS-Chem-TOMAS global aerosol microphysics model. We find improved agreement with in situ measurements (SMPS) of aerosol size at both Alert, Nunavut, and Mt. Zeppelin, Svalbard following model developments: 1) increase the efficiency of wet scavenging in the Arctic summer and 2) represent coagulation between interstitial aerosols and aerosols activated to form cloud droplets. Our simulations indicate that the dominant summer-time Aitken mode is associated with increased efficiency of wet removal, which limits the number of larger aerosols and promotes local new-aerosol formation. We also find an important role of interstitial coagulation in clouds in the Arctic, which limits the number of Aitken-mode aerosols in the non-summer seasons when direct wet removal of these aerosols is inefficient. The summertime Arctic atmosphere is particularly pristine and strongly influenced by natural regional emissions which have poorly understood climate impacts. Especially influenced are the climatic roles of atmospheric particles and clouds. Here we present evidence that ammonia (NH3) emissions from migratory-seabird guano (dung) are the primary contributor to summertime free ammonia levels recently measured in the Canadian Arctic atmosphere. These findings suggest that ammonia from seabird guano is a key factor contributing to bursts of new-particle formation, which are observed every summer in the near-surface atmosphere at Alert, Canada. Chemical transport model simulations show that these newly formed particles can grow by vapour condensation to diameters sufficiently large to influence Arctic cloud properties and lead to a pan-Arctic cooling over -0.1 W m-2 with local cooling exceeding -1 W m-2 near some bird colonies. These coupled ecological-chemical processes may be susceptible to Arctic warming and industrialization.

Atmospheric particles retrieval using satellite remote sensing: Applications for sandstorms and volcanic clouds

NASA Astrophysics Data System (ADS)

Gu, Yingxin

This thesis is concerned with atmospheric particles produced by sandstorms and volcanic eruptions. Three studies were conducted in order to examine particle retrieval methodology, and apply these towards an improved understanding of large-scale sandstorms. A thermal infrared remote sensing retrieval method developed by Wen and Rose [1994], which retrieves particle sizes, optical depth, and total masses of silicate particles in the volcanic cloud, was applied to an April 07, 2001 sandstorm over northern China, using MODIS. Results indicate that the area of the dust cloud observed was 1.34 million km2, the mean particle radius of the dust was 1.44 mum, and the mean optical depth at 11 mum was 0.79. The mean burden of dust was approximately 4.8 tons/km2 and the main portion of the dust storm on April 07, 2001 contained 6.5 million tons of dust. The results are supported by both independent remote sensing data (TOMS) and in-situ data for a similar event in 1998, therefore suggesting that the technique is appropriate for quantitative analysis of silicate dust clouds. This is the first quantitative evaluation of annual and seasonal dust loading in 2003 produced by Saharan dust storms by satellite remote sensing analysis. The retrieved mean particle effective radii of 2003 dust events are between 1.7--2.6 mum which is small enough to be inhaled and is hazardous to human health. The retrieved yearly dust mass load is 658--690 Tg, which is ˜45% of the annual global mineral dust production. Winter is the heaviest dust loading season in the year 2003, which is more than 5 times larger than that in the summer season in 2003.The mean optical depths at 11 mum in the winter season (around 0.7) are higher than those in the summer season (around 0.5). The results could help both meteorologists and environmental scientists to evaluate and predict the hazard degree caused by Saharan dust storms. (Abstract shortened by UMI.)

Far Infrared Measurements of Cirrus

NASA Technical Reports Server (NTRS)

Nolt, I. G.; Vanek, M. D.; Tappan, N. D.; Minnis, P.; Alltop, J. L.; Ade, A. R.; Lee, C.; Hamilton, P. A.; Evans, K. F.; Evans, A. H.

1999-01-01

Improved techniques for remote sensing of cirrus are needed to obtain global data for assessing the effect of cirrus in climate change models. Model calculations show that the far infrared/sub-millimeter spectral region is well suited for retrieving cirrus Ice Water Path and particle size parameters. Especially useful cirrus information is obtained at frequencies below 60 cm-1 where single particle scattering dominates over thermal emission for ice particles larger than about 50 m. Earth radiance spectra have been obtained for a range of cloud conditions using an aircraft-based Fourier transform spectrometer. The Far InfraRed Sensor for Cirrus (FIRSC) is a Martin-Puplett interferometer which incorporates a polarizer for the beamsplitter and can be operated in either intensity or linear polarization measurement mode. Two detector channels span 10 to 140 cm-1 with a spectral resolution of 0.1 cm-1; achieving a Noise Equivalent Temperature of approximately 1K at 30 cm-1 in a 4 sec scan. Examples are shown of measured and modeled Earth radiance for a range of cloud conditions from 1998 and 1999 flights.

A long-term study of aerosol–cloud interactions and their radiative effect at the Southern Great Plains using ground-based measurements

DOE PAGES

Sena, Elisa T.; McComiskey, Allison; Feingold, Graham

2016-09-13

Empirical estimates of the microphysical response of cloud droplet size distribution to aerosol perturbations are commonly used to constrain aerosol–cloud interactions in climate models. Instead of empirical microphysical estimates, here macroscopic variables are analyzed to address the influence of aerosol particles and meteorological descriptors on instantaneous cloud albedo and the radiative effect of shallow liquid water clouds. Long-term ground-based measurements from the Atmospheric Radiation Measurement (ARM) program over the Southern Great Plains are used. A broad statistical analysis was performed on 14 years of coincident measurements of low clouds, aerosol, and meteorological properties. Here two cases representing conflicting results regardingmore » the relationship between the aerosol and the cloud radiative effect were selected and studied in greater detail. Microphysical estimates are shown to be very uncertain and to depend strongly on the methodology, retrieval technique and averaging scale. For this continental site, the results indicate that the influence of the aerosol on the shallow cloud radiative effect and albedo is weak and that macroscopic cloud properties and dynamics play a much larger role in determining the instantaneous cloud radiative effect compared to microphysical effects. On a daily basis, aerosol shows no correlation with cloud radiative properties (correlation = -0.01 ± 0.03), whereas the liquid water path shows a clear signal (correlation = 0.56 ± 0.02).« less

Assessing the failure of continuum formula for solid-solid drag force using discrete element method in large size ratios

NASA Astrophysics Data System (ADS)

Jalali, Payman; Hyppänen, Timo

2017-06-01

In loose or moderately-dense particle mixtures, the contact forces between particles due to successive collisions create average volumetric solid-solid drag force between different granular phases (of different particle sizes). The derivation of the mathematical formula for this drag force is based on the homogeneity of mixture within the calculational control volume. This assumption especially fails when the size ratio of particles grows to a large value of 10 or greater. The size-driven inhomogeneity is responsible to the deviation of intergranular force from the continuum formula. In this paper, we have implemented discrete element method (DEM) simulations to obtain the volumetric mean force exchanged between the granular phases with the size ratios greater than 10. First, the force is calculated directly from DEM averaged over a proper time window. Second, the continuum formula is applied to calculate the drag forces using the DEM quantities. We have shown the two volumetric forces are in good agreement as long as the homogeneity condition is maintained. However, the relative motion of larger particles in a cloud of finer particles imposes the inhomogeneous distribution of finer particles around the larger ones. We have presented correction factors to the volumetric force from continuum formula.

Airborne measurements of cloud-forming nuclei and aerosol particles in stabilized ground clouds produced by solid rocket booster firings

NASA Technical Reports Server (NTRS)

Hindman, E. E., II; Ala, G. G.; Parungo, F. P.; Willis, P. T.; Bendura, R. J.; Woods, D.

1978-01-01

Airborne measurements of cloud volumes, ice nuclei and cloud condensation nuclei, liquid particles, and aerosol particles were obtained from stabilized ground clouds (SGCs) produced by Titan 3 launches at Kennedy Space Center, 20 August and 5 September 1977. The SGCs were bright, white, cumulus clouds early in their life and contained up to 3.5 g/m3 of liquid in micron to millimeter size droplets. The measured cloud volumes were 40 to 60 cu km five hours after launch. The SGCs contained high concentrations of cloud condensation nuclei active at 0.2%, 0.5%, and 1.0% supersaturation for periods of three to five hours. The SGCs also contained high concentrations of submicron particles. Three modes existed in the particle population: a 0.05 to 0.1 micron mode composed of aluminum-containing particles, a 0.2 to 0.8 micron mode, and a 2.0 to 10 micron mode composed of particles that contained primarily aluminum.

Observed aerosol effects on marine cloud nucleation and supersaturation

NASA Astrophysics Data System (ADS)

Russell, Lynn M.; Sorooshian, Armin; Seinfeld, John H.; Albrecht, Bruce A.; Nenes, Athanasios; Leaitch, W. Richard; Macdonald, Anne Marie; Ahlm, Lars; Chen, Yi-Chun; Coggon, Matthew; Corrigan, Ashley; Craven, Jill S.; Flagan, Richard C.; Frossard, Amanda A.; Hawkins, Lelia N.; Jonsson, Haflidi; Jung, Eunsil; Lin, Jack J.; Metcalf, Andrew R.; Modini, Robin; Mülmenstädt, Johannes; Roberts, Greg C.; Shingler, Taylor; Song, Siwon; Wang, Zhen; Wonaschütz, Anna

2013-05-01

Aerosol particles in the marine boundary layer include primary organic and salt particles from sea spray and combustion-derived particles from ships and coastal cities. These particle types serve as nuclei for marine cloud droplet activation, although the particles that activate depend on the particle size and composition as well as the supersaturation that results from cloud updraft velocities. The Eastern Pacific Emitted Aerosol Cloud Experiment (EPEACE) 2011 was a targeted aircraft campaign to assess how different particle types nucleate cloud droplets. As part of E-PEACE 2011, we studied the role of marine particles as cloud droplet nuclei and used emitted particle sources to separate particle-induced feedbacks from dynamical variability. The emitted particle sources included shipboard smoke-generated particles with 0.05-1 μm diameters (which produced tracks measured by satellite and had drop composition characteristic of organic smoke) and combustion particles from container ships with 0.05-0.2 μm diameters (which were measured in a variety of conditions with droplets containing both organic and sulfate components) [1]. Three central aspects of the collaborative E-PEACE results are: (1) the size and chemical composition of the emitted smoke particles compared to ship-track-forming cargo ship emissions as well as background marine particles, with particular attention to the role of organic particles, (2) the characteristics of cloud track formation for smoke and cargo ships, as well as the role of multi-layered low clouds, and (3) the implications of these findings for quantifying aerosol indirect effects. For comparison with the E-PEACE results, the preliminary results of the Stratocumulus Observations of Los-Angeles Emissions Derived Aerosol-Droplets (SOLEDAD) 2012 provided evidence of the cloud-nucleating roles of both marine organic particles and coastal urban pollution, with simultaneous measurements of the effective supersaturations of the clouds in the California coastal region.

SPARSE—A subgrid particle averaged Reynolds stress equivalent model: testing with a priori closure

PubMed Central

Davis, Sean L.; Sen, Oishik; Udaykumar, H. S.

2017-01-01

A Lagrangian particle cloud model is proposed that accounts for the effects of Reynolds-averaged particle and turbulent stresses and the averaged carrier-phase velocity of the subparticle cloud scale on the averaged motion and velocity of the cloud. The SPARSE (subgrid particle averaged Reynolds stress equivalent) model is based on a combination of a truncated Taylor expansion of a drag correction function and Reynolds averaging. It reduces the required number of computational parcels to trace a cloud of particles in Eulerian–Lagrangian methods for the simulation of particle-laden flow. Closure is performed in an a priori manner using a reference simulation where all particles in the cloud are traced individually with a point-particle model. Comparison of a first-order model and SPARSE with the reference simulation in one dimension shows that both the stress and the averaging of the carrier-phase velocity on the cloud subscale affect the averaged motion of the particle. A three-dimensional isotropic turbulence computation shows that only one computational parcel is sufficient to accurately trace a cloud of tens of thousands of particles. PMID:28413341

SPARSE-A subgrid particle averaged Reynolds stress equivalent model: testing with a priori closure.

PubMed

Davis, Sean L; Jacobs, Gustaaf B; Sen, Oishik; Udaykumar, H S

2017-03-01

A Lagrangian particle cloud model is proposed that accounts for the effects of Reynolds-averaged particle and turbulent stresses and the averaged carrier-phase velocity of the subparticle cloud scale on the averaged motion and velocity of the cloud. The SPARSE (subgrid particle averaged Reynolds stress equivalent) model is based on a combination of a truncated Taylor expansion of a drag correction function and Reynolds averaging. It reduces the required number of computational parcels to trace a cloud of particles in Eulerian-Lagrangian methods for the simulation of particle-laden flow. Closure is performed in an a priori manner using a reference simulation where all particles in the cloud are traced individually with a point-particle model. Comparison of a first-order model and SPARSE with the reference simulation in one dimension shows that both the stress and the averaging of the carrier-phase velocity on the cloud subscale affect the averaged motion of the particle. A three-dimensional isotropic turbulence computation shows that only one computational parcel is sufficient to accurately trace a cloud of tens of thousands of particles.

Effects of variation in coagulation and photochemistry parameters on the particle size distributions in the Venus clouds

NASA Astrophysics Data System (ADS)

McGouldrick, Kevin

2017-12-01

This paper explores the effects that variation in the coalescence efficiency of the Venus cloud particles can have on the structure of the Venus cloud. It is motivated by the acknowledgment of uncertainties in the measured parameters—and the assumptions made to account for them—that define our present knowledge of the particle characteristics. Specifically, we explore the consequence of allowing the coalescence efficiency of supercooled sulfuric acid in the upper clouds to tend to zero. This produces a cloud that occasionally exhibits an enhancement of small particles at altitude (similar to the upper hazes observed by Pioneer Venus and subsequently shown to be somewhat transient). This simulated cloud occasionally exhibits a rapid growth of particle size near cloud base, exhibiting characteristics similar to those seen in the controversial Mode 3 particles. These results demonstrate that a subset of the variations observed as near-infrared opacity variations in the lower and middle clouds of Venus can be explained by microphysical, in addition to dynamical, variations. Furthermore, the existence of a population of particles exhibiting less efficient coalescence efficiencies would support the likelihood of conditions suitable for charge exchange, hence lightning, in the Venus clouds. We recommend future laboratory studies on the coalescence properties of sulfuric acid under the range of conditions experienced in the Venus clouds. We also recommend future in situ measurements to better characterize the properties of the cloud particles themselves, especially composition and particle habits (shapes).[Figure not available: see fulltext.

Intercomparison study and optical asphericity measurements of small ice particles in the CERN CLOUD experiment

NASA Astrophysics Data System (ADS)

Nichman, Leonid; Järvinen, Emma; Dorsey, James; Connolly, Paul; Duplissy, Jonathan; Fuchs, Claudia; Ignatius, Karoliina; Sengupta, Kamalika; Stratmann, Frank; Möhler, Ottmar; Schnaiter, Martin; Gallagher, Martin

2017-09-01

Optical probes are frequently used for the detection of microphysical cloud particle properties such as liquid and ice phase, size and morphology. These properties can eventually influence the angular light scattering properties of cirrus clouds as well as the growth and accretion mechanisms of single cloud particles. In this study we compare four commonly used optical probes to examine their response to small cloud particles of different phase and asphericity. Cloud simulation experiments were conducted at the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber at European Organisation for Nuclear Research (CERN). The chamber was operated in a series of multi-step adiabatic expansions to produce growth and sublimation of ice particles at super- and subsaturated ice conditions and for initial temperatures of -30, -40 and -50 °C. The experiments were performed for ice cloud formation via homogeneous ice nucleation. We report the optical observations of small ice particles in deep convection and in situ cirrus simulations. Ice crystal asphericity deduced from measurements of spatially resolved single particle light scattering patterns by the Particle Phase Discriminator mark 2 (PPD-2K, Karlsruhe edition) were compared with Cloud and Aerosol Spectrometer with Polarisation (CASPOL) measurements and image roundness captured by the 3View Cloud Particle Imager (3V-CPI). Averaged path light scattering properties of the simulated ice clouds were measured using the Scattering Intensity Measurements for the Optical detectioN of icE (SIMONE) and single particle scattering properties were measured by the CASPOL. We show the ambiguity of several optical measurements in ice fraction determination of homogeneously frozen ice in the case where sublimating quasi-spherical ice particles are present. Moreover, most of the instruments have difficulties of producing reliable ice fraction if small aspherical ice particles are present, and all of the instruments cannot separate perfectly spherical ice particles from supercooled droplets. Correlation analysis of bulk averaged path depolarisation measurements and single particle measurements of these clouds showed higher R2 values at high concentrations and small diameters, but these results require further confirmation. We find that none of these instruments were able to determine unambiguously the phase of the small particles. These results have implications for the interpretation of atmospheric measurements and parametrisations for modelling, particularly for low particle number concentration clouds.

Why Did the 2010 Eyjafjallajokull Volcanic Eruption Cloud Last So Long?

NASA Astrophysics Data System (ADS)

Jellinek, M.; Carazzo, G.

2013-12-01

The global economic consequences of the relatively small Eyjafjallajokull eruption in the spring of 2010 caught the world off guard. That the eruption cloud lasted for several months rather than weeks, efficiently disrupting air travel and the holiday plans of thousands of tourists, drew arguably more attention and a certainly garnered a highly emotional response. The longevity of this eruption cloud was touted to be "an anomaly". However, this anomaly nearly repeated itself the following year in the form of the 2011 Puyehue-Cordon Caulle eruption cloud. A major reason that the behavior of the 2010 Eyjafjallajokul cloud was surprising is that "standard" models for ash sedimentation (i.e., heavy particles fall out of the cloud faster than light particles) are incomplete. Observations of the 2010 Eyjafjallajokull, as well as the structure of atmospheric aerosol clouds from the 1991 Mt Pinatubo event, suggest that an additional key process in addition to particle settling is the production of internal layering. We use analog experiments on turbulent particle-laden umbrella clouds and simple models to show that this layering occurs where natural convection driven by particle sedimentation and the differential diffusion of primarily heat and fine particles give rise to a large scale instability leading to this layering. This 'particle diffusive convection' strongly influences cloud longevity where volcanic umbrella clouds are enriched in fine ash. More generally, volcanic cloud residence times will depend on ash fluxes related to both individual particle settling and diffusive convection. We discuss a new sedimentation model that includes both contributions to the particle flux and explains the the rate of change of particle concentration in the 1982 El Chichon, 1991 Mt Pinatubo and 1992 Mt Spurr ash-clouds. Examples of periodic layering in volcanic clouds compared with experiments in which periodic layering emerges as a result of buoyancy effects related to a particle-salt double diffusive instability.

Analysis of smoke impact on clouds in Brazilian biomass burning regions: An extension of Twomey's approach

NASA Astrophysics Data System (ADS)

Feingold, Graham; Remer, Lorraine A.; Ramaprasad, Jaya; Kaufman, Yoram J.

2001-10-01

Satellite remote sensing of smoke aerosol-cloud interaction during the recent Smoke, Clouds, and Radiation-Brazil (SCAR-B) experiment is analyzed to explore the factors that determine the magnitude of the cloud response to smoke aerosol. Analysis of 2 years worth of data revealed that the response is greatest in the north of Brazil where aerosol optical depth is smallest, and tends to decrease as one moves southward, and as aerosol optical depth increases. Saturation in this response occurs at an aerosol optical depth of 0.8 in 1987 and 0.4 in 1995. To explore the reasons for this, a framework is developed in which the satellite-measured response can be compared to simple analytical models of this response and to numerical models of smoke aerosol-cloud interaction. Three types of response are identified: (1) cloud droplet concentrations increase with increasing aerosol loading, followed by saturation in the response at high concentrations; (2) as in type 1, followed by increasing droplet concentrations with further increases in aerosol loading. This increase in droplet concentration is due to the suppression of supersaturation by abundant large particles, which prevents the activation of smaller particles. This enables renewed activation of larger particles when smoke loadings exceed some threshold; (3) as in type 1, followed by a decrease in droplet number concentrations with increasing aerosol loading as intense competition for vapor evaporates the smaller droplets. The latter implies an unexpected increase in drop size with increasing smoke loading. The conditions under which each of these responses are expected to occur are discussed. It is shown that although to first-order smoke optical depth is a good proxy for aerosol indirect forcing, under some conditions the size distribution and hygroscopicity can be important factors. We find no evidence that indirect forcing depends on precipitable water vapor.

Remote Sensing of the Optical and Physical Densities of Smoke, Dust, and Water Clouds.

DTIC Science & Technology

1982-12-01

systems to measure variability of aerosol concentration distributions along horizontal optical paths . Analysis of backscatter... extinction measurements using a single- laser lidar system operating at 1.06- and 0.53-pm wavelengths. For larger mean particle sizes the extinction ratio...clear air paths and The transmissometers were mounted across a 10-m complete blockage of the source energy. Transmisso- long aerosol tunnel that

Effects of cloud condensation nuclei and ice nucleating particles on precipitation processes and supercooled liquid in mixed-phase orographic clouds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fan, Jiwen; Leung, L. Ruby; Rosenfeld, Daniel

How orographic mixed-phase clouds respond to the change in cloud condensation nuclei (CCN) and ice nucleating particles (INPs) are highly uncertain. The main snow production mechanism in warm and cold mixed-phase orographic clouds (referred to as WMOCs and CMOCs, respectively, distinguished here as those having cloud tops warmer and colder than -20°C) could be very different. We quantify the CCN and INP impacts on supercooled water content, cloud phases, and precipitation for a WMOC case and a CMOC case, with sensitivity tests using the same CCN and INP concentrations between the WMOC and CMOC cases. It was found that depositionmore » plays a more important role than riming for forming snow in the CMOC case, while the role of riming is dominant in the WMOC case. As expected, adding CCN suppresses precipitation, especially in WMOCs and low INPs. However, this reverses strongly for CCN of 1000 cm -3 and larger. We found a new mechanism through which CCN can invigorate mixed-phase clouds over the Sierra Nevada and drastically intensify snow precipitation when CCN concentrations are high (1000 cm -3 or higher). In this situation, more widespread shallow clouds with a greater amount of cloud water form in the Central Valley and foothills west of the mountain range. The increased latent heat release associated with the formation of these clouds strengthens the local transport of moisture to the windward slope, invigorating mixed-phase clouds over the mountains, and thereby producing higher amounts of snow precipitation. Under all CCN conditions, increasing the INPs leads to decreased riming and mixed-phase fraction in the CMOC as a result of liquid-limited conditions, but has the opposite effects in the WMOC as a result of ice-limited conditions. However, precipitation in both cases is increased by increasing INPs due to an increase in deposition for the CMOC but enhanced riming and deposition in the WMOC. Increasing the INPs dramatically reduces supercooled water content and increases the cloud glaciation temperature, while increasing CCN has the opposite effect with much smaller significance.« less

Effects of cloud condensation nuclei and ice nucleating particles on precipitation processes and supercooled liquid in mixed-phase orographic clouds

DOE PAGES

Fan, Jiwen; Leung, L. Ruby; Rosenfeld, Daniel; ...

2017-01-23

How orographic mixed-phase clouds respond to the change in cloud condensation nuclei (CCN) and ice nucleating particles (INPs) are highly uncertain. The main snow production mechanism in warm and cold mixed-phase orographic clouds (referred to as WMOCs and CMOCs, respectively, distinguished here as those having cloud tops warmer and colder than -20°C) could be very different. We quantify the CCN and INP impacts on supercooled water content, cloud phases, and precipitation for a WMOC case and a CMOC case, with sensitivity tests using the same CCN and INP concentrations between the WMOC and CMOC cases. It was found that depositionmore » plays a more important role than riming for forming snow in the CMOC case, while the role of riming is dominant in the WMOC case. As expected, adding CCN suppresses precipitation, especially in WMOCs and low INPs. However, this reverses strongly for CCN of 1000 cm -3 and larger. We found a new mechanism through which CCN can invigorate mixed-phase clouds over the Sierra Nevada and drastically intensify snow precipitation when CCN concentrations are high (1000 cm -3 or higher). In this situation, more widespread shallow clouds with a greater amount of cloud water form in the Central Valley and foothills west of the mountain range. The increased latent heat release associated with the formation of these clouds strengthens the local transport of moisture to the windward slope, invigorating mixed-phase clouds over the mountains, and thereby producing higher amounts of snow precipitation. Under all CCN conditions, increasing the INPs leads to decreased riming and mixed-phase fraction in the CMOC as a result of liquid-limited conditions, but has the opposite effects in the WMOC as a result of ice-limited conditions. However, precipitation in both cases is increased by increasing INPs due to an increase in deposition for the CMOC but enhanced riming and deposition in the WMOC. Increasing the INPs dramatically reduces supercooled water content and increases the cloud glaciation temperature, while increasing CCN has the opposite effect with much smaller significance.« less

Cloud occurrences and cloud radiative effects (CREs) from CERES-CALIPSO-CloudSat-MODIS (CCCM) and CloudSat radar-lidar (RL) products

NASA Astrophysics Data System (ADS)

Ham, Seung-Hee; Kato, Seiji; Rose, Fred G.; Winker, David; L'Ecuyer, Tristan; Mace, Gerald G.; Painemal, David; Sun-Mack, Sunny; Chen, Yan; Miller, Walter F.

2017-08-01

Two kinds of cloud products obtained from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), CloudSat, and Moderate Resolution Imaging Spectroradiometer (MODIS) are compared and analyzed in this study: Clouds and the Earth's Radiant Energy System (CERES)-CALIPSO-CloudSat-MODIS (CCCM) product and CloudSat radar-lidar products such as GEOPROF-LIDAR and FLXHR-LIDAR. Compared to GEOPROF-LIDAR, low-level (<1 km) cloud occurrences in CCCM are larger over tropical oceans because the CCCM algorithm uses a more relaxed threshold of cloud-aerosol discrimination score for CALIPSO Vertical Feature Mask product. In contrast, midlevel (1-8 km) cloud occurrences in GEOPROF-LIDAR are larger than CCCM at high latitudes (>40°). The difference occurs when hydrometeors are detected by CALIPSO lidar but are undetected by CloudSat radar. In the comparison of cloud radiative effects (CREs), global mean differences between CCCM and FLXHR-LIDAR are mostly smaller than 5 W m-2, while noticeable regional differences are found. For example, CCCM shortwave (SW) and longwave (LW) CREs are larger than FXLHR-LIDAR along the west coasts of Africa and America because the GEOPROF-LIDAR algorithm misses shallow marine boundary layer clouds. In addition, FLXHR-LIDAR SW CREs are larger than the CCCM counterpart over tropical oceans away from the west coasts of America. Over midlatitude storm-track regions, CCCM SW and LW CREs are larger than the FLXHR-LIDAR counterpart.

Snowfall retrieval at X, Ka and W bands: consistency of backscattering and microphysical properties using BAECC ground-based measurements

NASA Astrophysics Data System (ADS)

Tecla Falconi, Marta; von Lerber, Annakaisa; Ori, Davide; Silvio Marzano, Frank; Moisseev, Dmitri

2018-05-01

Radar-based snowfall intensity retrieval is investigated at centimeter and millimeter wavelengths using co-located ground-based multi-frequency radar and video-disdrometer observations. Using data from four snowfall events, recorded during the Biogenic Aerosols Effects on Clouds and Climate (BAECC) campaign in Finland, measurements of liquid-water-equivalent snowfall rate S are correlated to radar equivalent reflectivity factors Ze, measured by the Atmospheric Radiation Measurement (ARM) cloud radars operating at X, Ka and W frequency bands. From these combined observations, power-law Ze-S relationships are derived for all three frequencies considering the influence of riming. Using microwave radiometer observations of liquid water path, the measured precipitation is divided into lightly, moderately and heavily rimed snow. Interestingly lightly rimed snow events show a spectrally distinct signature of Ze-S with respect to moderately or heavily rimed snow cases. In order to understand the connection between snowflake microphysical and multi-frequency backscattering properties, numerical simulations are performed by using the particle size distribution provided by the in situ video disdrometer and retrieved ice particle masses. The latter are carried out by using both the T-matrix method (TMM) applied to soft-spheroid particle models with different aspect ratios and exploiting a pre-computed discrete dipole approximation (DDA) database for rimed aggregates. Based on the presented results, it is concluded that the soft-spheroid approximation can be adopted to explain the observed multi-frequency Ze-S relations if a proper spheroid aspect ratio is selected. The latter may depend on the degree of riming in snowfall. A further analysis of the backscattering simulations reveals that TMM cross sections are higher than the DDA ones for small ice particles, but lower for larger particles. The differences of computed cross sections for larger and smaller particles are compensating for each other. This may explain why the soft-spheroid approximation is satisfactory for radar reflectivity simulations under study.

Nucleation and condensational growth to CCN sizes during a sustained pristine biogenic SOA event in a forested mountain valley

NASA Astrophysics Data System (ADS)

Liggio, J.; Pierce, J. R.; Leaitch, R.; Macdonald, A.; Whistler Aerosol; Cloud Study (WACS2010) Team

2011-12-01

The Whistler Aerosol and Cloud Study (WACS 2010), included intensive measurements of trace gases and particles at two sites on Whistler Mountain. Between July 6-11, 2010 there was a sustained high-pressure system over the region with cloud-free and higher-temperature conditions. During this period, the organic aerosol concentrations rose from <1 to 6 μ g m-3. Precursor gas and aerosol composition measurements show that these organics were almost entirely of secondary biogenic nature. Throughout July 6-11, the anthropogenic influence was minimal with sulfate concentrations < 0.2 μ g m-3 and SO2 mixing ratios ≈ 0.5 ppbv. Although SO2 mixing ratios were relatively low, companion box-model simulations show that nucleation and growth may be modeled accurately if Jnuc=3x10-7[H2SO4] and the organics are treated as effectively non-volatile. Due to the low condensation sink and the fast rate of condensing organics, the nucleated particles grew rapidly (2-5 nm hr-1) with a high probability of growing to CCN sizes before being scavenged by coagulation with larger particles (>10% growing to 100 nm in the first two days). The particles were observed to ultimately grow to ~200 nm after three days. Comparisons of SMPS with DMT CCN data show that particle hygroscopicity was generally around 0.1-0.11. The concentration of particles with diameters larger than 100 nm as well as CCN at 3% supersaturation rise from about 300 cm-3 to 1200 cm-3 during the 5 days due entirely to nucleation and growth. Relatively little SO2 is necessary to generate nucleation and growth to CCN sizes when biogenic SOA is abundant. This case offers a unique look at processes that may have controlled CCN formation in the pristine pre-industrial forested continental atmosphere.

The vertical structure of convectively-driven cloud microphysics and its dependency on atmospheric conditions: An investigation through observations and modeling

NASA Astrophysics Data System (ADS)

van Diedenhoven, B.; Fridlind, A. M.; Sinclair, K.; Ackerman, A. S.

2016-12-01

It is generally observed that ice crystal sizes decrease as a function of altitude within clouds. This dependency is often explained as resulting from size sorting owing to the greater fall speeds of larger particles, but may also be related to dependence of ice diffusional growth on available water vapor and temperature, or other factors. Furthermore, the vertical variation of ice sizes is expected to be affected by the glaciation temperature of convectively-driven clouds. Realistic modeling of ice formation, growth and sedimentation is crucial to reliably represent vertical structures of ice clouds and cloud evolution in general. In this presentation we use remote sensing observations of glaciation temperature and ice effective radius obtained with airborne instruments to explore how their vertical dependencies vary with atmospheric conditions, such as humidity and wind profiles. Our focus will be on convectively-driven clouds. Subsequently, we test the ability of a quasi-idealized cloud permitting model to reproduce these dependencies of ice formation and size to atmospheric conditions, applying various ice growth and multiplication assumptions. The goal of this study is to identify variables that determine the vertical structure of cold clouds that can be used to evaluate model simulations.

Aerosol nucleation and its role for clouds and Earth's radiative forcing in the aerosol-climate model ECHAM5-HAM

NASA Astrophysics Data System (ADS)

Kazil, J.; Stier, P.; Zhang, K.; Quaas, J.; Kinne, S.; O'Donnell, D.; Rast, S.; Esch, M.; Ferrachat, S.; Lohmann, U.; Feichter, J.

2010-05-01

Nucleation from the gas phase is an important source of aerosol particles in the Earth's atmosphere, contributing to the number of cloud condensation nuclei, which form cloud droplets. We have implemented in the aerosol-climate model ECHAM5-HAM a new scheme for neutral and charged nucleation of sulfuric acid and water based on laboratory data, and nucleation of an organic compound and sulfuric acid using a parametrization of cluster activation based on field measurements. We give details of the implementation, compare results with observations, and investigate the role of the individual aerosol nucleation mechanisms for clouds and the Earth's radiative budget. The results of our simulations are most consistent with observations when neutral and charged nucleation of sulfuric acid proceed throughout the troposphere and nucleation due to cluster activation is limited to the forested boundary layer. The globally averaged annual mean contributions of the individual nucleation processes to total absorbed solar short-wave radiation via the direct, semi-direct, indirect cloud-albedo and cloud-lifetime effects in our simulations are -1.15 W/m2 for charged H2SO4/H2O nucleation, -0.235 W/m2 for cluster activation, and -0.05 W/m2 for neutral H2SO4/H2O nucleation. The overall effect of nucleation is -2.55 W/m2, which exceeds the sum of the individual terms due to feedbacks and interactions in the model. Aerosol nucleation contributes over the oceans with -2.18 W/m2 to total absorbed solar short-wave radiation, compared to -0.37 W/m2 over land. We explain the higher effect of aerosol nucleation on Earth's radiative budget over the oceans with the larger area covered by ocean clouds, due to the larger contrast in albedo between clouds and the ocean surface compared to continents, and the larger susceptibility of pristine clouds owing to the saturation of effects. The large effect of charged nucleation in our simulations is not in contradiction with small effects seen in local measurements: over southern Finland, where cluster activation proceeds efficiently, we find that charged nucleation of sulfuric acid and water contributes on average less than 10% to ultrafine aerosol concentrations, in good agreement with observations.

Aerosol nucleation and its role for clouds and Earth's radiative forcing in the aerosol-climate model ECHAM5-HAM

NASA Astrophysics Data System (ADS)

Kazil, J.; Stier, P.; Zhang, K.; Quaas, J.; Kinne, S.; O'Donnell, D.; Rast, S.; Esch, M.; Ferrachat, S.; Lohmann, U.; Feichter, J.

2010-11-01

Nucleation from the gas phase is an important source of aerosol particles in the Earth's atmosphere, contributing to the number of cloud condensation nuclei, which form cloud droplets. We have implemented in the aerosol-climate model ECHAM5-HAM a new scheme for neutral and charged nucleation of sulfuric acid and water based on laboratory data, and nucleation of an organic compound and sulfuric acid using a parametrization of cluster activation based on field measurements. We give details of the implementation, compare results with observations, and investigate the role of the individual aerosol nucleation mechanisms for clouds and the Earth's radiative forcing. The results of our simulations are most consistent with observations when neutral and charged nucleation of sulfuric acid proceed throughout the troposphere and nucleation due to cluster activation is limited to the forested boundary layer. The globally averaged annual mean contributions of the individual nucleation processes to total absorbed solar short-wave radiation via the direct, semi-direct, indirect cloud-albedo and cloud-lifetime effects in our simulations are -1.15 W/m2 for charged H2SO4/H2O nucleation, -0.235 W/m2 for cluster activation, and -0.05 W/m2 for neutral H2SO4/H2O nucleation. The overall effect of nucleation is -2.55 W/m2, which exceeds the sum of the individual terms due to feedbacks and interactions in the model. Aerosol nucleation contributes over the oceans with -2.18 W/m2 to total absorbed solar short-wave radiation, compared to -0.37 W/m2 over land. We explain the higher effect of aerosol nucleation on Earth's radiative forcing over the oceans with the larger area covered by ocean clouds, due to the larger contrast in albedo between clouds and the ocean surface compared to continents, and the larger susceptibility of pristine clouds owing to the saturation of effects. The large effect of charged nucleation in our simulations is not in contradiction with small effects seen in local measurements: over southern Finland, where cluster activation proceeds efficiently, we find that charged nucleation of sulfuric acid and water contributes on average less than 10% to ultrafine aerosol concentrations, in good agreement with observations.

The 1991 Eruption of Mt. Pinatubo: Changes in Climate and Atmospheric Chemistry- Lesson Learned and Questions Left Unanswered

NASA Astrophysics Data System (ADS)

Toon, O. B.

2016-12-01

Mt. Pinatubo injected the largest amount of SO2 into the stratosphere of any 20th Century eruption. I will survey what we learned, and point out issues that require more data, or further analysis. Beautiful purple twilight glows, hazy gray skies, and sunsets so bright they caused traffic accidents made the volcanic cloud evident to even casual observers for more than a year. High altitude aircraft, balloons, satellites and ground-based instruments measured many properties of the cloud and its impact on the Earth. Scattering of sunlight to space created a temporary negative radiative forcing, larger than the positive forcing from greenhouse gases in the previous century. As a result the surface cooled, but the cloud faded before the cooling reached its full potential. Absorption of near infrared sunlight, and of upwelling mid-infrared radiation heated the stratosphere. The heating was unequal, which may have induced local dynamical changes that sped the movement of the cloud into the Southern Hemisphere. The ascending motion in the tropical branch of the Brewer-Dobson circulation sped up, leading to tropical ozone reductions. Mid-latitude declines in ozone were caused by heterogeneous chemical reactions on the volcanic cloud. Polar ozone loss was enhanced by increased heterogeneous reactions due to the increased surface area provided by the volcanic particles. A number of important microphysical insights were gained that are not always recognized. Stratospheric particle sizes increase with the addition of SO2, and even Pinatubo particles did not have a constant or uniform particle size distribution. The optical depth was not uniform over the globe, or even one hemisphere. In fact, the maximum optical depth moved from the tropics to high northern latitudes over the first year. Many questions have been left unanswered. Theory suggests the optical depth of volcanic clouds increases less than linearly with the mass of SO2 injected, is this correct? Observations did not show injections of water or halogens, will other eruptions have significant injections? Do large eruptions have an effect on El Nino or winter warming in the Northern Hemisphere, and if so what is the mechanism? Other large eruptions are inevitable, but rare. How can we prepare to measure the properties and effects of their clouds?

Mesoscale modeling of smoke transport over the Southeast Asian Maritime Continent: Coupling of smoke direct radiative feedbacks below and above the low-level clouds

NASA Astrophysics Data System (ADS)

Ge, C.; Wang, J.; Reid, J. S.

2013-12-01

The online-coupled Weather Research and Forecasting model with Chemistry (WRF-Chem) is used to simulate the direct and semi-direct radiative impacts of smoke particles over the southeast Asian Marine Continents (MC, 10°S - 10°N, 90°E-150°E) during October 2006 when a significant El Nino event caused the highest biomass burning activity since 1997. With the use of OC (Organic Carbon) /BC (Black Carbon) ratio of 10 in the smoke emission inventory, the baseline simulation shows that the low-level clouds amplifying effect on smoke absorption led to a warming effect at the top-of-atmosphere (TOA) with a domain/monthly average forcing value of ~20 Wm-2 over the islands of Borneo and Sumatra. The smoke-induced monthly average daytime heating (0.3K) that is largely confined above the low-level clouds results in the local convergence over the smoke source region. This heating-induced convergence coupled with daytime planetary boundary layer turbulent mixing, transports more smoke particles above the planetary boundary layer height (PBLH), hence rendering a positive feedback. This positive feedback contrasts with the decrease of cloud fraction resulted from the combined effects of smoke heating within the cloud layer and the more stability in the boundary layer; the latter can be considered as a negative feedback in which decrease of cloud fraction weakens the heating by smoke particles above the clouds. During nighttime, the elevated smoke layer (above clouds in daytime) is decoupled from boundary layer, and the reduction of PBLH due to the residual surface cooling from the daytime lead to the accumulation of smoke particles near the surface. Because of smoke radiative extinction, on monthly basis, the amount of the solar input at the surface is reduced as large as 60 Wm-2, which lead to the decrease of sensible heat, latent heat, 2-m air temperature, and PBLH by a maximum of 20 Wm-2, 20 Wm-2, 1K, 120 m, respectively. The cloud changes over continents are mostly occurred over the islands of Sumatra and Borneo during the daytime, where the low-level cloud fraction decreases more than 10%. However, the change of local wind (include sea breeze) induced by the smoke radiative feedback leads to more convergence over Karimata Strait and south coastal area of Kalimantan during both daytime and night time; consequently, cloud fraction is increased there up to 20%. The sensitivities with different OC/BC ratio show the importance of the smoke single scattering albedo for the smoke semi-direct effects. A case study on 31 October 2006 further demonstrated a much larger (more than twice of the monthly average) feedback induced by smoke aerosols. The decreased sea breeze during big events can lead to prominent increase (40%) of low-level cloud over coastal water. Lastly, the direct and semi-direct radiative impact of smoke particles over the Southeast Asian Marine Continents is summarized as a conceptual model.

Contrasting Cloud Composition Between Coupled and Decoupled Marine Boundary Layer Clouds

NASA Astrophysics Data System (ADS)

WANG, Z.; Mora, M.; Dadashazar, H.; MacDonald, A.; Crosbie, E.; Bates, K. H.; Coggon, M. M.; Craven, J. S.; Xian, P.; Campbell, J. R.; AzadiAghdam, M.; Woods, R. K.; Jonsson, H.; Flagan, R. C.; Seinfeld, J.; Sorooshian, A.

2016-12-01

Marine stratocumulus clouds often become decoupled from the vertical layer immediately above the ocean surface. This study contrasts cloud chemical composition between coupled and decoupled marine stratocumulus clouds. Cloud water and droplet residual particle composition were measured in clouds off the California coast during three airborne experiments in July-August of separate years (E-PEACE 2011, NiCE 2013, BOAS 2015). Decoupled clouds exhibited significantly lower overall mass concentrations in both cloud water and droplet residual particles, consistent with reduced cloud droplet number concentration and sub-cloud aerosol (Dp > 100 nm) number concentration, owing to detachment from surface sources. Non-refractory sub-micrometer aerosol measurements show that coupled clouds exhibit higher sulfate mass fractions in droplet residual particles, owing to more abundant precursor emissions from the ocean and ships. Consequently, decoupled clouds exhibited higher mass fractions of organics, nitrate, and ammonium in droplet residual particles, owing to effects of long-range transport from more distant sources. Total cloud water mass concentration in coupled clouds was dominated by sodium and chloride, and their mass fractions and concentrations exceeded those in decoupled clouds. Conversely, with the exception of sea salt constituents (e.g., Cl, Na, Mg, K), cloud water mass fractions of all species examined were higher in decoupled clouds relative to coupled clouds. These results suggest that an important variable is the extent to which clouds are coupled to the surface layer when interpreting microphysical data relevant to clouds and aerosol particles.

Thunderstorms over Brazil

NASA Technical Reports Server (NTRS)

2002-01-01

This photograph, acquired in February 1984 by an astronaut aboard the space shuttle, shows a series of mature thunderstorms located near the Parana River in southern Brazil. With abundant warm temperatures and moisture-laden air in this part of Brazil, large thunderstorms are commonplace. A number of overshooting tops and anvil clouds are visible at the tops of the clouds. Storms of this magnitude can drop large amounts of rainfall in a short period of time, causing flash floods. However, a NASA-funded researcher has discovered that tiny airborne particles of pollution may modify developing thunderclouds by increasing the quantity and reducing the size of the ice crystals within them. These modifications may affect the clouds' impact on the Earth's 'radiation budget,' or the amount of radiation that enters and leaves our planet. Steven Sherwood, a professor at Yale University, found that airborne aerosols reduce the size of ice crystals in thunderclouds and may reduce precipitation as well. Using several satellites and instruments including NASA's Total Ozone Mapping Spectrometer (TOMS) and NASA's Tropical Rainfall Measuring Mission (TRMM) satellite, Sherwood observed how airborne pollution particles (aerosols) affect large thunderstorms, or cumulonimbus clouds in the tropics. Common aerosols include mineral dust, smoke, and sulfates. An increased number of these particles create a larger number of smaller ice crystals in cumulonimbus clouds. As a result of their smaller size, the ice crystals evaporate from a solid state directly into a gas, instead of falling as rain. Sherwood noted that this effect is more prevalent over land than open ocean areas. Previous research by Daniel Rosenfeld of Hebrew University revealed that aerosols and pollution reduced rainfall in shallow cumulus clouds of liquid water, which do not have the capability to produce as much rainfall. Sherwood expanded on that research by looking at cumulonimbus clouds with more ice particles. Studies have also proven that ice particles are smaller in the upper reaches of thunderclouds when there is more pollution and when the rising air in the clouds (convection) is stronger. Aerosols seem to have the most influence on seasonal and longer timescales such as during the warmer months when plants and undergrowth are burned to clear fields. Over areas where biomass burning occurs, such as South America, aerosols have been found to reduce the diameter of ice crystals in the clouds by as much as 20 percent. Areas over deserts, such as Africa's Sahel Region where dust is a primary aerosol, there was a 10 percent decrease in the diameter of ice crystals in cumulonimbus clouds. Aerosol particles are necessary for clouds to form, and it has been suspected that clouds might be altered by large concentrations of them. By looking at ten years of aerosol data and statistically analyzing many thunderclouds, Sherwood was able to confirm that they were affected. Sherwood found that ice crystals are smaller in clouds over continents than oceans, which could be attributed to the amount of pollution generated over land. The highest values occur widely over Northern Africa, where desert dust and smoke from agricultural burning occur. Intermediate values prevail over much of Asia, through the Indonesia region and into the south Pacific. The largest ice crystal sizes were found over the eastern Pacific and southern Indian Oceans. Sherwood's article, 'Aerosols and Ice Particle Size in Tropical Cumulonimbus,' appears in the May 1, 2002, issue of the American Meteorological Society Journal of Climate. This work was performed under the NASA Earth Observing System/Interdisciplinary Science (IDS) program under the Earth Science Enterprise (ESE). Image STS41B-41-2347 was provided by the Earth Sciences and Image Analysis Laboratory at Johnson Space Center. Additional images taken by astronauts and cosmonauts can be viewed at the NASA-JSC Gateway to Astronaut Photography of Earth

Aqueous Processing of Atmospheric Organic Particles in Cloud Water Collected via Aircraft Sampling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boone, Eric J.; Laskin, Alexander; Laskin, Julia

2015-07-21

Cloud water and below-cloud atmospheric particle samples were collected onboard a research aircraft during the Southern Oxidant and Aerosol Study (SOAS) over a forested region of Alabama in June 2013. The organic molecular composition of the samples was studied to gain insights into the aqueous-phase processing of organic compounds within cloud droplets. High resolution mass spectrometry with nanospray desorption electrospray ionization and direct infusion electrospray ionization were utilized to compare the organic composition of the particle and cloud water samples, respectively. Isoprene and monoterpene-derived organosulfates and oligomers were identified in both the particles and cloud water, showing the significant influencemore » of biogenic volatile organic compound oxidation above the forested region. While the average O:C ratios of the organic compounds were similar between the atmospheric particle and cloud water samples, the chemical composition of these samples was quite different. Specifically, hydrolysis of organosulfates and formation of nitrogen-containing compounds were observed for the cloud water when compared to the atmospheric particle samples, demonstrating that cloud processing changes the composition of organic aerosol.« less

Relationship Between Cirrus Particle Size and Cloud Top Temperature

NASA Technical Reports Server (NTRS)

Han, Qingyuan; Chou, Joyce; Welch, Ronald M.

1997-01-01

The relationship between cirrus particle size and cloud top temperature is surveyed on a near-global scale. The cirrus particle size is retrieved assuming ice crystals are hexagonal columns and the cloud top temperature and the radiances in channel 1 and 3 of AVHRR used to retrieve ice particle sizes are from ISCCP product. The results show that for thick clouds over North America, the relation between particle size and cloud top temperature is consistent with a summary of this relationship based on aircraft measurement over that region for thick clouds. However, this relationship is not universal for other regions especially for for tropical zone, which has been found by other in situ measurements.

Novel Transport Characterizations in Layered Two-Dimensional Materials and Bulk Chalcogenides

NASA Astrophysics Data System (ADS)

Pennypacker, Sam

We present a case study (September 20 - October 13, 2015) of synergistic, multi-instrument observations of aerosols, clouds and the marine boundary layer (MBL) at the Eastern North Atlantic (ENA) ARM site centered on a period of exceptionally low (20 - 50 cm-3) surface accumulation mode (0.1 - 1 mum) aerosol particle number concentrations. We divide the case study into three regimes (high, clean and ultra-clean) based on daily median number concentrations, and compare finer resolution (hourly or less) observations between these regimes. The analysis focuses on the possibility of using these ultra-clean events to study pristine conditions in the remote MBL, as well as examining evidence for a recently proposed conceptual model for the large-scale depletion of CCN-sized particles in post-frontal air masses. Relative to the high and clean regimes, the ultra-clean regime tends to exhibit significantly fewer particles between 0.1 and 0.4 mum in diameter and a relatively increased prevalence of larger accumulation mode particles. In addition, supermicron particles tend to dominate total scattering in the ultra-clean regime, and there is little evidence for absorbing aerosol. These observations are more in line with a heavily scavenged but natural marine aerosol population and minimal contribution from continental sources such as anthropogenic pollution, biomass burning or dust. The air masses with the consistently lowest accumulation mode aerosol number concentrations are largely dominated by heavily drizzling clouds with high liquid water path (LWP) cores, deep decoupled boundary layers, open cellular organization and notable surface forcing of sub-cloud turbulence, even at night. We end with a discussion of the implications of this work the second aerosol indirect effect and pristine conditions in the remote MBL.

Retrieval of radiative and microphysical properties of clouds from multispectral infrared measurements

NASA Astrophysics Data System (ADS)

Iwabuchi, Hironobu; Saito, Masanori; Tokoro, Yuka; Putri, Nurfiena Sagita; Sekiguchi, Miho

2016-12-01

Satellite remote sensing of the macroscopic, microphysical, and optical properties of clouds are useful for studying spatial and temporal variations of clouds at various scales and constraining cloud physical processes in climate and weather prediction models. Instead of using separate independent algorithms for different cloud properties, a unified, optimal estimation-based cloud retrieval algorithm is developed and applied to moderate resolution imaging spectroradiometer (MODIS) observations using ten thermal infrared bands. The model considers sensor configurations, background surface and atmospheric profile, and microphysical and optical models of ice and liquid cloud particles and radiative transfer in a plane-parallel, multilayered atmosphere. Measurement and model errors are thoroughly quantified from direct comparisons of clear-sky observations over the ocean with model calculations. Performance tests by retrieval simulations show that ice cloud properties are retrieved with high accuracy when cloud optical thickness (COT) is between 0.1 and 10. Cloud-top pressure is inferred with uncertainty lower than 10 % when COT is larger than 0.3. Applying the method to a tropical cloud system and comparing the results with the MODIS Collection 6 cloud product shows good agreement for ice cloud optical thickness when COT is less than about 5. Cloud-top height agrees well with estimates obtained by the CO2 slicing method used in the MODIS product. The present algorithm can detect optically thin parts at the edges of high clouds well in comparison with the MODIS product, in which these parts are recognized as low clouds by the infrared window method. The cloud thermodynamic phase in the present algorithm is constrained by cloud-top temperature, which tends not to produce results with an ice cloud that is too warm and liquid cloud that is too cold.

Aerosol chemical composition in cloud events by high resolution time-of-flight aerosol mass spectrometry.

PubMed

Hao, Liqing; Romakkaniemi, Sami; Kortelainen, Aki; Jaatinen, Antti; Portin, Harri; Miettinen, Pasi; Komppula, Mika; Leskinen, Ari; Virtanen, Annele; Smith, James N; Sueper, Donna; Worsnop, Douglas R; Lehtinen, Kari E J; Laaksonen, Ari

2013-03-19

This study presents results of direct observations of aerosol chemical composition in clouds. A high-resolution time-of-flight aerosol mass spectrometer was used to make measurements of cloud interstitial particles (INT) and mixed cloud interstitial and droplet residual particles (TOT). The differences between these two are the cloud droplet residuals (RES). Positive matrix factorization analysis of high-resolution mass spectral data sets and theoretical calculations were performed to yield distributions of chemical composition of the INT and RES particles. We observed that less oxidized hydrocarbon-like organic aerosols (HOA) were mainly distributed into the INT particles, whereas more oxidized low-volatile oxygenated OA (LVOOA) mainly in the RES particles. Nitrates existed as organic nitrate and in chemical form of NH(4)NO(3). Organic nitrates accounted for 45% of total nitrates in the INT particles, in clear contrast to 26% in the RES particles. Meanwhile, sulfates coexist in forms of acidic NH(4)HSO(4) and neutralized (NH(4))(2)SO(4). Acidic sulfate made up 64.8% of total sulfates in the INT particles, much higher than 10.7% in the RES particles. The results indicate a possible joint effect of activation ability of aerosol particles, cloud processing, and particle size effects on cloud formation.

Impacts of New Particle Formation on Midwestern Climate and Air Quality as Determined by the NPF-explicit WRF-Chem

NASA Astrophysics Data System (ADS)

Dong, C.; Stanier, C. O.; Bullard, R.; Singh, A.

2016-12-01

A one month simulation has been performed using the New particle formation (NPF)-explicit WRF-Chem (Matsui et al, Journal of Geophysical Research, 116(D19208), 2011). The simulation was run for a domain of the continental United States, with analysis focused on the Midwestern and eastern portions of the U.S. Analysis focused on quantification and explanation of planetary boundary layer (PBL) NPF in the model on variables beyond condensation nuclei (CN), cloud condensation nuclei (CCN), and cloud droplet size distributions. The model was evaluated against meteorology, chemical species and aerosol physical property observations. Comparison shows the model performance was comparable to that of other studies. Nucleation enhanced the concentration of condensation nuclei (CN). Cloud condensation nuclei (CCN) concentrations were enhanced and suppressed at high and low supersaturations, respectively. For air pollutants, the most pronounced influence of PBL nucleation was PM2.5 reduction, which was mainly caused by SO4 decreases (62.7%). For shortwave radiation, changes due to indirect effects of NPF were larger than direct effects. Shortwave radiation and cloud droplet concentration typically changed in the same way. Similar change patterns were found for T2 and PBL height. PBL nucleation led to a net increase of precipitation during the simulation period. Sensitivity tests showed that the combination of PBL NPF together with aqueous chemistry was the predominant cause of SO4 reduction.

Detailed analysis of particle launch velocities, size distributions and gas densities during normal explosions at Stromboli

NASA Astrophysics Data System (ADS)

Harris, Andrew J. L.; Ripepe, Maurizio; Hughes, Elizabeth A.

2012-06-01

Using high frame rate (33 Hz) thermal video data we describe and parameterize the emission and ascent dynamics of a mixed plume of gas and particles emitted during a normal explosion at Stromboli (Aeolian Islands, Italy). Analysis of 34 events showed that 31 of them were characterized by a first phase characterized by an initial diffuse spray of relatively small (lapilli-sized) particles moving at high velocities (up to 213 m s- 1; average 66-82 m s- 1). This was followed, typically within 0.1 s, by a burst comprising a mixture of ash and lapilli, but dominated by larger bomb-sized particles, moving at lower exit velocities of up to 129 m s- 1, but typically 46 m s- 1. We interpret these results as revealing initial emission of a previously unrecorded high velocity gas-jet phase, to which the lapilli are coupled. This is followed by emission of slower moving larger particles that are decoupled from the faster moving gas-phase. Diameters for particles carried by the gas phase are typically around 4 cm, but can be up to 9 cm, with the diameter of the particles carried by the gas jet (D) decreasing with increased density and velocity of the erupted gas cloud (ρgas and Ugas). Data for 101 particles identified as moving with the gas jet during 32 eruptions allow us to define a new relation, whereby Ugas = Uparticle + a [ρgas√{D}]b. Here, Uparticle is the velocity of bombs whose motion is decoupled from that of the gas cloud, and a and b are two empirically-derived coefficients. This replaces the old relation, whereby Ugas = Uparticle + k √{D}; a relation that requires a constant gas density for each eruption. This is an assumption that we show to be invalid, with gas density potentially varying between 0.04 kg m- 3 and 9 kg m- 3 for the 32 cases considered, so that k varies between 54 m1/2 s- 1 and 828 m1/2 s- 1, compared with the traditionally used constant of 150 m1/2 s- 1.

Ice nucleation properties of atmospheric aerosol particles collected during a field campaign in Cyprus

NASA Astrophysics Data System (ADS)

Yordanova, Petya; Maier, Stefanie; Lang-Yona, Naama; Tamm, Alexandra; Meusel, Hannah; Pöschl, Ulrich; Weber, Bettina; Fröhlich-Nowoisky, Janine

2017-04-01

Atmospheric aerosol particles, including desert and soil dust as well as marine aerosols, are well known to act as ice nuclei (IN) and thus have been investigated in numerous ice nucleation studies. Based on their cloud condensation nuclei potential and their impacts on radiative properties of clouds (via scattering and absorption of solar radiation), aerosol particles may significantly affect the cloud and precipitation development. Atmospheric aerosols of the Eastern Mediterranean have been described to be dominated by desert dust, but only little is known on their composition and ice nucleating properties. In this study we investigated the ice nucleating ability of total suspended particles (TSP), collected at the remote site Agia Marina Xyliatou on Cyprus during a field campaign in April 2016. Airborne TSP samples containing air masses of various types such as African (Saharan) and Arabian dust and European and Middle Eastern pollution were collected on glass fiber filters at 24 h intervals. Sampling was performed ˜5 m above ground level and ˜521 m above sea level. During the sampling period, two major dust storms (PM 10max 118 μg/m3 and 66 μg/m3) and a rain event (rainfall amount: 3.4 mm) were documented. Chemical and physical characterizations of the particles were analyzed experimentally through filtration, thermal, chemical and enzyme treatments. Immersion freezing experiments were performed at relatively high subzero temperatures (-1 to -15˚ C) using the mono ice nucleation array. Preliminary results indicate that highest IN particle numbers (INPs) occurred during the second dust storm event with lower particle concentrations. Treatments at 60˚ C lead to a gradual IN deactivation, indicating the presence of biological INPs, which were observed to be larger than 300 kDa. Additional results originating from this study will be shown. Acknowledgement: This work was funded by the DFG Ice Nuclei Research Unit (INUIT).

Ambient in-situ immersion freezing measurements - findings from the ZAMBIS 2014 field campaign for three ice nucleation techniques

NASA Astrophysics Data System (ADS)

Kohn, Monika; Atkinson, James D.; Lohmann, Ulrike; Kanji, Zamin A.

2015-04-01

To estimate the influence of clouds on the Earth's radiation budget, it is crucial to understand cloud formation processes in the atmosphere. A key process, which significantly affects cloud microphysical properties and the initiation of precipitation thus contributing to the hydrological cycle, is the prevailing type of ice nucleation mechanism. In mixed-phase clouds immersion freezing is the dominant ice crystal forming mechanism, whereby ice nucleating particles (INP) first act as cloud condensation nuclei (CCN) and are activated to cloud droplets followed by freezing upon supercooling. There are a number of experimental methods and techniques to investigate the ice nucleating ability in the immersion mode, however most techniques are offline for field sampling or only suitable for laboratory measurements. In-situ atmospheric studies are needed to understand the ice formation processes of 'real world' particles. Laboratory experiments simulate conditions of atmospheric processes like ageing or coating but are still idealized. Our method is able to measure ambient in-situ immersion freezing on single immersed aerosol particles. The instrumental setup consists of the recently developed portable immersion mode cooling chamber (PIMCA) as a vertical extension to the portable ice nucleation chamber (PINC, [1]), where the frozen fraction of activated aerosol particles are detected by the ice optical depolarization detector (IODE, [2]). Two additional immersion freezing techniques based on a droplet freezing array [3,4] are used to sample ambient aerosol particles either in a suspension (fraction larger ~0.6 μm) or on PM10-filters to compare different ice nucleation techniques. Here, we present ambient in-situ measurements at an urban forest site in Zurich, Switzerland held during the Zurich ambient immersion freezing study (ZAMBIS) in spring 2014. We investigated the ice nucleating ability of natural atmospheric aerosol with the PIMCA/PINC immersion freezing setup as well as a droplet freezing method on aerosol particles either collected in a suspension or on PM10-filters to obtain atmospheric IN concentrations based on the measured ambient aerosol. Investigation of physical properties (number and size distribution) and chemical composition as well as the meteorological conditions provide supplementary information that help to understand the nature of particles and air masses that contribute to immersion freezing. Acknowledgements We thank Hannes Wydler and Hansjörg Frei from ETH Zurich for their technical support. Furthermore, the authors want thank Franz Conen from the University of Basel for sharing equipment and training in the drop freezing experiment. References [1] Chou et al. (2011), Atmos. Chem. Phys., 11, 4725-4738. [2] Nicolet et al. (2010), Atmos. Chem. Phys., 10, 313-325. [3] Conen et al. (2012), Atmos. Meas. Tech., 5, 321-327. [4] Stopelli et al. (2014), Atmos. Meas. Tech., 7, 129-134.

New particle formation in the sulfuric acid-dimethylamine-water system: reevaluation of CLOUD chamber measurements and comparison to an aerosol nucleation and growth model

NASA Astrophysics Data System (ADS)

Kürten, Andreas; Li, Chenxi; Bianchi, Federico; Curtius, Joachim; Dias, António; Donahue, Neil M.; Duplissy, Jonathan; Flagan, Richard C.; Hakala, Jani; Jokinen, Tuija; Kirkby, Jasper; Kulmala, Markku; Laaksonen, Ari; Lehtipalo, Katrianne; Makhmutov, Vladimir; Onnela, Antti; Rissanen, Matti P.; Simon, Mario; Sipilä, Mikko; Stozhkov, Yuri; Tröstl, Jasmin; Ye, Penglin; McMurry, Peter H.

2018-01-01

A recent CLOUD (Cosmics Leaving OUtdoor Droplets) chamber study showed that sulfuric acid and dimethylamine produce new aerosols very efficiently and yield particle formation rates that are compatible with boundary layer observations. These previously published new particle formation (NPF) rates are reanalyzed in the present study with an advanced method. The results show that the NPF rates at 1.7 nm are more than a factor of 10 faster than previously published due to earlier approximations in correcting particle measurements made at a larger detection threshold. The revised NPF rates agree almost perfectly with calculated rates from a kinetic aerosol model at different sizes (1.7 and 4.3 nm mobility diameter). In addition, modeled and measured size distributions show good agreement over a wide range of sizes (up to ca. 30 nm). Furthermore, the aerosol model is modified such that evaporation rates for some clusters can be taken into account; these evaporation rates were previously published from a flow tube study. Using this model, the findings from the present study and the flow tube experiment can be brought into good agreement for the high base-to-acid ratios (˜ 100) relevant for this study. This confirms that nucleation proceeds at rates that are compatible with collision-controlled (a.k.a. kinetically controlled) NPF for the conditions during the CLOUD7 experiment (278 K, 38 % relative humidity, sulfuric acid concentration between 1 × 106 and 3 × 107 cm-3, and dimethylamine mixing ratio of ˜ 40 pptv, i.e., 1 × 109 cm-3).

Experimental demonstration of plasma-drag acceleration of a dust cloud to hypervelocities.

PubMed

Ticoş, C M; Wang, Zhehui; Wurden, G A; Kline, J L; Montgomery, D S; Dorf, L A; Shukla, P K

2008-04-18

Simultaneous acceleration of hundreds of dust particles to hypervelocities by collimated plasma flows ejected from a coaxial gun is demonstrated. Graphite and diamond grains with radii between 5 and 30 microm, and flying at speeds up to 3.7 km/s, have been recorded with a high-speed camera. The observations agree well with a model for plasma-drag acceleration of microparticles much larger than the plasma screening length.

Volcanic explosion clouds - Density, temperature, and particle content estimates from cloud motion

NASA Technical Reports Server (NTRS)

Wilson, L.; Self, S.

1980-01-01

Photographic records of 10 vulcanian eruption clouds produced during the 1978 eruption of Fuego Volcano in Guatemala have been analyzed to determine cloud velocity and acceleration at successive stages of expansion. Cloud motion is controlled by air drag (dominant during early, high-speed motion) and buoyancy (dominant during late motion when the cloud is convecting slowly). Cloud densities in the range 0.6 to 1.2 times that of the surrounding atmosphere were obtained by fitting equations of motion for two common cloud shapes (spheres and vertical cylinders) to the observed motions. Analysis of the heat budget of a cloud permits an estimate of cloud temperature and particle weight fraction to be made from the density. Model results suggest that clouds generally reached temperatures within 10 K of that of the surrounding air within 10 seconds of formation and that dense particle weight fractions were less than 2% by this time. The maximum sizes of dense particles supported by motion in the convecting clouds range from 140 to 1700 microns.

The Influence of Thermodynamic Phase on the Retrieval of Mixed-Phase Cloud Microphysical and Optical Properties in the Visible and Near Infrared Region

NASA Technical Reports Server (NTRS)

Lee, Joonsuk; Yang, Ping; Dessler, Andrew E.; Baum, Bryan A.; Platnick, Steven

2005-01-01

Cloud microphysical and optical properties are inferred from the bidirectional reflectances simulated for a single-layered cloud consisting of an external mixture of ice particles and liquid droplets. The reflectances are calculated with a rigorous discrete ordinates radiative transfer model and are functions of the cloud effective particle size, the cloud optical thickness, and the values of the ice fraction in the cloud (i.e., the ratio of ice water content to total water content). In the present light scattering and radiative transfer simulations, the ice fraction is assumed to be vertically homogeneous; the habit (shape) percentage as a function of ice particle size is consistent with that used for the Moderate Resolution Imaging Spectroradiometer (MODIS) operational (Collection 4 and earlier) cloud products; and the surface is assumed to be Lambertian with an albedo of 0.03. Furthermore, error analyses pertaining to the inference of the effective particle sizes and optical thicknesses of mixed-phase clouds are performed. Errors are calculated with respect to the assumption of a cloud containing solely liquid or ice phase particles. The analyses suggest that the effective particle size inferred for a mixed-phase cloud can be underestimated (or overestimated) if pure liquid phase (or pure ice phase) is assumed for the cloud, whereas the corresponding cloud optical thickness can be overestimated (or underestimated).

Ice Cloud Formation and Dehydration in the Tropical Tropopause Layer

NASA Technical Reports Server (NTRS)

Jensen, Eric; Gore, Warren J. (Technical Monitor)

2002-01-01

Stratospheric water vapor is important not only for its greenhouse forcing, but also because it plays a significant role in stratospheric chemistry. Several recent studies have focused on the potential for dehydration due to ice cloud formation in air rising slowly through the tropical tropopause layer (TTL). Holton and Gettelman showed that temperature variations associated with horizontal transport of air in the TTL can drive ice cloud formation and dehydration, and Gettelman et al. recently examined the cloud formation and dehydration along kinematic trajectories using simple assumptions about the cloud properties. In this study, a Lagrangian, one-dimensional cloud model has been used to further investigate cloud formation and dehydration as air is transported horizontally and vertically through the TTL. Time-height curtains of temperature are extracted from meteorological analyses. The model tracks the growth, advection, and sedimentation of individual cloud particles. The regional distribution of clouds simulated in the model is comparable to the subvisible cirrus distribution indicated by SAGE II. The simulated cloud properties and cloud frequencies depend strongly on the assumed supersaturation threshold for ice nucleation. The clouds typically do not dehydrate the air along trajectories down to the temperature minimum saturation mixing ratio. Rather the water vapor mixing ratio crossing the tropopause along trajectories is 10-50% larger than the saturation mixing ratio. I will also discuss the impacts of Kelvin waves and gravity waves on cloud properties and dehydration efficiency. These simulations can be used to determine whether observed lower stratospheric water vapor mixing ratios can be explained by dehydration associated with in situ TTL cloud formation alone.

The immersion freezing behavior of size-segregated soot and kaolinite particles

NASA Astrophysics Data System (ADS)

Hartmann, S.; Augustin, S.; Clauss, T.; Niedermeier, D.; Raddatz, M.; Wex, H.; Shaw, R. A.; Stratmann, F.

2011-12-01

Heterogeneous ice nucleation plays a crucial role for ice formation in mixed-phase and cirrus clouds and has an important impact on precipitation formation, global radiation balances, and therefore Earth's climate (Cantrell and Heymsfield, 2005). Mineral dust and soot particles are found to be a major component of ice crystal residues (e.g., Pratt et al., 2009) so these substances are potential sources of atmospheric ice nuclei (IN). Experimental studies investigating the immersion freezing behavior of size-segregated soot and kaolinite particles conducted at the Leipzig Aerosol Cloud Interaction Simulator (LACIS) are presented. In our measurements only one aerosol particle is immersed in an air suspended water droplet which can trigger ice nucleation. The method facilitates very precise examinations with respect to temperature, ice nucleation time and ice nucleus size. Considering laboratory studies, the picture of the IN ability of soot particles is quite heterogeneous. Our studies show that submicron flame, spark soot particles and optionally coated with sulfuric acid to simulate chemically aging do not act as IN at temperatures higher than homogeneous freezing taking place. Therefore soot particles might not be an important source of IN for immersion freezing in the atmosphere. In contrast, kaolinite being representative for natural mineral dust with a well known composition and structure is found to be very active in forming ice for all freezing modes (e.g., Mason and Maybank, 1958). Analyzing the immersion freezing behavior of different sized kaolinite particles (300, 500 and 700 nm in diameter) the size effect was clearly observed, i.e. the ice fraction (number of frozen droplets per total number) scales with particle surface, i.e. the larger the ice nucleus surface the higher the ice fraction. The slope of the logarithm of the ice fraction as function of temperature is similar for all particle sizes investigated and fits very well with the results of Lüönd et al. (2010) and Murray et al. (2011). Heterogeneous ice nucleation rate coefficients are derived which can be used to describe the immersion freezing process size-segregated in cloud microphysical models.

Aerodynamic generation of electric fields in turbulence laden with charged inertial particles.

PubMed

Di Renzo, M; Urzay, J

2018-04-26

Self-induced electricity, including lightning, is often observed in dusty atmospheres. However, the physical mechanisms leading to this phenomenon remain elusive as they are remarkably challenging to determine due to the high complexity of the multi-phase turbulent flows involved. Using a fast multi-pole method in direct numerical simulations of homogeneous turbulence laden with hundreds of millions of inertial particles, here we show that mesoscopic electric fields can be aerodynamically created in bi-disperse suspensions of oppositely charged particles. The generation mechanism is self-regulating and relies on turbulence preferentially concentrating particles of one sign in clouds while dispersing the others more uniformly. The resulting electric field varies over much larger length scales than both the mean inter-particle spacing and the size of the smallest eddies. Scaling analyses suggest that low ambient pressures, such as those prevailing in the atmosphere of Mars, increase the dynamical relevance of this aerodynamic mechanism for electrical breakdown.

The Role of Aerosols on Precipitation Processes: Cloud Resolving Model Simulations

NASA Technical Reports Server (NTRS)

Tao, Wei-Kuo; Li, X.; Matsui, T.

2012-01-01

Cloud microphysics is inevitably affected by the smoke particle (CCN, cloud condensation nuclei) size distributions below the clouds. Therefore, size distributions parameterized as spectral bin microphysics are needed to explicitly study the effects of atmospheric aerosol concentration on cloud development, rainfall production, and rainfall rates for convective clouds. Recently, a detailed spectral-bin microphysical scheme was implemented into the Goddard Cumulus Ensemble (GCE) model. The formulation for the explicit spectral bin microphysical processes is based on solving stochastic kinetic equations for the size distribution functions of water droplets (i.e., cloud droplets and raindrops), and several types of ice particles [i.e. pristine ice crystals (columnar and plate-like), snow (dendrites and aggregates), graupel and frozen drops/hail]. Each type is described by a special size distribution function containing many categories (i.e., 33 bins). Atmospheric aerosols are also described using number density size-distribution functions. The model is tested by studying the evolution of deep cloud systems in the west Pacific warm pool region, the sub-tropics (Florida) and midlatitudes using identical thermodynamic conditions but with different concentrations of CCN: a low "clean" concentration and a high "dirty" concentration. Results indicate that the low CCN concentration case produces rainfall at the surface sooner than the high CeN case but has less cloud water mass aloft. Because the spectral-bin model explicitly calculates and allows for the examination of both the mass and number concentration of species in each size category, a detailed analysis of the instantaneous size spectrum can be obtained for these cases. It is shown that since the low (CN case produces fewer droplets, larger sizes develop due to greater condensational and collection growth, leading to a broader size spectrum in comparison to the high CCN case. Sensitivity tests were performed to identify the impact of ice processes, radiation and large-scale influence on cloud-aerosol interactive processes, especially regarding surface rainfall amounts and characteristics (i.e., heavy or convective versus light or stratiform types). In addition, an inert tracer was included to follow the vertical redistribution of aerosols by cloud processes. We will also give a brief review from observational evidence on the role of aerosol on precipitation processes.

The Role of CO2 Clouds on the Stability of the Early Mars Atmosphere Against Collapse

NASA Astrophysics Data System (ADS)

Kahre, Melinda A.; Haberle, Robert; Steakley, Kathryn; Murphy, Jim; Kling, Alexandre

2017-10-01

The early Mars atmosphere was likely significantly more massive than it is today, given the growing body of evidence that liquid water flowed on the surface early in the planet’s history. Although the CO2 inventory was likely larger in the past, there is much we still do not understand about the state of that CO2. As surface pressure increases, the temperature at which CO2 condenses also increases, making it more likely that CO2 ice would form and persist on the surface when the atmospheric mass increases. An atmosphere that is stable against collapse must contain enough energy, distributed globally, to prohibit the formation of permanents CO2 ice reservoirs that lead to collapse. The presence of the “faint young sun” compounds this issue. Previous global climate model (GCM) investigations show that atmospheres within specific ranges of obliquities and atmospheric masses are stable against collapse. We use the NASA Ames Mars GCM to expand on these works by focusing specifically on the role of CO2 clouds in atmospheric stability. Two end member simulations are executed, one that includes CO2 cloud formation and one that does not. The simulation that explicitly includes CO2 clouds is stable, while the simulation without CO2 clouds collapses into permanent surface CO2 reservoirs. In both cases, significant atmospheric condensation is occurring in the atmosphere throughout the year. In the case without CO2 clouds, all atmospheric condensation (even if it occurs at altitude) leads directly to the accumulation of surface ice, whereas in the case with CO2 clouds, there is a finite settling timescale for the cloud particles. Depending on this timescale and the local conditions, the cloud particles could stay aloft or sublimate as they fall toward the surface. Thus, the striking difference between these two cases illustrates the important role of CO2 clouds. We plan to conduct and present further simulations to better understand how atmospheric stability depends on the details of CO2 cloud microphysical processes and assumptions.

Formation of Silicate and Titanium Clouds on Hot Jupiters

NASA Astrophysics Data System (ADS)

Powell, Diana; Zhang, Xi; Gao, Peter; Parmentier, Vivien

2018-06-01

We present the first application of a bin-scheme microphysical and vertical transport model to determine the size distribution of titanium and silicate cloud particles in the atmospheres of hot Jupiters. We predict particle size distributions from first principles for a grid of planets at four representative equatorial longitudes, and investigate how observed cloud properties depend on the atmospheric thermal structure and vertical mixing. The predicted size distributions are frequently bimodal and irregular in shape. There is a negative correlation between the total cloud mass and equilibrium temperature as well as a positive correlation between the total cloud mass and atmospheric mixing. The cloud properties on the east and west limbs show distinct differences that increase with increasing equilibrium temperature. Cloud opacities are roughly constant across a broad wavelength range, with the exception of features in the mid-infrared. Forward-scattering is found to be important across the same wavelength range. Using the fully resolved size distribution of cloud particles as opposed to a mean particle size has a distinct impact on the resultant cloud opacities. The particle size that contributes the most to the cloud opacity depends strongly on the cloud particle size distribution. We predict that it is unlikely that silicate or titanium clouds are responsible for the optical Rayleigh scattering slope seen in many hot Jupiters. We suggest that cloud opacities in emission may serve as sensitive tracers of the thermal state of a planet’s deep interior through the existence or lack of a cold trap in the deep atmosphere.

Strong control of Southern Ocean cloud reflectivity by ice-nucleating particles

NASA Astrophysics Data System (ADS)

Vergara-Temprado, Jesús; Miltenberger, Annette K.; Furtado, Kalli; Grosvenor, Daniel P.; Shipway, Ben J.; Hill, Adrian A.; Wilkinson, Jonathan M.; Field, Paul R.; Murray, Benjamin J.; Carslaw, Ken S.

2018-03-01

Large biases in climate model simulations of cloud radiative properties over the Southern Ocean cause large errors in modeled sea surface temperatures, atmospheric circulation, and climate sensitivity. Here, we combine cloud-resolving model simulations with estimates of the concentration of ice-nucleating particles in this region to show that our simulated Southern Ocean clouds reflect far more radiation than predicted by global models, in agreement with satellite observations. Specifically, we show that the clouds that are most sensitive to the concentration of ice-nucleating particles are low-level mixed-phase clouds in the cold sectors of extratropical cyclones, which have previously been identified as a main contributor to the Southern Ocean radiation bias. The very low ice-nucleating particle concentrations that prevail over the Southern Ocean strongly suppress cloud droplet freezing, reduce precipitation, and enhance cloud reflectivity. The results help explain why a strong radiation bias occurs mainly in this remote region away from major sources of ice-nucleating particles. The results present a substantial challenge to climate models to be able to simulate realistic ice-nucleating particle concentrations and their effects under specific meteorological conditions.

Strong control of Southern Ocean cloud reflectivity by ice-nucleating particles

PubMed Central

Miltenberger, Annette K.; Furtado, Kalli; Grosvenor, Daniel P.; Shipway, Ben J.; Hill, Adrian A.; Wilkinson, Jonathan M.; Field, Paul R.

2018-01-01

Large biases in climate model simulations of cloud radiative properties over the Southern Ocean cause large errors in modeled sea surface temperatures, atmospheric circulation, and climate sensitivity. Here, we combine cloud-resolving model simulations with estimates of the concentration of ice-nucleating particles in this region to show that our simulated Southern Ocean clouds reflect far more radiation than predicted by global models, in agreement with satellite observations. Specifically, we show that the clouds that are most sensitive to the concentration of ice-nucleating particles are low-level mixed-phase clouds in the cold sectors of extratropical cyclones, which have previously been identified as a main contributor to the Southern Ocean radiation bias. The very low ice-nucleating particle concentrations that prevail over the Southern Ocean strongly suppress cloud droplet freezing, reduce precipitation, and enhance cloud reflectivity. The results help explain why a strong radiation bias occurs mainly in this remote region away from major sources of ice-nucleating particles. The results present a substantial challenge to climate models to be able to simulate realistic ice-nucleating particle concentrations and their effects under specific meteorological conditions. PMID:29490918

Thin ice clouds in the Arctic: cloud optical depth and particle size retrieved from ground-based thermal infrared radiometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blanchard, Yann; Royer, Alain; O'Neill, Norman T.

Multiband downwelling thermal measurements of zenith sky radiance, along with cloud boundary heights, were used in a retrieval algorithm to estimate cloud optical depth and effective particle diameter of thin ice clouds in the Canadian High Arctic. Ground-based thermal infrared (IR) radiances for 150 semitransparent ice clouds cases were acquired at the Polar Environment Atmospheric Research Laboratory (PEARL) in Eureka, Nunavut, Canada (80° N, 86° W). We analyzed and quantified the sensitivity of downwelling thermal radiance to several cloud parameters including optical depth, effective particle diameter and shape, water vapor content, cloud geometric thickness and cloud base altitude. A lookupmore » table retrieval method was used to successfully extract, through an optimal estimation method, cloud optical depth up to a maximum value of 2.6 and to separate thin ice clouds into two classes: (1) TIC1 clouds characterized by small crystals (effective particle diameter ≤ 30 µm), and (2) TIC2 clouds characterized by large ice crystals (effective particle diameter > 30 µm). The retrieval technique was validated using data from the Arctic High Spectral Resolution Lidar (AHSRL) and Millimeter Wave Cloud Radar (MMCR). Inversions were performed over three polar winters and results showed a significant correlation ( R 2 = 0.95) for cloud optical depth retrievals and an overall accuracy of 83 % for the classification of TIC1 and TIC2 clouds. A partial validation relative to an algorithm based on high spectral resolution downwelling IR radiance measurements between 8 and 21µm was also performed. It confirms the robustness of the optical depth retrieval and the fact that the broadband thermal radiometer retrieval was sensitive to small particle (TIC1) sizes.« less

Thin ice clouds in the Arctic: cloud optical depth and particle size retrieved from ground-based thermal infrared radiometry

NASA Astrophysics Data System (ADS)

Blanchard, Yann; Royer, Alain; O'Neill, Norman T.; Turner, David D.; Eloranta, Edwin W.

2017-06-01

Multiband downwelling thermal measurements of zenith sky radiance, along with cloud boundary heights, were used in a retrieval algorithm to estimate cloud optical depth and effective particle diameter of thin ice clouds in the Canadian High Arctic. Ground-based thermal infrared (IR) radiances for 150 semitransparent ice clouds cases were acquired at the Polar Environment Atmospheric Research Laboratory (PEARL) in Eureka, Nunavut, Canada (80° N, 86° W). We analyzed and quantified the sensitivity of downwelling thermal radiance to several cloud parameters including optical depth, effective particle diameter and shape, water vapor content, cloud geometric thickness and cloud base altitude. A lookup table retrieval method was used to successfully extract, through an optimal estimation method, cloud optical depth up to a maximum value of 2.6 and to separate thin ice clouds into two classes: (1) TIC1 clouds characterized by small crystals (effective particle diameter ≤ 30 µm), and (2) TIC2 clouds characterized by large ice crystals (effective particle diameter > 30 µm). The retrieval technique was validated using data from the Arctic High Spectral Resolution Lidar (AHSRL) and Millimeter Wave Cloud Radar (MMCR). Inversions were performed over three polar winters and results showed a significant correlation (R2 = 0.95) for cloud optical depth retrievals and an overall accuracy of 83 % for the classification of TIC1 and TIC2 clouds. A partial validation relative to an algorithm based on high spectral resolution downwelling IR radiance measurements between 8 and 21 µm was also performed. It confirms the robustness of the optical depth retrieval and the fact that the broadband thermal radiometer retrieval was sensitive to small particle (TIC1) sizes.

Thin ice clouds in the Arctic: cloud optical depth and particle size retrieved from ground-based thermal infrared radiometry

DOE PAGES

Blanchard, Yann; Royer, Alain; O'Neill, Norman T.; ...

2017-06-09

Multiband downwelling thermal measurements of zenith sky radiance, along with cloud boundary heights, were used in a retrieval algorithm to estimate cloud optical depth and effective particle diameter of thin ice clouds in the Canadian High Arctic. Ground-based thermal infrared (IR) radiances for 150 semitransparent ice clouds cases were acquired at the Polar Environment Atmospheric Research Laboratory (PEARL) in Eureka, Nunavut, Canada (80° N, 86° W). We analyzed and quantified the sensitivity of downwelling thermal radiance to several cloud parameters including optical depth, effective particle diameter and shape, water vapor content, cloud geometric thickness and cloud base altitude. A lookupmore » table retrieval method was used to successfully extract, through an optimal estimation method, cloud optical depth up to a maximum value of 2.6 and to separate thin ice clouds into two classes: (1) TIC1 clouds characterized by small crystals (effective particle diameter ≤ 30 µm), and (2) TIC2 clouds characterized by large ice crystals (effective particle diameter > 30 µm). The retrieval technique was validated using data from the Arctic High Spectral Resolution Lidar (AHSRL) and Millimeter Wave Cloud Radar (MMCR). Inversions were performed over three polar winters and results showed a significant correlation ( R 2 = 0.95) for cloud optical depth retrievals and an overall accuracy of 83 % for the classification of TIC1 and TIC2 clouds. A partial validation relative to an algorithm based on high spectral resolution downwelling IR radiance measurements between 8 and 21µm was also performed. It confirms the robustness of the optical depth retrieval and the fact that the broadband thermal radiometer retrieval was sensitive to small particle (TIC1) sizes.« less

The role of ions in the self-healing behavior of soft particle suspensions

PubMed Central

Scotti, Andrea; Gasser, Urs; Herman, Emily S.; Pelaez-Fernandez, Miguel; Han, Jun; Menzel, Andreas; Lyon, L. Andrew; Fernández-Nieves, Alberto

2016-01-01

Impurities in crystals generally cause point defects and can even suppress crystallization. This general rule, however, does not apply to colloidal crystals formed by soft microgel particles [Iyer ASJ, Lyon LA (2009) Angew Chem Int Ed 48:4562–4566], as, in this case, the larger particles are able to shrink and join the crystal formed by a majority of smaller particles. Using small-angle X-ray scattering, we find the limit in large-particle concentration for this spontaneous deswelling to persist. We rationalize our data in the context of those counterions that are bound to the microgel particles as a result of the electrostatic attraction exerted by the fixed charges residing on the particle periphery. These bound counterions do not contribute to the suspension osmotic pressure in dilute conditions, as they can be seen as internal degrees of freedom associated with each microgel particle. In contrast, at sufficiently high particle concentrations, the counterion cloud of each particle overlaps with that of its neighbors, allowing these ions to freely explore the space outside the particles. We confirm this scenario by directly measuring the osmotic pressure of the suspension. Because these counterions are then no longer bound, they create an osmotic pressure difference between the inside and outside of the microgels, which, if larger than the microgel bulk modulus, can cause deswelling, explaining why large, soft microgel particles feel the squeeze when suspended with a majority of smaller particles. We perform small-angle neutron scattering measurements to further confirm this remarkable behavior. PMID:27125854

Japan's research on particle clouds and sprays

NASA Technical Reports Server (NTRS)

Sato, Jun'ichi

1995-01-01

Most of energy used by us is generated by combustion of liquid and solid fuels. These fuels are burned in combustors mainly as liquid sprays and pulverized solids, respectively. A knowledge of the combustion processes in combustors is needed to achieve proper designs that have stable operation, high efficiency, and low emission levels. However, current understanding of liquid and solid particle cloud combustion is far from complete. If combustion experiments for these fuels are performed under a normal gravity field, some experimental difficulties are encountered. These difficulties encountered include, that since the particles fall by the force of gravity it is impossible to stop the particles in the air, the falling speeds of particles are different from each other, and are depend on the particle size, the flame is lifted up and deformed by the buoyancy force, and natural convection makes the flow field more complex. Since these experimental difficulties are attributable to the gravity force, a microgravity field can eliminate the above problems. This means that the flame propagation experiments in static homogeneous liquid and solid particle clouds can be carried out under a microgravity field. This will provide much information for the basic questions related to combustion processes of particle clouds and sprays. In Japan, flame propagation processes in the combustible liquid and solid particle clouds have been studied experimentally by using a microgravity field generated by a 4.5 s dropshaft, a 10 s dropshaft, and by parabolic flight. Described in this presentation are the recent results of flame propagations studies in a homogeneous liquid particle cloud, in a mixture of liquid particles/gas fuel/air, in a PMMA particle cloud, and in a pulverized coal particle cloud.

Ice Particle Impact on Cloud Water Content Instrumentation

NASA Technical Reports Server (NTRS)

Emery, Edward F.; Miller, Dean R.; Plaskon, Stephen R.; Strapp, Walter; Lillie, Lyle

2004-01-01

Determining the total amount of water contained in an icing cloud necessitates the measurement of both the liquid droplets and ice particles. One commonly accepted method for measuring cloud water content utilizes a hot wire sensing element, which is maintained at a constant temperature. In this approach, the cloud water content is equated with the power required to keep the sense element at a constant temperature. This method inherently assumes that impinging cloud particles remain on the sensing element surface long enough to be evaporated. In the case of ice particles, this assumption requires that the particles do not bounce off the surface after impact. Recent tests aimed at characterizing ice particle impact on a thermally heated wing section, have raised questions about the validity of this assumption. Ice particles were observed to bounce off the heated wing section a very high percentage of the time. This result could have implications for Total Water Content sensors which are designed to capture ice particles, and thus do not account for bouncing or breakup of ice particles. Based on these results, a test was conducted to investigate ice particle impact on the sensing elements of the following hot-wire cloud water content probes: (1) Nevzorov Total Water Content (TWC)/Liquid Water Content (LWC) probe, (2) Science Engineering Associates TWC probe, and (3) Particle Measuring Systems King probe. Close-up video imaging was used to study ice particle impact on the sensing element of each probe. The measured water content from each probe was also determined for each cloud condition. This paper will present results from this investigation and attempt to evaluate the significance of ice particle impact on hot-wire cloud water content measurements.

CALIPSO Polar Stratospheric Cloud Observations from 2006-2015

NASA Technical Reports Server (NTRS)

Pitts, Michael C.; Poole, Lamont R.

2015-01-01

Polar stratospheric clouds (PSCs) play a crucial role in the springtime chemical depletion of ozone at high latitudes. PSC particles (primarily supercooled ternary solution, or STS droplets) provide sites for heterogeneous chemical reactions that transform stable chlorine and bromine reservoir species into highly reactive ozone-destructive forms. Furthermore, large nitric acid trihydrate (NAT) PSC particles can irreversibly redistribute odd nitrogen through gravitational sedimentation (a process commonly known as denitrification), which prolongs the ozone depletion process by slowing the reformation of the stable chlorine reservoirs. Spaceborne observations from the CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) lidar on the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) satellite are providing a rich new dataset for studying PSCs. CALIPSO is an excellent platform for studying polar processes with CALIOP acquiring, on average, over 300,000 backscatter profiles daily at latitudes between 55o and 82o in both hemispheres. PSCs are detected in the CALIOP backscatter profiles using a successive horizontal averaging scheme that enables detection of strongly scattering PSCs (e.g., ice) at the finest possible spatial resolution (5 km), while enhancing the detection of very tenuous PSCs (e.g., low number density NAT) at larger spatial scales (up to 135 km). CALIOP PSCs are separated into composition classes (STS; liquid/NAT mixtures; and ice) based on the ensemble 532-nm scattering ratio (the ratio of total-to-molecular backscatter) and 532-nm particulate depolarization ratio (which is sensitive to the presence of non-spherical, i.e. NAT and ice particles). In this paper, we will provide an overview of the CALIOP PSC detection and composition classification algorithm and then examine the vertical and spatial distribution of PSCs in the Arctic and Antarctic on vortex-wide scales for entire PSC seasons over the more than nine-year data record from 2006- 2015.

Particle cloud mixing in microgravity

NASA Technical Reports Server (NTRS)

Ross, H.; Facca, L.; Tangirala, V.; Berlad, A. L.

1989-01-01

Quasi-steady flame propagation through clouds of combustible particles requires quasi-steady transport properties and quasi-steady particle number density. Microgravity conditions may be employed to help achieve the conditions of quiescent, uniform clouds needed for such combustion studies. Joint experimental and theoretical NASA-UCSD studies were concerned with the use of acoustic, electrostatic, and other methods of dispersion of fuel particulates. Results of these studies are presented for particle clouds in long cylindrical tubes.

The local environment of ice particles in arctic mixed-phase clouds

NASA Astrophysics Data System (ADS)

Schlenczek, Oliver; Fugal, Jacob P.; Schledewitz, Waldemar; Borrmann, Stephan

2015-04-01

During the RACEPAC field campaign in April and May 2014, research flights were made with the Polar 5 and Polar 6 aircraft from the Alfred Wegener Institute in Arctic clouds near Inuvik, Northwest Territories, Canada. One flight with the Polar 6 aircraft, done on May 16, 2014, flew under precipitating, stratiform, mid-level clouds with several penetrations through cloud base. Measurements with HALOHolo, an airborne digital in-line holographic instrument for cloud particles, show ice particles in a field of other cloud particles in a local three-dimensional sample volume (~14x19x130 mm3 or ~35 cm^3). Each holographic sample volume is a snapshot of a 3-dimensional piece of cloud at the cm-scale with typically thousands of cloud droplets per sample volume, so each sample volume yields a statistically significant droplet size distribution. Holograms are recorded at a rate of six times per second, which provides one volume sample approx. every 12 meters along the flight path. The size resolution limit for cloud droplets is better than 1 µm due to advanced sizing algorithms. Shown are preliminary results of, (1) the ice/liquid water partitioning at the cloud base and the distribution of water droplets around each ice particle, and (2) spatial and temporal variability of the cloud droplet size distributions at cloud base.

Cloud-In-Cell modeling of shocked particle-laden flows at a ``SPARSE'' cost

NASA Astrophysics Data System (ADS)

Taverniers, Soren; Jacobs, Gustaaf; Sen, Oishik; Udaykumar, H. S.

2017-11-01

A common tool for enabling process-scale simulations of shocked particle-laden flows is Eulerian-Lagrangian Particle-Source-In-Cell (PSIC) modeling where each particle is traced in its Lagrangian frame and treated as a mathematical point. Its dynamics are governed by Stokes drag corrected for high Reynolds and Mach numbers. The computational burden is often reduced further through a ``Cloud-In-Cell'' (CIC) approach which amalgamates groups of physical particles into computational ``macro-particles''. CIC does not account for subgrid particle fluctuations, leading to erroneous predictions of cloud dynamics. A Subgrid Particle-Averaged Reynolds-Stress Equivalent (SPARSE) model is proposed that incorporates subgrid interphase velocity and temperature perturbations. A bivariate Gaussian source distribution, whose covariance captures the cloud's deformation to first order, accounts for the particles' momentum and energy influence on the carrier gas. SPARSE is validated by conducting tests on the interaction of a particle cloud with the accelerated flow behind a shock. The cloud's average dynamics and its deformation over time predicted with SPARSE converge to their counterparts computed with reference PSIC models as the number of Gaussians is increased from 1 to 16. This work was supported by AFOSR Grant No. FA9550-16-1-0008.

A New Ka-Band Scanning Radar Facility: Polarimetric and Doppler Spectra Measurements of Snow Events

NASA Astrophysics Data System (ADS)

Oue, M.; Kollias, P.; Luke, E. P.; Mead, J.

2017-12-01

Polarimetric radar analyses offer the capability of identification of ice hydrometeor species as well as their spatial distributions. In addition to polarimetric parameter observations, Doppler spectra measurements offer unique insights into ice particle properties according to particle fall velocities. In particular, millimeter-wavelength radar Doppler spectra can reveal supercooled liquid cloud droplets embedded in ice precipitation clouds. A Ka-band scanning polarimetric radar, named KASPR, was installed in an observation facility at Stony Brook University, located 22 km west of the KOKX NEXRAD radar at Upton, NY. The KASPR can measure Doppler spectra and full polarimetric variables, including radar reflectivity, differential reflectivity (ZDR), differential phase (φDP), specific differential phase (KDP), correlation coefficient (ρhv), and linear depolarization ratio (LDR). The facility also includes a micro-rain radar and a microwave radiometer capable of measuring reflectivity profiles and integrated liquid water path, respectively. The instruments collected initial datasets during two snowstorm events and two snow shower events in March 2017. The radar scan strategy was a combination of PPI scans at 4 elevation angles (10, 20, 45, and 60°) and RHI scans in polarimetry mode, and zenith pointing with Doppler spectra collection. During the snowstorm events the radar observed relatively larger ZDR (1-1.5 dB) and enhanced KDP (1-2 ° km-1) at heights corresponding to a plate/dendrite crystal growth regime. The Doppler spectra showed that slower-falling particles (< 0.5 m s-1) coexisted with faster-falling particles (> 1 m s-1). The weakly increased ZDR could be produced by large, faster falling particles such as quasi-spherical aggregates, while the enhanced KDP could be produced by highly-oriented oblate, slowly-falling particles. Below 2 km altitude, measurements of dual wavelength ratio (DWR) based on Ka and S-band reflectivities from the KASPR and NEXRAD radars were available. Larger DWR (>10 dB) suggested large, faster-falling, high-reflectivity particles, consistent with large aggregates (> 1 cm) observed at the ground. The presentation will show an advanced analysis using synergy between multi frequency, polarimetry, and Doppler spectra measurements.

First correlated measurements of the shape and light scattering properties of cloud particles using the new Particle Habit Imaging and Polar Scattering (PHIPS) probe

NASA Astrophysics Data System (ADS)

Abdelmonem, A.; Schnaiter, M.; Amsler, P.; Hesse, E.; Meyer, J.; Leisner, T.

2011-10-01

Studying the radiative impact of cirrus clouds requires knowledge of the relationship between their microphysics and the single scattering properties of cloud particles. Usually, this relationship is obtained by modeling the optical scattering properties from in situ measurements of ice crystal size distributions. The measured size distribution and the assumed particle shape might be erroneous in case of non-spherical ice particles. We present here a novel optical sensor (the Particle Habit Imaging and Polar Scattering probe, PHIPS) designed to measure simultaneously the 3-D morphology and the corresponding optical and microphysical parameters of individual cloud particles. Clouds containing particles ranging from a few micrometers to about 800 μm diameter in size can be characterized systematically with an optical resolution power of 2 μm and polar scattering resolution of 1° for forward scattering directions (from 1° to 10°) and 8° for side and backscattering directions (from 18° to 170°). The maximum acquisition rates for scattering phase functions and images are 262 KHz and 10 Hz, respectively. Some preliminary results collected in two ice cloud campaigns conducted in the AIDA cloud simulation chamber are presented. PHIPS showed reliability in operation and produced size distributions and images comparable to those given by other certified cloud particles instruments. A 3-D model of a hexagonal ice plate is constructed and the corresponding scattering phase function is compared to that modeled using the Ray Tracing with Diffraction on Facets (RTDF) program. PHIPS is a highly promising novel airborne optical sensor for studying the radiative impact of cirrus clouds and correlating the particle habit-scattering properties which will serve as a reference for other single, or multi-independent, measurement instruments.

GASP cloud- and particle-encounter statistics and their application to LPC aircraft studies. Volume 1: Analysis and conclusions

NASA Technical Reports Server (NTRS)

Jasperson, W. H.; Nastrom, G. D.; Davis, R. E.; Holdeman, J. D.

1984-01-01

Summary studies are presented for the entire cloud observation archieve from the NASA Global Atmospheric Sampling Program (GASP). Studies are also presented for GASP particle concentration data gathered concurrently with the cloud observations. Cloud encounters are shown on about 15 percent of the data samples overall, but the probability of cloud encounter is shown to vary significantly with altitude, latitude, and distance from the tropopause. Several meteorological circulation features are apparent in the latitudinal distribution of cloud cover, and the cloud encounter statistics are shown to be consistent with the classical mid-latitude cyclone model. Observations of clouds spaced more closely than 90 minutes are shown to be statistically dependent. The statistics for cloud and particle encounter are utilized to estimate the frequency of cloud encounter on long range airline routes, and to assess the probability and extent of laminar flow loss due to cloud or particle encounter by aircraft utilizing laminar flow control (LFC). It is shown that the probability of extended cloud encounter is too low, of itself, to make LFC impractical.

Constraining the Global, Cloud-Free Reflected Solar Radiation Flux (RSRF) with Earth Observing System (EOS) Instruments

NASA Technical Reports Server (NTRS)

Kahn, Ralph

1999-01-01

Variations in the top-of-atmosphere reflected solar radiation flux, and in the factors that determine its value, are among the most important diagnostic indicators of changes in Earth's energy balance. Data from the MISR (Multi-angle Imaging SpectroRadiometer), MODIS (Moderate-resolution Imaging Spectroradiometer), SAGE-3 (Stratospheric Aerosol and Gas Experiment), and CERES (Clouds and Earth's Radiant Energy System), all of which are spacecraft instruments scheduled for launch in 1999, will each constrain pieces of the RSRF budget. Prior to launch, we are performing studies to determine the sensitivity of these instruments to key factors that influence the cloud-free RSRF: aerosol optical depth, aerosol scattering properties, and surface visible bidirectional reflectance distribution function (BRDF). We are also assessing the ability of the aggregate of instruments to constrain the overall RSRF budget under natural conditions over the globe. Consider the MISR retrieval of aerosols: according to simulations over cloud-free, calm ocean, for pure particles with natural ranges of optical depth, particle size, and indices of refraction, MISR can retrieve column aerosol optical depth for all but the darkest particles, to an uncertainty of at most 0.05 or 20%, whichever is larger, even if the particle properties are poorly known. For one common particle type, soot, constraints on the optical depth over dark ocean are very poor. The simulated measurements also allow us to distinguish spherical from non-spherical particles, to separate two to four compositional groups based on indices of refraction, and to identify three to four distinct size groups between 0. 1 and 2.0 microns characteristic radius at most latitudes. Based on these results, we expect to distinguish air masses containing different aerosol types, routinely and globally, with multiangle remote sensing data. Such results far exceed current satellite aerosol retrieval capabilities, which provide only total optical depth for assumed particle properties; the new information will complement in situ data, which give details about aerosol size and composition locally. In addition, our team is using climatologies that reflect the constraints each instrument is expected to provide, along with ERBE (Earth Radiation Budget Experiment) data and a radiative transfer code, to study overall sensitivity to RSRF, helping us prepare for similar studies with new data from the EOS-era instruments.

Diurnal Forcing of Planetary Atmospheres

NASA Technical Reports Server (NTRS)

Houben, Howard C.

1997-01-01

Much progress has been made on calculations of the Martian seasonal water cycle using the Mars Climate Model developed for this purpose. Two papers, documenting the model and the water transport results obtained with it have been published in the Journal of Geophysical Research - Planets. An additional paper describing results related to the evolution of the seasonal water cycle as a result of orbital changes was published in Advances in Space Research. Since that time, further studies have concentrated on the consequences of the soil adsorption required to match the observed water cycle and its relation to the stability of ground ice and other potential water reservoirs. Earth-related studies have concentrated on incorporating an efficient and realistic microphysical model into the Ames Stratospheric General Circulation Model used to simulate the spread of the ML Pinatubo and other volcanic clouds in the stratosphere. In addition, visualizations of the simulations are being incorporated into a video describing the UARS mission. A paper describing the new stratospheric aerosol microphysics package (and its consequences for volcanic cloud evolution) will be submitted in the near future. The paper will discuss the relative importance of condensation and coagulation to early particle growth and the separation of the cloud by sedimentation of the larger particles. A more general paper which highlights the observation that particle number densities did not increase dramatically after the ML Pinatubo eruption is planned. Simulations of atmospheric transport will be extended to include studies of terrestrial tropospheric tracers using the Fifth-Generation Penn State/NCAR Mesoscale Model.

Insights into Aqueous-phase processing through Comparison of the Organic Chemical Composition of Atmospheric Particles and Cloud Water in the Southeast United States

NASA Astrophysics Data System (ADS)

Boone, E.; Laskin, J.; Laskin, A.; Wirth, C.; Shepson, P. B.; Stirm, B. H.; Pratt, K.

2014-12-01

Organic compounds comprise a significant mass fraction of submicron atmospheric particles with considerable contribution from secondary organic aerosol (SOA), a large fraction of which is formed from the oxidation of biogenic volatile organic compounds. Aqueous-phase reactions in particles and cloud droplets are suggested to increase SOA mass and change the chemical composition the particles following cloud evaporation. Aqueous-phase processing may also explain discrepancies between measurements and models. To gain a better understanding of these processes, cloud water and below-cloud atmospheric particles were collected onboard a research aircraft during the Southeast Oxidants and Aerosol Study (SOAS) over Alabama in June 2013. Nanospray desorption electrospray ionization (nano-DESI) and direct electrospray ionization (ESI) coupled with high resolution mass spectrometry were utilized to compare the organic molecular composition of the particle and cloud water samples, respectively. Several hundred unique compounds have been identified in the particle and cloud water samples, allowing possible aqueous-phase reactions to be examined. Hydrolysis of organosulfate compounds, aqueous-phase formation of nitrogen-containing compounds, and possible fragmentation of oligomeric compounds will be discussed, with comparisons to previous laboratory studies. This study provides insights into aqueous-phase reactions in ambient cloud droplets.

Chemical characterization of individual particles and residuals of cloud droplets and ice crystals collected on board research aircraft in the ISDAC 2008 study

NASA Astrophysics Data System (ADS)

Hiranuma, N.; Brooks, S. D.; Moffet, R. C.; Glen, A.; Laskin, A.; Gilles, M. K.; Liu, P.; MacDonald, A. M.; Strapp, J. W.; McFarquhar, G. M.

2013-06-01

Ambient particles and the dry residuals of mixed-phase cloud droplets and ice crystals were collected during the Indirect and Semi-Direct Aerosol Campaign (ISDAC) near Barrow, Alaska, in spring of 2008. The collected particles were analyzed using Computer Controlled Scanning Electron Microscopy with Energy Dispersive X-ray analysis and Scanning Transmission X-ray Microscopy coupled with Near Edge X-ray Absorption Fine Structure spectroscopy to identify physico-chemical properties that differentiate cloud-nucleating particles from the total aerosol population. A wide range of individually mixed components was identified in the ambient particles and residuals including organic carbon compounds, inorganics, carbonates, and black carbon. Our results show that cloud droplet residuals differ from the ambient particles in both size and composition, suggesting that both properties may impact the cloud-nucleating ability of aerosols in mixed-phase clouds. The percentage of residual particles which contained carbonates (47%) was almost four times higher than those in ambient samples. Residual populations were also enhanced in sea salt and black carbon and reduced in organic compounds relative to the ambient particles. Further, our measurements suggest that chemical processing of aerosols may improve their cloud-nucleating ability. Comparison of results for various time periods within ISDAC suggests that the number and composition of cloud-nucleating particles over Alaska can be influenced by episodic events bringing aerosols from both the local vicinity and as far away as Siberia.

Particle growth kinetics over the Amazon rainforest

NASA Astrophysics Data System (ADS)

Pinterich, T.; Andreae, M. O.; Artaxo, P.; Kuang, C.; Longo, K.; Machado, L.; Manzi, A. O.; Martin, S. T.; Mei, F.; Pöhlker, C.; Pöhlker, M. L.; Poeschl, U.; Shilling, J. E.; Shiraiwa, M.; Tomlinson, J. M.; Zaveri, R. A.; Wang, J.

2016-12-01

Aerosol particles larger than 100 nm play a key role in global climate by acting as cloud condensation nuclei (CCN). Most of these particles, originated from new particle formation or directly emitted into the atmospheric, are initially too small to serve as CCN. These small particles grow to CCN size mainly through condensation of secondary species. In one extreme, the growth is dictated by kinetic condensation of very low-volatility compounds, favoring the growth of the smallest particles; in the other extreme, the process is driven by Raoult's law-based equilibrium partitioning of semi-volatile organic compound, favoring the growth of larger particles. These two mechanisms can lead to very different production rates of CCN. The growth of particles depends on a number of parameters, including the volatility of condensing species, particle phase, and diffusivity inside the particles, and this process is not well understood in part due to lack of ambient data. Here we examine atmospheric particle growth using high-resolution size distributions measured onboard the DOE G-1 aircraft during GoAmazon campaign, which took place from January 2014 to December 2015 near Manaus, Brazil, a city surrounded by natural forest for over 1000 km in every direction. City plumes are clearly identified by the strong enhancement of nucleation and Aitken mode particle concentrations over the clean background. As the plume traveled downwind, particle growth was observed, and is attributed to condensation of secondary species and coagulation (Fig.1). Observed aerosol growth is modeled using MOSAIC (Model for Simulating Aerosol Interactions and Chemistry), which dynamically partitions multiple compounds to all particle size bins by taking into account compound volatility, gas-phase diffusion, interfacial mass accommodation, particle-phase diffusion, and particle-phase reaction. The results from both wet and dry seasons will be discussed.

Simultaneously inferring above-cloud absorbing aerosol optical thickness and underlying liquid phase cloud optical and microphysical properties using MODIS

NASA Astrophysics Data System (ADS)

Meyer, Kerry; Platnick, Steven; Zhang, Zhibo

2015-06-01

The regional haze over the southeast (SE) Atlantic Ocean induced by biomass burning in southern Africa can be problematic for passive imager-based retrievals of the underlying quasi-permanent marine boundary layer (MBL) clouds and for estimates of top-of-atmosphere (TOA) aerosol direct radiative effect (DRE). Here an algorithm is introduced to simultaneously retrieve above-cloud aerosol optical thickness (AOT), the cloud optical thickness (COT), and cloud effective particle radius (CER) of the underlying MBL clouds while also providing pixel-level estimates of retrieval uncertainty. This approach utilizes reflectance measurements at six Moderate Resolution Imaging Spectroradiometer (MODIS) channels from the visible to the shortwave infrared. Retrievals are run under two aerosol model assumptions on 8 years (2006-2013) of June-October Aqua MODIS data over the SE Atlantic, from which a regional cloud and above-cloud aerosol climatology is produced. The cloud retrieval methodology is shown to yield COT and CER consistent with those from the MODIS operational cloud product (MOD06) when forcing AOT to zero, while the full COT-CER-AOT retrievals that account for the above-cloud aerosol attenuation increase regional monthly mean COT and CER by up to 9% and 2%, respectively. Retrieved AOT is roughly 3 to 5 times larger than the collocated 532 nm Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) retrievals, though closer agreement is observed with the CALIOP 1064 nm retrievals, a result consistent with previous case study analyses. Regional cloudy-sky above-cloud aerosol DRE calculations are also performed that illustrate the importance of the aerosol model assumption and underlying cloud retrievals.

Integrated approach towards understanding interactions of mineral dust aerosol with warm clouds

NASA Astrophysics Data System (ADS)

Kumar, Prashant

2011-12-01

Mineral dust is ubiquitous in the atmosphere and represents a dominant type of particulate matter by mass. Dust particles can serve as cloud condensation nuclei (CCN), giant CCN (GCCN), or ice nuclei (IN), thereby, affecting cloud microphysics, albedo, and lifetime. Despite its well-recognized importance, assessments of dust impacts on clouds and climate remain highly uncertain. This thesis addresses the role of dust as CCN and GCCN with the goal of improving our understanding of dust-warm cloud interactions and their representation in climate models. Most studies to date focus on the soluble fraction of aerosol particles when describing cloud droplet nucleation, and overlook the interactions of the hydrophilic insoluble fraction with water vapor. A new approach to include such interactions (expressed by the process of water vapor adsorption) is explored, by combining multilayer Frenkel-Halsey-Hill (FHH) physical adsorption isotherm and curvature (Kelvin) effects. The importance of adsorption activation theory (FHH-AT) is corroborated by measurements of CCN activity of mineral aerosols generated from clays, calcite, quartz, and desert soil samples from Northern Africa, East Asia/China, and Northern America. A new aerosol generation setup for CCN measurements was developed based on a dry generation technique capable of reproducing natural dust aerosol emission. Based on the dependence of critical supersaturation with particle dry diameter, it is found that the FHH-AT is a better framework for describing fresh (and unprocessed) dust CCN activity than the classical Kohler theory (KT). Ion Chromatography (IC) measurements performed on fresh regional dust samples indicate negligible soluble fraction, and support that water vapor adsorption is the prime source of CCN activity in the dust. CCN measurements with the commonly used wet generated mineral aerosol (from atomization of a dust aqueous suspension) are also carried out. Results indicate that the method is subject to biases as it generates a bimodal size distribution with a broad range of hygroscopicity. It is found that smaller particles generated in the more hygroscopic peak follow CCN activation by KT, while the larger peak is less hydrophilic with activation similar to dry generated dust that follow FHH-AT. Droplet activation kinetics measurements demonstrate that dry generated mineral aerosol display retarded activation kinetics with an equivalent water vapor uptake coefficient that is 30 - 80% lower relative to ammonium sulfate aerosol. Wet generated mineral aerosols, however, display similar activation kinetics to ammonium sulfate. These results suggest that at least a monolayer of water vapor (the rate-limiting step for adsorption) persists during the timescale of aerosol generation in the experiment, and questions the atmospheric relevance of studies on mineral aerosol generated from wet atomization method. A new parameterization of cloud droplet formation from insoluble dust CCN for regional and global climate models is also developed. The parameterization framework considers cloud droplet formation from dust CCN activating via FHH-AT, and soluble aerosol with activation described through KT. The parameterization is validated against a numerical parcel model, agreeing with predictions to within 10% (R2 ˜ 0.98). The potential role of dust GCCN activating by FHH-AT within warm stratocumulus and convective clouds is also evaluated. It is found that under pristine aerosol conditions, dust GCCN can act as collector drops with implications to dust-cloud-precipitation linkages. Biases introduced from describing dust GCCN activation by KT are also addressed. The results demonstrate that dust particles do not require deliquescent material to act as CCN in the atmosphere. Furthermore, the impact of dust particles as giant CCN on warm cloud and precipitation must be considered. Finally, the new parameterization of cloud droplet formation can be implemented in regional and global models providing an improved treatment of mineral aerosol on clouds and precipitation. The new framework is uniquely placed to address dust aerosol indirect effects on climate.

AP-Cloud: Adaptive particle-in-cloud method for optimal solutions to Vlasov–Poisson equation

DOE PAGES

Wang, Xingyu; Samulyak, Roman; Jiao, Xiangmin; ...

2016-04-19

We propose a new adaptive Particle-in-Cloud (AP-Cloud) method for obtaining optimal numerical solutions to the Vlasov–Poisson equation. Unlike the traditional particle-in-cell (PIC) method, which is commonly used for solving this problem, the AP-Cloud adaptively selects computational nodes or particles to deliver higher accuracy and efficiency when the particle distribution is highly non-uniform. Unlike other adaptive techniques for PIC, our method balances the errors in PDE discretization and Monte Carlo integration, and discretizes the differential operators using a generalized finite difference (GFD) method based on a weighted least square formulation. As a result, AP-Cloud is independent of the geometric shapes ofmore » computational domains and is free of artificial parameters. Efficient and robust implementation is achieved through an octree data structure with 2:1 balance. We analyze the accuracy and convergence order of AP-Cloud theoretically, and verify the method using an electrostatic problem of a particle beam with halo. Here, simulation results show that the AP-Cloud method is substantially more accurate and faster than the traditional PIC, and it is free of artificial forces that are typical for some adaptive PIC techniques.« less

New particle formation leads to cloud dimming

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sullivan, Ryan C.; Crippa, Paola; Matsui, Hitoshi

New particle formation (NPF), nucleation of condensable vapors to the solid or liquid phase, is a significant source of atmospheric aerosol particle number concentrations. With sufficient growth, these nucleated particles may be a significant source of cloud condensation nuclei (CCN), thus altering cloud albedo, structure, and lifetimes, and insolation reaching the Earth's surface. Herein we present one of the first numerical experiments to quantify the impact of NPF on cloud radiative properties that is conducted at a convection permitting resolution and that explicitly simulates cloud droplet number concentrations. Consistent with observations, these simulations suggest that in spring over the Midwesternmore » U.S.A., NPF occurs frequently and on regional scales. However, the simulations suggest that NPF is not associated with enhancement of regional cloud albedos as would be expected from an increase of CCN. These simulations indicate that NPF reduces ambient sulfuric acid concentrations sufficiently to inhibit growth of preexisting particles to CCN sizes. This reduction in CCN-sized particles reduces cloud albedo, resulting in a domain average positive top of atmosphere cloud radiative forcing of 10 W m-2 and up to ~ 50 W m-2 in individual grid cells relative to a simulation in which NPF is excluded.« less

Strong control of Southern Ocean cloud reflectivity by ice-nucleating particles.

PubMed

Vergara-Temprado, Jesús; Miltenberger, Annette K; Furtado, Kalli; Grosvenor, Daniel P; Shipway, Ben J; Hill, Adrian A; Wilkinson, Jonathan M; Field, Paul R; Murray, Benjamin J; Carslaw, Ken S

2018-03-13

Large biases in climate model simulations of cloud radiative properties over the Southern Ocean cause large errors in modeled sea surface temperatures, atmospheric circulation, and climate sensitivity. Here, we combine cloud-resolving model simulations with estimates of the concentration of ice-nucleating particles in this region to show that our simulated Southern Ocean clouds reflect far more radiation than predicted by global models, in agreement with satellite observations. Specifically, we show that the clouds that are most sensitive to the concentration of ice-nucleating particles are low-level mixed-phase clouds in the cold sectors of extratropical cyclones, which have previously been identified as a main contributor to the Southern Ocean radiation bias. The very low ice-nucleating particle concentrations that prevail over the Southern Ocean strongly suppress cloud droplet freezing, reduce precipitation, and enhance cloud reflectivity. The results help explain why a strong radiation bias occurs mainly in this remote region away from major sources of ice-nucleating particles. The results present a substantial challenge to climate models to be able to simulate realistic ice-nucleating particle concentrations and their effects under specific meteorological conditions. Copyright © 2018 the Author(s). Published by PNAS.

AP-Cloud: Adaptive Particle-in-Cloud method for optimal solutions to Vlasov–Poisson equation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Xingyu; Samulyak, Roman, E-mail: roman.samulyak@stonybrook.edu; Computational Science Initiative, Brookhaven National Laboratory, Upton, NY 11973

We propose a new adaptive Particle-in-Cloud (AP-Cloud) method for obtaining optimal numerical solutions to the Vlasov–Poisson equation. Unlike the traditional particle-in-cell (PIC) method, which is commonly used for solving this problem, the AP-Cloud adaptively selects computational nodes or particles to deliver higher accuracy and efficiency when the particle distribution is highly non-uniform. Unlike other adaptive techniques for PIC, our method balances the errors in PDE discretization and Monte Carlo integration, and discretizes the differential operators using a generalized finite difference (GFD) method based on a weighted least square formulation. As a result, AP-Cloud is independent of the geometric shapes ofmore » computational domains and is free of artificial parameters. Efficient and robust implementation is achieved through an octree data structure with 2:1 balance. We analyze the accuracy and convergence order of AP-Cloud theoretically, and verify the method using an electrostatic problem of a particle beam with halo. Simulation results show that the AP-Cloud method is substantially more accurate and faster than the traditional PIC, and it is free of artificial forces that are typical for some adaptive PIC techniques.« less

AP-Cloud: Adaptive particle-in-cloud method for optimal solutions to Vlasov–Poisson equation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Xingyu; Samulyak, Roman; Jiao, Xiangmin

We propose a new adaptive Particle-in-Cloud (AP-Cloud) method for obtaining optimal numerical solutions to the Vlasov–Poisson equation. Unlike the traditional particle-in-cell (PIC) method, which is commonly used for solving this problem, the AP-Cloud adaptively selects computational nodes or particles to deliver higher accuracy and efficiency when the particle distribution is highly non-uniform. Unlike other adaptive techniques for PIC, our method balances the errors in PDE discretization and Monte Carlo integration, and discretizes the differential operators using a generalized finite difference (GFD) method based on a weighted least square formulation. As a result, AP-Cloud is independent of the geometric shapes ofmore » computational domains and is free of artificial parameters. Efficient and robust implementation is achieved through an octree data structure with 2:1 balance. We analyze the accuracy and convergence order of AP-Cloud theoretically, and verify the method using an electrostatic problem of a particle beam with halo. Here, simulation results show that the AP-Cloud method is substantially more accurate and faster than the traditional PIC, and it is free of artificial forces that are typical for some adaptive PIC techniques.« less

Remote sensing of smoke, clouds, and fire using AVIRIS data

NASA Technical Reports Server (NTRS)

Gao, Bo-Cai; Kaufman, Yorman J.; Green, Robert O.

1993-01-01

Clouds remain the greatest element of uncertainty in predicting global climate change. During deforestation and biomass burning processes, a variety of atmospheric gases, including CO2 and SO2, and smoke particles are released into the atmosphere. The smoke particles can have important effects on the formation of clouds because of the increased concentration of cloud condensation nuclei. They can also affect cloud albedo through changes in cloud microphysical properties. Recently, great interest has arisen in understanding the interaction between smoke particles and clouds. We describe our studies of smoke, clouds, and fire using the high spatial and spectral resolution data acquired with the NASA/JPL Airborne Visible/Infrared Imaging Spectrometer (AVIRIS).

Comparison Between CCCM and CloudSat Radar-Lidar (RL) Cloud and Radiation Products

NASA Technical Reports Server (NTRS)

Ham, Seung-Hee; Kato, Seiji; Rose, Fred G.; Sun-Mack, Sunny

2015-01-01

To enhance cloud properties, LaRC and CIRA developed each combination algorithm for obtained properties from passive, active and imager in A-satellite constellation. When comparing global cloud fraction each other, LaRC-produced CERES-CALIPSO-CloudSat-MODIS (CCCM) products larger low-level cloud fraction over tropic ocean, while CIRA-produced Radar-Lidar (RL) shows larger mid-level cloud fraction for high latitude region. The reason for different low-level cloud fraction is due to different filtering method of lidar-detected cloud layers. Meanwhile difference in mid-level clouds is occurred due to different priority of cloud boundaries from lidar and radar.

A cloud/particle model of the interstellar medium - Galactic spiral structure

NASA Technical Reports Server (NTRS)

Levinson, F. H.; Roberts, W. W., Jr.

1981-01-01

A cloud/particle model for gas flow in galaxies is developed that incorporates cloud-cloud collisions and supernovae as dominant local processes. Cloud-cloud collisions are the main means of dissipation. To counter this dissipation and maintain local dispersion, supernova explosions in the medium administer radial snowplow pushes to all nearby clouds. The causal link between these processes is that cloud-cloud collisions will form stars and that these stars will rapidly become supernovae. The cloud/particle model is tested and used to investigate the gas dynamics and spiral structures in galaxies where these assumptions may be reasonable. Particular attention is given to whether large-scale galactic shock waves, which are thought to underlie the regular well-delineated spiral structure in some galaxies, form and persist in a cloud-supernova dominated interstellar medium; this question is answered in the affirmative.

A new airborne sampler for interstitial particles in ice and liquid clouds

NASA Astrophysics Data System (ADS)

Moharreri, A.; Craig, L.; Rogers, D. C.; Brown, M.; Dhaniyala, S.

2011-12-01

In-situ measurements of cloud droplets and aerosols using aircraft platforms are required for understanding aerosol-cloud processes and aiding development of improved aerosol-cloud models. A variety of clouds with different temperature ranges and cloud particle sizes/phases must be studied for comprehensive knowledge about the role of aerosols in the formation and evolution of cloud systems under different atmospheric conditions. While representative aerosol measurements are regularly made from aircrafts under clear air conditions, aerosol measurements in clouds are often contaminated by the generation of secondary particles from the high speed impaction of ice particles and liquid droplets on the surfaces of the aircraft probes/inlets. A new interstitial particle sampler, called the blunt-body aerosol sampler (BASE) has been designed and used for aerosol sampling during two recent airborne campaigns using NCAR/NSF C-130 aircraft: PLOWS (2009-2010) and ICE-T (2011). Central to the design of the new interstitial inlet is an upstream blunt body housing that acts to shield/deflect large cloud droplets and ice particles from an aft sampling region. The blunt-body design also ensures that small shatter particles created from the impaction of cloud-droplets on the blunt-body are not present in the aft region where the interstitial inlet is located. Computational fluid dynamics (CFD) simulations along with particle transport modeling and wind tunnel studies have been utilized in different stages of design and development of this inlet. The initial flights tests during the PLOWS campaign showed that the inlet had satisfactory performance only in warm clouds and when large precipitation droplets were absent. In the presence of large droplets and ice, the inlet samples were contaminated with significant shatter artifacts. These initial results were reanalyzed in conjunction with a computational droplet shatter model and the numerical results were used to arrive at an improved sampler design. Analysis of the data from the recent ICE-T campaign with the improved sampler design shows that the modified version of BASE can provide shatter-artifact free sampling of aerosol particles in the presence of ice particles and significantly reduced shatter artifacts in warm clouds. Detailed design and modeling aspects of the sampler will be discussed and the sampler performance in warm and cold clouds will be presented and compared with measurements made using other aerosol inlets flown on the NCAR/NSF C-130 aircraft.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jian; Krejci, Radovan; Giangrande, Scott

A necessary prerequisite of cloud formation, aerosol particles represent one of the largest uncertainties in computer simulations of climate change1,2, in part because of a poor understanding of processes under natural conditions3,4. The Amazon rainforest is one of the few continental regions where aerosol particles and their precursors can be studied under near-natural conditions5-7. Cloud condensation nuclei (CCN) in clean Amazonia are mostly produced by the growth of smaller particles in the boundary layer8-10, whereas these smaller particles themselves 31 appear to be produced elsewhere5,11. Key questions are in what part of the atmosphere they might 32 be produced andmore » what could be the transport processes that deliver them to the boundary layer, where they grow into CCN. Here, using recent aircraft measurements above central Amazonia, we show high concentrations of small particles in the lower free troposphere. The particle size spectrum shifts towards larger sizes with decreasing altitude, implying particle growth as air descends from the free troposphere towards Earth's surface. Complementary measurements at ground sites show that free tropospheric air having high concentrations of small particles (diameters of less than 50 nm) is transported into the boundary layer during precipitation events, both by strong convective downdrafts and by weaker downward motions in the trailing stratiform region. This vertical transport helps maintain the population of small particles and ultimately CCN in the boundary layer, thereby playing an important role in controlling the climate state under natural conditions. In contrast, this mechanism becomes masked under polluted conditions, which sometimes prevail at times in Amazonia as well as over other tropical continental regions5,12.« less

The structure of particle cloud premixed flames

NASA Technical Reports Server (NTRS)

Seshadri, K.; Berlad, A. L.

1992-01-01

The structure of premixed flames propagating in combustible systems containing uniformly distributed volatile fuel particles in an oxidizing gas mixture is analyzed. This analysis is motivated by experiments conducted at NASA Lewis Research Center on the structure of flames propagating in combustible mixtures of lycopodium particles and air. Several interesting modes of flame propagation were observed in these experiments depending on the number density and the initial size of the fuel particle. The experimental results show that steady flame propagation occurs even if the initial equivalence ratio of the combustible mixture based on the gaseous fuel available in the particles, phi sub u, is substantially larger than unity. A model is developed to explain these experimental observations. In the model, it is presumed that the fuel particles vaporize first to yield a gaseous fuel of known chemical composition which then reacts with oxygen in a one-step overall process. The activation energy of the chemical reaction is presumed to be large. The activation energy characterizing the kinetics of vaporization is also presumed to be large. The equations governing the structure of the flame were integrated numerically. It is shown that the interplay of vaporization kinetics and oxidation process can result in steady flame propagation in combustible mixtures where the value of phi sub u is substantially larger than unity. This prediction is in agreement with experimental observations.

Thermodynamic Conditions Favorable to Superlative Thunderstorm Updraft, Mixed Phase Microphysics and Lightning Flash Rate. Revised

NASA Technical Reports Server (NTRS)

Williams, E.; Mushtak, V.; Rosenfeld, D.; Goodman, S.; Boccippio, D.

2004-01-01

Satellite observations of lightning flash rate have been merged with proximal surface station thermodynamic observations toward improving the understanding of the response of the updraft and lightning activity in the tropical atmosphere to temperature. The tropical results have led in turn to an examination of thermodynamic climatology over the continental United States in summertime and its comparison with exceptional electrical conditions documented in earlier studies. The tropical and mid-latitude results taken together support an important role for cloud base height in regulating the transfer of Convective Available Potential Energy (CAPE) to updraft kinetic energy in thunderstorms. In the tropics, cloud base height is dominated by the dry bulb temperature over the wet bulb temperature as the lightning-regulating temperature in regions characterized by moist convection. In the extratropics, an elevated cloud base height may enable larger cloud water concentrations in the mixed phase region, a favorable condition for the positive charging of large ice particles that may result in thunderclouds with a reversed polarity of the main cloud dipole. The combined requirements of instability and cloud base height serve to confine the region of superlative electrification to the vicinity of the ridge in moist entropy in the western Great Plains.

The relation between pre-eruptive bubble size distribution, ash particle morphology, and their internal density: Implications to volcanic ash transport and dispersion models

NASA Astrophysics Data System (ADS)

Proussevitch, Alexander

2014-05-01

Parameterization of volcanic ash transport and dispersion (VATD) models strongly depends on particle morphology and their internal properties. Shape of ash particles affects terminal fall velocities (TFV) and, mostly, dispersion. Internal density combined with particle size has a very strong impact on TFV and ultimately on the rate of ash cloud thinning and particle sedimentation on the ground. Unlike other parameters, internal particle density cannot be measured directly because of the micron scale sizes of fine ash particles, but we demonstrate that it varies greatly depending on the particle size. Small simple type ash particles (fragments of bubble walls, 5-20 micron size) do not contain whole large magmatic bubbles inside and their internal density is almost the same as that of volcanic glass matrix. On the other side, the larger compound type ash particles (>40 microns for silicic fine ashes) always contain some bubbles or the whole spectra of bubble size distribution (BSD), i.e. bubbles of all sizes, bringing their internal density down as compared to simple ash. So, density of the larger ash particles is a function of the void fraction inside them (magmatic bubbles) which, in turn, is controlled by BSD. Volcanic ash is a product of the fragmentation of magmatic foam formed by pre-eruptive bubble population and characterized by BSD. The latter can now be measured from bubble imprints on ash particle surfaces using stereo-scanning electron microscopy (SSEM) and BubbleMaker software developed at UNH, or using traditional high-resolution X-Ray tomography. In this work we present the mathematical and statistical formulation for this problem connecting internal ash density with particle size and BSD, and demonstrate how the TFV of the ash population is affected by variation of particle density.

Mass spectrometric airborne measurements of submicron aerosol and cloud residual composition in tropic deep convection during ACRIDICON-CHUVA

NASA Astrophysics Data System (ADS)

Schulz, Christiane; Schneider, Johannes; Mertes, Stephan; Kästner, Udo; Weinzierl, Bernadett; Sauer, Daniel; Fütterer, Daniel; Walser, Adrian; Borrmann, Stephan

2015-04-01

Airborne measurements of submicron aerosol and cloud particles were conducted in the region of Manaus (Amazonas, Brazil) during the ACRIDICON-CHUVA campaign in September 2014. ACRIDICON-CHUVA aimed at the investigation of convective cloud systems in order to get a better understanding and quantification of aerosol-cloud-interactions and radiative effects of convective clouds. For that, data from airborne measurements within convective cloud systems are combined with satellite and ground-based data. We used a C-ToF-AMS (Compact-Time-of-Flight-Aerosol-Mass-Spectrometer) to obtain information on aerosol composition and vertical profiles of different aerosol species, like organics, sulphate, nitrate, ammonium and chloride. The instrument was operated behind two different inlets: The HASI (HALO Aerosol Submicrometer Inlet) samples aerosol particles, whereas the CVI (Counterflow Virtual Impactor) samples cloud droplets and ice particles during in-cloud measurements, such that cloud residual particles can be analyzed. Differences in aerosol composition inside and outside of clouds and cloud properties over forested or deforested region were investigated. Additionally, the in- and outflow of convective clouds was sampled on dedicated cloud missions in order to study the evolution of the clouds and the processing of aerosol particles. First results show high organic aerosol mass concentrations (typically 15 μg/m3 and during one flight up to 25 μg/m3). Although high amounts of organic aerosol in tropic air over rainforest regions were expected, such high mass concentrations were not anticipated. Next to that, high sulphate aerosol mass concentrations (about 4 μg/m3) were measured at low altitudes (up to 5 km). During some flights organic and nitrate aerosol was observed with higher mass concentrations at high altitudes (10-12 km) than at lower altitudes, indicating redistribution of boundary layer particles by convection. The cloud residuals measured during in-cloud sampling through the CVI contained mainly organic material and, to a lesser extent, nitrate.

Planetary astronomy

NASA Technical Reports Server (NTRS)

1976-01-01

Color and spectral data from spectrometer observations and computerized analyses of asteroid spectra are discussed. Potential occultations of bright asteroids by the moon are summarized. Analysis of anisotropic scattering within Saturn's rings indicates that mineral contamination of the 120 particles cannot exceed 5 percent by weight, and that the rings formed from particle breakup rather than from particle condensation. Raman probe applications to Jupiter and Uranus atmospheres indicate the presence of aerosol particles. A review of Mariner 9 Mars cloud topography data establishes that most blue clouds are orographic uplift clouds composed of condensates, and that sporadic red clouds are associated with blue clouds or volcanoes and thus probably do not represent dust storm phenomena.

GASP cloud- and particle-encounter statistics and their application to LFC aircraft studies. Volume 2: Appendixes

NASA Technical Reports Server (NTRS)

Jasperson, W. H.; Nastron, G. D.; Davis, R. E.; Holdeman, J. D.

1984-01-01

Summary studies are presented for the entire cloud observation archive from the NASA Global Atmospheric Sampling Program (GASP). Studies are also presented for GASP particle-concentration data gathered concurrently with the cloud observations. Cloud encounters are shown on about 15 percent of the data samples overall, but the probability of cloud encounter is shown to vary significantly with altitude, latitude, and distance from the tropopause. Several meteorological circulation features are apparent in the latitudinal distribution of cloud cover, and the cloud-encounter statistics are shown to be consistent with the classical mid-latitude cyclone model. Observations of clouds spaced more closely than 90 minutes are shown to be statistically dependent. The statistics for cloud and particle encounter are utilized to estimate the frequency of cloud encounter on long-range airline routes, and to assess the probability and extent of laminaar flow loss due to cloud or particle encounter by aircraft utilizing laminar flow control (LFC). It is shown that the probability of extended cloud encounter is too low, of itself, to make LFC impractical. This report is presented in two volumes. Volume I contains the narrative, analysis, and conclusions. Volume II contains five supporting appendixes.

Temperature uniformity in the CERN CLOUD chamber

NASA Astrophysics Data System (ADS)

Dias, António; Ehrhart, Sebastian; Vogel, Alexander; Williamson, Christina; Almeida, João; Kirkby, Jasper; Mathot, Serge; Mumford, Samuel; Onnela, Antti

2017-12-01

The CLOUD (Cosmics Leaving OUtdoor Droplets) experiment at CERN (European Council for Nuclear Research) investigates the nucleation and growth of aerosol particles under atmospheric conditions and their activation into cloud droplets. A key feature of the CLOUD experiment is precise control of the experimental parameters. Temperature uniformity and stability in the chamber are important since many of the processes under study are sensitive to temperature and also to contaminants that can be released from the stainless steel walls by upward temperature fluctuations. The air enclosed within the 26 m3 CLOUD chamber is equipped with several arrays (strings) of high precision, fast-response thermometers to measure its temperature. Here we present a study of the air temperature uniformity inside the CLOUD chamber under various experimental conditions. Measurements were performed under calibration conditions and run conditions, which are distinguished by the flow rate of fresh air and trace gases entering the chamber at 20 and up to 210 L min-1, respectively. During steady-state calibration runs between -70 and +20 °C, the air temperature uniformity is better than ±0.06 °C in the radial direction and ±0.1 °C in the vertical direction. Larger non-uniformities are present during experimental runs, depending on the temperature control of the make-up air and trace gases (since some trace gases require elevated temperatures until injection into the chamber). The temperature stability is ±0.04 °C over periods of several hours during either calibration or steady-state run conditions. During rapid adiabatic expansions to activate cloud droplets and ice particles, the chamber walls are up to 10 °C warmer than the enclosed air. This results in temperature differences of ±1.5 °C in the vertical direction and ±1 °C in the horizontal direction, while the air returns to its equilibrium temperature with a time constant of about 200 s.

Interannual Variations in Aerosol Sources and Their Impact on Orographic Precipitation over California's Central Sierra Nevada

NASA Astrophysics Data System (ADS)

Creamean, J.; Ault, A. P.; White, A. B.; Neiman, P. J.; Minnis, P.; Prather, K. A.

2014-12-01

Aerosols that serve as cloud condensation nuclei (CCN) and ice nuclei (IN) have the potential to profoundly influence precipitation processes. Furthermore, changes in orographic precipitation have broad implications for reservoir storage and flood risks. As part of the CalWater I field campaign (2009-2011), the impacts of aerosol sources on precipitation were investigated in the California Sierra Nevada Mountains. In 2009, the precipitation collected on the ground was influenced by both local biomass burning and long-range transported dust and biological particles, while in 2010, by mostly local sources of biomass burning and pollution, and in 2011 by mostly long-range transport of dust and biological particles from distant sources. Although vast differences in the sources of residues were observed from year-to-year, dust and biological residues were omnipresent (on average, 55% of the total residues combined) and were associated with storms consisting of deep convective cloud systems and larger quantities of precipitation initiated in the ice phase. Further, biological residues were dominant during storms with relatively warm cloud temperatures (up to -15°C), suggesting biological components were more efficient IN than mineral dust. On the other hand, when precipitation quantities were lower, local biomass burning and pollution residues were observed (on average 31% and 9%, respectively), suggesting these residues potentially served as CCN at the base of shallow cloud systems and that lower level polluted clouds of storm systems produced less precipitation than non-polluted (i.e., marine) clouds. The direct connection of the sources of aerosols within clouds and precipitation type and quantity can be used in models to better assess how local emissions versus long-range transported dust and biological aerosols play a role in impacting regional weather and climate, ultimately with the goal of more accurate predictive weather forecast models and water resource management.

PHIPS-HALO: the airborne Particle Habit Imaging and Polar Scattering probe - Part 1: Design and operation

NASA Astrophysics Data System (ADS)

Abdelmonem, Ahmed; Järvinen, Emma; Duft, Denis; Hirst, Edwin; Vogt, Steffen; Leisner, Thomas; Schnaiter, Martin

2016-07-01

The number and shape of ice crystals present in mixed-phase and ice clouds influence the radiation properties, precipitation occurrence and lifetime of these clouds. Since clouds play a major role in the climate system, influencing the energy budget by scattering sunlight and absorbing heat radiation from the earth, it is necessary to investigate the optical and microphysical properties of cloud particles particularly in situ. The relationship between the microphysics and the single scattering properties of cloud particles is usually obtained by modelling the optical scattering properties from in situ measurements of ice crystal size distributions. The measured size distribution and the assumed particle shape might be erroneous in case of non-spherical ice particles. There is a demand to obtain both information correspondently and simultaneously for individual cloud particles in their natural environment. For evaluating the average scattering phase function as a function of ice particle habit and crystal complexity, in situ measurements are required. To this end we have developed a novel airborne optical sensor (PHIPS-HALO) to measure the optical properties and the corresponding microphysical parameters of individual cloud particles simultaneously. PHIPS-HALO has been tested in the AIDA cloud simulation chamber and deployed in mountain stations as well as research aircraft (HALO and Polar 6). It is a successive version of the laboratory prototype instrument PHIPS-AIDA. In this paper we present the detailed design of PHIPS-HALO, including the detection mechanism, optical design, mechanical construction and aerodynamic characterization.

Selection of quasi-monodisperse super-micron aerosol particles

NASA Astrophysics Data System (ADS)

Rösch, Michael; Pfeifer, Sascha; Wiedensohler, Alfred; Stratmann, Frank

2014-05-01

Size-segregated quasi monodisperse particles are essential for e.g. fundamental research concerning cloud microphysical processes. Commonly a DMA (Differential Mobility Analyzer) is used to produce quasi-monodisperse submicron particles. Thereto first, polydisperse aerosol particles are bipolarly charged by a neutralizer, and then selected according to their electrical mobility with the DMA [Knutson et al. 1975]. Selecting a certain electrical mobility with a DMA results in a particle size distribution, which contains singly charged particles as well as undesired multiply charged larger particles. Often these larger particles need to either be removed from the generated aerosol or their signals have to be corrected for in the data inversion and interpretation process. This problem becomes even more serious when considering super-micron particles. Here we will present two different techniques for generating quasi-monodisperse super-micron aerosol particles with no or only an insignificant number of larger sized particles being present. First, we use a combination of a cyclone with adjustable aerodynamic cut-off diameter and our custom-built Maxi-DMA [Raddatz et al. 2013]. The cyclone removes particles larger than the desired ones prior to mobility selection with the DMA. This results in a reduction of the number of multiply charged particles of up to 99.8%. Second, we utilize a new combination of cyclone and PCVI (Pumped Counterflow Virtual Impactor), which is based on purely inertial separation and avoids particle charging. The PCVI instrument was previously described by Boulter et al. (2006) and Kulkarni et al. (2011). With our two setups we are able to produce quasi-monodisperse aerosol particles in the diameter range from 0.5 to 4.4 µm without a significant number of larger undesired particles being present. Acknowledgements: This work was done within the framework of the DFG funded Ice Nucleation research UnIT (INUIT, FOR 1525) under WE 4722/1-1. References: Knutson, E. O. and Whitby, K. T.: Aerosol classification by electric mobility: apparatus, theory, and applications. Aerosol Science, 6:443--451, 1975 Raddatz, M., Wiedensohler, A., Wex, H., and Stratmann, F.: Size selection of sub- and super-micron clay mineral kaolinite particles using a custom-built Maxi-DMA. Nucleation and Atmospheric Aerosols, Vol. 1527, AIP Conference Proceedings, pages 457-460. AMER INST PHYSICS, 2013 Boulter, J. E., Cziczo, D. J., Middlebrook, A. M., Thomson, D. S., and Murphy, D. M.: Design and performance of a Pumped Counterflow Virtual Impactor. Aerosol Science and Technology, 40(11): 969-976, 2006 Kulkarni, G., Pekour, M., Afchine, A., Murphy, D. M., and Cziczo, D. J.: Comparison of experimental and numerical studies of the performance characteristics of a pumped counterflow virtual impactor. Aerosol Science and Technology, 45:382-392, 2011

In-Situ Characterization of Cloud Condensation Nuclei, Interstitial, and background Particles using Single Particle Mass Spectrometer, SPLAT II

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zelenyuk, Alla; Imre, D.; Earle, Michael

2010-10-01

Aerosol indirect effect remains the most uncertain aspect of climate change modeling because proper test requires knowledge of individual particles sizes and compositions with high spatial and temporal resolution. We present the first deployment of a single particle mass spectrometer (SPLAT II) that is operated in a dual data acquisition mode to measure all the required individual particle properties with sufficient temporal resolution to definitively resolve the aerosol-cloud interaction in this exemplary case. We measured particle number concentrations, asphericity, and individual particle size, composition, and density with better than 60 seconds resolution. SPLAT II measured particle number concentrations between 70more » particles cm-3and 300 particles cm-3, an average particle density of 1.4 g cm-3. Found that most particles are composed of oxygenated organics, many of which are mixed with sulfates. Biomass burn particles some with sulfates were prevalent, particularly at higher altitudes, and processed sea-salt was observed over the ocean. Analysis of cloud residuals shows that with time cloud droplets acquire sulfate by the reaction of peroxide with SO2. Based on the particle mass spectra and densities we find that the compositions of cloud condensation nuclei are similar to those of background aerosol but, contain on average ~7% more sulfate, and do not include dust and metallic particles. A comparison between the size distributions of background, activated, and interstitial particles shows that while nearly none of the activated particles is smaller than 115 nm, more than 80% of interstitial particles are smaller than 115 nm. We conclude that for this cloud the most important difference between CCN and background aerosol is particle size although having more sulfate also helps.« less

Mixed Calcium Dust and Carbonaceous Particles from Asia Contributing to Precipitation Changes in California

NASA Astrophysics Data System (ADS)

Kristensen, L.; Cornwell, G.; Sedlacek, A. J., III; Prather, K. A.

2016-12-01

Mineral dust particles can serve as cloud condensation nuclei (CCN), with enhanced CCN activity observed when the dust is mixed with additional soluble species. Long range atmospheric transport can change the composition of dust particles through aging, cloud processing and mixing with other particles. The CalWater2 campaign measured single particles and cloud dynamics to investigate the influence aerosols have on the hydrological cycle in California. An Aircraft Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) was used to characterize and identify single particles within clouds potentially acting as ice and cloud nuclei. Two matching flights over California's mountains in March 2015 detected significantly different particle types that resulted in different precipitation totals. Calcium dust dominated the particle composition during the first flight which had an observed decrease in orographic precipitation. Particle composition and air mass back trajectories indicate an Asian desert origin. The calcium dust particles contained secondary acids, in particular oxalic acid, acquired during transport from Asia to California. This chemical processing likely increased the solubility of the dust, enabling the particles to act as more effective CCN. The chemical composition also showed oligomeric carbonaceous species were mixed with the calcium dust particles, potentially further increasing the solubility the particles. A single particle soot photometer (SP2) measured black carbon concurrently and returned intense incandescence when calcium dust was present, confirming the calcium dust particles were internally mixed with a carbonaceous species. Dust particles were greatly reduced during the second flight with local biomass burning particles the dominant type. Observed precipitation in California were within forecast levels during the second flight. These single particle measurements from CalWater2 show that dust particles from Asia can affect cloud process and thus precipitation in California.

Characterization of Individual Aerosol Particles Associated with Clouds (CRYSTAL-FACE)

NASA Technical Reports Server (NTRS)

Buseck, Peter R.

2004-01-01

The aim of our research was to obtain data on the chemical and physical properties of individual aerosol particles from near the bottoms and tops of the deep convective systems that lead to the generation of tropical cirrus clouds and to provide insights into the particles that serve as CCN or IN. We used analytical transmission electron microscopy (ATEM), including energy-dispersive X-ray spectrometry (EDS) and electron energy-loss spectroscopy (EELS), and field-emission electron microscopy (FESEM) to compare the compositions, concentrations, size distributions, shapes, surface coatings, and degrees of aggregation of individual particles from cloud bases and the anvils near the tropopause. Aggregates of sea salt and mineral dust, ammonium sulfate, and soot particles are abundant in in-cloud samples. Cirrus samples contain many H2SO4 droplets, but acidic sulfate particles are rare at the cloud bases. H2SO4 probably formed at higher altitudes through oxidation of SO2 in cloud droplets. The relatively high extent of ammoniation in the upper troposphere in-cloud samples appears to have resulted from vertical transport by strong convection. The morphology of H2SO4 droplets indicates that they had been at least yartiy ammoniated at the time of collection. They are internally mixed with organic materials, metal sulfates, and solid particles of various compositions. Ammoniation and internal mixing of result in freezing at higher temperature than in pure H2SO4 aerosols. K- and S-bearing organic particles and Si-Al-rich particles are common throughout. Sea salt and mineral dust were incorporated into the convective systems from the cloud bases and worked as ice nuclei while being vertically transported. The nonsulfate particles originated from the lower troposphere and were transported to the upper troposphere and lower stratosphere.

Strong Deformation of the Thick Electric Double Layer around a Charged Particle during Sedimentation or Electrophoresis.

PubMed

Khair, Aditya S

2018-01-23

The deformation of the electric double layer around a charged colloidal particle during sedimentation or electrophoresis in a binary, symmetric electrolyte is studied. The surface potential of the particle is assumed to be small compared to the thermal voltage scale. Additionally, the Debye length is assumed to be large compared to the particle size. These assumptions enable a linearization of the electrokinetic equations. The particle appears as a point charge in this thick-double-layer limit; the distribution of charge in the diffuse cloud surrounding it is determined by a balance of advection due to the particle motion, Brownian diffusion of ions, and electrostatic screening of the particle by the cloud. The ability of advection to deform the charge cloud from its equilibrium state is parametrized by a Péclet number, Pe. For weak advection (Pe ≪ 1), the cloud is only slightly deformed. In contrast, the cloud can be completely stripped from the particle at Pe ≫ 1; consequently, electrokinetic effects on the particle motion vanish in this regime. Therefore, in sedimentation the drag limits to Stokes' law for an uncharged particle as Pe → ∞. Likewise, the particle velocity for electrophoresis approaches Huckel's result. The strongly deformed cloud at large Pe is predicted to generate a concomitant increase in the sedimentation field in a dilute settling suspension.

Individual aerosol particles in ambient and updraft conditions below convective cloud bases in the Oman mountain region

NASA Astrophysics Data System (ADS)

Semeniuk, T. A.; Bruintjes, R. T.; Salazar, V.; Breed, D. W.; Jensen, T. L.; Buseck, P. R.

2014-03-01

An airborne study of cloud microphysics provided an opportunity to collect aerosol particles in ambient and updraft conditions of natural convection systems for transmission electron microscopy (TEM). Particles were collected simultaneously on lacey carbon and calcium-coated carbon (Ca-C) TEM grids, providing information on particle morphology and chemistry and a unique record of the particle's physical state on impact. In total, 22 particle categories were identified, including single, coated, aggregate, and droplet types. The fine fraction comprised up to 90% mixed cation sulfate (MCS) droplets, while the coarse fraction comprised up to 80% mineral-containing aggregates. Insoluble (dry), partially soluble (wet), and fully soluble particles (droplets) were recorded on Ca-C grids. Dry particles were typically silicate grains; wet particles were mineral aggregates with chloride, nitrate, or sulfate components; and droplets were mainly aqueous NaCl and MCS. Higher numbers of droplets were present in updrafts (80% relative humidity (RH)) compared with ambient conditions (60% RH), and almost all particles activated at cloud base (100% RH). Greatest changes in size and shape were observed in NaCl-containing aggregates (>0.3 µm diameter) along updraft trajectories. Their abundance was associated with high numbers of cloud condensation nuclei (CCN) and cloud droplets, as well as large droplet sizes in updrafts. Thus, compositional dependence was observed in activation behavior recorded for coarse and fine fractions. Soluble salts from local pollution and natural sources clearly affected aerosol-cloud interactions, enhancing the spectrum of particles forming CCN and by forming giant CCN from aggregates, thus, making cloud seeding with hygroscopic flares ineffective in this region.

Aerosol partitioning between the interstitial and the condensed phase in mixed-phase clouds

NASA Astrophysics Data System (ADS)

Verheggen, Bart; Cozic, Julie; Weingartner, Ernest; Bower, Keith; Mertes, Stephan; Connolly, Paul; Gallagher, Martin; Flynn, Michael; Choularton, Tom; Baltensperger, Urs

2007-12-01

The partitioning of aerosol particles between the cloud and the interstitial phase (i.e., unactivated aerosol) has been investigated during several Cloud and Aerosol Characterization Experiments (CLACE-3, CLACE-3? and CLACE-4) conducted in winter and summer 2004 and winter 2005 at the high alpine research station Jungfraujoch (3580 m altitude, Switzerland). Ambient air was sampled using different inlets in order to determine the activated fraction of aerosol particles, FN, defined as the fraction of the total aerosol number concentration (with particle diameter dp > 100 nm) that has been incorporated into cloud particles. The liquid and ice water content of mixed-phase clouds were characterized by analyzing multiple cloud probes. The dependence of the activated fraction on several environmental factors is discussed on the basis of more than 900 h of in-cloud observations and parameterizations for key variables are given. FN is found to increase with increasing liquid water content and to decrease with increasing particle number concentration in liquid clouds. FN also decreases with increasing cloud ice mass fraction and with decreasing temperature from 0 to -25°C. The Wegener-Bergeron-Findeisen process probably contributed to this trend, since the presence of ice crystals causes liquid droplets to evaporate, thus releasing the formerly activated particles back into the interstitial phase. Ice nucleation could also have prevented additional cloud condensation nuclei from activating. The observed activation behavior has significant implications for our understanding of the indirect effect of aerosols on climate.

Black carbon mixing state impacts on cloud microphysical properties: effects of aerosol plume and environmental conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ching, Ping Pui; Riemer, Nicole; West, Matthew

2016-05-27

Black carbon (BC) is usually mixed with other aerosol species within individual aerosol particles. This mixture, along with the particles' size and morphology, determines the particles' optical and cloud condensation nuclei properties, and hence black carbon's climate impacts. In this study the particle-resolved aerosol model PartMC-MOSAIC was used to quantify the importance of black carbon mixing state for predicting cloud microphysical quantities. Based on a set of about 100 cloud parcel simulations a process level analysis framework was developed to attribute the response in cloud microphysical properties to changes in the underlying aerosol population ("plume effect") and the cloud parcelmore » cooling rate ("parcel effect"). It shows that the response of cloud droplet number concentration to changes in BC emissions depends on the BC mixing state. When the aerosol population contains mainly aged BC particles an increase in BC emission results in increasing cloud droplet number concentrations ("additive effect"). In contrast, when the aerosol population contains mainly fresh BC particles they act as sinks for condensable gaseous species, resulting in a decrease in cloud droplet number concentration as BC emissions are increased ("competition effect"). Additionally, we quantified the error in cloud microphysical quantities when neglecting the information on BC mixing state, which is often done in aerosol models. The errors ranged from -12% to +45% for the cloud droplet number fraction, from 0% to +1022% for the nucleation-scavenged black carbon (BC) mass fraction, from -12% to +4% for the effective radius, and from -30% to +60% for the relative dispersion.« less

First correlated measurements of the shape and scattering properties of cloud particles using the new Particle Habit Imaging and Polar Scattering (PHIPS) probe

NASA Astrophysics Data System (ADS)

Abdelmonem, A.; Schnaiter, M.; Amsler, P.; Hesse, E.; Meyer, J.; Leisner, T.

2011-05-01

Studying the radiative impact of cirrus clouds requires the knowledge of the link between their microphysics and the single scattering properties of the cloud particles. Usually, this link is created by modeling the optical scattering properties from in situ measurements of ice crystal size distributions. The measured size distribution and the assumed particle shape might be erroneous in case of non-spherical ice particles. We present here a novel optical sensor (the Particle Habit Imaging and Polar Scattering probe, PHIPS) designed to measure the 3-D morphology and the corresponding optical and microphysical parameters of individual cloud particles, simultaneously. Clouds containing particles ranging in size from a few micrometers to about 800 μm diameter can be systematically characterized with an optical resolution power of 2 μm and polar scattering resolution of 1° for forward scattering directions (from 1° to 10°) and 8° for side and backscattering directions (from 18° to 170°). The maximum acquisition rates for scattering phase functions and images are 262 KHz and 10 Hz, respectively. Some preliminary results collected in two ice cloud campaigns which were conducted in the AIDA cloud simulation chamber are presented. PHIPS showed reliability in operation and produced comparable size distributions and images to those given by other certified cloud particles instruments. A 3-D model of a hexagonal ice plate is constructed and the corresponding scattering phase function is compared to that modeled using the Ray Tracing with Diffraction on Facets (RTDF) program. PHIPS is candidate to be a novel air borne optical sensor for studying the radiative impact of cirrus clouds and correlating the particle habit-scattering properties which will serve as a reference for other single, or multi-independent, measurements instruments.

Probing the magnetic topologies of magnetic clouds by means of solar energetic particles

NASA Technical Reports Server (NTRS)

Kahler, S. W.; Reames, D. V.

1991-01-01

Solar energetic particles (SEPs) have been used as probes of magnetic cloud topologies. The rapid access of SEPs to the interiors of many clouds indicates that the cloud field lines extend back to the sun and hence are not plasmoids. The small modulation of galactic cosmic rays associated with clouds also suggests that the magnetic fields of clouds are not closed.

Seasonal Bias of Retrieved Ice Cloud Optical Properties Based on MISR and MODIS Measurements

NASA Astrophysics Data System (ADS)

Wang, Y.; Hioki, S.; Yang, P.; Di Girolamo, L.; Fu, D.

2017-12-01

The precise estimation of two important cloud optical and microphysical properties, cloud particle optical thickness and cloud particle effective radius, is fundamental in the study of radiative energy budget and hydrological cycle. In retrieving these two properties, an appropriate selection of ice particle surface roughness is important because it substantially affects the single-scattering properties. At present, using a predetermined ice particle shape without spatial and temporal variations is a common practice in satellite-based retrieval. This approach leads to substantial uncertainties in retrievals. The cloud radiances measured by each of the cameras of the Multi-angle Imaging SpectroRadiometer (MISR) instrument are used to estimate spherical albedo values at different scattering angles. By analyzing the directional distribution of estimated spherical albedo values, the degree of ice particle surface roughness is estimated. With an optimal degree of ice particle roughness, cloud optical thickness and effective radius are retrieved based on a bi-spectral shortwave technique in conjunction with two Moderate Resolution Imaging Spectroradiometer (MODIS) bands centered at 0.86 and 2.13 μm. The seasonal biases of retrieved cloud optical and microphysical properties, caused by the uncertainties in ice particle roughness, are investigated by using one year of MISR-MODIS fused data.

Homogenous Surface Nucleation of Solid Polar Stratospheric Cloud Particles

NASA Technical Reports Server (NTRS)

Tabazadeh, A.; Hamill, P.; Salcedo, D.; Gore, Warren J. (Technical Monitor)

2002-01-01

A general surface nucleation rate theory is presented for the homogeneous freezing of crystalline germs on the surfaces of aqueous particles. While nucleation rates in a standard classical homogeneous freezing rate theory scale with volume, the rates in a surface-based theory scale with surface area. The theory is used to convert volume-based information on laboratory freezing rates (in units of cu cm, seconds) of nitric acid trihydrate (NAT) and nitric acid dihydrate (NAD) aerosols into surface-based values (in units of sq cm, seconds). We show that a surface-based model is capable of reproducing measured nucleation rates of NAT and NAD aerosols from concentrated aqueous HNO3 solutions in the temperature range of 165 to 205 K. Laboratory measured nucleation rates are used to derive free energies for NAT and NAD germ formation in the stratosphere. NAD germ free energies range from about 23 to 26 kcal mole, allowing for fast and efficient homogeneous NAD particle production in the stratosphere. However, NAT germ formation energies are large (greater than 26 kcal mole) enough to prevent efficient NAT particle production in the stratosphere. We show that the atmospheric NAD particle production rates based on the surface rate theory are roughly 2 orders of magnitude larger than those obtained from a standard volume-based rate theory. Atmospheric volume and surface production of NAD particles will nearly cease in the stratosphere when denitrification in the air exceeds 40 and 78%, respectively. We show that a surface-based (volume-based) homogeneous freezing rate theory gives particle production rates, which are (not) consistent with both laboratory and atmospheric data on the nucleation of solid polar stratospheric cloud particles.

Impact of Aerosol Processing on Orographic Clouds

NASA Astrophysics Data System (ADS)

Pousse-Nottelmann, Sara; Zubler, Elias M.; Lohmann, Ulrike

2010-05-01

Aerosol particles undergo significant modifications during their residence time in the atmosphere. Physical processes like coagulation, coating and water uptake, and aqueous surface chemistry alter the aerosol size distribution and composition. At this, clouds play a primary role as physical and chemical processing inside cloud droplets contributes considerably to the changes in aerosol particles. A previous study estimates that on global average atmospheric particles are cycled three times through a cloud before being removed from the atmosphere [1]. An explicit and detailed treatment of cloud-borne particles has been implemented in the regional weather forecast and climate model COSMO-CLM. The employed model version includes a two-moment cloud microphysical scheme [2] that has been coupled to the aerosol microphysical scheme M7 [3] as described by Muhlbauer and Lohmann, 2008 [4]. So far, the formation, transfer and removal of cloud-borne aerosol number and mass were not considered in the model. Following the parameterization for cloud-borne particles developed by Hoose et al., 2008 [5], distinction between in-droplet and in-crystal particles is made to more physically account for processes in mixed-phase clouds, such as the Wegener-Bergeron-Findeisen process and contact and immersion freezing. In our model, this approach has been extended to allow for aerosol particles in five different hydrometeors: cloud droplets, rain drops, ice crystals, snow flakes and graupel. We account for nucleation scavenging, freezing and melting processes, autoconversion, accretion, aggregation, riming and selfcollection, collisions between interstitial aerosol particles and hydrometeors, ice multiplication, sedimentation, evaporation and sublimation. The new scheme allows an evaluation of the cloud cycling of aerosol particles by tracking the particles even when scavenged into hydrometeors. Global simulations of aerosol processing in clouds have recently been conducted by Hoose et al. [6]. Our investigation regarding the influence of aerosol processing will focus on the regional scale using a cloud-system resolving model with a much higher resolution. Emphasis will be placed on orographic mixed-phase precipitation. Different two-dimensional simulations of idealized orographic clouds will be conducted to estimate the effect of aerosol processing on orographic cloud formation and precipitation. Here, cloud lifetime, location and extent as well as the cloud type will be of particular interest. In a supplementary study, the new parameterization will be compared to observations of total and interstitial aerosol concentrations and size distribution at the remote high alpine research station Jungfraujoch in Switzerland. In addition, our simulations will be compared to recent simulations of aerosol processing in warm, mixed-phase and cold clouds, which have been carried out at the location of Jungfraujoch station [5]. References: [1] Pruppacher & Jaenicke (1995), The processing of water vapor and aerosols by atmospheric clouds, a global estimate, Atmos. Res., 38, 283295. [2] Seifert & Beheng (2006), A two-moment microphysics parameterization for mixed-phase clouds. Part 1: Model description, Meteorol. Atmos. Phys., 92, 4566. [3] Vignati et al. (2004), An efficient size-resolved aerosol microphysics module for large-scale transport models, J. Geophys. Res., 109, D22202 [4] Muhlbauer & Lohmann (2008), Sensitivity studies of the role of aerosols in warm-phase orographic precipitation in different flow regimes, J. Atmos. Sci., 65, 25222542. [5] Hoose et al. (2008), Aerosol processing in mixed-phase clouds in ECHAM5HAM: Model description and comparison to observations, J. Geophys. Res., 113, D071210. [6] Hoose et al. (2008), Global simulations of aerosol processing in clouds, Atmos. Chem. Phys., 8, 69396963.

Preliminary Results from the First Deployment of a Tethered-Balloon Cloud Particle Imager Instrument Package in Arctic Stratus Clouds at Ny-Alesund

NASA Astrophysics Data System (ADS)

Lawson, P.; Stamnes, K.; Stamnes, J.; Zmarzly, P.; O'Connor, D.; Koskulics, J.; Hamre, B.

2008-12-01

A tethered balloon system specifically designed to collect microphysical data in mixed-phase clouds was deployed in Arctic stratus clouds during May 2008 near Ny-Alesund, Svalbard, at 79 degrees North Latitude. This is the first time a tethered balloon system with a cloud particle imager (CPI) that records high-resolution digital images of cloud drops and ice particles has been operated in cloud. The custom tether supplies electrical power to the instrument package, which in addition to the CPI houses a 4-pi short-wavelength radiometer and a met package that measures temperature, humidity, pressure, GPS position, wind speed and direction. The instrument package was profiled vertically through cloud up to altitudes of 1.6 km. Since power was supplied to the instrument package from the ground, it was possible to keep the balloon package aloft for extended periods of time, up to 9 hours at Ny- Ålesund, which was limited only by crew fatigue. CPI images of cloud drops and the sizes, shapes and degree of riming of ice particles are shown throughout vertical profiles of Arctic stratus clouds. The images show large regions of mixed-phase cloud from -8 to -2 C. The predominant ice crystal habits in these regions are needles and aggregates of needles. The amount of ice in the mixed-phase clouds varied considerably and did not appear to be a function of temperature. On some occasions, ice was observed near cloud base at -2 C with supercooled cloud above to - 8 C that was devoid of ice. Measurements of shortwave radiation are also presented. Correlations between particle distributions and radiative measurements will be analyzed to determine the effect of these Arctic stratus clouds on radiative forcing.

Condensed-Phase Nitric Acid in a Tropical Subvisible Cirrus Cloud

NASA Technical Reports Server (NTRS)

Popp, P. J.; Marcy, T. P.; Watts, O. A.; Gao, R. S.; Fahey, D. W.; Weinstock, E. M.; Smith, J. B.; Herman, R. L.; Tropy, R. F.; Webster, C. r.;

Disk and circumsolar radiances in the presence of ice clouds

DOE PAGES

Haapanala, Päivi; Räisänen, Petri; McFarquhar, Greg M.; ...

2017-06-12

The impact of ice clouds on solar disk and circumsolar radiances is investigated using a Monte Carlo radiative transfer model. The monochromatic direct and diffuse radiances are simulated at angles of 0 to 8° from the center of the sun. Input data for the model are derived from measurements conducted during the 2010 Small Particles in Cirrus (SPARTICUS) campaign together with state-of-the-art databases of optical properties of ice crystals and aerosols. For selected cases, the simulated radiances are compared with ground-based radiance measurements obtained by the Sun and Aureole Measurements (SAM) instrument. First, the sensitivity of the radiances to themore » ice cloud properties and aerosol optical thickness is addressed. The angular dependence of the disk and circumsolar radiances is found to be most sensitive to assumptions about ice crystal roughness (or, more generally, non-ideal features of ice crystals) and size distribution, with ice crystal habit playing a somewhat smaller role. Second, in comparisons with SAM data, the ice cloud optical thickness is adjusted for each case so that the simulated radiances agree closely (i.e., within 3 %) with the measured disk radiances. Circumsolar radiances at angles larger than ≈ 3° are systematically underestimated when assuming smooth ice crystals, whereas the agreement with the measurements is better when rough ice crystals are assumed. In conclusion, our results suggest that it may well be possible to infer the particle roughness directly from ground-based SAM measurements. In addition, the results show the necessity of correcting the ground-based measurements of direct radiation for the presence of diffuse radiation in the instrument's field of view, in particular in the presence of ice clouds.« less

A numerical study of aerosol effects on the dynamics and microphysics of a deep convective cloud in a continental environment

NASA Astrophysics Data System (ADS)

Cui, Zhiqiang; Carslaw, Kenneth S.; Yin, Yan; Davies, Stewart

2006-03-01

The effects of aerosols on a deep convective cloud in a midlatitude continental environment are studied using an axisymmetric cloud model with a sectional treatment of aerosol and hydrometeor microphysical processes. Simulations are conducted using observations from the Cooperative Convective Precipitation Experiments (CCOPE). The isolated cloud occurred in an environment with low wind shear and with relatively dry air in the midtroposphere and upper troposphere. By varying the concentration of aerosol particles in the accumulation mode within realistic limits for a continental environment, the simulated cloud exhibited different properties. The overall impact as the aerosol concentration increased is that (1) the cloud development was inhibited; (2) the precipitation was suppressed; (3) the maximum values of liquid water content decreased, but the maximum values of droplet number concentration increased before the dissipating stage; (4) a clear tendency was found for ice crystals to be larger and less numerous in the anvil cloud; and (5) there was a significant reduction of the inflow in the lower 2 km of the atmosphere. In the relatively dry environment in the midtroposphere, the latent heat changes associated with the Wegener-Bergeron-Findeisen mechanism played an important role in the upper part of the cloud at altitudes below the homogeneous freezing level. In particular, immersion freezing and latent heat release were much more rapid in the base simulation than in the increased aerosol simulation. Less latent heat release and insufficient inflow together impeded the development of the cloud with the higher aerosol loading. Our simulations suggest that continental clouds existing below the homogeneous freezing level could show an opposite response of cloud top height and anvil crystal concentrations to changes in aerosol to what has previously been reported for clouds ascending to higher levels.

Ice Cloud Formation and Dehydration in the Tropical Tropopause Layer

NASA Technical Reports Server (NTRS)

Jensen, Eric; Pfister, Leonhard; Gore, Warren J. (Technical Monitor)

2002-01-01

Stratospheric water vapor is important not only for its greenhouse forcing, but also because it plays a significant role in stratospheric chemistry. several recent studies have focused on the potential for dehydration due to ice cloud formation in air rising slowly through the tropical tropopause layer. Holton and Gettelman showed that temperature variations associated with horizontal transport of air in the tropopause layer can drive ice cloud formation and dehydration, and Gettelman et al. recently examined the cloud formation and dehydration along kinematic trajectories using simple assumptions about the cloud properties. In this study, we use a Lagrangian, one-dimensional cloud model to further investigate cloud formation and dehydration as air is transported horizontally and vertically through the tropical tropopause layer. Time-height curtains of temperature are extracted from meteorological analyses. The model tracks the growth and sedimentation of individual cloud particles. The regional distribution of clouds simulated in the model is comparable to the subvisible cirrus distribution indicated by SAGE II. The simulated cloud properties depend strongly on the assumed ice supersaturation threshold for ice nucleation. with effective nuclei present (low supersaturation threshold), ice number densities are high (0.1--10 cm(circumflex)-3), and ice crystals do not grow large enough to fall very far, resulting in limited dehydration. With higher supersaturation thresholds, ice number densities are much lower (less than 0.01 cm(circumflex)-3), and ice crystals grow large enough to fall substantially; however, supersaturated air often crosses the tropopause without cloud formation. The clouds typically do not dehydrate the air along trajectories down to the temperature minimum saturation mixing ratio. Rather the water vapor mixing ratio crossing the tropopause along trajectories is typically 10-50% larger than the saturation mixing ratio.

The role of marine organic ice nuclei in a global climate model

NASA Astrophysics Data System (ADS)

Hummel, Matthias; Egill Kristjansson, Jon

2016-04-01

Ice particle concentrations are a key parameter for cold clouds, exerting a strong influence on cloud lifetime, precipitation release, and the cloud radiative effect. The availability of ice-nucleating particles (INPs) and the temperature range in which they become activated determine the rate of ice formation in clouds (Hoose und Möhler, 2012). Particles from marine sources may contribute to ice formation in clouds, as they are abundant in the atmosphere and some of them have been found to be ice-nucleating active, but the extent of their influence on clouds is not known (Wilson et al., 2015). Wilson et al. (2015) collected marine INPs from the sea surface microlayer and analyzed their ice nucleation efficiency with a cold stage. Even in cirrus clouds, marine INPs may play a role, as their ice nucleation surface site density as a function of RHice at -40° C has been shown to be larger than for mineral dusts (ATD, kaolinite, and feldspar). In this study, we test the influence of marine organic aerosols on clouds via immersion freezing with the earth system model NorESM2 (Version 2 of the Norwegian Earth System Model; Bentsen et al., 2013). The model is based on the Community Earth System Model (CESM1.2) and its atmospheric part (CAM5 Oslo) is based on the Community Atmosphere Model (CAM5.3). The parameterization of ice nucleation of marine INPs is expressed as an exponential function of temperature multiplied by the total organic content. Marine organic aerosols are part of the sea spray aerosol and are ejected during bubble bursting. INPs are associated with exudates or other macromolecules mainly from diatoms. Hence, their concentration is related to the sea salt aerosols in the model simulation. Our first results indicate that the high marine INP concentrations at around 850 hPa occur at high latitudes. These regions have low mineral dust concentrations, which might increase the influence of marine INP on clouds. However, they do not coincide with regions of high winds and therefore large sea spray aerosol concentrations, contrary to model simulations in Wilson et al. (2015) with the global aerosol process model (GLOMAP), but are shifted further polewards. Therefore, marine INP concentrations strongly depend on temperature and do not necessarily coincide with large sea spray concentrations. At mid-latitudes, marine INP concentrations rank below dust INP by at least one order of magnitude. Further, this presentation will describe the influence of marine INP on cloud properties and give an estimate of the cloud radiative effect of marine INP. Bentsen, M., I. Bethke, et al. (2013): The Norwegian Earth System Model, NorESM1-M - Part 1: Description and basic evaluation of the physical climate, Geosci. Model Dev. 6(3): 687-720. Hoose, C. und O. Möhler (2012): Heterogeneous ice nucleation on atmospheric aerosols: a review of results from laboratory experiments, Atmos. Chem. Phys. 12(20): 9817-9854. Wilson, T. W., L. A. Ladino, et al. (2015): A marine biogenic source of atmospheric ice-nucleating particles, Nature 525(7568): 234-238.

Parameterization of aerosol scavenging due to atmospheric ionization under varying relative humidity

NASA Astrophysics Data System (ADS)

Zhang, Liang; Tinsley, Brian A.

2017-05-01

Simulations and parameterizations of the modulation of aerosol scavenging by electric charges on particles and droplets for different relative humidities have been made for 3 μm radii droplets and a wide range of particle radii. For droplets and particles with opposite-sign charges, the attractive Coulomb force increases the collision rate coefficients above values due to other forces. With same-sign charges, the repulsive Coulomb force decreases the rate coefficients, and the short-range attractive image forces become important. The phoretic forces are attractive for relative humidity less than 100% and repulsive for relative humidity greater than 100% and have increasing overall effect for particle radii up to about 1 μm. There is an analytic solution for rate coefficients if only inverse square forces are present, but due to the presence of image forces, and for larger particles the intercept, weight, and the flow around the particle affecting the droplet trajectory, the simulated results usually depart far from the analytic solution. We give simple empirical parameterization formulas for some cases and more complex parameterizations for more exact fits to the simulated results. The results can be used in cloud models with growing droplets, as in updrafts, as well as with evaporating droplets in downdrafts. There is considered to be little scavenging of uncharged ice-forming nuclei in updrafts, but with charged ice-forming nuclei it is possible for scavenging in updrafts in cold clouds to produce contact ice nucleation. Scavenging in updrafts below the freezing level produces immersion nuclei that promote enhanced freezing as droplets rise above it.

Leading and Trailing Anvil Clouds of West African Squall Lines

NASA Technical Reports Server (NTRS)

Centrone, Jasmine; Houze, Robert A.

2011-01-01

The anvil clouds of tropical squall-line systems over West Africa have been examined using cloud radar data and divided into those that appear ahead of the leading convective line and those on the trailing side of the system. The leading anvils are generally higher in altitude than the trailing anvil, likely because the hydrometeors in the leading anvil are directly connected to the convective updraft, while the trailing anvil generally extends out of the lower-topped stratiform precipitation region. When the anvils are subdivided into thick, medium, and thin portions, the thick leading anvil is seen to have systematically higher reflectivity than the thick trailing anvil, suggesting that the leading anvil contains numerous larger ice particles owing to its direct connection to the convective region. As the leading anvil ages and thins, it retains its top. The leading anvil appears to add hydrometeors at the highest altitudes, while the trailing anvil is able to moisten a deep layer of the atmosphere.

Application of a Snow Growth Model to Radar Remote Sensing

NASA Astrophysics Data System (ADS)

Erfani, E.; Mitchell, D. L.

2014-12-01

Microphysical growth processes of diffusion, aggregation and riming are incorporated analytically in a steady-state snow growth model (SGM) to solve the zeroth- and second- moment conservation equations with respect to mass. The SGM is initiated by radar reflectivity (Zw), supersaturation, temperature, and a vertical profile of the liquid water content (LWC), and it uses a gamma size distribution (SD) to predict the vertical evolution of size spectra. Aggregation seems to play an important role in the evolution of snowfall rates and the snowfall rates produced by aggregation, diffusion and riming are considerably greater than those produced by diffusion and riming alone, demonstrating the strong interaction between aggregation and riming. The impact of ice particle shape on particle growth rates and fall speeds is represented in the SGM in terms of ice particle mass-dimension (m-D) power laws (m = αDβ). These growth rates are qualitatively consistent with empirical growth rates, with slower (faster) growth rates predicted for higher (lower) β values. In most models, β is treated constant for a given ice particle habit, but it is well known that β is larger for the smaller crystals. Our recent work quantitatively calculates β and α for cirrus clouds as a function of D where the m-D expression is a second-order polynomial in log-log space. By adapting this method to the SGM, the ice particle growth rates and fall speeds are predicted more accurately. Moreover, the size spectra predicted by the SGM are in good agreement with those from aircraft measurements during Lagrangian spiral descents through frontal clouds, indicating the successful modeling of microphysical processes. Since the lowest Zw over complex topography is often significantly above cloud base, the precipitation is often underestimated by radar quantitative precipitation estimates (QPE). Our SGM is capable of being initialized with Zw at the lowest reliable radar echo and consequently improves QPE at ground level.

Investigation of methods to produce a uniform cloud of fuel particles in a flame tube

NASA Technical Reports Server (NTRS)

Siegert, Clifford E.; Pla, Frederic G.; Rubinstein, Robert; Niezgoda, Thomas F.; Burns, Robert J.; Johnson, Jerome A.

1990-01-01

The combustion of a uniform, quiescent cloud of 30-micron fuel particles in a flame tube was proposed as a space-based, low-gravity experiment. The subject is the normal- and low-gravity testing of several methods to produce such a cloud, including telescoping propeller fans, air pumps, axial and quadrature acoustical speakers, and combinations of these devices. When operated in steady state, none of the methods produced an acceptably uniform cloud (+ or - 5 percent of the mean concentration), and voids in the cloud were clearly visible. In some cases, severe particle agglomeration was observed; however, these clusters could be broken apart by a short acoustic burst from an axially in-line speaker. Analyses and experiments reported elsewhere suggest that transient, acoustic mixing methods can enhance cloud uniformity while minimizing particle agglomeration.

Cloud condensation nuclei closure study on summer arctic aerosol

NASA Astrophysics Data System (ADS)

Martin, M.; Chang, R. Y.-W.; Sierau, B.; Sjogren, S.; Swietlicki, E.; Abbatt, J. P. D.; Leck, C.; Lohmann, U.

2011-11-01

We present an aerosol - cloud condensation nuclei (CCN) closure study on summer high Arctic aerosol based on measurements that were carried out in 2008 during the Arctic Summer Cloud Ocean Study (ASCOS) on board the Swedish ice breaker Oden. The data presented here were collected during a three-week time period in the pack ice (>85° N) when the icebreaker Oden was moored to an ice floe and drifted passively during the most biological active period into autumn freeze up conditions. CCN number concentrations were obtained using two CCN counters measuring at different supersaturations. The directly measured CCN number concentration was then compared with a CCN number concentration calculated using both bulk aerosol mass composition data from an aerosol mass spectrometer (AMS) and aerosol number size distributions obtained from a differential mobility particle sizer, assuming κ-Köhler theory, surface tension of water and an internally mixed aerosol. The last assumption was supported by measurements made with a hygroscopic tandem differential mobility analyzer (HTDMA) for particles >70 nm. For the two highest measured supersaturations, 0.73 and 0.41%, closure could not be achieved with the investigated settings concerning hygroscopicity and density. The calculated CCN number concentration was always higher than the measured one for those two supersaturations. This might be caused by a relative larger insoluble organic mass fraction of the smaller particles that activate at these supersaturations, which are thus less good CCN than the larger particles. On average, 36% of the mass measured with the AMS was organic mass. At 0.20, 0.15 and 0.10% supersaturation, closure could be achieved with different combinations of hygroscopic parameters and densities within the uncertainty range of the fit. The best agreement of the calculated CCN number concentration with the observed one was achieved when the organic fraction of the aerosol was treated as nearly water insoluble (κorg=0.02), leading to a mean total κ, κtot, of 0.33 ± 0.13. However, several settings led to closure and κorg=0.2 is found to be an upper limit at 0.1% supersaturation. κorg≤0.2 leads to a κtot range of 0.33 ± 013 to 0.50 ± 0.11. Thus, the organic material ranges from being sparingly soluble to effectively insoluble. These results suggest that an increase in organic mass fraction in particles of a certain size would lead to a suppression of the Arctic CCN activity.

Influence of Ice Cloud Microphysics on Imager-Based Estimates of Earth's Radiation Budget

NASA Astrophysics Data System (ADS)

Loeb, N. G.; Kato, S.; Minnis, P.; Yang, P.; Sun-Mack, S.; Rose, F. G.; Hong, G.; Ham, S. H.

2016-12-01

A central objective of the Clouds and the Earth's Radiant Energy System (CERES) is to produce a long-term global climate data record of Earth's radiation budget from the TOA down to the surface along with the associated atmospheric and surface properties that influence it. CERES relies on a number of data sources, including broadband radiometers measuring incoming and reflected solar radiation and OLR, high-resolution spectral imagers, meteorological, aerosol and ozone assimilation data, and snow/sea-ice maps based on microwave radiometer data. While the TOA radiation budget is largely determined directly from accurate broadband radiometer measurements, the surface radiation budget is derived indirectly through radiative transfer model calculations initialized using imager-based cloud and aerosol retrievals and meteorological assimilation data. Because ice cloud particles exhibit a wide range of shapes, sizes and habits that cannot be independently retrieved a priori from passive visible/infrared imager measurements, assumptions about the scattering properties of ice clouds are necessary in order to retrieve ice cloud optical properties (e.g., optical depth) from imager radiances and to compute broadband radiative fluxes. This presentation will examine how the choice of an ice cloud particle model impacts computed shortwave (SW) radiative fluxes at the top-of-atmosphere (TOA) and surface. The ice cloud particle models considered correspond to those from prior, current and future CERES data product versions. During the CERES Edition2 (and Edition3) processing, ice cloud particles were assumed to be smooth hexagonal columns. In the Edition4, roughened hexagonal columns are assumed. The CERES team is now working on implementing in a future version an ice cloud particle model comprised of a two-habit ice cloud model consisting of roughened hexagonal columns and aggregates of roughened columnar elements. In each case, we use the same ice particle model in both the imager-based cloud retrievals (inverse problem) and the computed radiative fluxes (forward calculation). In addition to comparing radiative fluxes using the different ice cloud particle models, we also compare instantaneous TOA flux calculations with those observed by the CERES instrument.

Contrasting cloud composition between coupled and decoupled marine boundary layer clouds

NASA Astrophysics Data System (ADS)

Wang, Zhen; Mora Ramirez, Marco; Dadashazar, Hossein; MacDonald, Alex B.; Crosbie, Ewan; Bates, Kelvin H.; Coggon, Matthew M.; Craven, Jill S.; Lynch, Peng; Campbell, James R.; Azadi Aghdam, Mojtaba; Woods, Roy K.; Jonsson, Haflidi; Flagan, Richard C.; Seinfeld, John H.; Sorooshian, Armin

2016-10-01

Marine stratocumulus clouds often become decoupled from the vertical layer immediately above the ocean surface. This study contrasts cloud chemical composition between coupled and decoupled marine stratocumulus clouds for dissolved nonwater substances. Cloud water and droplet residual particle composition were measured in clouds off the California coast during three airborne experiments in July-August of separate years (Eastern Pacific Emitted Aerosol Cloud Experiment 2011, Nucleation in California Experiment 2013, and Biological and Oceanic Atmospheric Study 2015). Decoupled clouds exhibited significantly lower air-equivalent mass concentrations in both cloud water and droplet residual particles, consistent with reduced cloud droplet number concentration and subcloud aerosol (Dp > 100 nm) number concentration, owing to detachment from surface sources. Nonrefractory submicrometer aerosol measurements show that coupled clouds exhibit higher sulfate mass fractions in droplet residual particles, owing to more abundant precursor emissions from the ocean and ships. Consequently, decoupled clouds exhibited higher mass fractions of organics, nitrate, and ammonium in droplet residual particles, owing to effects of long-range transport from more distant sources. Sodium and chloride dominated in terms of air-equivalent concentration in cloud water for coupled clouds, and their mass fractions and concentrations exceeded those in decoupled clouds. Conversely, with the exception of sea-salt constituents (e.g., Cl, Na, Mg, and K), cloud water mass fractions of all species examined were higher in decoupled clouds relative to coupled clouds. Satellite and Navy Aerosol Analysis and Prediction System-based reanalysis data are compared with each other, and the airborne data to conclude that limitations in resolving boundary layer processes in a global model prevent it from accurately quantifying observed differences between coupled and decoupled cloud composition.

Evaluation of cloud detection instruments and performance of laminar-flow leading-edge test articles during NASA Leading-Edge Flight-Test Program

NASA Technical Reports Server (NTRS)

Davis, Richard E.; Maddalon, Dal V.; Wagner, Richard D.; Fisher, David F.; Young, Ronald

1989-01-01

Summary evaluations of the performance of laminar-flow control (LFC) leading edge test articles on a NASA JetStar aircraft are presented. Statistics, presented for the test articles' performance in haze and cloud situations, as well as in clear air, show a significant effect of cloud particle concentrations on the extent of laminar flow. The cloud particle environment was monitored by two instruments, a cloud particle spectrometer (Knollenberg probe) and a charging patch. Both instruments are evaluated as diagnostic aids for avoiding laminar-flow detrimental particle concentrations in future LFC aircraft operations. The data base covers 19 flights in the simulated airline service phase of the NASA Leading-Edge Flight-Test (LEFT) Program.

Observing relationships between lightning and cloud profiles by means of a satellite-borne cloud radar

NASA Astrophysics Data System (ADS)

Buiat, Martina; Porcù, Federico; Dietrich, Stefano

2017-01-01

Cloud electrification and related lightning activity in thunderstorms have their origin in the charge separation and resulting distribution of charged iced particles within the cloud. So far, the ice distribution within convective clouds has been investigated mainly by means of ground-based meteorological radars. In this paper we show how the products from Cloud Profiling Radar (CPR) on board CloudSat, a polar satellite of NASA's Earth System Science Pathfinder (ESSP), can be used to obtain information from space on the vertical distribution of ice particles and ice content and relate them to the lightning activity. The analysis has been carried out, focusing on 12 convective events over Italy that crossed CloudSat overpasses during significant lightning activity. The CPR products considered here are the vertical profiles of cloud ice water content (IWC) and the effective radius (ER) of ice particles, which are compared with the number of strokes as measured by a ground lightning network (LINET). Results show a strong correlation between the number of strokes and the vertical distribution of ice particles as depicted by the 94 GHz CPR products: in particular, cloud upper and middle levels, high IWC content and relatively high ER seem to be favourable contributory causes for CG (cloud to ground) stroke occurrence.

Characterization of residuals from ice particles and droplets sampled in mid-latitude natural and aviation-influenced cirrus and in tropical deep convective cloud systems during ML-CIRRUS and ACRIDICON

NASA Astrophysics Data System (ADS)

Mertes, Stephan; Kästner, Udo; Schulz, Christiane; Klimach, Thomas; Krüger, Mira; Schneider, Johannes

2015-04-01

Airborne sampling of cloud particles inside different cirrus cloud types and inside deep convective clouds was conducted during the HALO missions ML-CIRRUS over Europe in March/April 2014 and ACRIDICON over Amazonia in September 2014. ML-CIRRUS aims at the investigation of the for-mation, evolution, microphysical state and radiative effects of different natural and aviation-induced cirrus clouds in the mid-latitudes. The main objectives of ACRIDICON are the microphysical vertical profiling, vertical aerosol transport and the cloud processing of aerosol particles (compari-son in- and outflow) of tropical deep convective cloud systems in clean and polluted air masses and over forested and deforested regions. The hydrometeors (drops and ice particles) are sampled by a counterflow virtual impactor (CVI) which has to be installed in the front part of the upper fuselage of the HALO aircraft. Such an intake position implies a size dependent abundance of cloud particles with respect to ambient conditions that was studied by particle trajectory simulations (Katrin Witte, HALO Technical Note 2008-003-A). On the other hand, this sampling location avoids that large ice crystals which could potentially bias the cloud particle sampling by shattering and break-up at the inlet shroud and tip enter the inlet. Both aspects as well as the flight conditions of HALO were taken into account for an optimized CVI design for HALO (HALO-CVI). Interstitial particles are pre-segregated and the condensed phase is evaporated/sublimated by the CVI, such that the residuals from cloud droplets and ice particles (CDR and IPR) can be microphysically and chemically analyzed by respective aerosol sensors located in the cabin. Although an even more comprehensive characterization of CDR and IPR was carried out, we like to report on the following measurements of certain aerosol properties. Particle number concentra-tion and size distribution are measured by a condensation particle counter (CPC) and an ultra-high sensitivity aerosol spectrometer (UHSAS). The absorption coefficient and thus a measure for the black carbon mass concentration is derived from the particle soot absorption photometer (PSAP). In the lower warm parts of the probed convective clouds during the ACRIDICON mission the mean charge of droplets was inferred by means of electrometer measurements. For the determination of the chemical properties of CDR and IPR, the Aircraft-based Laser Ablation Aerosol Mass Spec-trometer (ALABAMA) and a Compact-Time-of-Flight-Aerosol-Mass-Spectrometer (C-ToF-AMS) was operated during ML-CIRRUS and ACRIDICON, respectively, to obtain the mixing state and chemical composition of the cloud particle residues. During ML-CIRRUS, differences in IPR concentration, size distribution, and chemical composition between natural and aviation influenced cirrus clouds could be observed as well as between dif-ferent natural cirrus types and between young and aged contrail cirrus. During ACRIDICON, CDR concentration, size distribution, and chemical composition are found to be different for convective cloud systems evolving from more clean air masses compared to systems evolving from more polluted air masses. Droplet charges change from negative to positive values with height in all vertical cloud profiles. The measured IPR concentration strongly vary in the anvil outflow regions.

Lagrangian Particle Tracking Simulation for Warm-Rain Processes in Quasi-One-Dimensional Domain

NASA Astrophysics Data System (ADS)

Kunishima, Y.; Onishi, R.

2017-12-01

Conventional cloud simulations are based on the Euler method and compute each microphysics process in a stochastic way assuming infinite numbers of particles within each numerical grid. They therefore cannot provide the Lagrangian statistics of individual particles in cloud microphysics (i.e., aerosol particles, cloud particles, and rain drops) nor discuss the statistical fluctuations due to finite number of particles. We here simulate the entire precipitation process of warm-rain, with tracking individual particles. We use the Lagrangian Cloud Simulator (LCS), which is based on the Euler-Lagrangian framework. In that framework, flow motion and scalar transportation are computed with the Euler method, and particle motion with the Lagrangian one. The LCS tracks particle motions and collision events individually with considering the hydrodynamic interaction between approaching particles with a superposition method, that is, it can directly represent the collisional growth of cloud particles. It is essential for trustworthy collision detection to take account of the hydrodynamic interaction. In this study, we newly developed a stochastic model based on the Twomey cloud condensation nuclei (CCN) activation for the Lagrangian tracking simulation and integrated it into the LCS. Coupling with the Euler computation for water vapour and temperature fields, the initiation and condensational growth of water droplets were computed in the Lagrangian way. We applied the integrated LCS for a kinematic simulation of warm-rain processes in a vertically-elongated domain of, at largest, 0.03×0.03×3000 (m3) with horizontal periodicity. Aerosol particles with a realistic number density, 5×107 (m3), were evenly distributed over the domain at the initial state. Prescribed updraft at the early stage initiated development of a precipitating cloud. We have confirmed that the obtained bulk statistics fairly agree with those from a conventional spectral-bin scheme for a vertical column domain. The centre of the discussion will be the Lagrangian statistics which is collected from the individual behaviour of the tracked particles.

Lightweight Electronic Camera for Research on Clouds

NASA Technical Reports Server (NTRS)

Lawson, Paul

2006-01-01

"Micro-CPI" (wherein "CPI" signifies "cloud-particle imager") is the name of a small, lightweight electronic camera that has been proposed for use in research on clouds. It would acquire and digitize high-resolution (3- m-pixel) images of ice particles and water drops at a rate up to 1,000 particles (and/or drops) per second.

Simultaneous observations of solar MeV particles in a magnetic cloud and in the earth's northern tail lobe - Implications for the global field line topology of magnetic clouds and for the entry of solar particles into the magnetosphere during cloud passage

NASA Technical Reports Server (NTRS)

Farrugia, C. J.; Richardson, I. G.; Burlaga, L. F.; Lepping, R. P.; Osherovich, V. A.

1993-01-01

Simultaneous ISEE 3 and IMP 8 spacecraft observations of magnetic fields and flow anisotropies of solar energetic protons and electrons during the passage of an interplanetary magnetic cloud show various particle signature differences at the two spacecraft. These differences are interpretable in terms of the magnetic line topology of the cloud, the connectivity of the cloud field lines to the solar surface, and the interconnection between the magnetic fields of the magnetic clouds and of the earth. These observations are consistent with a magnetic cloud model in which these mesoscale configurations are curved magnetic flux ropes attached at both ends to the sun's surface, extending out to 1 AU.

How do changes in warm-phase microphysics affect deep convective clouds?

NASA Astrophysics Data System (ADS)

Chen, Qian; Koren, Ilan; Altaratz, Orit; Heiblum, Reuven H.; Dagan, Guy; Pinto, Lital

2017-08-01

Understanding aerosol effects on deep convective clouds and the derived effects on the radiation budget and rain patterns can largely contribute to estimations of climate uncertainties. The challenge is difficult in part because key microphysical processes in the mixed and cold phases are still not well understood. For deep convective clouds with a warm base, understanding aerosol effects on the warm processes is extremely important as they set the initial and boundary conditions for the cold processes. Therefore, the focus of this study is the warm phase, which can be better resolved. The main question is: How do aerosol-derived changes in the warm phase affect the properties of deep convective cloud systems? To explore this question, we used a weather research and forecasting (WRF) model with spectral bin microphysics to simulate a deep convective cloud system over the Marshall Islands during the Kwajalein Experiment (KWAJEX). The model results were validated against observations, showing similarities in the vertical profile of radar reflectivity and the surface rain rate. Simulations with larger aerosol loading resulted in a larger total cloud mass, a larger cloud fraction in the upper levels, and a larger frequency of strong updrafts and rain rates. Enlarged mass both below and above the zero temperature level (ZTL) contributed to the increase in cloud total mass (water and ice) in the polluted runs. Increased condensation efficiency of cloud droplets governed the gain in mass below the ZTL, while both enhanced condensational and depositional growth led to increased mass above it. The enhanced mass loading above the ZTL acted to reduce the cloud buoyancy, while the thermal buoyancy (driven by the enhanced latent heat release) increased in the polluted runs. The overall effect showed an increased upward transport (across the ZTL) of liquid water driven by both larger updrafts and larger droplet mobility. These aerosol effects were reflected in the larger ratio between the masses located above and below the ZTL in the polluted runs. When comparing the net mass flux crossing the ZTL in the clean and polluted runs, the difference was small. However, when comparing the upward and downward fluxes separately, the increase in aerosol concentration was seen to dramatically increase the fluxes in both directions, indicating the aerosol amplification effect of the convection and the affected cloud system properties, such as cloud fraction and rain rate.

Cloud Macro- and Microphysical Properties Derived from GOES over the ARM SGP Domain

NASA Technical Reports Server (NTRS)

Minnis, P.; Smith, W. L., Jr.; Young, D. F.

2001-01-01

Cloud macrophysical properties like fractional coverage and height Z(sub c) and microphysical parameters such as cloud liquid water path (LWP), effective droplet radius r(sub e), and cloud phase, are key factors affecting both the radiation budget and the hydrological cycle. Satellite data have been used to complement surface observations from Atmospheric Radiation Measurements (ARM) by providing additional spatial coverage and top-of-atmosphere boundary conditions of these key parameters. Since 1994, the Geostationary Operational Environmental Satellite (GOES) has been used for deriving at each half-hour over the ARM Southern Great Plains (SGP) domain: cloud amounts, altitudes, temperatures, and optical depths as well as broadband shortwave (SW) albedo and outgoing longwave radiation at the top of the atmosphere. A new operational algorithm has been implemented to increase the number of value-added products to include cloud particle phase and effective size (r(sub e) or effective ice diameter D(sub e)) as well as LWP and ice water path. Similar analyses have been performed on the data from the Visible Infrared Scanner (VIRS) on the Tropical Rainfall Measuring Mission satellite as part of the Clouds and Earth's Radiant Energy System project. This larger suite of cloud properties will enhance our knowledge of cloud processes and further constrain the mesoscale and single column models using ARM data as a validation/initialization resource. This paper presents the results of applying this new algorithm to GOES-8 data taken during 1998 and 2000. The global VIRS results are compared to the GOES SGP results to provide appropriate context and to test consistency.

Cloud Cover Increase with Increasing Aerosol Absorptivity: A Counterexample to the Conventional Semidirect Aerosol Effect

NASA Technical Reports Server (NTRS)

Perlwitz, Jan; Miller, Ron L.

2010-01-01

We reexamine the aerosol semidirect effect using a general circulation model and four cases of the single-scattering albedo of dust aerosols. Contrary to the expected decrease in low cloud cover due to heating by tropospheric aerosols, we find a significant increase with increasing absorptivity of soil dust particles in regions with high dust load, except during Northern Hemisphere winter. The strongest sensitivity of cloud cover to dust absorption is found over land during Northern Hemisphere summer. Here even medium and high cloud cover increase where the dust load is highest. The cloud cover change is directly linked to the change in relative humidity in the troposphere as a result of contrasting changes in specific humidity and temperature. More absorption by aerosols leads to larger diabatic heating and increased warming of the column, decreasing relative humidity. However, a corresponding increase in the specific humidity exceeds the temperature effect on relative humidity. The net effect is more low cloud cover with increasing aerosol absorption. The higher specific humidity where cloud cover strongly increases is attributed to an enhanced convergence of moisture driven by dust radiative heating. Although in some areas our model exhibits a reduction of low cloud cover due to aerosol heating consistent with the conventional description of the semidirect effect, we conclude that the link between aerosols and clouds is more varied, depending also on changes in the atmospheric circulation and the specific humidity induced by the aerosols. Other absorbing aerosols such as black carbon are expected to have a similar effect.

Size distribution, chemical composition, and hygroscopicity of fine particles emitted from an oil-fired heating plant.

PubMed

Happonen, Matti; Mylläri, Fanni; Karjalainen, Panu; Frey, Anna; Saarikoski, Sanna; Carbone, Samara; Hillamo, Risto; Pirjola, Liisa; Häyrinen, Anna; Kytömäki, Jorma; Niemi, Jarkko V; Keskinen, Jorma; Rönkkö, Topi

2013-12-17

Heavy fuel oil (HFO) is a commonly used fuel in industrial heating and power generation and for large marine vessels. In this study, the fine particle emissions of a 47 MW oil-fired boiler were studied at 30 MW power and with three different fuels. The studied fuels were HFO, water emulsion of HFO, and water emulsion of HFO mixed with light fuel oil (LFO). With all the fuels, the boiler emitted considerable amounts of particles smaller than 200 nm in diameter. Further, these small particles were quite hygroscopic even as fresh and, in the case of HFO+LFO emulsion, the hygroscopic growth of the particles was dependent on particle size. The use of emulsions and the addition of LFO to the fuel had a reducing effect on the hygroscopic growth of particles. The use of emulsions lowered the sulfate content of the smallest particles but did not affect significantly the sulfate content of particles larger than 42 nm and, further, the addition of LFO considerably increased the black carbon content of particulate matter. The results indicate that even the fine particles emitted from HFO based combustion can have a significant effect on cloud formation, visibility, and air quality.

Coupling dynamical and collisional evolution of small bodies:. an application to the early ejection of planetesimals from the Jupiter-Saturn region

NASA Astrophysics Data System (ADS)

Charnoz, Sébastien; Morbidelli, Alessandro

2003-11-01

We present a new algorithm designed to compute the collisional erosion of a population of small bodies undergoing a complex and rapid dynamical evolution induced by strong gravitational perturbations. Usual particle-in-a-box models have been extensively and successfully used to study the evolution of asteroids or KBOs. However, they cannot track the evolution of small bodies in rapid dynamical evolution, due to their oversimplified description of the dynamics. Our code is based on both (1) a direct simulation of the dynamical evolution which is used to compute local encounter rates and (2) a classical fragmentation model. Such a code may be used to track the erosional evolution of the planetesimal disk under the action of newly formed giant-planets, a passing star or a population of massive planetary-embryos. We present here an application to a problem related to the formation of the Oort cloud. The usually accepted formation scenario is that planetesimals, originally formed in the giant planet region, have been transported to the Oort cloud by gravitational scattering. However, it has been suggested that, during the initial transport phase, the mutual large encounter velocities might have induced a rapid and intense collisional evolution of the planetesimal population, potentially causing a significant reduction of the Oort cloud formation process. This mechanism is explored with our new algorithm. Because the advantages of our new approach are better highlighted for a population undergoing a violent dynamical evolution, we concentrate in this paper on the planetesimals originally in the Jupiter-Saturn region, although it is known that they are only minor contributors to the final Oort cloud population. A wide range of parameters is explored (mass of the particle disk, initial size-distribution, material strength): depending upon the assumed parameter values, we find that from 15 to 90% of the mass contained in bodies larger than 1 km survives the collisional process; for our preferred choice of the parameters this fraction is ˜70%. It is also found that the majority of planetesimals larger than 1-10 km are pristine, and not fragments. We show also that collisional damping may not prevent planetesimals from being ejected to the outer Solar System. Thus, although the collisional activity is high during the scattering by Jupiter and Saturn, collisional grinding does not lower by orders of magnitude the mass contained in bodies larger than 1 km, originally in the Jupiter-Saturn region. These conclusions seem to support the classical collisionless scenario of Oort cloud formation, at least for the Jupiter-Saturn region.

Measurement Comparisons Towards Improving the Understanding of Aerosol-Cloud Processing

NASA Astrophysics Data System (ADS)

Noble, Stephen R.

Cloud processing of aerosol is an aerosol-cloud interaction that is not heavily researched but could have implications on climate. The three types of cloud processing are chemical processing, collision and coalescence processing, and Brownian capture of interstitial particles. All types improve cloud condensation nuclei (CCN) in size or hygroscopicity (kappa). These improved CCN affect subsequent clouds. This dissertation focuses on measurement comparisons to improve our observations and understanding of aerosol-cloud processing. Particle size distributions measured at the continental Southern Great Plains (SGP) site were compared with ground based measurements of cloud fraction (CF) and cloud base altitude (CBA). Particle size distributions were described by a new objective shape parameter to define bimodality rather than an old subjective one. Cloudy conditions at SGP were found to be correlated with lagged shape parameter. Horizontal wind speed and regional CF explained 42%+ of this lag time. Many of these surface particle size distributions were influenced by aerosol-cloud processing. Thus, cloud processing may be more widespread with more implications than previously thought. Particle size distributions measured during two aircraft field campaigns (MArine Stratus/stratocumulus Experiment; MASE; and Ice in Cloud Experiment-Tropical; ICE-T) were compared to CCN distributions. Tuning particle size to critical supersaturation revealed hygroscopicity expressed as ? when the distributions were overlain. Distributions near cumulus clouds (ICE-T) had a higher frequency of the same ?s (48% in ICE-T to 42% in MASE) between the accumulation (processed) and Aitken (unprocessed) modes. This suggested physical processing domination in ICE-T. More MASE (stratus cloud) kappa differences between modes pointed to chemical cloud processing. Chemistry measurements made in MASE showed increases in sulfates and nitrates with distributions that were more processed. This supported chemical cloud processing in MASE. This new method to determine kappa provides the needed information without interrupting ambient measurements. MODIS derived cloud optical thickness (COT), cloud liquid water path (LWP), and cloud effective radius (re) were compared to the same in situ derived variables from cloud probe measurements of two stratus/stratocumulus cloud campaigns (MASE and Physics Of Stratocumulus Tops; POST). In situ data were from complete vertical cloud penetrations, while MODIS data were from pixels along the aircraft penetration path. Comparisons were well correlated except that MODIS LWP (14-36%) and re (20-30%) were biased high. The LWP bias was from re bias and was not improved by using the vertically stratified assumption. MODIS re bias was almost removed when compared to cloud top maximum in situ re, but, that does not describe re for the full depth of the cloud. COT is validated by in situ COT. High correlations suggest that MODIS variables are useful in self-comparisons such as gradient changes in stratus cloud re during aerosol-cloud processing.

A statistical comparison of cirrus particle size distributions measured using the 2-D stereo probe during the TC4, SPARTICUS, and MACPEX flight campaigns with historical cirrus datasets

NASA Astrophysics Data System (ADS)

Schwartz, M. Christian

2017-08-01

This paper addresses two straightforward questions. First, how similar are the statistics of cirrus particle size distribution (PSD) datasets collected using the Two-Dimensional Stereo (2D-S) probe to cirrus PSD datasets collected using older Particle Measuring Systems (PMS) 2-D Cloud (2DC) and 2-D Precipitation (2DP) probes? Second, how similar are the datasets when shatter-correcting post-processing is applied to the 2DC datasets? To answer these questions, a database of measured and parameterized cirrus PSDs - constructed from measurements taken during the Small Particles in Cirrus (SPARTICUS); Mid-latitude Airborne Cirrus Properties Experiment (MACPEX); and Tropical Composition, Cloud, and Climate Coupling (TC4) flight campaigns - is used.Bulk cloud quantities are computed from the 2D-S database in three ways: first, directly from the 2D-S data; second, by applying the 2D-S data to ice PSD parameterizations developed using sets of cirrus measurements collected using the older PMS probes; and third, by applying the 2D-S data to a similar parameterization developed using the 2D-S data themselves. This is done so that measurements of the same cloud volumes by parameterized versions of the 2DC and 2D-S can be compared with one another. It is thereby seen - given the same cloud field and given the same assumptions concerning ice crystal cross-sectional area, density, and radar cross section - that the parameterized 2D-S and the parameterized 2DC predict similar distributions of inferred shortwave extinction coefficient, ice water content, and 94 GHz radar reflectivity. However, the parameterization of the 2DC based on uncorrected data predicts a statistically significantly higher number of total ice crystals and a larger ratio of small ice crystals to large ice crystals than does the parameterized 2D-S. The 2DC parameterization based on shatter-corrected data also predicts statistically different numbers of ice crystals than does the parameterized 2D-S, but the comparison between the two is nevertheless more favorable. It is concluded that the older datasets continue to be useful for scientific purposes, with certain caveats, and that continuing field investigations of cirrus with more modern probes is desirable.

Aerosolization, Chemical Characterization, Hygroscopicity and Ice Formation of Marine Biogenic Particles

NASA Astrophysics Data System (ADS)

Alpert, P. A.; Radway, J.; Kilthau, W.; Bothe, D.; Knopf, D. A.; Aller, J. Y.

2013-12-01

The oceans cover the majority of the earth's surface, host nearly half the total global primary productivity and are a major source of atmospheric aerosol particles. However, effects of biological activity on sea spray generation and composition, and subsequent cloud formation are not well understood. Our goal is to elucidate these effects which will be particularly important over nutrient rich seas, where microorganisms can reach concentrations of 10^9 per mL and along with transparent exopolymer particles (TEP) can become aerosolized. Here we report the results of mesocosm experiments in which bubbles were generated by two methods, either recirculating impinging water jets or glass frits, in natural or artificial seawater containing bacteria and unialgal cultures of three representative phytoplankton species, Thalassiosira pseudonana, Emiliania huxleyi, and Nannochloris atomus. Over time we followed the size distribution of aerosolized particles as well as their hygroscopicity, heterogeneous ice nucleation potential, and individual physical-chemical characteristics. Numbers of cells and the mass of dissolved and particulate organic carbon (DOC, POC), TEP (which includes polysaccharide-containing microgels and nanogels >0.4 μm in diameter) were determined in the bulk water, the surface microlayer, and aerosolized material. Aerosolized particles were also impacted onto substrates for ice nucleation and water uptake experiments, elemental analysis using computer controlled scanning electron microscopy and energy dispersive analysis of X-rays (CCSEM/EDX), and determination of carbon bonding with scanning transmission X-ray microscopy and near-edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS). Regardless of bubble generation method, the overall concentration of aerosol particles, TEP, POC and DOC increased as concentrations of bacterial and phytoplankton cells increased, stabilized, and subsequently declined. Particles <100 nm generated by means of jets were enhanced with time compared with larger sizes. In contrast, all particle sizes were equally enhanced when frits were used. Aerosolized particles were hygroscopic, a finding with significance for warm cloud formation and potential liquid-to-ice phase transformations. Aqueous and dry aerosolized particles from biologically active mesocosm water were found to efficiently nucleate ice exposed to supersaturated water vapor. The majority of particles, including those nucleating ice, consisted of a sea salt core coated with organic material dominated by the carboxyl functional group, and corresponded to a particle type commonly found in marine air. Our results provide improved estimates of marine aerosol production, chemical composition, and hygroscopicity, as well as an accurate physical and chemical representation of ice nucleation by marine biogenic aerosol particles for use in cloud and climate models.

Retrieval of subvisual cirrus cloud optical thickness from limb-scatter measurements

NASA Astrophysics Data System (ADS)

Wiensz, J. T.; Degenstein, D. A.; Lloyd, N. D.; Bourassa, A. E.

2013-01-01

We present a technique for estimating the optical thickness of subvisual cirrus clouds detected by OSIRIS (Optical Spectrograph and Infrared Imaging System), a limb-viewing satellite instrument that measures scattered radiances from the UV to the near-IR. The measurement set is composed of a ratio of limb radiance profiles at two wavelengths that indicates the presence of cloud-scattering regions. Cross-sections and phase functions from an in situ database are used to simulate scattering by cloud-particles. With appropriate configurations discussed in this paper, the SASKTRAN successive-orders of scatter radiative transfer model is able to simulate accurately the in-cloud radiances from OSIRIS. Configured in this way, the model is used with a multiplicative algebraic reconstruction technique (MART) to retrieve the cloud extinction profile for an assumed effective cloud particle size. The sensitivity of these retrievals to key auxiliary model parameters is shown, and it is shown that the retrieved extinction profile, for an assumed effective cloud particle size, models well the measured in-cloud radiances from OSIRIS. The greatest sensitivity of the retrieved optical thickness is to the effective cloud particle size. Since OSIRIS has an 11-yr record of subvisual cirrus cloud detections, the work described in this manuscript provides a very useful method for providing a long-term global record of the properties of these clouds.

Effect of Amazon Smoke on Cloud Microphysics and Albedo-Analysis from Satellite Imagery.

NASA Astrophysics Data System (ADS)

Kaufman, Yoram J.; Nakajima, Teruyuki

1993-04-01

NOAA Advanced Very High Resolution Radiometer images taken over the Brazilian Amazon Basin during the biomass burning season of 1987 are used to study the effect of smoke aerosol particles on the properties of low cumulus and stratocumulus clouds. The reflectance at a wavelength of 0.64 µm and the drop size, derived from the cloud reflectance at 3.75 µm, are studied for tens of thousands of clouds. The opacity of the smoke layer adjacent to each cloud is also monitored simultaneously. Though from satellite data it is impossible to derive all the parameters that influence cloud properties and smoke cloud interaction (e.g., detailed aerosol particles size distribution and chemistry, liquid water content, etc.); satellite data can be used to generate large-scale statistics of the properties of clouds and surrounding aerosol (e.g., smoke optical thickness, cloud-drop size, and cloud reflection of solar radiation) from which the interaction of aerosol with clouds can be surmised. In order to minimize the effect of variations in the precipitable water vapor and in other smoke and cloud properties, biomass burning in the tropics is chosen as the study topic, and the results are averaged for numerous clouds with the same ambient smoke optical thickness.It is shown in this study that the presence of dense smoke (an increase in the optical thickness from 0.1 to 2.0) can reduce the remotely sensed drop size of continental cloud drops from 15 to 9 µm. Due to both the high initial reflectance of clouds in the visible part of the spectrum and the presence of graphitic carbon, the average cloud reflectance at 0.64 µm is reduced from 0.71 to 0.68 for an increase in smoke optical thickness from 0.1 to 2.0. The measurements are compared to results from other years, and it is found that, as predicted, high concentration of aerosol particles causes a decrease in the cloud-drop size and that smoke darkens the bright Amazonian clouds. Comparison with theoretical computations based on Twomey's model show that by using the measured reduction in the cloud-drop size due to the presence of smoke it is possible to explain the reduction in the cloud reflectance at 0.64 µm for smoke imagery index of 0.02 to 0.03.Smoke particles are hygroscopic and have a similar size distribution to maritime and anthropogenic sulfuric aerosol particles. Therefore, these results may also be representative of the interaction of sulfuric particles with clouds.

In situ observations of snow particle size distributions over a cold frontal rainband within an extratropical cyclone

NASA Astrophysics Data System (ADS)

Yang, Jiefan; Lei, Hengchi

2016-02-01

Cloud microphysical properties of a mixed phase cloud generated by a typical extratropical cyclone in the Tongliao area, Inner Mongolia on 3 May 2014, are analyzed primarily using in situ flight observation data. This study is mainly focused on ice crystal concentration, supercooled cloud water content, and vertical distributions of fit parameters of snow particle size distributions (PSDs). The results showed several discrepancies of microphysical properties obtained during two penetrations. During penetration within precipitating cloud, the maximum ice particle concentration, liquid water content, and ice water content were increased by a factor of 2-3 compared with their counterpart obtained during penetration of a nonprecipitating cloud. The heavy rimed and irregular ice crystals obtained by 2D imagery probe as well as vertical distributions of fitting parameters within precipitating cloud show that the ice particles grow during falling via riming and aggregation process, whereas the lightly rimed and pristine ice particles as well as fitting parameters within non-precipitating cloud indicate the domination of sublimation process. During the two cloud penetrations, the PSDs were generally better represented by gamma distributions than the exponential form in terms of the determining coefficient ( R 2). The correlations between parameters of exponential /gamma form within two penetrations showed no obvious differences compared with previous studies.

Applying super-droplets as a compact representation of warm-rain microphysics for aerosol-cloud-aerosol interactions

NASA Astrophysics Data System (ADS)

Arabas, S.; Jaruga, A.; Pawlowska, H.; Grabowski, W. W.

2012-12-01

Clouds may influence aerosol characteristics of their environment. The relevant processes include wet deposition (rainout or washout) and cloud condensation nuclei (CCN) recycling through evaporation of cloud droplets and drizzle drops. Recycled CCN physicochemical properties may be altered if the evaporated droplets go through collisional growth or irreversible chemical reactions (e.g. SO2 oxidation). The key challenge of representing these processes in a numerical cloud model stems from the need to track properties of activated CCN throughout the cloud lifecycle. Lack of such "memory" characterises the so-called bulk, multi-moment as well as bin representations of cloud microphysics. In this study we apply the particle-based scheme of Shima et al. 2009. Each modelled particle (aka super-droplet) is a numerical proxy for a multiplicity of real-world CCN, cloud, drizzle or rain particles of the same size, nucleus type,and position. Tracking cloud nucleus properties is an inherent feature of the particle-based frameworks, making them suitable for studying aerosol-cloud-aerosol interactions. The super-droplet scheme is furthermore characterized by linear scalability in the number of computational particles, and no numerical diffusion in the condensational and in the Monte-Carlo type collisional growth schemes. The presentation will focus on processing of aerosol by a drizzling stratocumulus deck. The simulations are carried out using a 2D kinematic framework and a VOCALS experiment inspired set-up (see http://www.rap.ucar.edu/~gthompsn/workshop2012/case1/).

Direct Observations of Isoprene Secondary Organic Aerosol Formation in Ambient Cloud Droplets

NASA Astrophysics Data System (ADS)

Zelenyuk, A.; Bell, D.; Thornton, J. A.; Fast, J. D.; Shrivastava, M. B.; Berg, L. K.; Imre, D. G.; Mei, F.; Shilling, J.; Suski, K. J.; Liu, J.; Tomlinson, J. M.; Wang, J.

2017-12-01

Multiphase chemistry of isoprene photooxidation products has been shown to be one of the major sources of secondary organic aerosol (SOA) in the atmosphere. A number of recent studies indicate that aqueous aerosol phase provides a medium for reactive uptake of isoprene photooxidation products, and in particular, isomeric isoprene epoxydiols (IEPOX), with reaction rates and yields being dependent on aerosol acidity, water content, sulfate concentration, and organic coatings. However, very few studies focused on chemistry occurring within actual cloud droplets. We will present data acquired during recent Holistic Interactions of Shallow Clouds, Aerosols, and Land Ecosystems (HI-SCALE) Campaign, which provide direct evidence for IEPOX-SOA formation in cloud droplets. Single particle mass spectrometer, miniSPLAT, and a high-resolution, time-of-flight aerosol mass spectrometer were used to characterize the composition of aerosol particles and cloud droplet residuals, while a high-resolution, time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS) was used to characterize gas-phase compounds. We find that the composition of cloud droplet residuals was markedly different than that of aerosol particles sampled outside the cloud. Cloud droplet residuals were comprised of individual particles with high relative fractions of sulfate and nitrate and significant fraction of particles with mass spectra that are nearly identical to those of laboratory-generated IEPOX-SOA particles. The observed cloud-induced formation of IEPOX-SOA was accompanied by simultaneous decrease in measured concentrations of IEPOX and other gas-phase isoprene photooxidation products. Ultimately, the combined cloud, aerosol, and gas-phase measurements conducted during HI-SCALE will be used to develop and evaluate model treatments of aqueous-phase isoprene SOA formation.

Stability of the Early Mars Atmosphere to Collapse into Permanent Polarcaps

NASA Technical Reports Server (NTRS)

Haberle, R. M.; Kahre, M. A.; Wordsworth, R.; Forget, F.

2016-01-01

The presence of a permanent CO2 polar ice cap on Mars has important consequences for the planet's climate system. The heat balance of such a cap, which is determined mainly by atmospheric heat transport, and the downward solar in infrared radiative fluxes, determines its surface temperature, which through the vapor pressure relation sets the mean annual surface pressure. On Mars today, for example, the south residual CO2 cap is present year-round with a mean annual temperature of approximately 145 K which corresponds to a mean annual CO2 vapor pressure of approximately 600 Pa. On early Mars, permanent polar caps are also possible especially since the sun was less luminous 3.5-4.0 Gya. Thus, the existence of permanent polar caps on early Mars is central to understanding the nature of the planets climate system in those ancient times and whether or not the atmosphere might have been capable of sustaining conditions suitable for liquid water flowing over the surface as is indicated in the geological record. Forget et al [1] showed that for present orbital properties atmospheric collapse into permanent polar caps could only be prevented for surface pressures roughly between 500 - 3000 hPa. Though follow-on studies confirm and extend the Forget et al. results [2], the full sensitivity of this "window" of stability has not been explored. There are many factors to consider such the albedo of the caps, dust content of the atmosphere, and the presence of water ice clouds. However, we begin our exploration of the stability of the early Martian atmosphere by focusing on the role of CO2 ice clouds. In some preliminary simulations with the Ames Mars General Circulation Model (GCM) we found that atmospheric collapse depends on assumptions regarding the fate of CO2 ice clouds. If, for example, we assume the clouds immediately fall to the surface, then in some cases collapse is favored. On the other hand if the clouds are allowed to fall and evaporate, collapse can be averted. This implies that CO2 ice cloud microphysics is important to the overall stability of the atmosphere. Though the Ames GCM has a sophisticated CO2 cloud microphysics package that includes nucleation, growth, and sedimentation (see accompanying poster by Kahre et al. [3]), we have implemented a simpler scheme based on the Forget et al. [1] approach to CO2 ice clouds. Our goal is to reproduce and expand their study. The key parameter in this approach is the concentration and vertical distribution of cloud condensation nuclei (CCN), i.e., dust particles. Fewer CCN lead to larger particles which fall faster, while higher CCN concentrations lead to smaller particles and thicker clouds that remain suspended for longer periods of time. We plan to explore the stability of the atmosphere to CCN concentrations and distributions and then assess the capability of thick early atmospheres to loft and distribute dust particles (CCN) around the planet. Thus, our work will shed light on the nature of the coupling between the dust and CO2 cycles and the implications it has for the early Mars climate system.

Cloud Condensation Nuclei in Cumulus Humilis - Selected Case Study During the CHAPS Campaign

NASA Astrophysics Data System (ADS)

Yu, X.; Berg, L. K.; Berkowitz, C. M.; Alexander, M. L.; Lee, Y.; Laskin, A.; Ogren, J. A.; Andrews, B.

2009-12-01

The Cumulus Humilis Aerosol Processing Study (CHAPS) provided a unique opportunity to study aerosol and cloud processing. Clouds play an active role in the processing and cycling of atmospheric constituents. Gases and particles can partition to cloud droplets by absorption and condensation as well as activation and pact scavenging. The Department of Energy (DOE) G-1 aircraft was used as one of the main platforms in CHAPS. Flight tracks were designed and implemented to characterize freshly emitted aerosols on cloud top and cloud base as well as with cloud, i.e., cumulus humilis (or fair-weather cumulus), in the vicinity of Oklahoma City. Measurements of interstitial aerosols and residuals of activated condensation cloud nuclei were conducted simultaneously. The interstitial aerosols were determined downstream of an isokinetic inlet; and the activated particles downstream of a counter-flow virtual impactor (CVI). The sampling line to the Aerodyne Aerosol Mass Spectrometer was switched between the isokinetic inlet and the CVI to allow characterization of interstitial particles out of clouds in contrast to particles activated in clouds. Trace gases including ozone, carbon monoxide, sulfur dioxide, and a series of volatile organic compounds (VOCs) were also measured as were key meteorological state parameters including liquid water content, cloud drop size, and dew point temperature were measured. This work will focus on studying CCN properties in cumulus humilis. Several approaches will be taken. The first is single particle analysis of particles collected by the Time-Resolved Aerosol Sampler (TRAC) by SEM/TEM coupled with EDX. We will specifically look into differences in particle properties such as chemical composition and morphology between activated and interstitial ones. The second analysis will link in situ measurements with the snap shots observations by TRAC. For instance, by looking into the characteristic m/z obtained by AMS vs. CO or isoprene, one can gain more insight into the role of primary and secondary organic aerosols in CCNs and background aerosols. Combined with observations of cloud properties, an improved picture of CCN activation in cumulus humilis can be made.

Pre-activation of aerosol particles by ice preserved in pores

NASA Astrophysics Data System (ADS)

Marcolli, Claudia

2017-02-01

Pre-activation denotes the capability of particles or materials to nucleate ice at lower relative humidities or higher temperatures compared to their intrinsic ice nucleation efficiency after having experienced an ice nucleation event or low temperature before. This review presumes that ice preserved in pores is responsible for pre-activation and analyses pre-activation under this presumption. Idealized trajectories of air parcels are used to discuss the pore characteristics needed for ice to persist in pores and to induce macroscopic ice growth out of the pores. The pore width needed to keep pores filled with water decreases with decreasing relative humidity as described by the inverse Kelvin equation. Thus, narrow pores remain filled with ice well below ice saturation. However, the smaller the pore width, the larger the melting and freezing point depressions within the pores. Therefore, pre-activation due to pore ice is constrained by the melting of ice in narrow pores and the sublimation of ice from wide pores imposing restrictions on the temperature and relative humidity range of pre-activation for cylindrical pores. Ice is better protected in ink-bottle-shaped pores with a narrow opening leading to a large cavity. However, whether pre-activation is efficient also depends on the capability of ice to grow macroscopically, i.e. out of the pore. A strong effect of pre-activation is expected for swelling pores, because at low relative humidity (RH) their openings narrow and protect the ice within them against sublimation. At high relative humidities, they open up and the ice can grow to macroscopic size and form an ice crystal. Similarly, ice protected in pockets is perfectly sheltered against sublimation but needs the dissolution of the surrounding matrix to be effective. Pores partially filled with condensable material may also show pre-activation. In this case, complete filling occurs at lower RH than for empty pores and freezing shifts to lower temperatures.Pre-activation experiments confirm that materials susceptible to pre-activation are indeed porous. Pre-activation was observed for clay minerals like illite, kaolinite, and montmorillonite with inherent porosity. The largest effect was observed for the swelling clay mineral montmorillonite. Some materials may acquire porosity, depending on the formation and processing conditions. Particles of CaCO3, meteoritic material, and volcanic ash showed pre-activation for some samples or in some studies but not in other ones. Quartz and silver iodide were not susceptible to pre-activation.Atmospheric relevance of pre-activation by ice preserved in pores may not be generally given but depend on the atmospheric scenario. Lower-level cloud seeding by pre-activated particles released from high-level clouds crucially depends on the ability of pores to retain ice at the relative humidities and temperatures of the air masses they pass through. Porous particles that are recycled in wave clouds may show pre-activation with subsequent ice growth as soon as ice saturation is exceeded after having passed a first cloud event. Volcanic ash particles and meteoritic material likely influence ice cloud formation by pre-activation. Therefore, the possibility of pre-activation should be considered when ice crystal number densities in clouds exceed the number of ice-nucleating particles measured at the cloud forming temperature.

Two-dimensional positive column structure with dust cloud: Experiment and nonlocal kinetic simulation

NASA Astrophysics Data System (ADS)

Zobnin, A. V.; Usachev, A. D.; Petrov, O. F.; Fortov, V. E.; Thoma, M. H.; Fink, M. A.

2018-03-01

The influence of a dust cloud on the structure of the positive column of a direct current gas discharge in a cylindrical glass tube under milligravity conditions has been studied both experimentally and numerically. The discharge was produced in neon at 60 Pa in a glass tube with a diameter of 30 mm at a discharge current 1 mA. Spherical monodisperse melamine formaldehyde dust particles with a diameter of 6.86 μm were injected into the positive column and formed there a uniform dust cloud with a maximum diameter of 14.4 mm. The shape of the cloud and the dust particle number density were measured. The cloud was stationary in the radial direction and slowly drifted in the axial direction. It was found that in the presence of the dust cloud, the intensity of the neon spectral line with a wavelength by 585.25 nm emitted by the discharge plasma increased by 2.3 times and 2 striations appeared on the anode side of the cloud. A numerical simulation of the discharge was performed using the 2D (quasi-3D) nonlocal self-consistent kinetic model of a longitudinally inhomogeneous axially symmetric positive column [Zobnin et al., Phys. Plasmas 21, 113503 (2014)], which was supplemented by a program module performing a self-consistent calculation of dust particle charges, the plasma recombination rate on dust particles, and ion scattering on dust particles. A new approach to the calculation of particle charges and the screening radius in dense dust clouds is proposed. The results of the simulation are presented, compared with experimental data and discussed. It is demonstrated that for the best agreement between simulated and experimental data, it is necessary to take into account the reflection of electrons from the dust particle surface in order to correctly describe the recombination rate in the cloud, its radial stability, and the dust particle charges.

Representation of Arctic mixed-phase clouds and the Wegener-Bergeron-Findeisen process in climate models: Perspectives from a cloud-resolving study

NASA Astrophysics Data System (ADS)

Fan, Jiwen; Ghan, Steven; Ovchinnikov, Mikhail; Liu, Xiaohong; Rasch, Philip J.; Korolev, Alexei

2011-01-01

Two types of Arctic mixed-phase clouds observed during the ISDAC and M-PACE field campaigns are simulated using a 3-dimensional cloud-resolving model (CRM) with size-resolved cloud microphysics. The modeled cloud properties agree reasonably well with aircraft measurements and surface-based retrievals. Cloud properties such as the probability density function (PDF) of vertical velocity (w), cloud liquid and ice, regimes of cloud particle growth, including the Wegener-Bergeron-Findeisen (WBF) process, and the relationships among properties/processes in mixed-phase clouds are examined to gain insights for improving their representation in General Circulation Models (GCMs). The PDF of the simulated w is well represented by a Gaussian function, validating, at least for arctic clouds, the subgrid treatment used in GCMs. The PDFs of liquid and ice water contents can be approximated by Gamma functions, and a Gaussian function can describe the total water distribution, but a fixed variance assumption should be avoided in both cases. The CRM results support the assumption frequently used in GCMs that mixed phase clouds maintain water vapor near liquid saturation. Thus, ice continues to grow throughout the stratiform cloud but the WBF process occurs in about 50% of cloud volume where liquid and ice co-exist, predominantly in downdrafts. In updrafts, liquid and ice particles grow simultaneously. The relationship between the ice depositional growth rate and cloud ice strongly depends on the capacitance of ice particles. The simplified size-independent capacitance of ice particles used in GCMs could lead to large deviations in ice depositional growth.

Volcanic ash cloud detection from space: a preliminary comparison between RST approach and water vapour corrected BTD procedure

NASA Astrophysics Data System (ADS)

Piscini, Alessandro; Marchese, Francesco; Merucci, Luca; Pergola, Nicola; Corradini, Stefano; Tramutoli, Valerio

2010-05-01

Volcanic eruptions can inject large amounts (Tg) of gas and particles into the troposphere and, sometimes, into the stratosphere. Besides the main gases (H2O, CO2 , SO2 and HCl), volcanic clouds contain a mix of silicate ash particles in the size range 0.1μm to mm or larger. Interest in the ash presence detection is high in particular because it represents a serious hazard for air traffic. Particles with dimension of several millimeters can damage the aircraft structure (windows, wings, ailerons), while particles less than 10μm may be extremely dangerous for the jet engines and are undetectable by the pilots during night or in low visibility conditions. Satellite data are useful for measuring volcanic clouds because of the large vertical range of these emissions and their likely large horizontal spread. Moreover, since volcanoes are globally distributed and inherently dangerous, satellite measurements offer a practical and safe platform from which to make observations. Two different techniques used to detect volcanic clouds from satellite data are considered here for a preliminary comparison, with possible implications on quantitative retrievals of plume parameters. In particular, the Robust Satellite Techniques (RST) approach and a water vapour corrected version of the Brightness Temperature Difference (BTD) procedure, will be compared. The RST approach is based on the multi-temporal analysis of historical, long-term satellite records, devoted to a former characterization of the measured signal, in terms of expected value and natural variability and a further recognition of signal anomalies by an automatic, unsupervised change detection step. The BTD method is based on the difference between the brightness temperature measured in two channels centered around 11 and 12 mm. To take into account the atmospheric water vapour differential absorption in the 11-12 μm spectral range that tends to reduce (and in some cases completely mask) the BTD signal, a water vapor correction procedure, based on measured or synthetic atmospheric profiles, has been applied. Results independently achieved by both methods during recent Mt. Etna eruptions are presented, compared and discussed also in terms of further implications for quantitative retrievals of plume parameters.

Ionisation and discharge in cloud-forming atmospheres of brown dwarfs and extrasolar planets

NASA Astrophysics Data System (ADS)

Helling, Ch; Rimmer, P. B.; Rodriguez-Barrera, I. M.; Wood, Kenneth; Robertson, G. B.; Stark, C. R.

2016-07-01

Brown dwarfs and giant gas extrasolar planets have cold atmospheres with rich chemical compositions from which mineral cloud particles form. Their properties, like particle sizes and material composition, vary with height, and the mineral cloud particles are charged due to triboelectric processes in such dynamic atmospheres. The dynamics of the atmospheric gas is driven by the irradiating host star and/or by the rotation of the objects that changes during its lifetime. Thermal gas ionisation in these ultra-cool but dense atmospheres allows electrostatic interactions and magnetic coupling of a substantial atmosphere volume. Combined with a strong magnetic field \\gg {{B}\\text{Earth}} , a chromosphere and aurorae might form as suggested by radio and x-ray observations of brown dwarfs. Non-equilibrium processes like cosmic ray ionisation and discharge processes in clouds will increase the local pool of free electrons in the gas. Cosmic rays and lighting discharges also alter the composition of the local atmospheric gas such that tracer molecules might be identified. Cosmic rays affect the atmosphere through air showers in a certain volume which was modelled with a 3D Monte Carlo radiative transfer code to be able to visualise their spacial extent. Given a certain degree of thermal ionisation of the atmospheric gas, we suggest that electron attachment to charge mineral cloud particles is too inefficient to cause an electrostatic disruption of the cloud particles. Cloud particles will therefore not be destroyed by Coulomb explosion for the local temperature in the collisional dominated brown dwarf and giant gas planet atmospheres. However, the cloud particles are destroyed electrostatically in regions with strong gas ionisation. The potential size of such cloud holes would, however, be too small and might occur too far inside the cloud to mimic the effect of, e.g. magnetic field induced star spots.

The thin border between cloud and aerosol: Sensitivity of several ground based observation techniques

NASA Astrophysics Data System (ADS)

Calbó, Josep; Long, Charles N.; González, Josep-Abel; Augustine, John; McComiskey, Allison

2017-11-01

Cloud and aerosol are two manifestations of what it is essentially the same physical phenomenon: a suspension of particles in the air. The differences between the two come from the different composition (e.g., much higher amount of condensed water in particles constituting a cloud) and/or particle size, and also from the different number of such particles (10-10,000 particles per cubic centimeter depending on conditions). However, there exist situations in which the distinction is far from obvious, and even when broken or scattered clouds are present in the sky, the borders between cloud/not cloud are not always well defined, a transition area that has been coined as the ;twilight zone;. The current paper presents a discussion on the definition of cloud and aerosol, the need for distinguishing or for considering the continuum between the two, and suggests a quantification of the importance and frequency of such ambiguous situations, founded on several ground-based observing techniques. Specifically, sensitivity analyses are applied on sky camera images and broadband and spectral radiometric measurements taken at Girona (Spain) and Boulder (Co, USA). Results indicate that, at these sites, in more than 5% of the daytime hours the sky may be considered cloudless (but containing aerosols) or cloudy (with some kind of optically thin clouds) depending on the observing system and the thresholds applied. Similarly, at least 10% of the time the extension of scattered or broken clouds into clear areas is problematic to establish, and depends on where the limit is put between cloud and aerosol. These findings are relevant to both technical approaches for cloud screening and sky cover categorization algorithms and radiative transfer studies, given the different effect of clouds and aerosols (and the different treatment in models) on the Earth's radiation balance.

Cirrus cloud model parameterizations: Incorporating realistic ice particle generation

NASA Technical Reports Server (NTRS)

Sassen, Kenneth; Dodd, G. C.; Starr, David OC.

1990-01-01

Recent cirrus cloud modeling studies have involved the application of a time-dependent, two dimensional Eulerian model, with generalized cloud microphysical parameterizations drawn from experimental findings. For computing the ice versus vapor phase changes, the ice mass content is linked to the maintenance of a relative humidity with respect to ice (RHI) of 105 percent; ice growth occurs both with regard to the introduction of new particles and the growth of existing particles. In a simplified cloud model designed to investigate the basic role of various physical processes in the growth and maintenance of cirrus clouds, these parametric relations are justifiable. In comparison, the one dimensional cloud microphysical model recently applied to evaluating the nucleation and growth of ice crystals in cirrus clouds explicitly treated populations of haze and cloud droplets, and ice crystals. Although these two modeling approaches are clearly incompatible, the goal of the present numerical study is to develop a parametric treatment of new ice particle generation, on the basis of detailed microphysical model findings, for incorporation into improved cirrus growth models. For example, the relation between temperature and the relative humidity required to generate ice crystals from ammonium sulfate haze droplets, whose probability of freezing through the homogeneous nucleation mode are a combined function of time and droplet molality, volume, and temperature. As an example of this approach, the results of cloud microphysical simulations are presented showing the rather narrow domain in the temperature/humidity field where new ice crystals can be generated. The microphysical simulations point out the need for detailed CCN studies at cirrus altitudes and haze droplet measurements within cirrus clouds, but also suggest that a relatively simple treatment of ice particle generation, which includes cloud chemistry, can be incorporated into cirrus cloud growth.

Modeling the effects of an offset of the center of symmetry in the zodiacal cloud

NASA Astrophysics Data System (ADS)

Holmes, E. K.; Dermott, S. F.; Xu, Y. L.; Wyatt, M.; Jayaraman, S.

1998-04-01

There is a possible connection between structure in circumstellar dust clouds and the presence of planets, our own zodiacal cloud being the prime example. Asymmetries in such clouds could be diagnostic of planets which would be otherwise undetectable. One such feature is an offset of the center of symmetry of the disk with respect to the central star. The offset is caused by the forced eccentricities (ef) of particles in the cloud. The orbit of a particle can be described by a set of five orbital elements: the semi-major axis (a), eccentricity (e), inclination (I), longitude of ascending node (Omega) and the argument of pericenter (omega). In low order secular perturbation theory, osculating elements of small bodies are decomposed into proper and forced elements. The proper elements are dependent on initial conditions while the forced elements are imposed on the particle's orbit by the gravitational perturbations of the planets. This decomposition is still applicable in the presence of drag forces. We compare COBE observations of the variation in average polar brightness of the background cloud, (N + S)/2, with ecliptic longitude of Earth with those of a model cloud made of asteroidal particles which populate the inner solar system according to a 1/rgamma where (gamma) = 1 (Poynting Robertson light drag) distribution. The variation with ecliptic longitude of Earth in mean polar brightness is shown in for the 25 micron waveband. Sine curves are fit to both the COBE observations and the model. The variation in (N+S)/2 with ecliptic longitude of Earth can be represented as a superposition of two sine curves: one for the variation in (N + S)/2 due to the Earth's eccentric orbit and the other for the variation in (N + S)/2 due to the forced eccentricities of particles in the cloud. If the cloud were symmetric about the Sun (i.e., if there were no offset), the maximum and minimum brightnesses of the cloud would occur at perihelion and aphelion, respectively. Looking at the model, one can see that the minimum does occur at Earth's aphelion (282.9 deg). However, the minimum of the COBE curve is clearly displaced from aphelion, showing that the center of symmetry of the cloud is displaced from the Sun. If we could turn off the effect of the Earth's eccentricity, we could isolate the sine curve due to ef. When we do this for the model cloud however, we do not see a variation in (N + S)/2 for two reasons: 1) Although the particle orbits are circularized due to Poynting Robertson drag (PR drag), the wedge shape of the cloud cancels out any number density variation as a function of radial distance; and 2) Even though we would expect the orbits of the particles to be more densely spaced at perihelion than at aphelion (provided all the particles had the same ef and omegaf, due to Kepler's Second Law the particles spend less time at perihelion than at aphelion thus canceling out any noticeable effect on the number density. However, when we build a new model cloud governed by a constant distribution of particles (1/rgamma where gamma = 0) instead of a 1/r distribution, we do see a sinusoidal variation in (N + S)/2 with ecliptic longitude of Earth. These results imply that the particles contributing to the observed offset do not have a PR drag distribution (i.e., they are not simply asteroidal particles). Future work will determine whether cometary particles (having a theoretical gamma = 1.5), collisionally evolved asteroidal particles, or a combination of both types of particles are responsible for the offset of the center of symmetry of the zodiacal cloud.

Microphysical processing of aerosol particles in orographic clouds

NASA Astrophysics Data System (ADS)

Pousse-Nottelmann, S.; Zubler, E. M.; Lohmann, U.

2015-01-01

An explicit and detailed treatment of cloud-borne particles allowing for the consideration of aerosol cycling in clouds has been implemented in the regional weather forecast and climate model COSMO. The effects of aerosol scavenging, cloud microphysical processing and regeneration upon cloud evaporation on the aerosol population and on subsequent cloud formation are investigated. For this, two-dimensional idealized simulations of moist flow over two bell-shaped mountains were carried out varying the treatment of aerosol scavenging and regeneration processes for a warm-phase and a mixed-phase orographic cloud. The results allowed to identify different aerosol cycling mechanisms. In the simulated non-precipitating warm-phase cloud, aerosol mass is incorporated into cloud droplets by activation scavenging and released back to the atmosphere upon cloud droplet evaporation. In the mixed-phase cloud, a first cycle comprises cloud droplet activation and evaporation via the Wegener-Bergeron-Findeisen process. A second cycle includes below-cloud scavenging by precipitating snow particles and snow sublimation and is connected to the first cycle via the riming process which transfers aerosol mass from cloud droplets to snow flakes. In the simulated mixed-phase cloud, only a negligible part of the total aerosol mass is incorporated into ice crystals. Sedimenting snow flakes reaching the surface remove aerosol mass from the atmosphere. The results show that aerosol processing and regeneration lead to a vertical redistribution of aerosol mass and number. However, the processes not only impact the total aerosol number and mass, but also the shape of the aerosol size distributions by enhancing the internally mixed/soluble accumulation mode and generating coarse mode particles. Concerning subsequent cloud formation at the second mountain, accounting for aerosol processing and regeneration increases the cloud droplet number concentration with possible implications for the ice crystal number concentration.

Self-generated clouds of micron-sized particles as a promising way of a Solar Probe shielding from intense thermal radiation of the Sun

NASA Astrophysics Data System (ADS)

Dombrovsky, Leonid A.; Reviznikov, Dmitry L.; Kryukov, Alexei P.; Levashov, Vladimir Yu

2017-10-01

An effect of shielding of an intense solar radiation towards a solar probe with the use of micron-sized SiC particles generated during ablation of a composite thermal protection material is estimated on a basis of numerical solution to a combined radiative and heat transfer problem. The radiative properties of particles are calculated using the Mie theory, and the spectral two-flux model is employed in radiative transfer calculations for non-uniform particle clouds. A computational model for generation and evolution of the cloud is based on a conjugated heat transfer problem taking into account heating and thermal destruction of the matrix of thermal protection material and sublimation of SiC particles in the generated cloud. The effect of light pressure, which is especially important for small particles, is also taken into account. The computational data for mass loss due to the particle cloud sublimation showed the low value about 1 kg/m2 per hour at the distance between the vehicle and the Sun surface of about four radii of the Sun. This indicates that embedding of silicon carbide or other particles into a thermal protection layer and the resulting generation of a particle cloud can be considered as a promising way to improve the possibilities of space missions due to a significant decrease in the vehicle working distance from the solar photosphere.

Aerosol partitioning in mixed-phase clouds at the Jungfraujoch (3580 m asl)

NASA Astrophysics Data System (ADS)

Henning, S.; Bojinski, S.; Diehl, K.; Ghan, S.; Nyeki, S.; Weingartner, E.; Wurzler, S.; Baltensperger, U.

2003-04-01

Field measurements on the partitioning between the interstitial and the liquid/ice phase in natural clouds were performed at the high-alpine research station Jungfraujoch (3580 m asl, Switzerland) during a summer and a winter campaign. The size distributions of the total and the interstitial aerosol were determined by means of a scanning mobility particle sizer (SMPS). From these, size resolved scavenging ratios were calculated. Simultaneously, cloud water content (CWC) and cloud particle size distributions along with meteorological data were obtained. In cold mixed phase clouds (existing of liquid droplets and ice crystals), strong differences were found in comparison to the warm summer clouds. In the warm cloud types all particles above a certain diameter were activated and thereby the scavenging ratio (number of activated particles divided by the total number concentration) above a certain threshold diameter approached 1. In the winter clouds, the scavenging ratio never reached the value of 1 and could be as low as 0. These observations are explained by the Bergeron-Findeisen process: Here, particles are also activated to droplets in the first step, but after the formation of the ice phase droplets evaporate while the ice crystals grow, due to difference in the saturation vapor pressure over water and ice. This release of aerosol particles to the interstitial aerosol has significant implications for the climate forcing: It can be expected that the number of CCN is of less importance as soon as ice crystals are formed.

Feasibility of reduced gravity experiments involving quiescent, uniform particle cloud combustion

NASA Technical Reports Server (NTRS)

Ross, Howard D.; Facca, Lily T.; Berlad, Abraham L.; Tangirala, Venkat

1989-01-01

The study of combustible particle clouds is of fundamental scientific interest as well as a practical concern. The principal scientific interests are the characteristic combustion properties, especially flame structure, propagation rates, stability limits, and the effects of stoichiometry, particle type, transport phenomena, and nonadiabatic processes on these properties. The feasibility tests for the particle cloud combustion experiment (PCCE) were performed in reduced gravity in the following stages: (1) fuel particles were mixed into cloud form inside a flammability tube; (2) when the concentration of particles in the cloud was sufficiently uniform, the particle motion was allowed to decay toward quiescence; (3) an igniter was energized which both opened one end of the tube and ignited the suspended particle cloud; and (4) the flame proceeded down the tube length, with its position and characteristic features being photographed by high-speed cameras. Gravitational settling and buoyancy effects were minimized because of the reduced gravity enviroment in the NASA Lewis drop towers and aircraft. Feasibility was shown as quasi-steady flame propagation which was observed for fuel-rich mixtures. Of greatest scientific interest is the finding that for near-stoichiometric mixtures, a new mode of flame propagation was observed, now called a chattering flame. These flames did not propagate steadily through the tube. Chattering modes of flame propagation are not expected to display extinction limits that are the same as those for acoustically undisturbed, uniform, quiescent clouds. A low concentration of fuel particles, uniformly distributed in a volume, may not be flammable but may be made flammable, as was observed, through induced segregation processes. A theory was developed which showed that chattering flame propagation was controlled by radiation from combustion products which heated the successive discrete laminae sufficiently to cause autoignition.

Improvements for retrieval of cloud droplet size by the POLDER instrument

NASA Astrophysics Data System (ADS)

Shang, H.; Husi, L.; Bréon, F. M.; Ma, R.; Chen, L.; Wang, Z.

2017-12-01

The principles of cloud droplet size retrieval via Polarization and Directionality of the Earth's Reflectance (POLDER) requires that clouds be horizontally homogeneous. The retrieval is performed by combining all measurements from an area of 150 km × 150 km to compensate for POLDER's insufficient directional sampling. Using POLDER-like data simulated with the RT3 model, we investigate the impact of cloud horizontal inhomogeneity and directional sampling on the retrieval and analyze which spatial resolution is potentially accessible from the measurements. Case studies show that the sub-grid-scale variability in droplet effective radius (CDR) can significantly reduce valid retrievals and introduce small biases to the CDR ( 1.5µm) and effective variance (EV) estimates. Nevertheless, the sub-grid-scale variations in EV and cloud optical thickness (COT) only influence the EV retrievals and not the CDR estimate. In the directional sampling cases studied, the retrieval using limited observations is accurate and is largely free of random noise. Several improvements have been made to the original POLDER droplet size retrieval. For example, measurements in the primary rainbow region (137-145°) are used to ensure retrievals of large droplet (>15 µm) and to reduce the uncertainties caused by cloud heterogeneity. A premium resoltion of 0.8° is determined by considering successful retrievals and cloud horizontal homogeneity. The improved algorithm is applied to measurements of POLDER in 2008, and we further compared our retrievals with cloud effective radii estimations of Moderate Resolution Imaging Spectroradiometer (MODIS). The results indicate that in global scale, the cloud effective radii and effective variance is larger in the central ocean than inland and coast areas. Over heavy polluted regions, the cloud droplets has small effective radii and narraw distribution due to the influence of aerosol particles.

Studying the influence of temperature and pressure on microphysical properties of mixed-phase clouds using airborne measurements

NASA Astrophysics Data System (ADS)

Andreea, Boscornea; Sabina, Stefan; Sorin-Nicolae, Vajaiac; Mihai, Cimpuieru

2015-04-01

One cloud type for which the formation and evolution process is not well-understood is the mixed-phase type. In general mixed-phase clouds consist of liquid droplets and ice crystals. The temperature interval within both liquid droplets and ice crystals can potentially coexist is limited to 0 °C and - 40 °C. Mixed-phase clouds account for 20% to 30% of the global cloud coverage. The need to understand the microphysical characteristics of mixed-phase clouds to improve numerical forecast modeling and radiative transfer calculation is of major interest in the atmospheric community. In the past, studies of cloud phase composition have been significantly limited by a lack of aircraft instruments capable of discriminating between the ice and liquid phase for a wide range of particle sizes. Presently, in situ airborne measurements provide the most accurate information about cloud microphysical characteristics. This information can be used for verification of both numerical models and cloud remote-sensing techniques. The knowledge of the temperature and pressure variation during the airborne measurements is crucial in order to understand their influence on the cloud dynamics and also their role in the cloud formation processes like accretion and coalescence. Therefore, in this paper is presented a comprehensive study of cloud microphysical properties in mixed-phase clouds in focus of the influence of temperature and pressure variation on both, cloud dynamics and the cloud formation processes, using measurements performed with the ATMOSLAB - Airborne Laboratory for Environmental Atmospheric Research in property of the National Institute for Aerospace Research "Elie Carafoli" (INCAS). The airborne laboratory equipped for special research missions is based on a Hawker Beechcraft - King Air C90 GTx aircraft and is equipped with a sensors system CAPS - Cloud, Aerosol and Precipitation Spectrometer (30 bins, 0.51-50 µm) and a HAWKEYE cloud probe. The analyzed data in this work is acquired during 2 flight hours on the 23th of October 2014 in mixed clouds formations over Romania ( Craiova, Lat 44°19', Lon 23°48' ). The temperature variation during the cloud sounding was between -14 °C and -2 °C, with a maximum altitude in the cloud of 4863 m and a minimum altitude of 3353 m. In total 6 horizontal lines of 10 minutes each where performed recording ice crystal number concentrations (using the CIP - Cloud Imaging Probe) between 10 to 20 particles/cm3 outside the cloud layer and over 100 particles/cm3 inside the cloud layer and a number concentration of small droplets, aerosol and small ice crystals (using the CAS - Cloud Aerosol Spectrometer) between 150 particles/cm3 outside the cloud layer and 1600 particles/cm3 inside the cloud layer, this values confirms also the presence of IN (ice nuclei) in the atmosphere between the cloud layers. The results in respect with size distribution of cloud's particles and LWC show to be controlled by the temperature and pressure variations.

Coherent clusters of inertial particles in homogeneous turbulence

NASA Astrophysics Data System (ADS)

Baker, Lucia; Frankel, Ari; Mani, Ali; Coletti, Filippo

2016-11-01

Clustering of heavy particles in turbulent flows manifests itself in a broad spectrum of physical phenomena, including sediment transport, cloud formation, and spray combustion. However, a clear topological definition of particle cluster has been lacking, limiting our ability to describe their features and dynamics. Here we introduce a definition of coherent cluster based on self-similarity, and apply it to the distribution of heavy particles in direct numerical simulations of homogeneous isotropic turbulence. We consider a range of particle Stokes numbers, with and without the effect of gravity. Clusters show self-similarity at length scales larger than twice the Kolmogorov length, with a specific fractal dimension. In the absence of gravity, clusters demonstrate a tendency to sample regions of the flow where strain is dominant over vorticity, and to align themselves with the local vorticity vector; when gravity is present, the clusters tend to align themselves with gravity, and their fall speed is different from the average settling velocity. This approach yields observations which are consistent with findings obtained from previous studies while opening new avenues for analysis of the topology and evolution of particle clusters in a wealth of applications.

Types, Sizes, Shapes and Distributions of Mars Ice and Dust Aerosols from the MGS TES Emission Phase Function Observations

NASA Astrophysics Data System (ADS)

Clancy, R. T.; Wolff, M. J.; Christensen, P. R.

2001-12-01

A full Mars year (1999-2001) of emission phase function (EPF observations from Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) provide the most complete study of Mars dust and ice aerosol properties to date. TES visible (solar band average) and infrared spectral (6-30 micron, 10 invcm res) EPF sequences are analyzed self-consistently with detailed multiple scattering radiative transfer (RT) codes to obtain first-time seasonal/latitudinal distributions of aerosol visible optical depths, particle sizes, and single scattering phase functions. As a consequence of the combined angular and wavelength coverage, we are able to define two distinct ice cloud types at 45S-45N latitudes on Mars. Type 1 ice clouds exhibit small particle sizes (1-2 micron radii), as well as a broad, deep minimum in side scattering indicative of aligned ice grains (see Wolff et al., 2001). Type 1 ice aerosols are most prevalent in the southern hemisphere during Mars aphelion, but also appear more widely distributed in season and latitude as topographic and high altitude (above 20 km) ice hazes. Type 2 ice clouds exhibit larger particle sizes (2-4 microns) and a much narrower side-scattering minimum, indicative of poorer grain alignment or a change in particle shape relative to the type 1 ice clouds (see Wolff et al., 2001). Type 2 ice clouds appear most prominently in the northern subtropical aphelion cloud belt, where relatively low altitudes of water vapor saturation (10 km) coincide with strong advective transport (Clancy et al., 1996). Retrieved dust particle radii of 1.5-1.8 micron are consistent with Pathfinder (Tomasko et al., 1999) and recent Viking/Mariner 9 reanalyses (e.g., size distribution B of Clancy et al., 1995). Detailed spectral modeling of the solar passband also implies agreement of EPF-derived dust single scattering albedos (ssa) with the ssa results from Tomasko et al.(table 8 therein). Spatial and seasonal changes in the dust ssa (0.92-0.95, solar band average) and phase functions suggest possible dust property variations, but may also be a consequence of variable high altitude ice hazes. The annual variations of both dust and ice clouds at 45S-45N latitudes are predominately orbital rather than seasonal in character and have shown close repeatability during the portions of first two Mars years observed by MGS (i.e., prior to the July 2001 global dust storm which began at Ls=185, a most striking departure from the previous two Mars years observed). Minimum visible dust opacities of 0.05-0.10 occur at southern latitudes in aphelion, maximum dust opacities of 1.0-1.5 at northern latitudes after Ls=200 (and greater than 3 in the 2001 global dust storm). Type 2 ice clouds abruptly disappear at Ls=145, as does the widespread occurrence of type 1 clouds in the southern hemisphere. Dust loading in the southern hemisphere increases at this time, but does not do so in the northern hemisphere. A comparison of dust solar band to thermal infrared optical depth ratios also provides strong evidence for non-uniform vertical mixing of the dust loading. A large fraction of the dust column (20-50 percent) appears to be concentrated in the lower boundary layer of the Mars atmosphere, particularly during conditions of low-to-moderate dust loading.

Evidence for Natural Variability in Marine Stratocumulus Cloud Properties Due to Cloud-Aerosol

NASA Technical Reports Server (NTRS)

Albrecht, Bruce; Sharon, Tarah; Jonsson, Haf; Minnis, Patrick; Minnis, Patrick; Ayers, J. Kirk; Khaiyer, Mandana M.

2004-01-01

In this study, aircraft observations from the Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter are used to characterize the variability in drizzle, cloud, and aerosol properties associated with cloud rifts and the surrounding solid clouds observed off the coast of California. A flight made on 16 July 1999 provided measurements directly across an interface between solid and rift cloud conditions. Aircraft instrumentation allowed for measurements of aerosol, cloud droplet, and drizzle spectra. CCN concentrations were measured in addition to standard thermodynamic variables and the winds. A Forward Scatter Spectrometer Probe (FSSP) measured size distribution of cloud-sized droplets. A Cloud Imaging Probe (CIP) was used to measure distributions of drizzle-sized droplets. Aerosol distributions were obtained from a Cloud Aerosol Scatterprobe (CAS). The CAS probe measured aerosols, cloud droplets and drizzle-sized drops; for this study. The CAS probe was used to measure aerosols in the size range of 0.5 micron - 1 micron. Smaller aerosols were characterized using an Ultrafine Condensation Particle Counter (CPC) sensor. The CPC was used to measure particles with diameters greater than 0.003 micron. By subtracting different count concentrations measured with the CPC, this probe was capable of identifying ultrafine particles those falling in the size range of 3 nanometers - 7 nanometers that are believed to be associated with new particle production.

Spatial and Temporal Distribution of Tropospheric Clouds and Aerosols Observed by MODIS Onboard the Terra and Aqua Satellites

NASA Technical Reports Server (NTRS)

King, Michael D.; Platnick, Steven; Menzel, W. Paul; Ackerman, Steven A.; Remer, Lorraine A.

2006-01-01

Remote sensing of cloud and aerosol optical properties is routinely obtained using the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra and Aqua satellites. Instruments that are being used to enhance our ability to characterize the global distribution of cloud and aerosol properties include well-calibrated multispectral radiometers that measure in the visible, near-infrared, and thermal infrared. The availability of thermal channels to enhance detection of cloud when estimating aerosol properties is an important improvement. In this paper, we describe the radiative properties of clouds as currently determined from satellites (cloud fraction, optical thickness, cloud top pressure, and cloud particle effective radius) and highlight the global/regional cloud microphysical properties currently available for assessing climate variability and forcing. These include the latitudinal distribution of cloud optical and radiative properties of both liquid water and ice clouds, as well as joint histograms of cloud optical thickness and effective particle radius for selected geographical locations around the world. In addition, we will illustrate the radiative and microphysical properties of aerosol particles (in cloud free regions) that are currently available from space-based observations, and show the latitudinal distribution of aerosol optical properties over both land and ocean surfaces.

Electroscavenging and Inferred Effects on Precipitation Efficiency

NASA Astrophysics Data System (ADS)

Tinsley, B. A.

2002-12-01

The evaporation of charged droplets leaves charged aerosol particles that can act as cloud condensation nuclei and ice forming nuclei. New calculations of scavenging of such charged particles by droplets have been made, that now include the effects of inertia and variable particle density, and variable cloud altitudes ranging into the stratosphere. They show that the Greenfield Gap closes for particles of low density, or for high altitude clouds, or for a few hundred elementary charges on the particles. A few tens of elementary charges on the particles gives collision efficiencies typically an order of magnitude greater than that due to phoretic forces alone. The numerical integrations show that electroscavenging of ice forming nuclei leading to contact ice nucleation is competitive with deposition ice nucleation, for cloud top temperatures in the range 0§C to -15§C and droplet size distributions extending past 10-15 mm radius. This implies that for marine stratocumulus or nimbostratus clouds with tops just below freezing temperature, where precipitation is initiated by the Wegener-Bergeron-Findeisen process, the precipitation efficiency can be affected by the amount of charge on the ice-forming nuclei. This in turn depends on the extent of the (weak) electrification of the cloud. Similarly, electroscavenging of condensation nuclei can increase the average droplet size in successive cycles of cloud evaporation and formation, and can also affect precipitation efficiency.

A new laboratory facility to study the interactions of aerosols, cloud droplets/ice crystals, and trace gases in a turbulent environment: The Π Chamber

NASA Astrophysics Data System (ADS)

Cantrell, W. H., II; Chang, K.; Ciochetto, D.; Niedermeier, D.; Bench, J.; Shaw, R. A.

2014-12-01

A detailed understanding of gas-aerosol-cloud interaction within the turbulent atmosphere is of prime importance for an accurate understanding of Earth's climate system. As one example: While every cloud droplet began as an aerosol particle, not every aerosol particle becomes a cloud droplet. The particle to droplet transformation requires that the particle be exposed to some critical concentration of water vapor, which differs for different combinations of particle size and chemical composition. Similarly, the formation of ice particles in mixed phase clouds is also catalyzed by aerosol particles. Even in the simplest scenarios it is challenging to gain a full understanding of the aerosol activation and ice nucleation processes. At least two other factors contribute significantly to the complexity observed in the atmosphere. First, aerosols and cloud particles are not static entities, but are continuously interacting with their chemical environment, and therefore changing in their properties. Second, clouds are ubiquitously turbulent, so thermodynamic and compositional variables, such as water vapor or other trace gas concentrations, fluctuate in space and time. Indeed, the coupling between turbulence and microphysical processes is one of the major research challenges in cloud physics. We have developed a multiphase, turbulent reaction chamber, (dubbed the Π Chamber, after the internal volume of 3.14 cubic meters) designed to address the problems outlined above. It is capable of pressures ranging from sea level to ~ 100 mbar, and can sustain temperatures of +40 to -55 ºC. We can independently control the temperatures on the surfaces of three heat transfer zones. This allows us to establish a temperature gradient between the floor and ceiling inducing Rayleigh-Benard convection and inducing a turbulent environment. Interior surfaces are electropolished stainless steel to facilitate cleaning before and after chemistry experiments. At present, supporting instrumentation includes a suite of aerosol generation and characterization techniques, a laser Doppler interferometer, and a holographic cloud particle imaging system.We will present detailed specifications, an overview of the supporting instrumentation, and initial characterization experiments from the Π chamber.

Insights into riming and aggregation processes as revealed by aircraft, radar, and disdrometer observations for a 27 April 2011 widespread precipitation event: Insights into Riming and Aggregation

DOE PAGES

Giangrande, Scott E.; Toto, Tami; Bansemer, Aaron; ...

2016-05-19

Our study presents aircraft spiral ascent and descent observations intercepting a transition to riming processes during widespread stratiform precipitation. The sequence is documented using collocated scanning and profiling radar, including longer-wavelength dual polarization measurements and shorter-wavelength Doppler spectra. Riming regions are supported using aircraft measurements recording elevated liquid water concentrations, spherical particle shapes, and saturation with respect to water. Profiling cloud radar observations indicate riming regions during the event as having increasing particle fall speeds, rapid time-height changes, and bimodalities in Doppler spectra. These particular riming signatures are coupled to scanning dual polarization radar observations of higher differential reflectivity (ZDR)more » aloft. Moreover, reduced melting layer enhancements and delayed radar bright-band signatures in the column are also observed during riming periods, most notably with the profiling radar observations. The bimodal cloud radar Doppler spectra captured near riming zones indicate two time-height spectral ice peaks, one rimed particle peak, and one peak associated with pristine ice needle generation and/or growth between -4°C and -7°C also sampled by aircraft probes. We observe this pristine needle population near the rimed particle region which gives a partial explanation for the enhanced ZDR. The riming signatures aloft and radar measurements within the melting level are weakly lag correlated (r~0.6) with smaller median drop sizes at the surface, as compared with later times when aggregation of larger particle sizes was believed dominant.« less

Insights into riming and aggregation processes as revealed by aircraft, radar, and disdrometer observations for a 27 April 2011 widespread precipitation event: Insights into Riming and Aggregation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Giangrande, Scott E.; Toto, Tami; Bansemer, Aaron

Our study presents aircraft spiral ascent and descent observations intercepting a transition to riming processes during widespread stratiform precipitation. The sequence is documented using collocated scanning and profiling radar, including longer-wavelength dual polarization measurements and shorter-wavelength Doppler spectra. Riming regions are supported using aircraft measurements recording elevated liquid water concentrations, spherical particle shapes, and saturation with respect to water. Profiling cloud radar observations indicate riming regions during the event as having increasing particle fall speeds, rapid time-height changes, and bimodalities in Doppler spectra. These particular riming signatures are coupled to scanning dual polarization radar observations of higher differential reflectivity (ZDR)more » aloft. Moreover, reduced melting layer enhancements and delayed radar bright-band signatures in the column are also observed during riming periods, most notably with the profiling radar observations. The bimodal cloud radar Doppler spectra captured near riming zones indicate two time-height spectral ice peaks, one rimed particle peak, and one peak associated with pristine ice needle generation and/or growth between -4°C and -7°C also sampled by aircraft probes. We observe this pristine needle population near the rimed particle region which gives a partial explanation for the enhanced ZDR. The riming signatures aloft and radar measurements within the melting level are weakly lag correlated (r~0.6) with smaller median drop sizes at the surface, as compared with later times when aggregation of larger particle sizes was believed dominant.« less

A Study of the Response of Deep Tropical Clouds to Mesoscale Processes. Part 1; Modeling Strategies and Simulations of TOGA-COARE Convective Systems

NASA Technical Reports Server (NTRS)

Johnson, Daniel E.; Tao, W.-K.; Simpson, J.; Sui, C.-H.; Einaudi, Franco (Technical Monitor)

2001-01-01

Interactions between deep tropical clouds over the western Pacific warm pool and the larger-scale environment are key to understanding climate change. Cloud models are an extremely useful tool in simulating and providing statistical information on heat and moisture transfer processes between cloud systems and the environment, and can therefore be utilized to substantially improve cloud parameterizations in climate models. In this paper, the Goddard Cumulus Ensemble (GCE) cloud-resolving model is used in multi-day simulations of deep tropical convective activity over the Tropical Ocean-Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE). Large-scale temperature and moisture advective tendencies, and horizontal momentum from the TOGA-COARE Intensive Flux Array (IFA) region, are applied to the GCE version which incorporates cyclical boundary conditions. Sensitivity experiments show that grid domain size produces the largest response to domain-mean temperature and moisture deviations, as well as cloudiness, when compared to grid horizontal or vertical resolution, and advection scheme. It is found that a minimum grid-domain size of 500 km is needed to adequately resolve the convective cloud features. The control experiment shows that the atmospheric heating and moistening is primarily a response to cloud latent processes of condensation/evaporation, and deposition/sublimation, and to a lesser extent, melting of ice particles. Air-sea exchange of heat and moisture is found to be significant, but of secondary importance, while the radiational response is small. The simulated rainfall and atmospheric heating and moistening, agrees well with observations, and performs favorably to other models simulating this case.

Characterization of Mesoscale Convective Systems by Means of Composite Radar Reflectivity Data

NASA Technical Reports Server (NTRS)

Geerts, Bart

1998-01-01

A mesoscale convective system (MCS) is broadly defined as a cloud and precipitation system of mesoscale dimensions (often too large for most aircraft to circumnavigate) with deep-convective activity concentrated in at least part of the MCS, or present during part of its evolution. A large areal fraction of MCSs is stratiform in nature, yet estimates from MCSs over the Great Plains, the Southeast, and tropical waters indicate that at least half of the precipitation is of convective origin. The presence of localized convection is important, because within convective towers cloud particles and hydrometeors are carried upward towards the cloud top. Ice crystals then move over more stratiform regions, either laterally, or through in situ settling over decaying and spreading convection. These ice crystals then grow to precipitation-size particles in mid- to upper tropospheric mesoscale updrafts. The convective portion of a MCS is often a more or less continuous line of thunderstorms, and may be either short-lived or long-lived. Geerts (1997) presents a preliminary climatology of MCSs in the southeastern USA, using just one year of composite digital radar reflectivity data. In this study MCSs are identified and characterized by means of visual inspection of animated images. A total of 398 MCSs were identified. In the warm season MCSs were found to be about twice as frequent as in the cold season. The average lifetime and maximum length of MCSs are 9 hours, and 350 km, respectively, but some MCSs are much larger and more persistent. In the summer months small and short-lived MCSs are relatively more common, whereas in winter larger and longer-lived systems occur more frequently. MCSs occur more commonly in the afternoon, in phase with thunderstorm activity, but the amplitude of the diurnal cycle is small compared to that of observed thunderstorms. It is estimated that in the Southeast more than half of all precipitation and severe weather results from MCSs.

Measurements of Ice Particles in Tropical Cirrus Anvils: Importance in Radiation Balance

NASA Technical Reports Server (NTRS)

Foster, Theodore; Arnott, William P.; Hallett, John; Pueschel, Rudi; Strawn, Anthony W. (Technical Monitor)

1994-01-01

Cirrus is important in the radiation balance of the global atmosphere, both at solar and thermal infrared (IR) wavelengths. In particular cirrus produced by deep convection over the oceans in the tropics may be critical in controlling processes whereby energy from warm tropical oceans is injected to different levels in the tropical atmosphere to subsequently influence not only tropical but mid latitude climate. Details of the cloud composition may differentiate between a net cooling or warming at these levels. The cloud composition may change depending on the input of nuclei from volcanic or other sources. Observations of cirrus during the FIRE-2 Project over Coffeyville, Kansas and by satellite demonstrate that cirrus, on occasion, is composed not only of larger particles with significant fall velocity (few hundred micrometers, 0.5 m/s) but much more numerous small particles, size 10-20 micrometers, with small fall velocity (cm/s), which may sometimes dominate the radiation field. This is consistent with emissivity measurements. In the thermal IR, ice absorption is strong, so that ice particles only 10 micrometers thick are opaque, at some wavelengths; on the other hand at other wavelengths and in the visible, ice is only moderately to weakly absorbing. It follows that for strongly absorbing wavelengths the average projected area of the ice particles is the important parameter, in weakly absorbing regions it is the volume (mass) of ice which is important. The shape of particles and also their internal structure may also have significant effect on their radiative properties. In order to access the role of cirrus in the radiation budget it is necessary to measure the distribution of ice particles sizes, shapes and concentrations in the regions of interest. A casual observation of any cirrus cloud shows that there is variability down to a scale of at least a few 100 m; this is confirmed by radar and lidar remote sensing. Thus aircraft measurements designed to give insight into the spatial distribution of radiation properties of ice crystals must be capable of examination of concentration, size and shape over a distance ideally of 100 m or less and to detect particles down to a size below which radiative effects are no longer significant.

A Comparison of Cloud Microphysical and Optical Properties during TOGA-COARE

NASA Technical Reports Server (NTRS)

Strawa, A. W.; Pueschel, R. F.; Pilewskie, P.; Valero, F. P. J.; Gore, Warren J. (Technical Monitor)

1996-01-01

The impact of cirrus clouds on climate is an issue of research interest currently. Whether cirrus clouds heat or cool the Earth-atmosphere system depends on the cloud shortwave albedo and infrared reflectance and absorptance. These in turn are determined by the size distribution, phase, and composition of particles in the clouds. The TOGA-COARE campaign presented an excellent opportunity to study cirrus clouds and their influence on climate. In this campaign, a microphysics instrument package was flown aboard the DC-8 aircraft at medium altitudes in cirrus clouds. This package included a 2D Greyscale Cloud Particle Probe, a Forward Scattering Spectrometer Aerosol Probe, and an ice crystal replicator. At the same time the ER-2 equipped with a radiation measurement system flew coordinated flight tracks above the DC-8 at very high altitude. The radiation measurement made were short and long wave fluxes, as well as narrowband fluxes, both upwelling and downwelling. In addition LIDAR data is available. The existence of these data sets allows for a the comparison of radiation measurement with microphysical measurements. For example, the optical depth and effective radius retrieved from the ER-2 radiation measurements can be compared to the microphysical data. Conversely, the optical properties and fluxes produced by the clouds can be calculated from the microphysical measurements and compared to those measured aboard the ER-2. The assumptions required to make these comparisons are discussed. Typical microphysical results show a prevalence of micron-sized particles, in addition to the cloud particles that exceed 100 mm. The large number of small particles or "haze" cause the effective cloud radii to shift to smaller sizes, leading to changes in optical parameters.

The 27-28 October 1986 FIRE IFO Cirrus Case Study: Cloud Optical Properties Determined by High Spectral Resolution Lidar

NASA Technical Reports Server (NTRS)

Grund, C. J.; Eloranta, E. W.

1996-01-01

During the First ISCCP Region Experiment (FIRE) cirrus intensive field observation (IFO) the High Spectral Resolution Lidar was operated from a roof top site on the University of Wisconsin-Madison campus. Because the HSRL technique separately measures the molecular and cloud particle backscatter components of the lidar return, the optical thickness is determined independent of particle backscatter. This is accomplished by comparing the known molecular density distribution to the observed decrease in molecular backscatter signal with altitude. The particle to molecular backscatter ratio yields calibrated measurements of backscatter cross sections that can be plotted ro reveal cloud morphology without distortion due to attenuation. Changes in cloud particle size, shape, and phase affect the backscatter to extinction ratio (backscatter-phase function). The HSRL independently measures cloud particle backscatter phase function. This paper presents a quantitative analysis of the HSRL cirrus cloud data acquired over an approximate 33 hour period of continuous near zenith observations. Correlations between small scale wind structure and cirrus cloud morphology have been observed. These correlations can bias the range averaging inherent in wind profiling lidars of modest vertical resolution, leading to increased measurement errors at cirrus altitudes. Extended periods of low intensity backscatter were noted between more strongly organized cirrus cloud activity. Optical thicknesses ranging from 0.01-1.4, backscatter phase functions between 0.02-0.065 sr (exp -1) and backscatter cross sections spanning 4 orders of magnitude were observed. the altitude relationship between cloud top and bottom boundaries and the cloud optical center altitude was dependent on the type of formation observed Cirrus features were observed with characteristic wind drift estimated horizontal sizes of 5-400 km. The clouds frequently exhibited cellular structure with vertical to horizontal dimension ratios of 1:5-1:1.

A Lab Based Method for Exoplanet Cloud and Aerosol Characterization

NASA Astrophysics Data System (ADS)

Johnson, A. V.; Schneiderman, T. M.; Bauer, A. J. R.; Cziczo, D. J.

2017-12-01

The atmospheres of some smaller, cooler exoplanets, like GJ 1214b, lack strong spectral features. This may suggest the presence of a high, optically thick cloud layer and poses great challenges for atmospheric characterization, but there is hope. The study of extraterrestrial atmospheres with terrestrial based techniques has proven useful for understanding the cloud-laden atmospheres of our solar system. Here we build on this by leveraging laboratory-based, terrestrial cloud particle instrumentation to better understand the microphysical and radiative properties of proposed exoplanet cloud and aerosol particles. The work to be presented focuses on the scattering properties of single particles, that may be representative of those suspended in exoplanet atmospheres, levitated in an Electrodynamic Balance (EDB). I will discuss how we leverage terrestrial based cloud microphysics for exoplanet applications, the instruments for single and ensemble particle studies used in this work, our investigation of ammonium nitrate (NH4NO3) scattering across temperature dependent crystalline phase changes, and the steps we are taking toward the collection of scattering phase functions and polarization of scattered light for exoplanet cloud analogs. Through this and future studies we hope to better understand how upper level cloud and/or aerosol particles in exoplanet atmospheres interact with incoming radiation from their host stars and what atmospheric information may still be obtainable through remote observations when no spectral features are observed.

Modeling Lidar Multiple Scattering

NASA Astrophysics Data System (ADS)

Sato, Kaori; Okamoto, Hajime; Ishimoto, Hiroshi

2016-06-01

A practical model to simulate multiply scattered lidar returns from inhomogeneous cloud layers are developed based on Backward Monte Carlo (BMC) simulations. The estimated time delay of the backscattered intensities returning from different vertical grids by the developed model agreed well with that directly obtained from BMC calculations. The method was applied to the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite data to improve the synergetic retrieval of cloud microphysics with CloudSat radar data at optically thick cloud grids. Preliminary results for retrieving mass fraction of co-existing cloud particles and drizzle size particles within lowlevel clouds are demonstrated.

Impact of the Bergeron-Findeisen process on the release of aerosol particles during the evolution of cloud ice

NASA Astrophysics Data System (ADS)

Schwarzenböck, A.; Mertes, S.; Heintzenberg, J.; Wobrock, W.; Laj, P.

The paper focuses on the redistribution of aerosol particles (APs) during the artificial nucleation and subsequent growth of ice crystals in a supercooled cloud. A significant number of the supercooled cloud droplets during icing periods (seeding agents: C 3H 8, CO 2) did not freeze as was presumed prior to the experiment but instead evaporated. The net mass flux of water vapour from the evaporating droplets to the nucleating ice crystals (Bergeron-Findeisen mechanism) led to the release of residual particles that simultaneously appeared in the interstitial phase. The strong decrease of the droplet residuals confirms the nucleation of ice particles on seeding germs without natural aerosol particles serving as ice nuclei. As the number of residual particles during the seedings did not drop to zero, other processes such as heterogeneous ice nucleation, spontaneous freezing, entrainment of supercooled droplets and diffusion to the created particle-free ice germs must have contributed to the experimental findings. During the icing periods, residual mass concentrations in the condensed phase dropped by a factor of 1.1-6.7, as compared to the unperturbed supercooled cloud. As the Bergeron-Findeisen process also occurs without artificial seeding in the atmosphere, this study demonstrated that the hydrometeors in mixed-phase clouds might be much cleaner than anticipated for the simple freezing process of supercooled droplets in tropospheric mid latitude clouds.

Interstellar and Cometary Dust

NASA Technical Reports Server (NTRS)

Mathis, John S.

1997-01-01

'Interstellar dust' forms a continuum of materials with differing properties which I divide into three classes on the basis of observations: (a) diffuse dust, in the low-density interstellar medium; (b) outer-cloud dust, observed in stars close enough to the outer edges of molecular clouds to be observed in the optical and ultraviolet regions of the spectrum, and (c) inner-cloud dust, deep within the cores of molecular clouds, and observed only in the infrared by means of absorption bands of C-H, C=O, 0-H, C(triple bond)N, etc. There is a surprising regularity of the extinction laws between diffuse- and outer-cloud dust. The entire mean extinction law from infrared through the observable ultraviolet spectrum can be characterized by a single parameter. There are real deviations from this mean law, larger than observational uncertainties, but they are much smaller than differences of the mean laws in diffuse- and outer-cloud dust. This fact shows that there are processes which operate over the entire distribution of grain sizes, and which change size distributions extremely efficiently. There is no evidence for mantles on grains in local diffuse and outer-cloud dust. The only published spectra of the star VI Cyg 12, the best candidate for showing mantles, does not show the 3.4 micro-m band which appreciable mantles would produce. Grains are larger in outer-cloud dust than diffuse dust because of coagulation, not accretion of extensive mantles. Core-mantle grains favored by J. M. Greenberg and collaborators, and composite grains of Mathis and Whiffen (1989), are discussed more extensively (naturally, I prefer the latter). The composite grains are fluffy and consist of silicates, amorphous carbon, and some graphite in the same grain. Grains deep within molecular clouds but before any processing within the solar system are presumably formed from the accretion of icy mantles on and within the coagulated outer-cloud grains. They should contain a mineral/carbonaceous matrix, without organic refractory mantles, in between the ices. Unfortunately, they may be significantly processed by chemical processes accompanying the warming (over the 10 K of the dark cloud cores) which occurs in the outer solar system. Evidence of this processing is the chemical anomalies present in interplanetary dust particles collected in the stratosphere, which may be the most primitive materials we have obtained to date. The comet return mission would greatly clarify the situation, and probably provide samples of genuine interstellar grains.

CLOTHES AS A SOURCE OF PARTICLES CONTRIBUTING TO THE "PERSONAL CLOUD"

EPA Science Inventory

Previous studies such as EPA's PTEAM Study have documented increased personal exposures to particles compared to either indoor or outdoor concentrations--a finding that bas been characterized as a "personal cloud." The sources of the personal cloud are unknown, but co...

The clouds are hazes of Venus

NASA Technical Reports Server (NTRS)

Esposito, L. W.; Knollenberg, R. G.; Marov, M. IA.; Toon, O. B.; Turco, R. P.

1983-01-01

Pioneer Venus and Venera probe data for the clouds of Venus are considered. These clouds consist of a main cloud deck at 45-70 km altitude, with thinner hazes above and below, although the microphysical properties of the main cloud are further subdivided into upper, middle and lower cloud levels. Much of the cloud exhibits a multimodal particle size distribution, with the mode most visible from the earth being H2SO4 droplets having 2-3 micron diameters. Despite variations, the vertical structure of the clouds indicates persistent features at sites separated by years and by great distances. The clouds are more strongly affected by radiation than by latent heat release, and the small particle size and weak convective activity observed are incompatible with lightning of cloud origin.

Comparison of Ice Cloud Particle Sizes Retrieved from Satellite Data Derived from In Situ Measurements

NASA Technical Reports Server (NTRS)

Han, Qingyuan; Rossow, William B.; Chou, Joyce; Welch, Ronald M.

1997-01-01

Cloud microphysical parameterizations have attracted a great deal of attention in recent years due to their effect on cloud radiative properties and cloud-related hydrological processes in large-scale models. The parameterization of cirrus particle size has been demonstrated as an indispensable component in the climate feedback analysis. Therefore, global-scale, long-term observations of cirrus particle sizes are required both as a basis of and as a validation of parameterizations for climate models. While there is a global scale, long-term survey of water cloud droplet sizes (Han et al.), there is no comparable study for cirrus ice crystals. This study is an effort to supply such a data set.

Towards a new parameterization of ice particles growth

NASA Astrophysics Data System (ADS)

Krakovska, Svitlana; Khotyayintsev, Volodymyr; Bardakov, Roman; Shpyg, Vitaliy

2017-04-01

Ice particles are the main component of polar clouds, unlike in warmer regions. That is why correct representation of ice particle formation and growth in NWP and other numerical atmospheric models is crucial for understanding of the whole chain of water transformation, including precipitation formation and its further deposition as snow in polar glaciers. Currently, parameterization of ice in atmospheric models is among the most difficult challenges. In the presented research, we present a renewed theoretical analysis of the evolution of mixed cloud or cold fog from the moment of ice nuclei activation until complete crystallization. The simplified model is proposed that includes both supercooled cloud droplets and initially uniform particles of ice, as well as water vapor. We obtain independent dimensionless input parameters of a cloud, and find main scenarios and stages of evolution of the microphysical state of the cloud. The characteristic times and particle sizes have been found, as well as the peculiarities of microphysical processes at each stage of evolution. In the future, the proposed original and physically grounded approximations may serve as a basis for a new scientifically substantiated and numerically efficient parameterizations of microphysical processes in mixed clouds for modern atmospheric models. The relevance of theoretical analysis is confirmed by numerical modeling for a wide range of combinations of possible conditions in the atmosphere, including cold polar regions. The main conclusion of the research is that until complete disappearance of cloud droplets, the growth of ice particles occurs at a practically constant humidity corresponding to the saturated humidity over water, regardless to all other parameters of a cloud. This process can be described by the one differential equation of the first order. Moreover, a dimensionless parameter has been proposed as a quantitative criterion of a transition from dominant depositional to intense collectional growth of ice particles; it could be used in models with bulk parameterization of cloud and precipitation formation processes.

Cirrus Cloud Seeding has Potential to Cool Climate

NASA Technical Reports Server (NTRS)

Storelvmo, T.; Kristjansson, J. E.; Muri, H.; Pfeffer, M.; Barahona, D.; Nenes, A.

2013-01-01

Cirrus clouds, thin ice clouds in the upper troposphere, have a net warming effect on Earth s climate. Consequently, a reduction in cirrus cloud amount or optical thickness would cool the climate. Recent research indicates that by seeding cirrus clouds with particles that promote ice nucleation, their lifetimes and coverage could be reduced. We have tested this hypothesis in a global climate model with a state-of-the-art representation of cirrus clouds and find that cirrus cloud seeding has the potential to cancel the entire warming caused by human activity from pre-industrial times to present day. However, the desired effect is only obtained for seeding particle concentrations that lie within an optimal range. With lower than optimal particle concentrations, a seeding exercise would have no effect. Moreover, a higher than optimal concentration results in an over-seeding that could have the deleterious effect of prolonging cirrus lifetime and contributing to global warming.

GCM Simulations of the Aerosol Indirect Effect: Sensitivity to Cloud Parameterization and Aerosol Burden

NASA Technical Reports Server (NTRS)

Menon, Surabi; DelGenio, Anthony D.; Koch, Dorothy; Tselioudis, George; Hansen, James E. (Technical Monitor)

2001-01-01

We describe the coupling of the Goddard Institute for Space Studies (GISS) general circulation model (GCM) to an online sulfur chemistry model and source models for organic matter and sea-salt that is used to estimate the aerosol indirect effect. The cloud droplet number concentration is diagnosed empirically from field experiment datasets over land and ocean that observe droplet number and all three aerosol types simultaneously; corrections are made for implied variations in cloud turbulence levels. The resulting cloud droplet number is used to calculate variations in droplet effective radius, which in turn allows us to predict aerosol effects on cloud optical thickness and microphysical process rates. We calculate the aerosol indirect effect by differencing the top-of-the-atmosphere net cloud radiative forcing for simulations with present-day vs. pre-industrial emissions. Both the first (radiative) and second (microphysical) indirect effects are explored. We test the sensitivity of our results to cloud parameterization assumptions that control the vertical distribution of cloud occurrence, the autoconversion rate, and the aerosol scavenging rate, each of which feeds back significantly on the model aerosol burden. The global mean aerosol indirect effect for all three aerosol types ranges from -1.55 to -4.36 W m(exp -2) in our simulations. The results are quite sensitive to the pre-industrial background aerosol burden, with low pre-industrial burdens giving strong indirect effects, and to a lesser extent to the anthropogenic aerosol burden, with large burdens giving somewhat larger indirect effects. Because of this dependence on the background aerosol, model diagnostics such as albedo-particle size correlations and column cloud susceptibility, for which satellite validation products are available, are not good predictors of the resulting indirect effect.

GCM Simulations of the Aerosol Indirect Effect: Sensitivity to Cloud Parameterization and Aerosol Burden

NASA Technical Reports Server (NTRS)

Menon, Surabi; DelGenio, Anthony D.; Koch, Dorothy; Tselioudis, George; Hansen, James E. (Technical Monitor)

2001-01-01

We describe the coupling of the Goddard Institute for Space Studies (GISS) general circulation model (GCM) to an online sulfur chemistry model and source models for organic matter and sea-salt that is used to estimate the aerosol indirect effect. The cloud droplet number concentration is diagnosed empirically from field experiment datasets over land and ocean that observe droplet number and all three aerosol types simultaneously; corrections are made for implied variations in cloud turbulence levels. The resulting cloud droplet number is used to calculate variations in droplet effective radius, which in turn allows us to predict aerosol effects on cloud optical thickness and microphysical process rates. We calculate the aerosol indirect effect by differencing the top-of-the-atmosphere net cloud radiative forcing for simulations with present-day vs. pre-industrial emissions. Both the first (radiative) and second (microphysical) indirect effects are explored. We test the sensitivity of our results to cloud parameterization assumptions that control the vertical distribution of cloud occurrence, the autoconversion rate, and the aerosol scavenging rate, each of which feeds back significantly on the model aerosol burden. The global mean aerosol indirect effect for all three aerosol types ranges from -1.55 to -4.36 W/sq m in our simulations. The results are quite sensitive to the pre-industrial background aerosol burden, with low pre-industrial burdens giving strong indirect effects, and to a lesser extent to the anthropogenic aerosol burden, with large burdens giving somewhat larger indirect effects. Because of this dependence on the background aerosol, model diagnostics such as albedo-particle size correlations and column cloud susceptibility, for which satellite validation products are available, are not good predictors of the resulting indirect effect.

Local Interactions of Hydrometeors by Diffusion in Mixed-Phase Clouds

NASA Astrophysics Data System (ADS)

Baumgartner, Manuel; Spichtinger, Peter

2017-04-01

Mixed-phase clouds, containing both ice particles and liquid droplets, are important for the Earth-Atmosphere system. They modulate the radiation budget by a combination of albedo effect and greenhouse effect. In contrast to liquid water clouds, the radiative impact of clouds containing ice particles is still uncertain. Scattering and absorption highly depends in microphysical properties of ice crystals, e.g. size and shape. In addition, most precipitation on Earth forms via the ice phase. Thus, better understanding of ice processes as well as their representation in models is required. A key process for determining shape and size of ice crystals is diffusional growth. Diffusion processes in mixed-phase clouds are highly uncertain; in addition they are usually highly simplified in cloud models, especially in bulk microphysics parameterizations. The direct interaction between cloud droplets and ice particles, due to spatial inhomogeneities, is ignored; the particles can only interact via their environmental conditions. Local effects as supply of supersaturation due to clusters of droplets around ice particles are usually not represented, although they form the physical basis of the Wegener-Bergeron-Findeisen process. We present direct numerical simulations of the interaction of single ice particles and droplets, especially their local competition for the available water vapor. In addition, we show an approach to parameterize local interactions by diffusion. The suggested parameterization uses local steady-state solutions of the diffusion equations for water vapor for an ice particle as well as a droplet. The individual solutions are coupled together to obtain the desired interaction. We show some results of the scheme as implemented in a parcel model.

9+ Years of CALIPSO PSC Observations: An Evolving Climatology

NASA Technical Reports Server (NTRS)

Pitts, Michael C.; Poole, Lamont R.

2015-01-01

Polar stratospheric clouds (PSCs) play a crucial role in the springtime chemical depletion of ozone at high latitudes. PSC particles (primarily supercooled ternary solution, or STS droplets) provide sites for heterogeneous chemical reactions that transform stable chlorine and bromine reservoir species into highly reactive ozone-destructive forms. Furthermore, large nitric acid trihydrate (NAT) PSC particles can irreversibly redistribute odd nitrogen through gravitational sedimentation (a process commonly known as denitrification), which prolongs the ozone depletion process by slowing the reformation of the stable chlorine reservoirs. Spaceborne observations from the CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) lidar on the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) satellite are providing a rich new dataset for studying PSCs. CALIPSO is an excellent platform for studying polar processes with CALIOP acquiring, on average, over 300,000 backscatter profiles daily at latitudes between 55o and 82o in both hemispheres. PSCs are detected in the CALIOP backscatter profiles using a successive horizontal averaging scheme that enables detection of strongly scattering PSCs (e.g., ice) at the finest possible spatial resolution (5 km), while enhancing the detection of very tenuous PSCs (e.g., low number density NAT) at larger spatial scales (up to 135 km). CALIOP PSCs are separated into composition classes (STS; liquid/NAT mixtures; and ice) based on the ensemble 532-nm scattering ratio (the ratio of total-to-molecular backscatter) and 532-nm particulate depolarization ratio (which is sensitive to the presence of non-spherical, i.e. NAT and ice particles). In this paper, we will provide an overview of the CALIOP PSC detection and composition classification algorithm and then examine the vertical and spatial distribution of PSCs in the Arctic and Antarctic on vortex-wide scales for entire PSC seasons over the more than nine-year data record from 2006- 2015.

A global modeling study on carbonaceous aerosol microphysical characteristics and radiative forcing

NASA Astrophysics Data System (ADS)

Bauer, S. E.; Menon, S.; Koch, D.; Bond, T. C.; Tsigaridis, K.

2010-02-01

Recently, attention has been drawn towards black carbon aerosols as a short-term climate warming mitigation candidate. However the global and regional impacts of the direct, cloud-indirect and semi-direct forcing effects are highly uncertain, due to the complex nature of aerosol evolution and the way that mixed, aged aerosols interact with clouds and radiation. A detailed aerosol microphysical scheme, MATRIX, embedded within the GISS climate model is used in this study to present a quantitative assessment of the impact of microphysical processes involving black carbon, such as emission size distributions and optical properties on aerosol cloud activation and radiative forcing. Our best estimate for net direct and indirect aerosol radiative forcing between 1750 and 2000 is -0.56 W/m2. However, the direct and indirect aerosol effects are quite sensitive to the black and organic carbon size distribution and consequential mixing state. The net radiative forcing can vary between -0.32 to -0.75 W/m2 depending on these carbonaceous particle properties at emission. Assuming that sulfates, nitrates and secondary organics form a coating around a black carbon core, rather than forming a uniformly mixed particle, changes the overall net aerosol radiative forcing from negative to positive. Taking into account internally mixed black carbon particles let us simulate correct aerosol absorption. Black carbon absorption is amplified by sulfate and nitrate coatings, but even more strongly by organic coatings. Black carbon mitigation scenarios generally showed reduced radiative forcing when sources with a large proportion of black carbon, such as diesel, are reduced; however reducing sources with a larger organic carbon component as well, such as bio-fuels, does not necessarily lead to climate benefits.

Impact of aerosol size representation on modeling aerosol-cloud interactions

DOE PAGES

Zhang, Y.; Easter, R. C.; Ghan, S. J.; ...

2002-11-07

In this study, we use a 1-D version of a climate-aerosol-chemistry model with both modal and sectional aerosol size representations to evaluate the impact of aerosol size representation on modeling aerosol-cloud interactions in shallow stratiform clouds observed during the 2nd Aerosol Characterization Experiment. Both the modal (with prognostic aerosol number and mass or prognostic aerosol number, surface area and mass, referred to as the Modal-NM and Modal-NSM) and the sectional approaches (with 12 and 36 sections) predict total number and mass for interstitial and activated particles that are generally within several percent of references from a high resolution 108-section approach.more » The modal approach with prognostic aerosol mass but diagnostic number (referred to as the Modal-M) cannot accurately predict the total particle number and surface areas, with deviations from the references ranging from 7-161%. The particle size distributions are sensitive to size representations, with normalized absolute differences of up to 12% and 37% for the 36- and 12-section approaches, and 30%, 39%, and 179% for the Modal-NSM, Modal-NM, and Modal-M, respectively. For the Modal-NSM and Modal-NM, differences from the references are primarily due to the inherent assumptions and limitations of the modal approach. In particular, they cannot resolve the abrupt size transition between the interstitial and activated aerosol fractions. For the 12- and 36-section approaches, differences are largely due to limitations of the parameterized activation for non-log-normal size distributions, plus the coarse resolution for the 12-section case. Differences are larger both with higher aerosol (i.e., less complete activation) and higher SO2 concentrations (i.e., greater modification of the initial aerosol distribution).« less

Beamlets from stochastic acceleration

NASA Astrophysics Data System (ADS)

Perri, Silvia; Carbone, Vincenzo

2008-09-01

We investigate the dynamics of a realization of the stochastic Fermi acceleration mechanism. The model consists of test particles moving between two oscillating magnetic clouds and differs from the usual Fermi-Ulam model in two ways. (i) Particles can penetrate inside clouds before being reflected. (ii) Particles can radiate a fraction of their energy during the process. Since the Fermi mechanism is at work, particles are stochastically accelerated, even in the presence of the radiated energy. Furthermore, due to a kind of resonance between particles and oscillating clouds, the probability density function of particles is strongly modified, thus generating beams of accelerated particles rather than a translation of the whole distribution function to higher energy. This simple mechanism could account for the presence of beamlets in some space plasma physics situations.

Biogenic Potassium Salt Particles as Seeds for Secondary Organic Aerosol in the Amazon

NASA Astrophysics Data System (ADS)

Pöhlker, Christopher; Wiedemann, Kenia T.; Sinha, Bärbel; Shiraiwa, Manabu; Gunthe, Sachin S.; Smith, Mackenzie; Su, Hang; Artaxo, Paulo; Chen, Qi; Cheng, Yafang; Elbert, Wolfgang; Gilles, Mary K.; Kilcoyne, Arthur L. D.; Moffet, Ryan C.; Weigand, Markus; Martin, Scot T.; Pöschl, Ulrich; Andreae, Meinrat O.

2012-08-01

The fine particles serving as cloud condensation nuclei in pristine Amazonian rainforest air consist mostly of secondary organic aerosol. Their origin is enigmatic, however, because new particle formation in the atmosphere is not observed. Here, we show that the growth of organic aerosol particles can be initiated by potassium-salt-rich particles emitted by biota in the rainforest. These particles act as seeds for the condensation of low- or semi-volatile organic compounds from the atmospheric gas phase or multiphase oxidation of isoprene and terpenes. Our findings suggest that the primary emission of biogenic salt particles directly influences the number concentration of cloud condensation nuclei and affects the microphysics of cloud formation and precipitation over the rainforest.

Venus Clouds: A dirty hydrochloric acid model

NASA Technical Reports Server (NTRS)

Hapke, B.

1971-01-01

The spectral and polarization data for Venus are consistent with micron-sized, aerosol cloud particles of hydrochloric acid containing soluble and insoluble iron compounds, whose source could be volcanic or crustal dust. The ultraviolet features could arise from variations in the Fe-HCl concentration in the cloud particles.

Intercomparison between Individual Particles Scavenged as CCN and Those Collected at Ground-based Site on West Coast of Japan During Asian Dust Storm

NASA Astrophysics Data System (ADS)

Ma, C. J.; Tohno, S.; Kasahara, M.; Hayakawa, S.

2002-12-01

Asian dust storm particles can affect precipitation composition because they are either incorporated into cloud via condensation of water vapour (nucleation) or due to the uptake of particles by existing droplets. And subsequently they affect aquatic and terrestrial ecosystems. In order to study the intercorrelation between the chemical natures of both the particles collected at ground-based site and those scavenged as CCN, the intensive field measurement was carried out on west coast of Japan (Yasaka, Tango Peninsula, 35.62°N; 135.07°E) during dense Asian dust storm event on March 22, 2002. Due to the size dependence of the chemical composition of aerosol particle, size-segregated aerosol particles were collect using Low pressure Andersen impactor sampler. Also, to collect cloud droplets individually, a particular method for the cloud droplet replication was newly applied using collodion (nitrocellulose) film. Sampling of cloud droplets was performed at summit of a mountain (680 m) in Yasaka. To analyze the ambient individual aerosol particles and individual retained particles in cloud droplet, X-ray fluorescence (XRF) analytical method set at SPring-8 on BL39XU was applied. Analytical result enables us not only to compare the characteristics of individual particles scavenged as CCN and those collected at ground-based site, but also to estimate the influence of long-range transport.

Noctilucent cloud polarimetry: Twilight measurements in a wide range of scattering angles

NASA Astrophysics Data System (ADS)

Ugolnikov, Oleg S.; Maslov, Igor A.; Kozelov, Boris V.; Dlugach, Janna M.

2016-06-01

Wide-field polarization measurements of the twilight sky background during several nights with bright and extended noctilucent clouds in central and northern Russia in 2014 and 2015 are used to build the phase dependence of the degree of polarization of sunlight scattered by cloud particles in a wide range of scattering angles (from 40° to 130°). This range covers the linear polarization maximum near 90° and large-angle slope of the curve. The polarization in this angle range is most sensitive to the particle size. The method of separation of scattering on cloud particles from the twilight background is presented. Results are compared with T-matrix simulations for different sizes and shapes of ice particles; the best-fit model radius of particles (0.06 μm) and maximum radius (about 0.1 μm) are estimated.

The motion of a cloud of solid spherical particles falling in a cellular flow field at low Stokes number

NASA Astrophysics Data System (ADS)

Marchetti, Benjamin; Bergougnoux, Laurence; Guazzelli, Elisabeth

2017-11-01

We present a jointed experimental and numerical study examining the influence of vortical structures on the settling of a cloud of solid spherical particles under the action of gravity at low Stokes numbers. The two-dimensional model experiment uses electro-convection to generate a two-dimensional array of controlled vortices which mimics a simplified vortical flow. Particle image-velocimetry and tracking are used to examine the motion of the cloud within this vortical flow. The cloud motion is compared to the predictions of a two-way-coupling numerical simulation.

Analysis of Individual Carbonaceous Particles Emitted from the Las Conchas Wildfire, Los Alamos, NM, in June-July 2011

NASA Astrophysics Data System (ADS)

Mazzoleni, C.; China, S.; Gorkowski, K.; Flowers, B. A.; Aiken, A. C.; Dubey, M. K.

2012-12-01

Carbonaceous aerosol emitted from biomass burning contributes significantly to atmospheric aerosol loadings regionally and globally. The net direct radiative forcing of biomass burning aerosol can be positive and/or negative and this depends on its composition, morphology and mixing state. Biomass burning aerosols can also change the cloud properties as they can act as cloud condensation nuclei. In this study we investigated biomass burning particles emitted from the Las Conchas wildfire in northern New Mexico that started on June 26, 2011 and burned an area of 245 square miles. Aerosol samples were collected on nucleopore filters at the Los Alamos National Laboratory during the third week of the wildfire event. Individual particles (~4000) were investigated using field-emission scanning electron microscopy and energy dispersive X-ray spectroscopy (EDS) to distinguish different carbonaceous particles and their shape, size, elemental composition and mixing state. A thermo-denuder was used to remove compounds that are volatile at temperatures up to 200 C, leaving behind the black carbon and any compounds that did not volatize completely. Smoke particles consisted of a) tar balls, which are amorphous spherical carbonaceous organic aerosols; b) organic particles with inorganic inclusions, c) soot particles and (d) soot with various inclusions. Two distinct kinds of tar balls, "electronically" dark and bright, were found using the field-emission scanning electron microscopy and were characterized for ambient and denuded conditions to understand coating effects and aging. It was found that dark tar balls are generally larger in size than the bright ones. Additionally, the difference between the size of ambient-bright and the size of denuded-bright tar balls was larger than the difference between the size of ambient-dark and the size of denuded-dark tar balls. EDS analysis showed that 70% of the dark tar balls had higher (~60%) relative oxygen content than in the bright tar balls. We conclude that there are two distinct kinds of biomass burning tar balls and that dark tar balls are less volatile than bright tar balls. The morphology of soot particles was also investigated by evaluating their fractal dimension for both ambient (coated with organic and inorganic material) and denuded samples at two different times of the day. The fractal dimension for ambient soot was found to be higher than for denuded soot due to the coating on the ambient soot particles. Finally, the monomer diameter decreased by up to 25% after denuding the particles. This study provides insights on the link between electron microscopy images of single particles and the mixing state, morphology, and evolution of different biomass burning aerosol at the beginning of their lifecycle.

Component-specific, cigarette particle deposition modeling in the human respiratory tract

PubMed Central

Price, Owen T.; Yurteri, Caner U.; Dickens, Colin; McAughey, John

2014-01-01

Inhalation of cigarette smoke particles (CSP) leads to adverse health effects in smokers. Determination of the localized dose to the lung of the inhaled smoke aids in determining vulnerable sites, and identifying components of the smoke that may be responsible for the adverse effects; thus providing a roadmap for harm reduction of cigarette smoking. A particle deposition model specific to CSP was developed for the oral cavity and the lung by accounting for cigarette particle size growth by hygroscopicity, phase change and coagulation. In addition, since the cigarette puff enters the respiratory tract as a dense cloud, the cloud effect on particle drag and deposition was accounted for in the deposition model. Models of particle losses in the oral cavities were developed during puff drawing and subsequent mouth-hold. Cigarette particles were found to grow by hygroscopicity and coagulation, but to shrink as a result of nicotine evaporation. The particle size reached a plateau beyond which any disturbances in the environmental conditions caused the various mechanisms to balance each other out and the particle size remain stable. Predicted particle deposition considering the cloud effects was greater than when treated as a collection of non-interacting particles (i.e. no cloud effects). Accounting for cloud movement provided the necessary physical mechanism to explain the greater than expected, experimentally observed and particle deposition. The deposition model for CSP can provide the necessary input to determine the fate of inhaled CSP in the lung. The knowledge of deposition will be helpful for health assessment and identification and reduction of harmful components of CSP. PMID:24354791

Clustering, randomness, and regularity in cloud fields. 4. Stratocumulus cloud fields

NASA Astrophysics Data System (ADS)

Lee, J.; Chou, J.; Weger, R. C.; Welch, R. M.

1994-07-01

To complete the analysis of the spatial distribution of boundary layer cloudiness, the present study focuses on nine stratocumulus Landsat scenes. The results indicate many similarities between stratocumulus and cumulus spatial distributions. Most notably, at full spatial resolution all scenes exhibit a decidedly clustered distribution. The strength of the clustering signal decreases with increasing cloud size; the clusters themselves consist of a few clouds (less than 10), occupy a small percentage of the cloud field area (less than 5%), contain between 20% and 60% of the cloud field population, and are randomly located within the scene. In contrast, stratocumulus in almost every respect are more strongly clustered than are cumulus cloud fields. For instance, stratocumulus clusters contain more clouds per cluster, occupy a larger percentage of the total area, and have a larger percentage of clouds participating in clusters than the corresponding cumulus examples. To investigate clustering at intermediate spatial scales, the local dimensionality statistic is introduced. Results obtained from this statistic provide the first direct evidence for regularity among large (>900 m in diameter) clouds in stratocumulus and cumulus cloud fields, in support of the inhibition hypothesis of Ramirez and Bras (1990). Also, the size compensated point-to-cloud cumulative distribution function statistic is found to be necessary to obtain a consistent description of stratocumulus cloud distributions. A hypothesis regarding the underlying physical mechanisms responsible for cloud clustering is presented. It is suggested that cloud clusters often arise from 4 to 10 triggering events localized within regions less than 2 km in diameter and randomly distributed within the cloud field. As the size of the cloud surpasses the scale of the triggering region, the clustering signal weakens and the larger cloud locations become more random.

Clustering, randomness, and regularity in cloud fields. 4: Stratocumulus cloud fields

NASA Technical Reports Server (NTRS)

Lee, J.; Chou, J.; Weger, R. C.; Welch, R. M.

1994-01-01

To complete the analysis of the spatial distribution of boundary layer cloudiness, the present study focuses on nine stratocumulus Landsat scenes. The results indicate many similarities between stratocumulus and cumulus spatial distributions. Most notably, at full spatial resolution all scenes exhibit a decidedly clustered distribution. The strength of the clustering signal decreases with increasing cloud size; the clusters themselves consist of a few clouds (less than 10), occupy a small percentage of the cloud field area (less than 5%), contain between 20% and 60% of the cloud field population, and are randomly located within the scene. In contrast, stratocumulus in almost every respect are more strongly clustered than are cumulus cloud fields. For instance, stratocumulus clusters contain more clouds per cluster, occupy a larger percentage of the total area, and have a larger percentage of clouds participating in clusters than the corresponding cumulus examples. To investigate clustering at intermediate spatial scales, the local dimensionality statistic is introduced. Results obtained from this statistic provide the first direct evidence for regularity among large (more than 900 m in diameter) clouds in stratocumulus and cumulus cloud fields, in support of the inhibition hypothesis of Ramirez and Bras (1990). Also, the size compensated point-to-cloud cumulative distribution function statistic is found to be necessary to obtain a consistent description of stratocumulus cloud distributions. A hypothesis regarding the underlying physical mechanisms responsible for cloud clustering is presented. It is suggested that cloud clusters often arise from 4 to 10 triggering events localized within regions less than 2 km in diameter and randomly distributed within the cloud field. As the size of the cloud surpasses the scale of the triggering region, the clustering signal weakens and the larger cloud locations become more random.

Effect of Particle Morphology on the Reactivity of Explosively Dispersed Titanium Particles

NASA Astrophysics Data System (ADS)

Frost, David L.; Cairns, Malcolm; Goroshin, Samuel; Zhang, Fan

2009-12-01

The effect of particle morphology on the reaction of titanium (Ti) particles explosively dispersed during the detonation of either cylindrical or spherical charges has been investigated experimentally. The explosive charges consisted of packed beds of Ti particles saturated with nitromethane. The reaction behaviour of irregularly-shaped Ti particles in three size ranges is compared with tests with spherical Ti particles. The particle reaction is strongly dependent on particle morphology, e.g., 95 μm spherical Ti particles failed to ignite (in cylinders up to 49 mm in dia), whereas similarly sized irregular Ti particles readily ignited. For irregular particles, the uniformity of ignition on the particle cloud surface was almost independent of particle size, but depended on charge diameter. As the charge diameter was reduced, ignition in the conically expanding particle cloud occurred only at isolated spots or bands. For spherical charges, whereas large irregular Ti particles ignited promptly and uniformly throughout the particle cloud, the smallest particles dispersed nonuniformly and ignition occurred at isolated locations after a delay. Hence the charge geometry, as well as particle morphology, influences the reaction behaviour of the particles.

Microphysical processing of aerosol particles in orographic clouds

NASA Astrophysics Data System (ADS)

Pousse-Nottelmann, S.; Zubler, E. M.; Lohmann, U.

2015-08-01

An explicit and detailed treatment of cloud-borne particles allowing for the consideration of aerosol cycling in clouds has been implemented into COSMO-Model, the regional weather forecast and climate model of the Consortium for Small-scale Modeling (COSMO). The effects of aerosol scavenging, cloud microphysical processing and regeneration upon cloud evaporation on the aerosol population and on subsequent cloud formation are investigated. For this, two-dimensional idealized simulations of moist flow over two bell-shaped mountains were carried out varying the treatment of aerosol scavenging and regeneration processes for a warm-phase and a mixed-phase orographic cloud. The results allowed us to identify different aerosol cycling mechanisms. In the simulated non-precipitating warm-phase cloud, aerosol mass is incorporated into cloud droplets by activation scavenging and released back to the atmosphere upon cloud droplet evaporation. In the mixed-phase cloud, a first cycle comprises cloud droplet activation and evaporation via the Wegener-Bergeron-Findeisen (WBF) process. A second cycle includes below-cloud scavenging by precipitating snow particles and snow sublimation and is connected to the first cycle via the riming process which transfers aerosol mass from cloud droplets to snowflakes. In the simulated mixed-phase cloud, only a negligible part of the total aerosol mass is incorporated into ice crystals. Sedimenting snowflakes reaching the surface remove aerosol mass from the atmosphere. The results show that aerosol processing and regeneration lead to a vertical redistribution of aerosol mass and number. Thereby, the processes impact the total aerosol number and mass and additionally alter the shape of the aerosol size distributions by enhancing the internally mixed/soluble Aitken and accumulation mode and generating coarse-mode particles. Concerning subsequent cloud formation at the second mountain, accounting for aerosol processing and regeneration increases the cloud droplet number concentration with possible implications for the ice crystal number concentration.

Satellite remote sensing of dust aerosol indirect effects on ice cloud formation.

PubMed

Ou, Steve Szu-Cheng; Liou, Kuo-Nan; Wang, Xingjuan; Hansell, Richard; Lefevre, Randy; Cocks, Stephen

2009-01-20

We undertook a new approach to investigate the aerosol indirect effect of the first kind on ice cloud formation by using available data products from the Moderate-Resolution Imaging Spectrometer (MODIS) and obtained physical understanding about the interaction between aerosols and ice clouds. Our analysis focused on the examination of the variability in the correlation between ice cloud parameters (optical depth, effective particle size, cloud water path, and cloud particle number concentration) and aerosol optical depth and number concentration that were inferred from available satellite cloud and aerosol data products. Correlation results for a number of selected scenes containing dust and ice clouds are presented, and dust aerosol indirect effects on ice clouds are directly demonstrated from satellite observations.

Aerosol-Cloud Interactions During Puijo Cloud Experiments - The effects of weather and local sources

NASA Astrophysics Data System (ADS)

Komppula, Mika; Portin, Harri; Leskinen, Ari; Romakkaniemi, Sami; Brus, David; Neitola, Kimmo; Hyvärinen, Antti-Pekka; Kortelainen, Aki; Hao, Liqing; Miettinen, Pasi; Jaatinen, Antti; Ahmad, Irshad; Lihavainen, Heikki; Laaksonen, Ari; Lehtinen, Kari E. J.

2013-04-01

The Puijo measurement station has provided continuous data on aerosol-cloud interactions since 2006. The station is located on top of the Puijo observation tower (306 m a.s.l, 224 m above the surrounding lake level) in Kuopio, Finland. The top of the tower is covered by cloud about 15 % of the time, offering perfect conditions for studying aerosol-cloud interactions. With a twin-inlet setup (total and interstitial inlets) we are able to separate the activated particles from the interstitial (non-activated) particles. The continuous twin-inlet measurements include aerosol size distribution, scattering and absorption. In addition cloud droplet number and size distribution are measured continuously with weather parameters. During the campaigns the twin-inlet system was additionally equipped with aerosol mass spectrometer (AMS) and Single Particle Soot Photometer (SP-2). This way we were able to define the differences in chemical composition of the activated and non-activated particles. Potential cloud condensation nuclei (CCN) in different supersaturations were measured with two CCN counters (CCNC). The other CCNC was operated with a Differential Mobility Analyzer (DMA) to obtain size selected CCN spectra. Other additional measurements included Hygroscopic Tandem Differential Mobility Analyzer (HTDMA) for particle hygroscopicity. Additionally the valuable vertical wind profiles (updraft velocities) are available from Halo Doppler lidar during the 2011 campaign. Cloud properties (droplet number and effective radius) from MODIS instrument onboard Terra and Aqua satellites were retrieved and compared with the measured values. This work summarizes the two latest intensive campaigns, Puijo Cloud Experiments (PuCE) 2010 & 2011. We study especially the effect of the local sources on the cloud activation behaviour of the aerosol particles. The main local sources include a paper mill, a heating plant, traffic and residential areas. The sources can be categorized and identified by wind direction. Clear changes can be seen in the aerosol and cloud properties when being under the influence of a local pollutant source. Also differences in the chemical composition of aerosol activated to cloud droplet and those staying interstitial has been observed. For example, the light absorption by cloud interstitial particles is higher when the wind blows from the local pollutant sources compared to a cleaner sector. This may be due to the fact that the absorptive material, e.g. fresh soot, is generally hydrophobic and therefore inhibits activation. Another point of interest is the occasional freezing conditions during the campaign (temperature below zero), which also affects the activation behaviour. The full usage of this special data set will provide new information on the properties and differences of activating and non-activating aerosol particles, as well as on the variables affecting the activation.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haapanala, Päivi; Räisänen, Petri; McFarquhar, Greg M.

The impact of ice clouds on solar disk and circumsolar radiances is investigated using a Monte Carlo radiative transfer model. The monochromatic direct and diffuse radiances are simulated at angles of 0 to 8° from the center of the sun. Input data for the model are derived from measurements conducted during the 2010 Small Particles in Cirrus (SPARTICUS) campaign together with state-of-the-art databases of optical properties of ice crystals and aerosols. For selected cases, the simulated radiances are compared with ground-based radiance measurements obtained by the Sun and Aureole Measurements (SAM) instrument. First, the sensitivity of the radiances to themore » ice cloud properties and aerosol optical thickness is addressed. The angular dependence of the disk and circumsolar radiances is found to be most sensitive to assumptions about ice crystal roughness (or, more generally, non-ideal features of ice crystals) and size distribution, with ice crystal habit playing a somewhat smaller role. Second, in comparisons with SAM data, the ice cloud optical thickness is adjusted for each case so that the simulated radiances agree closely (i.e., within 3 %) with the measured disk radiances. Circumsolar radiances at angles larger than ≈ 3° are systematically underestimated when assuming smooth ice crystals, whereas the agreement with the measurements is better when rough ice crystals are assumed. In conclusion, our results suggest that it may well be possible to infer the particle roughness directly from ground-based SAM measurements. In addition, the results show the necessity of correcting the ground-based measurements of direct radiation for the presence of diffuse radiation in the instrument's field of view, in particular in the presence of ice clouds.« less

Cloud Imagers Offer New Details on Earth's Health

NASA Technical Reports Server (NTRS)

2009-01-01

A stunning red sunset or purple sunrise is an aesthetic treat with a scientific explanation: The colors are a direct result of the absorption or reflectance of solar radiation by atmospheric aerosols, minute particles (either solid or liquid) in the Earth s atmosphere that occur both naturally and because of human activity. At the beginning or end of the day, the Sun s rays travel farther through the atmosphere to reach an observer s eyes and more green and yellow light is scattered, making the Sun appear red. Sunset and sunrise are especially colorful when the concentration of atmospheric particles is high. This ability of aerosols to absorb and reflect sunlight is not just pretty; it also determines the amount of radiation and heat that reaches the Earth s surface, and can profoundly affect climate. In the atmosphere, aerosols are also important as nuclei for the condensation of water droplets and ice crystals. Clouds with fewer aerosols cannot form as many water droplets (called cloud particles), and consequently, do not scatter light well. In this case, more sunlight reaches the Earth s surface. When aerosol levels in clouds are high, however, more nucleation points can form small liquid water droplets. These smaller cloud particles can reflect up to 90 percent of visible radiation to space, keeping the heat from ever reaching Earth s surface. The tendency for these particles to absorb or reflect the Sun s energy - called extinction by astronomers - depends on a number of factors, including chemical composition and the humidity and temperature in the surrounding air; because cloud particles are so small, they are affected quickly by minute changes in the atmosphere. Because of this sensitivity, atmospheric scientists study cloud particles to anticipate patterns and shifts in climate. Until recently, NASA s study of atmospheric aerosols and cloud particles has been focused primarily on satellite images, which, while granting large-scale atmospheric analysis, limited scientists ability to acquire detailed information about individual particles. Now, experiments with specialized equipment can be flown on standard jets, making it possible for researchers to monitor and more accurately anticipate changes in Earth s atmosphere and weather patterns.

Continuing Studies of Planetary Atmospheres Associated with Experiments on the Galileo Jupiter Probe and Infrared Observations of Venus

NASA Technical Reports Server (NTRS)

Ragent, Boris

1998-01-01

The results of the nephelometer experiment conducted aboard the Probe of the Galileo mission to Jupiter are presented. The tenuous clouds and sparse particulate matter in the relatively particle-free 5-micron "hot spot" region of the Probe's descent were documented from about 0.46 bars to about 12 bars. Three regions of apparent coherent structure were noted, in addition to many indications of extremely small particle concentrations along the descent path. From the first valid measurement at about 0.46 bars down to about 0.55 bars a feeble decaying lower portion of a cloud, corresponding with the predicted ammonia particle cloud, was encountered. A denser, but still very modest, particle structure was present in the pressure regime extending from about 0.76 to a distinctive base at 1.34 bars, and is compatible with the expected ammonium hydrosulfide cloud. No massive water cloud was encountered, although below the second structure, a small, vertically thin layer at about 1.65 bars may be detached from the cloud above, but may also be water condensation, compatible with reported measurements of water abundance from other Galileo Mission experiments. A third small signal region, extending from about 1.9 to 4.5 bars, exhibited quite weak but still distinctive structure, and, although the identification of the light scatterers in this region is uncertain, may also be a water cloud perhaps associated with lateral atmospheric motion and/or reduced to a small mass density by atmospheric subsidence or other explanations. Rough descriptions of the particle size distributions and cloud properties in these regions have been derived, although they may be imprecise because of the small signals and experimental difficulties. These descriptions document the small number densities of particles, the moderate particle sizes, generally in the slightly submicron to few micron range, and the resulting small optical depths, mass densities due to particles, column particle number loading and column mass loading in the atmosphere encountered by the Galileo Probe during its descent.

Continuing Studies of Planetary Atmospheres Associated With Experiments on the Galileo Jupiter Probe and Infrared Observations of Venus

NASA Technical Reports Server (NTRS)

Goodman,Jindra; Ragent, Boris

1998-01-01

The results of the nephelometer experiment conducted aboard the Probe of the Galileo mission to Jupiter are presented. The tenuous clouds and sparse particulate matter in the relatively particle-free 5-micron "hot spot" region of the Probe's descent were documented from about 0.46 bars to about 12 bars. Three regions of apparent coherent structure were noted, in addition to many indications of extremely small particle concentrations along the descent path. From the first valid measurement at about 0.46 bars down to about 0.55 bars a feeble decaying lower portion of a cloud, corresponding with the predicted ammonia particle cloud, was encountered. A denser, but still very modest, particle structure was present in the pressure regime extending from about 0.76 to a distinctive base at 1.34 bars, and is compatible with the expected ammonium hydrosulfide cloud. No massive water cloud was encountered, although below the second structure, a small, vertically thin layer at about 1.65 bars may be detached from the cloud above, but may also be water condensation, compatible with reported measurements of water abundance from other Galileo Mission experiments. A third small signal region, extending from about 1.9 to 4.5 bars, exhibited quite weak but still distinctive structure, and, although the identification of the light scatterers in this region is uncertain, may also be a water cloud perhaps associated with lateral atmospheric motion and/or reduced to a small mass density by atmospheric subsidence or other explanations. Rough descriptions of the particle size distributions and cloud properties in these regions have been derived, although they may be imprecise because of the small signals and experimental difficulties. These descriptions document the small number densities of particles, the moderate particle sizes, generally in the slightly submicron to few micron range, and the resulting small optical depths, mass densities due to particles, column particle number loading and column mass loading in the atmosphere encountered by the Galileo Probe during its descent.

Correlations among the Optical Properties of Cirrus-Cloud Particles: Microphysical Interpretation

NASA Technical Reports Server (NTRS)

Reichardt, J.; Reichardt, S.; Hess, M.; McGee, T. J.; Bhartia, P. K. (Technical Monitor)

2002-01-01

Cirrus measurements obtained with a ground-based polarization Raman lidar at 67.9 deg N in January 1997 reveal a strong positive correlation between the particle optical properties, specifically depolarization ratio delta(sub par) and extinction- to-backscatter (lidar) ratio S, for delta(sub par) less than approximately 40%, and an anti-correlation for delta(sub par) greater than approximately 40%. Over the length of the measurements the particle properties vary systematically. Initially, delta (sub par) approximately equals 60% and S approximately equals 10sr are observed. Then, with decreasing delta(sub par), S first increases to approximately 27sr (delta(sub par) approximately equals 40%) before decreasing to values around 10sr again (delta(sub par) approximately equals 20%). The analysis of lidar humidity and radiosonde temperature data shows that the measured optical properties stem from scattering by dry solid ice particles, while scattering by supercooled droplets, or by wetted or subliming ice particles can be excluded. For the microphysical interpretation of the lidar measurements, ray-tracing computations of particle scattering properties have been used. The comparison with the theoretical data suggests that the observed cirrus data can be interpreted in terms of size, shape, and, under the assumption that the lidar measurements of consecutive cloud segments can be mapped on the temporal development of a single cloud parcel moving along its trajectory, growth of the cirrus particles: Near the cloud top in the early stage of cirrus development, light scattering by nearly isometric particles that have the optical characteristics of hexagonal columns (short, column-like particles) is dominant. Over time the ice particles grow, and as the cloud base height extends to lower altitudes characterized by warmer temperatures they become morphologically diverse. For large S and depolarization values of approximately 40%, the scattering contributions of column- and plate-like particles are roughly the same. In the lower ranges of the cirrus clouds, light scattering is predominantly by plate-like ice particles. This interpretation assumes random orientation of the cirrus particles. Simulations with a simple model suggest, however, that the positive correlation between S and delta(sub par) which is observed for depolarization ratios less than 40% mainly at low cloud altitudes, can be alternatively explained by horizontal alignment of a fraction of the cirrus particle population.

Effects of Inert Dust Clouds on the Extinction of Strained, Laminar Flames at Normal and Micro Gravity

NASA Technical Reports Server (NTRS)

Andac, M. Gurhan; Egolfopoulos, Fokion N.; Campbell, Charles S.; Lauvergne, Romain; Wu, Ming-Shin (Technical Monitor)

2000-01-01

A combined experimental and detailed numerical study was conducted on the interaction between chemically inert solid particles and strained, atmospheric methane/air and propane/air laminar flames, both premixed and non-premixed. Experimentally, the opposed jet configuration was used with the addition of a particle seeder capable of operating in conditions of varying gravity. The particle seeding system was calibrated under both normal and micro gravity and a noticeable gravitational effect was observed. Flame extinction experiments were conducted at normal gravity by seeding inert particles at various number densities and sizes into the reacting gas phase. Experimental data were taken for 20 and 37 (mu) nickel alloy and 25 and 60 (mu) aluminum oxide particles. The experiments were simulated by solving along the stagnation streamline the conservation equations of mass, momentum, energy, and species conservation for both phases, with detailed descriptions of chemical kinetics, molecular transport, and thermal radiation. The experimental data were compared with numerical simulations, and insight was provided into the effects on extinction of the fuel type, equivalence ratio, flame configuration, strain rate. particle type. particle size. particle mass, delivery rate. the orientation of particle injection with respect to the flame and gravity. It was found that for the same injected solid mass, larger particles can result in more effective flame cooling compared to smaller particles, despite the fact that equivalent masses of the larger particles have smaller total surface area to volume ratio. This counter-intuitive finding resulted from the fact that the heat exchange between the two phases is controlled by the synergistic effect of the total contact area and the temperature difference between the two phases. Results also demonstrate that meaningful scaling of interactions between the two phases may not be possible due to the complexity of the couplings between the dynamic and thermal parameters of the problem.

Nitric Acid Uptake on Subtropical Cirrus Cloud Particles

NASA Technical Reports Server (NTRS)

2004-01-01

The redistribution of HNO3 via uptake and sedimentation by cirrus cloud particles is considered an important term in the upper tropospheric budget of reactive nitrogen. Numerous cirrus cloud encounters by the NASA WB-57F high-altitude research aircraft during CRYSTAL-FACE were accompanied by the observation of condensed-phase HNO3 with the NOAA chemical ionization mass spectrometer. The instrument measures HNO3 with two independent channels of detection connected to separate forward- and downward-facing inlets that allow a determination of the amount of HNO3 condensed on ice particles. Subtropical cirrus clouds, as indicated by the presence of ice particles, were observed coincident with condensed-phase HNO3 at temperatures of 197 K - 224 K and pressures of 122 hPa - 224 hPa. Maximum levels of condensed-phase HNO3 approached the gas-phase equivalent of 0.8 ppbv. Ice particle surface coverages as high as 1.4- 10(exp 14) molecules/sq cm were observed. A dissociative Langmuir adsorption model, when using an empirically derived HNO3 adsorption enthalpy of -11.0 kcal/mol, effectively describes the observed molecular coverages to within a factor of 5. The percentage of total HNO3 in the condensed phase ranged from near zero to 100% in the observed cirrus clouds. With volume-weighted mean particle diameters up to 700 pm and particle fall velocities up to 10 m/s, some observed clouds have significant potential to redistribute HNO3 in the upper troposphere.

HNSciCloud - Overview and technical Challenges

NASA Astrophysics Data System (ADS)

Gasthuber, Martin; Meinhard, Helge; Jones, Robert

2017-10-01

HEP is only one of many sciences with sharply increasing compute requirements that cannot be met by profiting from Moore’s law alone. Commercial clouds potentially allow for realising larger economies of scale. While some small-scale experience requiring dedicated effort has been collected, public cloud resources have not been integrated yet with the standard workflows of science organisations in their private data centres; in addition, European science has not ramped up to significant scale yet. The HELIX NEBULA Science Cloud project - HNSciCloud, partly funded by the European Commission, addresses these points. Ten organisations under CERN’s leadership, covering particle physics, bioinformatics, photon science and other sciences, have joined to procure public cloud resources as well as dedicated development efforts towards this integration. The HNSciCloud project faces the challenge to accelerate developments performed by the selected commercial providers. In order to guarantee cost efficient usage of IaaS resources across a wide range of scientific communities, the technical requirements had to be carefully constructed. With respect to current IaaS offerings, dataintensive science is the biggest challenge; other points that need to be addressed concern identity federations, network connectivity and how to match business practices of large IaaS providers with those of public research organisations. In the first section, this paper will give an overview of the project and explain the findings so far. The last section will explain the key points of the technical requirements and present first results of the experience of the procurers with the services in comparison to their’on-premise’ infrastructure.

In-situ single submicron particle composition analysis of ice residuals from mountain-top mixed-phase clouds in Central Europe

NASA Astrophysics Data System (ADS)

Schmidt, S.; Schneider, J.; Klimach, T.; Mertes, S.; Schenk, L. P.; Curtius, J.; Kupiszewski, P.; Hammer, E.; Vochezer, P.; Lloyd, G.; Ebert, M.; Kandler, K.; Weinbruch, S.; Borrmann, S.

2015-02-01

This paper presents results from the "INUIT-JFJ/CLACE 2013" field campaign at the high alpine research station Jungfraujoch in January/February 2013. The chemical composition of ice particle residuals (IPR) in a size diameter range of 200-900 nm was measured in orographic, convective and non-convective clouds with a single particle mass spectrometer (ALABAMA) under ambient conditions characterized by temperatures between -28 and -4 °C and wind speed from 0.1 to 21 km h-1. Additionally, background aerosol particles in cloud free air were investigated. The IPR were sampled from mixed-phase clouds with two inlets which selectively extract small ice crystals in-cloud, namely the Counterflow Virtual Impactor (Ice-CVI) and the Ice Selective Inlet (ISI). The IPR as well as the aerosol particles were classified into seven different particle types: (1) black carbon, (2) organic carbon, (3) black carbon internally mixed with organic carbon, (4) minerals, (5) one particle group (termed "BioMinSal") that may contain biological particles, minerals, or salts, (6) industrial metals, and (7) lead containing particles. For any sampled particle population it was determined by means of single particle mass spectrometer how many of the analyzed particles belonged to each of these categories. Accordingly, between 20 and 30% of the IPR and roughly 42% of the background particles contained organic carbon. The measured fractions of minerals in the IPR composition varied from 6 to 33%, while the values for the "BioMinSal" group were between 15 and 29%. Four percent to 31% of the IPR contained organic carbon mixed with black carbon. Both inlets delivered similar results of the chemical composition and of the particle size distribution, although lead was found only in the IPR sampled by the Ice-CVI. The results show that the ice particle residual composition varies substantially between different cloud events, which indicates the influence of different meteorological conditions, such as origin of the air masses, temperature and wind speed.

Influence of Ice Particle Surface Roughening on the Global Cloud Radiative Effect

NASA Technical Reports Server (NTRS)

Yi, Bingqi; Yang, Ping; Baum, Bryan A.; LEcuyer, Tristan; Oreopoulos, Lazaros; Mlawer, Eli J.; Heymsfield, Andrew J.; Liou, Kuo-Nan

2013-01-01

Ice clouds influence the climate system by changing the radiation budget and large-scale circulation. Therefore, climate models need to have an accurate representation of ice clouds and their radiative effects. In this paper, new broadband parameterizations for ice cloud bulk scattering properties are developed for severely roughened ice particles. The parameterizations are based on a general habit mixture that includes nine habits (droxtals, hollow/solid columns, plates, solid/hollow bullet rosettes, aggregate of solid columns, and small/large aggregates of plates). The scattering properties for these individual habits incorporate recent advances in light-scattering computations. The influence of ice particle surface roughness on the ice cloud radiative effect is determined through simulations with the Fu-Liou and the GCM version of the Rapid Radiative Transfer Model (RRTMG) codes and the National Center for Atmospheric Research Community Atmosphere Model (CAM, version 5.1). The differences in shortwave (SW) and longwave (LW) radiative effect at both the top of the atmosphere and the surface are determined for smooth and severely roughened ice particles. While the influence of particle roughening on the single-scattering properties is negligible in the LW, the results indicate that ice crystal roughness can change the SW forcing locally by more than 10 W m(exp -2) over a range of effective diameters. The global-averaged SW cloud radiative effect due to ice particle surface roughness is estimated to be roughly 1-2 W m(exp -2). The CAM results indicate that ice particle roughening can result in a large regional SW radiative effect and a small but nonnegligible increase in the global LW cloud radiative effect.

Uncertainty in aerosol hygroscopicity resulting from semi-volatile organic compounds

NASA Astrophysics Data System (ADS)

Goulden, Olivia; Crooks, Matthew; Connolly, Paul

2018-01-01

We present a novel method of exploring the effect of uncertainties in aerosol properties on cloud droplet number using existing cloud droplet activation parameterisations. Aerosol properties of a single involatile particle mode are randomly sampled within an uncertainty range and resulting maximum supersaturations and critical diameters calculated using the cloud droplet activation scheme. Hygroscopicity parameters are subsequently derived and the values of the mean and uncertainty are found to be comparable to experimental observations. A recently proposed cloud droplet activation scheme that includes the effects of co-condensation of semi-volatile organic compounds (SVOCs) onto a single lognormal mode of involatile particles is also considered. In addition to the uncertainties associated with the involatile particles, concentrations, volatility distributions and chemical composition of the SVOCs are randomly sampled and hygroscopicity parameters are derived using the cloud droplet activation scheme. The inclusion of SVOCs is found to have a significant effect on the hygroscopicity and contributes a large uncertainty. For non-volatile particles that are effective cloud condensation nuclei, the co-condensation of SVOCs reduces their actual hygroscopicity by approximately 25 %. A new concept of an effective hygroscopicity parameter is introduced that can computationally efficiently simulate the effect of SVOCs on cloud droplet number concentration without direct modelling of the organic compounds. These effective hygroscopicities can be as much as a factor of 2 higher than those of the non-volatile particles onto which the volatile organic compounds condense.

Microphysical Properties and Water Budget for Summer Convective Clouds over the Tibetan Plateau

NASA Astrophysics Data System (ADS)

Guo, X.; Tang, J.; Chang, Y.

2017-12-01

During the Third Tibetan Plateau Atmospheric Scientific Experiment (TIPEX-III), the clouds and precipitation processes over the Tibetan Plateau have been intensively investigated. On basis of field campaign, the cloud microphysical structure, water transformation and budget properties for typical convective precipitation processes in the summer season of 2014 over the plateau are studied using mesoscale numerical prediction model (WRF) combined with observational data collected during the experiment. The results indicate that WRF model could reproduce the general characteristics of diurnal variation of clouds and precipitation process over the plateau, however, the temporal and spatial distribution and intensity of cloud bands and precipitation simulated by WRF model still had large differences with those observed. Ice process played a critical role in the development of summer convective clouds and precipitation over the plateau. The surface precipitation was primarily formed by the melting process of graupel particles. Although the warm cloud microphysical process had small direct contribution on the surface precipitation, it had an important contribution in the formation of graupel embryos. High amount of supercooled cloud water content and graupel particles could be found in the clouds. The formation and growth of snow particles relied on the conversion of ice crystal and the aggregation with ice crystal over 12 km (-40°), but the formation of snow particles below 12 km (-40°)was dependent on the conversion of Bergeron process of ice crystals and its growth resulted from riming process with supercooled cloud water. The accretion process of supercooled raindrops by ice crystal and snow particles contributed to the production of graupel embryos and their growth mainly relied on the riming process with supercooled cloud water and aggregation process with snow particles. The mean daily conversion rate from vapor to precipitation was as high as 27.27%, which is close to Yangtze River downstream, and is higher than the regions of northern and northwestern China. The contribution of daily mean surface evaporation to precipitation was 10.92%, indicating that the 90% rainfall was from the conversion of water vapor outside the plateau.

Physical and chemical properties of ice residuals during the 2013 and 2014 CLACE campaigns

NASA Astrophysics Data System (ADS)

Kupiszewski, Piotr; Weingartner, Ernest; Vochezer, Paul; Hammer, Emanuel; Gysel, Martin; Färber, Raphael; Fuchs, Claudia; Schnaiter, Martin; Baltensperger, Urs; Schmidt, Susan; Schneider, Johannes; Bigi, Alessandro; Toprak, Emre; Linke, Claudia; Klimach, Thomas

2014-05-01

The shortcomings in our understanding and, thus, representation of aerosol-cloud interactions are one of the major sources of uncertainty in climate model projections. Among the poorly understood processes is mixed-phase cloud formation via heterogeneous nucleation, and the subsequent spatial and temporal evolution of such clouds. Cloud glaciation augments precipitation formation, resulting in decreased cloud cover and lifetime, and affects cloud radiative properties. Meanwhile, the physical and chemical properties of atmospherically relevant ice nuclei (IN), the sub-population of aerosol particles which enable heterogeneous nucleation, are not well known. Extraction of ice residuals (IR) in mixed-phase clouds is a difficult task, requiring separation of the few small, freshly formed ice crystals (the IR within such crystals can be deemed representative of the original IN) not only from interstitial particles, but also from the numerous supercooled droplets which have aerodynamic diameters similar to those of the ice crystals. In order to address the difficulties with ice crystal sampling and IR extraction in mixed-phase clouds, the new Ice Selective Inlet (ISI) has been designed and deployed at the Jungfraujoch field site. Small ice crystals are selectively sampled via the inlet with simultaneous counting, sizing and imaging of hydrometeors contained in the cloud by a set of optical particle spectrometers, namely Welas optical particle counters (OPC) and a Particle Phase Discriminator (PPD). The heart of the ISI is a droplet evaporation unit with ice-covered inner walls, resulting in removal of droplets using the Wegener-Bergeron-Findeisen process, while transmitting a relatively high fraction of small ice crystals. The ISI was deployed in the winters of 2013 and 2014 at the high alpine Jungfraujoch site (3580 m.a.s.l) during the intensive CLACE field campaigns. The measurements focused on analysis of the physical and chemical characteristics of IR and the microphysical properties of mixed-phase clouds. A host of aerosol instrumentation was deployed downstream of the ISI, including a Grimm OPC and a scanning mobility particle sizer (SMPS) for number size distribution measurements, as well as a single particle mass spectrometer (ALABAMA; 2013 only), single particle soot photometers (SP2) and a Wideband Integrated Bioaerosol Sensor (WIBS-4) for analysis of the chemical composition, with particular focus on the content of black carbon (BC) and biological particles in IR. Corresponding instrumentation sampled through a total aerosol inlet. By comparing observations from the ISI with those from the total inlet the characteristics of ice residuals relative to the total aerosol could be established. First results from these analyses will be presented.

Spectral signatures of polar stratospheric clouds and sulfate aerosol

NASA Technical Reports Server (NTRS)

Massie, S. T.; Bailey, P. L.; Gille, J. C.; Lee, E. C.; Mergenthaler, J. L.; Roche, A. E.; Kumer, J. B.; Fishbein, E. F.; Waters, J. W.; Lahoz, W. A.

1994-01-01

Multiwavelength observations of Antarctic and midlatitude aerosol by the Cryogenic Limb Array Etalon Spectrometer (CLAES) experiment on the Upper Atmosphere Research Satellite (UARS) are used to demonstrate a technique that identifies the location of polar stratospheric clouds. The technique discussed uses the normalized area of the triangle formed by the aerosol extinctions at 925, 1257, and 1605/cm (10.8, 8.0, and 6.2 micrometers) to derive a spectral aerosol measure M of the aerosol spectrum. Mie calculations for spherical particles and T-matrix calculations for spheriodal particles are used to generate theoretical spectral extinction curves for sulfate and polar stratospheric cloud particles. The values of the spectral aerosol measure M for the sulfate and polar stratospheric cloud particles are shown to be different. Aerosol extinction data, corresponding to temperatures between 180 and 220 K at a pressure of 46 hPa (near 21-km altitude) for 18 August 1992, are used to demonstrate the technique. Thermodynamic calculations, based upon frost-point calculations and laboratory phase-equilibrium studies of nitric acid trihydrate, are used to predict the location of nitric acid trihydrate cloud particles.

Interannual Variations in Aerosol Sources and Their Impact on Orographic Precipitation Over California's Central Sierra Nevada

NASA Technical Reports Server (NTRS)

Creamean, J. M.; Ault, A. P.; White, A. B.; Neiman, P. J.; Ralph, F. M.; Minnis, Patrick; Prather, K. A.

2014-01-01

Aerosols that serve as cloud condensation nuclei (CCN) and ice nuclei (IN) have the potential to profoundly influence precipitation processes. Furthermore, changes in orographic precipitation have broad implications for reservoir storage and flood risks. As part of the CalWater I field campaign (2009-2011), the impacts of aerosol sources on precipitation were investigated in the California Sierra Nevada. In 2009, the precipitation collected on the ground was influenced by both local biomass burning (up to 79% of the insoluble residues found in precipitation) and long-range transported dust and biological particles (up to 80% combined), while in 2010, by mostly local sources of biomass burning and pollution (30-79% combined), and in 2011 by mostly long-range transport from distant sources (up to 100% dust and biological). Although vast differences in the source of residues was observed from year-to-year, dust and biological residues were omnipresent (on average, 55% of the total residues combined) and were associated with storms consisting of deep convective cloud systems and larger quantities of precipitation initiated in the ice phase. Further, biological residues were dominant during storms with relatively warm cloud temperatures (up to -15 C), suggesting these particles were more efficient IN compared to mineral dust. On the other hand, lower percentages of residues from local biomass burning and pollution were observed (on average 31% and 9%, respectively), yet these residues potentially served as CCN at the base of shallow cloud systems when precipitation quantities were low. The direct connection of the source of aerosols within clouds and precipitation type and quantity can be used in models to better assess how local emissions versus long-range transported dust and biological aerosols play a role in impacting regional weather and climate, ultimately with the goal of more accurate predictive weather forecast models and water resource management.

GHOSTLY REFLECTIONS IN THE PLEIADES

NASA Technical Reports Server (NTRS)

2002-01-01

NASA's Hubble Space Telescope has caught the eerie, wispy tendrils of a dark interstellar cloud being destroyed by the passage of one of the brightest stars in the Pleiades star cluster. Like a flashlight beam shining off the wall of a cave, the star is reflecting light off the surface of pitch black clouds of cold gas laced with dust. These are called reflection nebulae. The famous cluster is easily visible in the evening sky during the winter months as a small grouping of bright blue stars, named after the 'Seven Sisters' of Greek mythology. Resembling a small dipper, this star cluster lies in the constellation Taurus at a distance of about 380 light-years from Earth. The unaided eye can discern about half a dozen bright stars in the cluster, but a small telescope will reveal that the Pleiades contains many hundreds of fainter stars. In many cases, the nebulae surrounding star clusters represent material from which the stars have formed recently. However the Pleiades nebulosity is actually an independent cloud, drifting through the cluster at a relative speed of about 6.8 miles/second (11 kilometers/second). In 1890, American astronomer E. E. Barnard, observing visually with the Lick Observatory 36-inch telescope in California, discovered an exceptionally bright nebulosity adjacent to the bright Pleiades star Merope. It is now cataloged as IC 349, or 'Barnard's Merope Nebula.' IC 349 is so bright because it lies extremely close to Merope--only about 3,500 times the separation of the Earth from the Sun, or about 0.06 light-year--and thus is strongly illuminated by the star's light. In the new Hubble image, Merope itself is just outside the frame on the upper right. The colorful rays of light at the upper right, pointing back to the star, are an optical phenomenon produced within the telescope, and are not real. However, the remarkable parallel wisps extending from lower left to upper right are real features, revealed for the first time through Hubble's high-resolution imaging capability. Astronomers George Herbig and Theodore Simon of the University of Hawaii obtained these broadband observations with Hubble's Wide Field and Planetary Camera 2 on September 19, 1999. Herbig and Simon propose that, as the Merope Nebula approaches Merope, the strong starlight shining on the dust decelerates the dust particles. Physicists call this phenomenon 'radiation pressure.' Smaller dust particles are slowed down more by the radiation pressure than the larger particles. Thus, as the cloud approaches the star, there is a sifting of particles by size, much like grain thrown in the air to separate wheat from chaff. The nearly straight lines pointing toward Merope are thus streams of larger particles, continuing on toward the star while the smaller decelerated particles are left behind at the lower left of the picture. Over the next few thousand years, the nebula--if it survives the close passage without being completely destroyed--will move on past Merope, somewhat like a comet swinging past our Sun. This chance collision allows astronomers to study interstellar material under very rare conditions, and thus learn more about the structure of the dust lying between the stars. Image Credit: NASA and The Hubble Heritage Team (STScI/AURA) Acknowledgment: George Herbig and Theodore Simon (Institute for Astronomy, University of Hawaii)

Water and organics in interplanetary dust particles

NASA Astrophysics Data System (ADS)

Bradley, John P.

2015-08-01

Interplanetary dust particles (IDPs) and larger micrometeorites (MMs) impinge on the upper atmosphere where they decelerate at ~90 km altitude and settle to the Earth’s surface. Comets and asteroids are the major sources and the flux, 30,000-40,000 tons/yr, is comparable to the mass of larger meteorites impacting the Earth’s surface. The sedimentary record suggests that the flux was much higher on the early Earth. The chondritic porous (CP) subset of IDPs together with their larger counterparts, ultracarbonaceous micrometeorites (UCMMs), appear to be unique among known meteoritic materials in that they are composed almost exclusively of anhydrous minerals, some of them contain >> 50% organic carbon by volume as well as the highest abundances of presolar silicate grains including GEMS. D/H and 15N abundances implicate the Oort Cloud or presolar molecular cloud as likely sources of the organic carbon. Prior to atmospheric entry, IDPs and MMs spend ~104-105 year lifetimes in solar orbit where their surfaces develop amorphous space weathered rims from exposure to the solar wind (SW). Similar rims are observed on lunar soil grains and on asteroid Itokawa regolith grains. Using valence electron energy-loss spectroscopy (VEELS) we have detected radiolytic water in the rims on IDPs formed by the interaction of solar wind protons with oxygen in silicate minerals. Therefore, IDPs and MMs continuously deliver both water and organics to the earth and other terrestrial planets. The interaction of protons with oxygen-rich minerals to form water is a universal process.Affiliations:a University of Hawaii at Manoa, Hawaii Institute of Geophysics and Planetology, 1680 East-West Road, Honolulu, HI 96822, USA.b National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.c Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.d Department of Materials Science & Engineering, University of California, Berkeley, CA 94720, USA.e Advanced Light Source Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.

Radiation Transfer in the Atmosphere: Scattering

NASA Technical Reports Server (NTRS)

Mishchenko, M.; Travis, L.; Lacis, Andrew A.

2014-01-01

Sunlight illuminating the Earth's atmosphere is scattered by gas molecules and suspended particles, giving rise to blue skies, white clouds, and optical displays such as rainbows and halos. By scattering and absorbing the shortwave solar radiation and the longwave radiation emitted by the underlying surface, cloud and aerosol particles strongly affect the radiation budget of the terrestrial climate system. As a consequence of the dependence of scattering characteristics on particle size, morphology, and composition, scattered light can be remarkably rich in information on particle properties and thus provides a sensitive tool for remote retrievals of macro- and microphysical parameters of clouds and aerosols.

Performance of McRAS-AC in the GEOS-5 AGCM: Part 1, Aerosol-Activated Cloud Microphysics, Precipitation, Radiative Effects, and Circulation

NASA Technical Reports Server (NTRS)

Sud, Y. C.; Lee, D.; Oreopoulos, L.; Barahona, D.; Nenes, A.; Suarez, M. J.

2012-01-01

A revised version of the Microphysics of clouds with Relaxed Arakawa-Schubert and Aerosol-Cloud interaction (McRAS-AC), including, among others, the Barahona and Nenes ice nucleation parameterization, is implemented in the GEOS-5 AGCM. Various fields from a 10-year long integration of the AGCM with McRAS-AC were compared with their counterparts from an integration of the baseline GEOS-5 AGCM, and with satellite data as observations. Generally using McRAS-AC reduced biases in cloud fields and cloud radiative effects are much better over most of the regions of the Earth. Two weaknesses are identified in the McRAS-AC runs, namely, too few cloud particles around 40S-60S, and too high cloud water path during northern hemisphere summer over the Gulf Stream and North Pacific. Sensitivity analyses showed that these biases potentially originated from biases in the aerosol input. The first bias is largely eliminated in a sensitivity test using 50% smaller aerosol particles, while the second bias is much reduced when interactive aerosol chemistry was turned on. The main drawback of McRAS-AC is dearth of low-level marine stratus clouds, probably due to lack of dry-convection, not yet implemented into the cloud scheme. Despite these biases, McRAS-AC does simulate realistic clouds and their optical properties that can improve with better aerosol-input and thereby has the potential to be a valuable tool for climate modeling research because of its aerosol indirect effect simulation capabilities involving prediction of cloud particle number concentration and effective particle size for both convective and stratiform clouds is quite realistic.

Scavenging of black carbon in mixed phase clouds at the high alpine site Jungfraujoch

NASA Astrophysics Data System (ADS)

Cozic, J.; Verheggen, B.; Mertes, S.; Connolly, P.; Bower, K.; Petzold, A.; Baltensperger, U.; Weingartner, E.

2006-11-01

The scavenging of black carbon (BC) in liquid and mixed phase clouds was investigated during intensive experiments in winter 2004, summer 2004 and winter 2005 at the high alpine research station Jungfraujoch (3580 m a.s.l., Switzerland). Aerosol residuals were sampled behind two well characterized inlets; a total inlet which collected cloud particles (drops and ice particles) as well as interstitial aerosol particles; an interstitial inlet which collected only interstitial (unactivated) aerosol particles. BC concentrations were measured behind each of these inlets along with the submicrometer aerosol number size distribution, from which a volume concentration was derived. These measurements were complemented by in-situ measurements of cloud microphysical parameters. BC was found to be scavenged into the cloud phase to the same extent as the bulk aerosol, which suggests that BC was covered with soluble material through aging processes, rendering it more hygroscopic. The scavenged fraction of BC (FScav,BC), defined as the fraction of BC that is incorporated into cloud droplets and ice crystals, decreases with increasing cloud ice mass fraction (IMF) from FScav,BC=60% in liquid phase clouds to FScav,BC~10% in mixed-phase clouds with IMF>0.2. This is explained by the evaporation of liquid droplets in the presence of ice crystals (Wegener-Bergeron-Findeisen process), releasing BC containing cloud condensation nuclei back into the interstitial phase. In liquid clouds, the scavenged BC fraction is found to decrease with decreasing cloud liquid water content. The scavenged BC fraction is also found to decrease with increasing BC mass concentration since there is an increased competition for the available water vapour.

Cirrus microphysics and radiative transfer: Cloud field study on October 28, 1986

NASA Technical Reports Server (NTRS)

Kinne, Stefan; Ackerman, Thomas P.; Heymsfield, Andrew J.; Valero, Francisco P. J.; Sassen, Kenneth; Spinhirne, James D.

1990-01-01

The radiative properties of cirrus clouds present one of the unresolved problems in weather and climate research. Uncertainties in ice particle amount and size and, also, the general inability to model the single scattering properties of their usually complex particle shapes, prevent accurate model predictions. For an improved understanding of cirrus radiative effects, field experiments, as those of the Cirrus IFO of FIRE, are necessary. Simultaneous measurements of radiative fluxes and cirrus microphysics at multiple cirrus cloud altitudes allows the pitting of calculated versus measured vertical flux profiles; with the potential to judge current cirrus cloud modeling. Most of the problems in this study are linked to the inhomogeneity of the cloud field. Thus, only studies on more homogeneous cirrus cloud cases promises a possibility to improve current cirrus parameterizations. Still, the current inability to detect small ice particles will remain as a considerable handicap.

Effluent sampling of Scout D and Delta launch vehicle exhausts

NASA Technical Reports Server (NTRS)

Hulten, W. C.; Storey, R. W.; Gregory, G. L.; Woods, D. C.; Harris, F. S., Jr.

1974-01-01

Characterization of engine-exhaust effluents (hydrogen chloride, aluminum oxide, carbon dioxide, and carbon monoxide) has been attempted by conducting field experiments monitoring the exhaust cloud from a Scout-Algol III vehicle launch and a Delta-Thor vehicle launch. The exhaust cloud particulate size number distribution (total number of particles as a function of particle diameter), mass loading, morphology, and elemental composition have been determined within limitations. The gaseous species in the exhaust cloud have been identified. In addition to the ground-based measurements, instrumented aircraft flights through the low-altitude, stabilized-exhaust cloud provided measurements which identified CO and HCI gases and Al2O3 particles. Measurements of the initial exhaust cloud during formation and downwind at several distances have established sampling techniques which will be used for experimental verification of model predictions of effluent dispersion and fallout from exhaust clouds.

Minimalist model of ice microphysics in mixed-phase stratiform clouds

NASA Astrophysics Data System (ADS)

Yang, Fan; Ovchinnikov, Mikhail; Shaw, Raymond A.

2013-07-01

The question of whether persistent ice crystal precipitation from supercooled layer clouds can be explained by time-dependent, stochastic ice nucleation is explored using an approximate, analytical model and a large-eddy simulation (LES) cloud model. The updraft velocity in the cloud defines an accumulation zone, where small ice particles cannot fall out until they are large enough, which will increase the residence time of ice particles in the cloud. Ice particles reach a quasi-steady state between growth by vapor deposition and fall speed at cloud base. The analytical model predicts that ice water content (wi) has a 2.5 power-law relationship with ice number concentration (ni). wi and ni from a LES cloud model with stochastic ice nucleation confirm the 2.5 power-law relationship, and initial indications of the scaling law are observed in data from the Indirect and Semi-Direct Aerosol Campaign. The prefactor of the power law is proportional to the ice nucleation rate and therefore provides a quantitative link to observations of ice microphysical properties.

Minimalist Model of Ice Microphysics in Mixed-phase Stratiform Clouds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, F.; Ovchinnikov, Mikhail; Shaw, Raymond A.

The question of whether persistent ice crystal precipitation from super cooled layer clouds can be explained by time-dependent, stochastic ice nucleation is explored using an approximate, analytical model, and a large-eddy simulation (LES) cloud model. The updraft velocity in the cloud defines an accumulation zone, where small ice particles cannot fall out until they are large enough, which will increase the residence time of ice particles in the cloud. Ice particles reach a quasi-steady state between growth by vapor deposition and fall speed at cloud base. The analytical model predicts that ice water content (wi) has a 2.5 power lawmore » relationship with ice number concentration ni. wi and ni from a LES cloud model with stochastic ice nucleation also confirm the 2.5 power law relationship. The prefactor of the power law is proportional to the ice nucleation rate, and therefore provides a quantitative link to observations of ice microphysical properties.« less

Statistical Analyses of Satellite Cloud Object Data from CERES. Part II; Tropical Convective Cloud Objects During 1998 El Nino and Validation of the Fixed Anvil Temperature Hypothesis

NASA Technical Reports Server (NTRS)

Xu, Kuan-Man; Wong, Takmeng; Wielicki, Bruce a.; Parker, Lindsay; Lin, Bing; Eitzen, Zachary A.; Branson, Mark

2006-01-01

Characteristics of tropical deep convective cloud objects observed over the tropical Pacific during January-August 1998 are examined using the Tropical Rainfall Measuring Mission/ Clouds and the Earth s Radiant Energy System single scanner footprint (SSF) data. These characteristics include the frequencies of occurrence and statistical distributions of cloud physical properties. Their variations with cloud-object size, sea surface temperature (SST), and satellite precessing cycle are analyzed in detail. A cloud object is defined as a contiguous patch of the Earth composed of satellite footprints within a single dominant cloud-system type. It is found that statistical distributions of cloud physical properties are significantly different among three size categories of cloud objects with equivalent diameters of 100 - 150 km (small), 150 - 300 km (medium), and > 300 km (large), respectively, except for the distributions of ice particle size. The distributions for the larger-size category of cloud objects are more skewed towards high SSTs, high cloud tops, low cloud-top temperature, large ice water path, high cloud optical depth, low outgoing longwave (LW) radiation, and high albedo than the smaller-size category. As SST varied from one satellite precessing cycle to another, the changes in macrophysical properties of cloud objects over the entire tropical Pacific were small for the large-size category of cloud objects, relative to those of the small- and medium-size categories. This result suggests that the fixed anvil temperature hypothesis of Hartmann and Larson may be valid for the large-size category. Combining with the result that a higher percentage of the large-size category of cloud objects occurs during higher SST subperiods, this implies that macrophysical properties of cloud objects would be less sensitive to further warming of the climate. On the other hand, when cloud objects are classified according to SSTs where large-scale dynamics plays important roles, statistical characteristics of cloud microphysical properties, optical depth and albedo are not sensitive to the SST, but those of cloud macrophysical properties are strongly dependent upon the SST. Frequency distributions of vertical velocity from the European Center for Medium-range Weather Forecasts model that is matched to each cloud object are used to interpret some of the findings in this study.

Dual polarisation C-band weather radar imagery of the 6 August 2012 Te Maari Eruption, Mount Tongariro, New Zealand

NASA Astrophysics Data System (ADS)

Crouch, John F.; Pardo, Natalia; Miller, Craig A.

2014-10-01

The 6 August 2012 eruption of Mt. Tongariro from Upper Te Maari Crater in the central North Island of New Zealand was the first volcanic eruption observed by an operational weather radar in New Zealand, and is believed to be one of only a small number of eruptions observed by a dual-polarisation radar worldwide. The eruption was also observed by a GeoNet webcam, and detailed ash deposit studies have permitted analysis of the plume characteristics. A combination of radar and webcam imagery show 5 pulses within the first 13 min of the eruption, and also the subsequent ash transport downwind. Comparison with ash samples show the radar was likely detecting ash particles down to about 0.5 mm diameter. The maximum plume height estimated by the radar is 7.8 ± 1.0 km above mean sea level (amsl), although it is possible this may be a slight under estimation if very small ash particles not detected by the radar rose higher and comprised the very top of the plume. The correlation coefficient and differential reflectivity fields that are additionally measured by the dual polarisation radar provide extra information about the structure and composition of the eruption column and ash cloud. The correlation coefficient easily discriminates between the eruption column and the ash plume, and provides some information about the diversity of ash particle size within both the ash plume and the subsequent detached ash cloud drifting downwind. The differential reflectivity shows that the larger ash particles are falling with a horizontal orientation, and indicates that ice nucleation and aggregation of fine ash particles was probably occurring at high altitudes within 20-25 min of the eruption.

Clouds and aerosols in Puerto Rico - a new evaluation

NASA Astrophysics Data System (ADS)

Allan, J. D.; Baumgardner, D.; Raga, G. B.; Mayol-Bracero, O. L.; Morales-García, F.; García-García, F.; Montero-Martínez, G.; Borrmann, S.; Schneider, J.; Mertes, S.; Walter, S.; Gysel, M.; Dusek, U.; Frank, G. P.; Krämer, M.

2008-03-01

The influence of aerosols, both natural and anthropogenic, remains a major area of uncertainty when predicting the properties and behaviour of clouds and their influence on climate. In an attempt to better understand warm cloud formation in a tropical marine environment, a period of intensive measurements took place in December 2004 in Puerto Rico, using some of the latest developments in online instrumentation such as aerosol mass spectrometers, cloud condensation nuclei counters and a hygroscopicity tandem differential mobility analyser. Simultaneous online measurements of aerosol size distributions, composition, hygroscopicity and optical properties were made near the lighthouse of Cape San Juan in the north-eastern corner of the island and at the top of East Peak mountain (1040 m a.s.l.), the two sites separated by 17 km. Additional measurements of the cloud droplet residual and interstitial aerosol properties were made at the mountain site, accompanied by measurements of cloud droplet size distributions, liquid water content and the chemical composition of cloud and rain water samples. Both aerosol composition and cloud properties were found to be sensitive to wind sector. Air from the east-northeast (ENE) was mostly free of anthropogenic influences, the submicron fraction being mainly composed of non-sea salt sulphate, while that from the east-southeast (ESE) was found to be moderately influenced by populated islands upwind, adding smaller (<100 nm), externally mixed, carbonaceous particles to the aerosol that increased the number concentrations by over a factor of 3. This change in composition was also accompanied with a reduction in the measured hygroscopicity and fractional cloud activation potential of the aerosol. At the mountain site, the average cloud droplet concentrations increased from 193 to 519 cm-3, median volume diameter decreased from 20 to 14 μm and the liquid water content increased from 0.24 to 0.31 g m-3 when the winds shifted from the ENE to ESE. Larger numbers of interstitial particles were recorded, most notably at sizes greater than 100 nm, which were absent during clean conditions. The average size of the residual particles and concentrations of cloudwater nitrate, sulphate and insoluble material increased during polluted conditions. Previous studies in Puerto Rico had reported the presence of a significant non-anthropogenic organic fraction in the aerosols measured and concluded that this was a factor controlling the in situ cloud properties. However, this was not observed in our case. In contrast to the 1.00±0.14 μg m-3 of organic carbon measured in 1992 and 1995, the organic matter measured in the current study of 0.17±0.35 μg m-3 is many times lower, most of which can be attributed to anthropogenic sources. During clean conditions, the submicron aerosol was observed to be almost entirely inorganic, an observation supported by the hygroscopicity measurements. This suggests that organic aerosols from marine sources may not be completely ubiquitous (either spatially or temporally) in this environment and requires further investigation to quantify their true extent and implications, with more extensive, longer-term sampling in conjunction with wind field analyses.

Opalescent and cloudy fruit juices: formation and particle stability.

PubMed

Beveridge, Tom

2002-07-01

Cloudy fruit juices, particularly from tropical fruit, are becoming a fast-growing part of the fruit juice sector. The classification of cloud as coarse and fine clouds by centrifugation and composition of cloud from apple, pineapple, orange, guava, and lemon juice are described. Fine particulate is shown to be the true stable cloud and to contain considerable protein, carbohydrate, and lipid components. Often, tannin is present as well. The fine cloud probably arises from cell membranes and appears not to be simply cell debris. Factors relating to the stability of fruit juice cloud, including particle sizes, size distribution, and density, are described and discussed. Factors promoting stable cloud in juice are presented.

Effect of Particle Morphology on the Reactivity of Explosively Dispersed Titanium Particles

NASA Astrophysics Data System (ADS)

Frost, David; Cairns, Malcolm; Goroshin, Samuel; Zhang, Fan

2009-06-01

The effect of particle morphology on the reaction of titanium (Ti) particles explosively dispersed during the detonation of either cylindrical or spherical charges has been investigated experimentally. The explosive charges consisted of packed beds of Ti particles saturated with nitromethane. The reaction behavior of irregularly-shaped Ti particles in three size ranges is compared with tests with spherical Ti particles. The particle reaction is strongly dependent on particle morphology, e.g., 95 μm spherical Ti particles failed to ignite (in cylinders up to 49 mm in dia), whereas similarly sized irregular Ti particles readily ignited. For irregular particles, the uniformity of ignition on the particle cloud surface was almost independent of particle size, but depended on charge diameter. As the charge diameter was reduced, ignition in the conically expanding particle cloud occurred only at isolated spots or bands. For spherical charges, although large irregular Ti particles ignited promptly and uniformly throughout the particle cloud, the smallest particles dispersed nonuniformly and ignition occurred at isolated locations. In general, particle ignition is a competition between particle heating (which is influenced by particle morphology, size, number density and the local thermodynamic history) and expansion cooling of the products.

Analysis of TRMM Microphysical Measurements: Tropical Rainfall Measuring Mission (TRMM)

NASA Technical Reports Server (NTRS)

2004-01-01

SPEC Incorporated participated in three of the four TRMM field campaigns (TEFLUN-A, TEFLUN-B and KWAJEX), installing and operating a cloud particle imager (CPI) and a high volume precipitation spectrometer (HVPS) on the SPEC Learjet in TEFLUN-A, the University of North Dakota Citation in TEFLUN-B and KWAJEX, and a CPI on the NASA DC-8 in KWAJEX. This report presents and discusses new software tools and algorithms that were developed to analyze microphysical data collected during these field campaigns, as well as scientific interpretations of the data themselves. Software algorithms were developed to improve the analysis of microphysical measurements collected by the TRMM aircraft during the field campaigns. Particular attention was paid to developing and/or improving algorithms used to compute particle size distributions and ice water content. Software was also developed in support of production of the TRMM Common Microphysical Product (CMP) data files. CMP data files for TEFLUN-A field campaign were produced and submitted to the DAAC. Typical microphysical properties of convective and stratiform regions from TEFLUN-A and KWAJEX clouds were produced. In general, it was found that in the upper cloud region near -20 to -25 C, stratiform clouds contain very high (greater than 1 per cubic centimeter) concentrations of small ice particles, which are suspected to be a residual from homogeneous freezing and sedimentation of small drops in a convective updraft. In the upper cloud region near -20 to -25 C, convective clouds contain aggregates, which are not found lower in the cloud. Stratiform clouds contain aggregates at all levels, with the majority in the lowest levels. Convective cloud regions contain much higher LWC and drop concentrations than stratiform regions at all levels, and higher LWC in the middle and upper regions. Stratiform clouds contain higher IWC than convective clouds only at the lowest level. Irregular shaped ice particles are found in very high concentrations throughout both convective and stratiform cloud regions. A striking difference in particle shape in cirrus formed in situ, cirrus formed from maritime anvils and cirrus formed from continental anvils. Over 50% of the mass of in situ cirrus ice particles is composed of bullet rosettes, while bullet rosettes are virtually non-existent in maritime and tropical anvils. Tropical anvils are composed of mostly singular, plates, capped columns, and blocky irregular shapes, while continental anvils have a much higher percentage of aggregates, some of which are chains of small spheroidal particles that appear to result from homogeneous freezing of drops. A correlation between high electric fields in continental anvils and the formation of aggregates is hypothesized.

A Condensation-coalescence Cloud Model for Exoplanetary Atmospheres: Formulation and Test Applications to Terrestrial and Jovian Clouds

NASA Astrophysics Data System (ADS)

Ohno, Kazumasa; Okuzumi, Satoshi

2017-02-01

A number of transiting exoplanets have featureless transmission spectra that might suggest the presence of clouds at high altitudes. A realistic cloud model is necessary to understand the atmospheric conditions under which such high-altitude clouds can form. In this study, we present a new cloud model that takes into account the microphysics of both condensation and coalescence. Our model provides the vertical profiles of the size and density of cloud and rain particles in an updraft for a given set of physical parameters, including the updraft velocity and the number density of cloud condensation nuclei (CCNs). We test our model by comparing with observations of trade-wind cumuli on Earth and ammonia ice clouds in Jupiter. For trade-wind cumuli, the model including both condensation and coalescence gives predictions that are consistent with observations, while the model including only condensation overestimates the mass density of cloud droplets by up to an order of magnitude. For Jovian ammonia clouds, the condensation-coalescence model simultaneously reproduces the effective particle radius, cloud optical thickness, and cloud geometric thickness inferred from Voyager observations if the updraft velocity and CCN number density are taken to be consistent with the results of moist convection simulations and Galileo probe measurements, respectively. These results suggest that the coalescence of condensate particles is important not only in terrestrial water clouds but also in Jovian ice clouds. Our model will be useful to understand how the dynamics, compositions, and nucleation processes in exoplanetary atmospheres affect the vertical extent and optical thickness of exoplanetary clouds via cloud microphysics.

Evaluation of simulated tropical convective updraft hydrometeor properties using aircraft observations

NASA Astrophysics Data System (ADS)

Stanford, McKenna W.

The High Altitude Ice Crystals - High Ice Water Content (HAIC-HIWC) field campaign produced aircraft retrievals of total condensed water content (TWC), hydrometeor particle size distributions, and vertical velocity (w) in high ice water content regions of tropical mesoscale convective systems (MCSs). These observations are used to evaluate deep convective updraft properties in high-resolution nested Weather Research and Forecasting (WRF) simulations of observed MCSs. Because simulated hydrometeor properties are highly sensitive to the parameterization of microphysics, three commonly used microphysical parameterizations are tested, including two bulk schemes (Thompson and Morrison) and one bin scheme (Fast Spectral Bin Microphysics). A commonly documented bias in cloud-resolving simulations is the exaggeration of simulated radar reflectivities aloft in tropical MCSs. This may result from overly strong convective updrafts that loft excessive condensate mass and from simplified approximations of hydrometeor size distributions, properties, species separation, and microphysical processes. The degree to which the reflectivity bias is a separate function of convective dynamics, condensate mass, and hydrometeor size has yet to be addressed. This research untangles these components by comparing simulated and observed relationships between w, TWC, and hydrometer size as a function of temperature. All microphysics schemes produce median mass diameters that are generally larger than observed for temperatures between -10 °C and -40 °C and TWC > 1 g m-3. Observations produce a prominent mode in the composite mass size distribution around 300 microm, but under most conditions, all schemes shift the distribution mode to larger sizes. Despite a much greater number of samples, all simulations fail to reproduce observed high TWC or high w conditions between -20 °C and -40 °C in which only a small fraction of condensate mass is found in relatively large particle sizes. Increasing model resolution and employing explicit cloud droplet nucleation decrease the size bias, but not nearly enough to reproduce observations. Because simulated particle sizes are too large across all schemes when controlling for temperature, w, and TWC, this bias is hypothesized to partly result from errors in parameterized microphysical processes in addition to overly simplified hydrometeor properties such as mass-size relationships and particle size distribution parameters.

Determination of polar stratospheric cloud particle refractive indices by use of in situ optical measurements and T-matrix calculations.

PubMed

Scarchilli, Claudio; Adriani, Alberto; Cairo, Francesco; Di Donfrancesco, Guido; Buontempo, Carlo; Snels, Marcel; Moriconi, Maria Luisa; Deshler, Terry; Larsen, Niels; Luo, Beiping; Mauersberger, Konrad; Ovarlez, Joelle; Rosen, Jim; Schreiner, Jochen

2005-06-01

A new algorithm to infer structural parameters such as refractive index and asphericity of cloud particles has been developed by use of in situ observations taken by a laser backscattersonde and an optical particle counter during balloon stratospheric flights. All three main particles, liquid, ice, and a no-ice solid (NAT, nitric acid trihydrate) of polar stratospheric clouds, were observed during two winter flights performed from Kiruna, Sweden. The technique is based on use of the T-matrix code developed for aspherical particles to calculate the backscattering coefficient and particle depolarizing properties on the basis of size distribution and concentration measurements. The results of the calculations are compared with observations to estimated refractive indices and particle asphericity. The method has also been used in cases when the liquid and solid phases coexist with comparable influence on the optical behavior of the cloud to estimate refractive indices. The main results prove that the index of refraction for NAT particles is in the range of 1.37-1.45 at 532 nm. Such particles would be slightly prolate spheroids. The calculated refractive indices for liquid and ice particles are 1.51-1.55 and 1.31-1.33, respectively. The results for solid particles confirm previous measurements taken in Antarctica during 1992 and obtained by a comparison of lidar and optical particle counter data.

Ice nucleation by cellulose and its potential impact on clouds and climate

NASA Astrophysics Data System (ADS)

Hiranuma, Naruki; Möhler, Ottmar; Yamashita, Katsuya; Tajiri, Takuya; Saito, Atsushi; Kiselev, Alexei; Hoose, Corinna; Murakami, Masataka

2014-05-01

Biological aerosol particles have recently been accentuated by their efficient ice nucleating activity as well as potential impact on clouds and global climate. Despite their potential importance, little is known about the abundance of biological particles in the atmosphere and their role compared to non-biological material and, consequently, their potential role in the cloud-hydrology and climate system is also poorly constrained. However, field observations show that the concentration of airborne cellulose, which is one of the most important derivatives of glucose and atmospherically relevant biopolymers, is consistently prevalent (>10 ng per cubic meter) throughout the whole year even at remote- and elevated locations. Here we use a novel cloud simulation chamber in Tsukuba, Japan to demonstrate that airborne cellulose of biological origin can act as efficient ice nucleating particles in super-cooled clouds of the lower and middle troposphere. In specific, we measured the surface-based ice nucleation activity of microcrystalline cellulose particles immersed in cloud droplets, which may add crucial importance to further quantify the role of biological particles as ice nuclei in the troposphere. Our results suggest that the concentration of ice nucleating cellulose to become significant (>0.1 per liter) below about -17 °C and nearly comparable to other known ice nucleating clay mineral particles (e.g., illite rich clay mineral - INUIT comparisons are also presented). An important and unique characteristic of microcrystalline cellulose compared to other particles of biological origin is its high molecular packing density, enhancing resistance to hydrolysis degradation. More in-depth microphysical understandings as well as quantitative observations of ice nucleating cellulose particles in the atmosphere are necessary to allow better estimates of their effects on clouds and the global climate. Acknowledgement: We acknowledge support by German Research Society (DfG) and Ice Nucleation research UnIT (FOR 1525 INUIT).

Violation of geometrical scaling in pp collisions at NA61/SHINE

NASA Astrophysics Data System (ADS)

Praszalowicz, Michal

2013-04-01

We analyze geometrical scaling (GS) of negative pion multiplicity pT distributions at NA61/SHINE energies. We show that even though NA61/SHINE energies are low, one may expect to find GS in the particle spectra. We argue that qualitative behavior of ratios of multiplicities at different energies is in agreement with a simple picture of GS which is violated for pT smaller than some nonperturbative scale Λ and when larger Bjorken x of one of the scattering patrons crosses xmax⁡ above which a gluonic cloud becomes dilute and quark degrees of freedom become important.

Microscopic evaluation of trace metals in cloud droplets in an acid precipitation region.

PubMed

Li, Weijun; Wang, Yan; Collett, Jeffrey L; Chen, Jianmin; Zhang, Xiaoye; Wang, Zifa; Wang, Wenxing

2013-05-07

Mass concentrations of soluble trace metals and size, number, and mixing properties of nanometal particles in clouds determine their toxicity to ecosystems. Cloud water was found to be acidic, with a pH of 3.52, at Mt. Lu (elevation 1,165 m) in an acid precipitation region in South China. A combination of Inductively Coupled Plasma Mass Spectrometry (ICPMS) and Transmission Electron Microscopy (TEM) for the first time demonstrates that the soluble metal concentrations and solid metal particle number are surprisingly high in acid clouds at Mt. Lu, where daily concentrations of SO2, NO2, and PM10 are 18 μg m(-3), 7 μg m(-3), and 22 μg m(-3). The soluble metals in cloudwater with the highest concentrations were zinc (Zn, 200 μg L(-1)), iron (Fe, 88 μg L(-1)), and lead (Pb, 77 μg L(-1)). TEM reveals that 76% of cloud residues include metal particles that range from 50 nm to 1 μm diameter with a median diameter of 250 nm. Four major metal-associated particle types are Pb-rich (35%), fly ash (27%), Fe-rich (23%), and Zn-rich (15%). Elemental mapping shows that minor soluble metals are distributed within sulfates of cloud residues. Emissions of fine metal particles from large, nonferrous industries and coal-fired power plants with tall stacks were transported upward to this high elevation. Our results suggest that the abundant trace metals in clouds aggravate the impacts of acid clouds or associated precipitation on the ecosystem and human health.

Vertical profiling of aerosol particles and trace gases over the central Arctic Ocean during summer

NASA Astrophysics Data System (ADS)

Kupiszewski, P.; Leck, C.; Tjernström, M.; Sjogren, S.; Sedlar, J.; Graus, M.; Müller, M.; Brooks, B.; Swietlicki, E.; Norris, S.; Hansel, A.

2013-12-01

Unique measurements of vertical size-resolved aerosol particle concentrations, trace gas concentrations and meteorological data were obtained during the Arctic Summer Cloud Ocean Study (ASCOS, www.ascos.se), an International Polar Year project aimed at establishing the processes responsible for formation and evolution of low-level clouds over the high Arctic summer pack ice. The experiment was conducted from on board the Swedish icebreaker Oden, and provided both ship- and helicopter-based measurements. This study focuses on the vertical helicopter profiles and onboard measurements obtained during a three-week period when Oden was anchored to a drifting ice floe, and sheds light on the characteristics of Arctic aerosol particles and their distribution throughout the lower atmosphere. Distinct differences in aerosol particle characteristics within defined atmospheric layers are identified. Within the lowermost couple hundred metres, transport from the marginal ice zone (MIZ), condensational growth and cloud processing develop the aerosol population. During two of the four representative periods defined in this study, such influence is shown. At altitudes above about 1 km, long-range transport occurs frequently. However, only infrequently does large-scale subsidence descend such air masses to become entrained into the mixed layer in the high Arctic, and therefore long-range transport plumes are unlikely to directly influence low-level stratiform cloud formation. Nonetheless, such plumes can influence the radiative balance of the planetary boundary layer (PBL) by influencing formation and evolution of higher clouds, as well as through precipitation transport of particles downwards. New particle formation was occasionally observed, particularly in the near-surface layer. We hypothesize that the origin of these ultrafine particles could be in biological processes, both primary and secondary, within the open leads between the pack ice and/or along the MIZ. In general, local sources, in combination with upstream boundary-layer transport of precursor gases from the MIZ, are considered to constitute the origin of cloud condensation nuclei (CCN) particles and thus be of importance for the formation of interior Arctic low-level clouds during summer, and subsequently, through cloud influences, for the melting and freezing of sea ice.

UNDERSTANDING AND REDUCING THE UNCERTAINTY ASSOCIATED WITH THE EFFECT OF ATMOSPHERIC PARTICLES ON CLOUDS AND CLIMATE

EPA Science Inventory

I predict that human-generated particles have modified clouds and cooled climate, somewhat masking the effect of greenhouse gases and that these particles have also modified the amount of sunlight reaching the ground, changing the thermodynamic cycles in the atmosphere. Wi...

Limits to Cloud Susceptibility

NASA Technical Reports Server (NTRS)

Coakley, James A., Jr.

2002-01-01

1-kilometer AVHRR observations of ship tracks in low-level clouds off the west coast of the U S. were used to determine limits for the degree to which clouds might be altered by increases in anthropogenic aerosols. Hundreds of tracks were analyzed to determine whether the changes in droplet radii, visible optical depths, and cloud top altitudes that result from the influx of particles from underlying ships were consistent with expectations based on simple models for the indirect effect of aerosols. The models predict substantial increases in sunlight reflected by polluted clouds due to the increases in droplet numbers and cloud liquid water that result from the elevated particle concentrations. Contrary to the model predictions, the analysis of ship tracks revealed a 15-20% reduction in liquid water for the polluted clouds. Studies performed with a large-eddy cloud simulation model suggested that the shortfall in cloud liquid water found in the satellite observations might be attributed to the restriction that the 1-kilometer pixels be completely covered by either polluted or unpolluted cloud. The simulation model revealed that a substantial fraction of the indirect effect is caused by a horizontal redistribution of cloud water in the polluted clouds. Cloud-free gaps in polluted clouds fill in with cloud water while the cloud-free gaps in the surrounding unpolluted clouds remain cloud-free. By limiting the analysis to only overcast pixels, the current study failed to account for the gap-filling predicted by the simulation model. This finding and an analysis of the spatial variability of marine stratus suggest new ways to analyze ship tracks to determine the limit to which particle pollution will alter the amount of sunlight reflected by clouds.

Observed microphysical structure of nimbostratus in northeast cold vortex over China

NASA Astrophysics Data System (ADS)

Zhao, Zhen; Lei, Hengchi

2014-06-01

Airborne measurements were collected during a stepwise ascent within a nimbostratus cloud associated with a northeast cold vortex in Jilin Province over China on 20 June 2005 to study cloud structure and ice particle spectra. The microphysical structure of the nimbostratus was elucidated by King liquid water probe and Particle Measuring Systems (PMS) probes aboard the research aircraft. The PMS 2D images provide detailed information on crystal habits. A thick layer of supercooled cloud is observed and Hallett-Mossop ice multiplication process is used to explain very high ice particle concentrations in the temperature region between - 3 °C and - 6 °C. From near cloud top to melting layer, ice crystals shape in the form of columns, needles, aggregations and plates. In addition, significant horizontal variability was evident on the scale of few hundred meters. Ice particle spectra in this cloud were adequately described by exponential relationships. Relationship between the intercept (N0) and slope (λ) parameters of an exponential size distribution was well characterized by a power law.

Nitric Acid Uptake on Subtropical Cirrus Cloud Particles

NASA Technical Reports Server (NTRS)

Popp, P. J.; Gao, R. S.; Marcy, T. P.; Fahey, D. W.; Hudson, P. K.; Thompson, T. L.; Kaercher, B.; Ridley, B. A.; Weinheimer, A. J.; Knapp, D. J.;

Aircraft Natural/Artificial Icing

DTIC Science & Technology

2009-02-12

LWC are 0.1 to 0.8 g/m3 for stratiform clouds and 0.2 to 2.5 g/m3 for cumuliform clouds. The drop size distribution in the cloud is usually...cloud hydrometeor size distributions from 0.5 to 50 um, particle shape (discrimination between water and ice), particle optical properties (refractive...index), precipitation size distributions from 25 um to 1550 um, liquid water content from 0.01 to 3 gm-3 and aircraft velocity and atmospheric

High-energy radiation from collisions of high-velocity clouds and the Galactic disc

NASA Astrophysics Data System (ADS)

del Valle, Maria V.; Müller, A. L.; Romero, G. E.

2018-04-01

High-velocity clouds (HVCs) are interstellar clouds of atomic hydrogen that do not follow normal Galactic rotation and have velocities of a several hundred kilometres per second. A considerable number of these clouds are falling down towards the Galactic disc. HVCs form large and massive complexes, so if they collide with the disc a great amount of energy would be released into the interstellar medium. The cloud-disc interaction produces two shocks: one propagates through the cloud and the other through the disc. The properties of these shocks depend mainly on the cloud velocity and the disc-cloud density ratio. In this work, we study the conditions necessary for these shocks to accelerate particles by diffusive shock acceleration and we study the non-thermal radiation that is produced. We analyse particle acceleration in both the cloud and disc shocks. Solving a time-dependent two-dimensional transport equation for both relativistic electrons and protons, we obtain particle distributions and non-thermal spectral energy distributions. In a shocked cloud, significant synchrotron radio emission is produced along with soft gamma rays. In the case of acceleration in the shocked disc, the non-thermal radiation is stronger; the gamma rays, of leptonic origin, might be detectable with current instruments. A large number of protons are injected into the Galactic interstellar medium, and locally exceed the cosmic ray background. We conclude that under adequate conditions the contribution from HVC-disc collisions to the galactic population of relativistic particles and the associated extended non-thermal radiation might be important.

Laboratory Study of Air Turbulence-Particle Coupling

NASA Astrophysics Data System (ADS)

Petersen, A.; Baker, L.; Coletti, F.

2017-12-01

Inertial particles suspended in a turbulent flow are unable to follow the fluid's rapid velocity fluctuations, leading to high concentrations in regions where fluid strain dominates vorticity. This phenomenon is known as preferential concentration or clustering and is thought to affect natural processes ranging from the collisional growth of raindrops to the formation of planetesimals in proto-planetary nebulas. In the present study, we use a large jet-stirred chamber to generate homogeneous air turbulence into which we drop particles with an aerodynamic response time comparable to the flow time scales. Using laser imaging we find that turbulence can lead to a multi-fold increase of settling velocity compared to still-air conditions. We then employ Voronoi tessellation to examine the particle spatial distribution, finding strong evidence of turbulence-driven particle clustering over a wide range of experimental conditions. We observe individual clusters of a larger size range than seen previously, sometimes beyond the integral length scale of the turbulence. We also investigate cluster topology and find that they (i) exhibit a fractal structure, (ii) have a nearly constant particle concentration over their entire size range, and (iii) are most often vertically oriented. Furthermore, clustered particles tend to fall faster than those outside clusters, and larger clusters fall faster on average than smaller ones. Finally, by simultaneous measurement of particle and air velocity fields, we provide the first experimental evidence of preferential sweeping, a mechanism previously proposed to explain the increase in particle settling velocity found in numerical simulations, and find it especially effective for clustered particles. These results are significant for the micro-scale physics of atmospheric clouds. The large cluster size range has implications for how droplets will influence the local environment through condensation, evaporation, drag and latent heat effects. Our results also suggest that large collections of droplets will interact due to differential settling, possibly enhancing raindrop formation.

On water in volcanic clouds

NASA Astrophysics Data System (ADS)

Durant, Adam J.

2007-12-01

Volcanic clouds and tephra fallout present a hazard to aviation, human and animal health (direct inhalation or ingestion, contamination of water supplies), and infrastructure (building collapse, burial of roads and railways, agriculture, abrasive and chemical effects on machinery). Understanding sedimentation processes is a fundamental component in the prediction of volcanic cloud lifetime and fallout at the ground, essential in the mitigation of these hazards. The majority of classical volcanic ash transport and dispersion models (VATDM) are based solely on fluid dynamics. The non-agreement between VATDM and observed regional-scale tephra deposit characteristics is especially obvious at large distances from the source volcano. In meteorology, the processes of hydrometeor nucleation, growth and collection have been long-established as playing a central role in sedimentation and precipitation. Taking this as motivation, the hypothesis that hydrometeor formation drives sedimentation from volcanic clouds was tested. The research objectives of this dissertation are: (1) To determine the effectiveness of tephra particles in the catalysis of the liquid water to ice phase transformation, with application to ice hydrometeor formation in volcanic clouds. (2) To determine the sedimentological characteristics of distal (100s km) tephra fallout from recent volcanic clouds. (3) To assess particle fallout rates from recent volcanic clouds in the context of observed deposit characteristics. (4) To assess the implications of hydrometeor formation on the enhancement of volcanic sedimentation and the potential for cloud destabilization from volcanic hydrometeor sublimation. Dissertation Overview. The following chapters present the analysis, results and conclusions of heterogeneous ice nucleation experiments and sedimentological characterization of several recent tephra deposits. The dissertation is organized in three chapters, each prepared in journal article format. In Chapter 1, single ash particle freezing experiments were carried out to investigate the effect of ash particle composition and surface area on water drop freezing temperature. In Chapter 2, the tephra deposit from the 18 May 1980 eruption of Mount St. Helens, USA, was reanalyzed using laser diffraction particle size analysis and hydrometeor-induced sedimentation mechanisms are considered. In Chapter 3, fallout from the 18 August 1992 and 16--17 September 1992 eruptions of Mount Spurr, USA, was analyzed and particle sedimentation and cloud microphysics were modeled to assess the potential for cloud destabilization from hydrometeor sublimation.

Contrasting influences of aerosols on cloud properties during deficient and abundant monsoon years

PubMed Central

Patil, Nitin; Dave, Prashant; Venkataraman, Chandra

2017-01-01

Direct aerosol radiative forcing facilitates the onset of Indian monsoon rainfall, based on synoptic scale fast responses acting over timescales of days to a month. Here, we examine relationships between aerosols and coincident clouds over the Indian subcontinent, using observational data from 2000 to 2009, from the core monsoon region. Season mean and daily timescales were considered. The correlation analyses of cloud properties with aerosol optical depth revealed that deficient monsoon years were characterized by more frequent and larger decreases in cloud drop size and ice water path, but increases in cloud top pressure, with increases in aerosol abundance. The opposite was observed during abundant monsoon years. The correlations of greater aerosol abundance, with smaller cloud drop size, lower evidence of ice processes and shallower cloud height, during deficient rainfall years, imply cloud inhibition; while those with larger cloud drop size, greater ice processes and a greater cloud vertical extent, during abundant rainfall years, suggest cloud invigoration. The study establishes that continental aerosols over India alter cloud properties in diametrically opposite ways during contrasting monsoon years. The mechanisms underlying these effects need further analysis. PMID:28337991

Contrasting influences of aerosols on cloud properties during deficient and abundant monsoon years.

PubMed

Patil, Nitin; Dave, Prashant; Venkataraman, Chandra

2017-03-24

Direct aerosol radiative forcing facilitates the onset of Indian monsoon rainfall, based on synoptic scale fast responses acting over timescales of days to a month. Here, we examine relationships between aerosols and coincident clouds over the Indian subcontinent, using observational data from 2000 to 2009, from the core monsoon region. Season mean and daily timescales were considered. The correlation analyses of cloud properties with aerosol optical depth revealed that deficient monsoon years were characterized by more frequent and larger decreases in cloud drop size and ice water path, but increases in cloud top pressure, with increases in aerosol abundance. The opposite was observed during abundant monsoon years. The correlations of greater aerosol abundance, with smaller cloud drop size, lower evidence of ice processes and shallower cloud height, during deficient rainfall years, imply cloud inhibition; while those with larger cloud drop size, greater ice processes and a greater cloud vertical extent, during abundant rainfall years, suggest cloud invigoration. The study establishes that continental aerosols over India alter cloud properties in diametrically opposite ways during contrasting monsoon years. The mechanisms underlying these effects need further analysis.

Gas- and particle-phase chemical composition measurements onboard the G-1 research aircraft during the GoAmazon campaign.

NASA Astrophysics Data System (ADS)

Shilling, J.; Pekour, M. S.; Fortner, E.; Hubbe, J. M.; Longo, K.; Martin, S. T.; Mei, F.; Springston, S. R.; Tomlinson, J. M.; Wang, J.

2014-12-01

The Green Ocean Amazon (GoAmazon) campaign conducted from January 2014 - December 2015 in the vicinity of Manaus, Brazil, was designed to study the aerosol lifecycle and aerosol-cloud interactions in both pristine and anthropogenically influenced conditions. As part of this campaign, the DOE G-1 research aircraft was deployed from February 17th - March 25th 2014 and September 6th - October 5th 2014 to investigate aerosol and cloud properties aloft. An Aerodyne High Resolution Aerosol Mass Spectrometer (AMS) and an Ionicon Proton Transfer Reaction Mass Spectrometer (PTRMS) were part of the G-1 research aircraft payload and were used to investigate aerosol gas- and particle-phase chemical composition. Here we present preliminary analysis of the aerosol and gas phase chemical composition. PTR-MS measurements show that isoprene and its oxidation products are the dominant VOCs during research flights. HR-AMS measurements reveal that the particle phase is dominated by organic material with smaller concentrations of sulfate and nitrate observed. Organic particle concentrations are enhanced when encountering the urban plume from Manaus. During the wet season, we observe increased concentrations of organic particle when passing through low-altitude clouds. PMF analysis of the organic mass spectra shows that the chemical composition of the particles observed in-cloud is distinctly different from particles observed outside clouds. We will also compare measurements made during the wet and dry seasons.

Laboratory Studies of the Cloud Droplet Activation Properties and Corresponding Chemistry of Saline Playa Dust

NASA Astrophysics Data System (ADS)

Gaston, C.; Pratt, K.; Suski, K. J.; May, N.; Gill, T. E.; Prather, K. A.

2016-12-01

Saline playas (dried lake beds) emit large quantities of dust that can facilitate the activation of cloud droplets. Despite the potential importance of playa dust for cloud formation, several models assume that dust is non-hygroscopic highlighting the need for measurements to clarify the role of dust from multiple sources in aerosol-cloud-climate interactions. Here we present water uptake measurements onto playa dust represented by the hygroscopicity parameter κ, which ranged from 0.002 ± 0.001 to 0.818 ± 0.094. Single-particle measurements made using an aircraft-aerosol time-of-flight mass spectrometer (A-ATOFMS) revealed the presence of halite, sodium sulfates, and sodium carbonates that were strongly correlated with κ underscoring the role that dust composition plays in water uptake. Predictions of κ made using bulk chemical techniques generally showed good agreement with measured values; however, several samples were poorly predicted using bulk particle composition. The lack of measurements/model agreement using this method and the strong correlations between κ and single-particle data are suggestive of chemical heterogeneities as a function of particle size and/or chemically distinct particle surfaces that dictate the water uptake properties of playa dust particles. Overall, our results highlight the ability of playa dust particles to act as cloud condensation nuclei that should be accounted for in models.

A multi-sensor study of the impact of ground-based glaciogenic seeding on orogrpahic clouds and precipitation

NASA Astrophysics Data System (ADS)

Pokharel, Binod

This dissertation examines reflectivity data from three different radar systems, as well as airborne and ground-based in situ particle imaging data, to study the impact of ground-based glaciogenic seeding on orographic clouds and precipitation formed over the mountains in southern Wyoming. The data for this study come from the AgI Seeding Cloud Impact Investigation (ASCII) field campaign conducted over the Sierra Madre mountains in 2012 (ASCII-12) and over the Medicine Bow mountains in 2013 (ASCII-13) in the context of the Wyoming Weather Modification Pilot Project (WWMPP). The campaigns were supported by a network of ground-based instruments, including a microwave radiometer, two profiling Ka-band Micro Rain Radars (MRRs), a Doppler on Wheels (DOW), rawinsondes, a Cloud Particle Imager, and a Parsivel disdrometer. The University of Wyoming King Air with profiling Wyoming Cloud Radar (WCR) conducted nine successful flights in ASCII-12, and eight flights in ASCII-13. WCR profiles from these flights are combined with those from seven other flights, which followed the same geographically-fixed pattern in 2008-09 (pre-ASCII) over the Medicine Bow range. All sampled storms were relatively shallow, with low-level air forced over the target mountain, and cold enough to support ice initiation by silver iodide (AgI) nuclei in cloud. Three detailed case studies are conducted, each with different atmospheric conditions and different cloud and snow growth properties: one case (21 Feb 2012) is stratiform, with strong winds and cloud droplets too small to enable snow growth by accretion (riming). A second case (13 Feb 2012) contains shallow convective cells. Clouds in the third case study (22 Feb 2012) are stratiform but contain numerous large droplets (mode ~35 microm in diameter), large enough for ice particle growth by riming. These cases and all others, each with a treated period following an untreated period, show that a clear seeding signature is not immediately apparent in individual WCR reflectivity transects downwind of the silver iodide (AgI) generators, and that the natural trends in the precipitation over short timescales can easily overwhelm any seeding-induced change. Therefore the ASCII experimental design included a control region, upwind of the AgI generators. The three case studies generally show an increase in surface snow particle concentration in the target region during the seeding period. Frequency-by-altitude displays of all WCR reflectivity data collected during the flights show slightly higher reflectivity values during seeding near the ground, at least when compared to the control region, in all three cases. This also applies to the two other radar systems (MRR and DOW), both with their own sampling strategy and target/control regions. An examination of all ASCII cases combined (the "composite" analysis) also shows a positive trend in low-level reflectivity relative to the control region, both in convective and in stratiform cases. Also, convective cells sampled at flight level downwind of the AgI generators contain a higher concentration of small ice crystals during seeding. A word of caution is warranted: both the magnitude and the sign of the change in the target region, compared to that in the control region, varies from case to case in the composite, and amongst the three radar systems (WCR, DOW and MRR). We speculate that this variation is only partly driven by different responses of orographic clouds to glaciogenic seeding, related to factors such as cloud base and cloud top temperature, cloud liquid water content, and snow growth mechanism. Instead, most of this variation probably relates to non-homogenous natural trends across the mountain range, and/or to sample unrepresentativeness, especially for the (relative small) control region, in other words to the sampling methods. The impact of natural variability and sampling aliasing can only be overcome by a storm sample size much larger than that collected in ASCII. As such, the ASCII sample size is not adequate either to quantify the magnitude of the seeding impact on snowfall, or to identify the conditions most suitable for ground-based seeding. This study is an exploration of cloud microphysical evidence linking AgI cloud seeding to snowfall. It is not a statistical study. The preponderance of evidence from different radars and ground-based and airborne particle probes deployed in ASCII, in three case studies and in the composite analysis, points to the ability of ground-based glaciogenic seeding to increase the snowfall rate in orographic clouds..

Aircraft-Measured Indirect Cloud Effects from Biomass Burning Smoke in the Arctic and Subarctic

NASA Technical Reports Server (NTRS)

Zamora, Lauren; Kahn, R. A.; Cubison, M. C.; Diskin, G. S.; Jimenez, J. L.; Kondo, Y.; McFarquhar, G. M.; Nenes, A.; Wisthaler, A.; Zelenyuk, A.;

Scavenging of black carbon in mixed phase clouds at the high alpine site Jungfraujoch

NASA Astrophysics Data System (ADS)

Cozic, J.; Verheggen, B.; Mertes, S.; Connolly, P.; Bower, K.; Petzold, A.; Baltensperger, U.; Weingartner, E.

2007-04-01

The scavenging of black carbon (BC) in liquid and mixed phase clouds was investigated during intensive experiments in winter 2004, summer 2004 and winter 2005 at the high alpine research station Jungfraujoch (3580 m a.s.l., Switzerland). Aerosol residuals were sampled behind two well characterized inlets; a total inlet which collected cloud particles (droplets and ice particles) as well as interstitial (unactivated) aerosol particles; an interstitial inlet which collected only interstitial aerosol particles. BC concentrations were measured behind each of these inlets along with the submicrometer aerosol number size distribution, from which a volume concentration was derived. These measurements were complemented by in-situ measurements of cloud microphysical parameters. BC was found to be scavenged into the condensed phase to the same extent as the bulk aerosol, which suggests that BC was covered with soluble material through aging processes, rendering it more hygroscopic. The scavenged fraction of BC (FScav,BC), defined as the fraction of BC that is incorporated into cloud droplets and ice crystals, decreases with increasing cloud ice mass fraction (IMF) from FScav,BC=60% in liquid phase clouds to FScav,BC~5-10% in mixed-phase clouds with IMF>0.2. This can be explained by the evaporation of liquid droplets in the presence of ice crystals (Wegener-Bergeron-Findeisen process), releasing BC containing cloud condensation nuclei back into the interstitial phase. In liquid clouds, the scavenged BC fraction is found to decrease with decreasing cloud liquid water content. The scavenged BC fraction is also found to decrease with increasing BC mass concentration since there is an increased competition for the available water vapour.

The Relationships Between Insoluble Precipitation Residues, Clouds, and Precipitation Over California's Southern Sierra Nevada During Winter Storms

NASA Technical Reports Server (NTRS)

Creamean, Jessie M.; White, Allen B.; Minnis, Patrick; Palikonda, Rabindra; Spangenberg, Douglas A.; Prather, Kimberly A.

2016-01-01

Ice formation in orographic mixed-phase clouds can enhance precipitation and depends on the type of aerosols that serve as ice nucleating particles (INP). The resulting precipitation from these clouds is a viable source of water, especially for regions such as the California Sierra Nevada. Thus, a better understanding of the sources of INP that impact orographic clouds is important for assessing water availability in California. This study presents a multi-site, multi-year analysis of single particle insoluble residues in precipitation samples that likely influenced cloud ice and precipitation formation above Yosemite National Park. Dust and biological particles represented the dominant fraction of the residues (64% on average). Cloud glaciation, determined using GOES satellite observations, not only depended on high cloud tops (greater than 6.2 km) and low temperatures (less than -26 C), but also on the composition of the dust and biological residues. The greatest prevalence of ice-phase clouds occurred in conjunction with biologically-rich residues and mineral dust rich in calcium, followed by iron and aluminosilicates. Dust and biological particles are known to be efficient INP, thus these residues are what likely influenced ice formation in clouds above the sites and subsequent precipitation quantities reaching the surface during events with similar meteorology. The goal of this study is to use precipitation chemistry information to gain a better understanding of the potential sources of INP in the south-central Sierra Nevada, where cloud-aerosol-precipitation interactions are under-studied and where mixed-phase orographic clouds represent a key element in the generation of precipitation and thus the water supply in California.

Nonspherical and Spherical Characterization of Ice in Hurricane Erin for Wideband Passive Microwave Comparisons

NASA Technical Reports Server (NTRS)

Skofronick-Jackson, Gail; Holthaus, Eric; Albers, Cerese; Kim, Min-Jeong

2007-01-01

In order to better understand the characteristics of frozen cloud particles in hurricane systems, computed brightness temperatures were compared with radiometric observations of Hurricane Erin (2001) from the NASA ER-2 aircraft. The focus was oil the frozen particle microphysics and the high frequencies (2 85 GHz) that are particularly sensitive to frozen particles. Frozen particles in hurricanes are an indicator of increasing hurricane intensity. In fact "hot towers" associated with increasing hurricane intensity are composed of frozen ice cloud particles. (They are called hot towers because their column of air is warmer than the surrounding air temperature, but above about 5-7 km to the tops of the towers at 15-19 km, the cloud particles are frozen.) This work showed that indeed, one can model information about cloud ice particle characteristics and indicated that nonspherical ice shapes, instead of spherical particles, provided the best match to the observations. Overall, this work shows that while non-spherical particles show promise, selecting and modeling a proper ice particle parameterization can be difficult and additional in situ measurements are needed to define and validate appropriate parameterizations. This work is important for developing Global Precipitation Measurement (GPM) mission satellite algorithms for the retrieval of ice characteristics both above the melting layer, as in Hurricane Erin, and for ice particles that reach the surface as falling snow.

Formation of Bidisperse Particle Clouds

NASA Astrophysics Data System (ADS)

Er, Jenn Wei; Zhao, Bing; Law, Adrian W. K.; Adams, E. Eric

2014-11-01

When a group of dense particles is released instantaneously into water, their motion has been conceptualized as a circulating particle thermal (Ruggerber 2000). However, Wen and Nacamuli (1996) observed the formation of particle clumps characterized by a narrow, fast moving core shedding particles into wakes. They observed the clump formation even for particles in the non-cohesive range as long as the source Rayleigh number was large (Ra > 1E3) or equivalently the source cloud number (Nc) was small (Nc < 3.2E2). This physical phenomenon has been investigated by Zhao et al. (2014) through physical experiments. They proposed the theoretical support for Nc dependence and categorized the formation processes into cloud formation, transitional regime and clump formation. Previous works focused mainly on the behavior of monodisperse particles. The present study further extends the experimental investigation to the formation process of bidisperse particles. Experiments are conducted in a glass tank with a water depth of 90 cm. Finite amounts of sediments with various weight proportions between coarser and finer particles are released from a cylindrical tube. The Nc being tested ranges from 6E-3 to 9.9E-2, which covers all the three formation regimes. The experimental results showed that the introduction of coarse particles promotes cloud formation and reduce the losses of finer particles into the wake. More quantitative descriptions of the effects of source conditions on the formation processes will be presented during the conference.

Clear-sky remote sensing in the vicinity of clouds: what can be learned about aerosol changes?

NASA Astrophysics Data System (ADS)

Marshak, Alexander; Varnai, Tamas; Wen, Guoyong

2010-05-01

Studies on aerosol direct and indirect effects require a precise separation of cloud-free and cloudy air. However, separation between cloud-free and cloudy areas from remotely-sensed measurements is ambiguous. The transition zone in the regions around clouds often stretches out tens of km, which are neither precisely clear nor precisely cloudy. We study the transition zone between cloud-free and cloudy air using MODerate-resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) measurements. Both instruments show enhanced clear-sky reflectance (MODIS) and clear-sky backscatterer (CALIPSO) near clouds. Analyzing a large dataset of MODIS observations we examine the effect of three-dimensional (3D) radiative interactions between clouds and cloud-free areas, also known as a cloud adjacency effect. Comparing with CALIPSO clear-sky backscatterer measurements, we show that the cloud adjacency effect may be responsible for a large portion of the enhanced clear sky reflectance observed by MODIS. While aerosol particles are responsible for a large part of the near-cloud enhancements in CALIPSO observations, misidentified or undetected cloud particles are also likely to contribute. As a result, both the nature of these particles (cloud vs. aerosol) and the processes creating them need to be clarified using a quantitative assessment of remote sensing limitations in particle detection and identification. The width and ubiquity of the transition zone near clouds imply that studies of aerosol-cloud interactions and aerosol direct radiative effects need to account for aerosol changes near clouds. Not accounted, these changes can cause systematic biases toward smaller aerosol radiative forcing. On the other hand, including aerosol products near clouds despite their uncertainties may overestimate aerosol radiative forcing. Therefore, there is an urgent need for developing methods that can assess and account for remote sensing challenges and thus allow for including the transition zone into the study. We describe a simple model that estimates the cloud-induced enhanced reflectances of cloud-free areas in the vicinity of clouds. The model assumes that the enhancement is due entirely to Rayleigh scattering and is therefore bigger at shorter wavelengths, thus creating a so-called apparent "bluing" of aerosols in remote sensing retrievals.

Clear-sky remote sensing in the vicinity of clouds: what we learned from MODIS and CALIPSO

NASA Astrophysics Data System (ADS)

Marshak, Alexander; Varnai, Tamas; Wen, Guoyong; Cahalan, Robert

Studies on aerosol direct and indirect effects require a precise separation of cloud-free and cloudy air. However, separation between cloud-free and cloudy areas from remotely-sensed measurements is ambiguous. The transition zone in the regions around clouds often stretches out tens of km, which are neither precisely clear nor precisely cloudy. We study the transition zone between cloud-free and cloudy air using MODerate-resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) measurements. Both instruments show enhanced clear-sky reflectance (MODIS) and clear-sky backscatterer (CALIPSO) near clouds. Analyzing a large dataset of MODIS observations we examine the effect of three-dimensional (3D) radiative interactions between clouds and cloud-free areas, also known as a cloud adjacency effect. Comparing with CALIPSO clear-sky backscatterer measurements, we show that the cloud adjacency effect may be responsible for a large portion of the enhanced clear sky reflectance observed by MODIS. While aerosol particles are responsible for a large part of the near-cloud enhancements in CALIPSO observations, misidentified or undetected cloud particles are also likely to contribute. As a result, both the nature of these particles (cloud vs. aerosol) and the processes creating them need to be clarified using a quantitative assessment of remote sensing limitations in particle detection and identification. The width and ubiquity of the transition zone near clouds imply that studies of aerosol-cloud interactions and aerosol direct radiative effects need to account for aerosol changes near clouds. Not accounted, these changes can cause systematic biases toward smaller aerosol radiative forcing. On the other hand, including aerosol products near clouds despite their uncertainties may overestimate aerosol radiative forcing. Therefore, there is an urgent need for developing methods that can assess and account for remote sensing challenges and thus allow for including the transition zone into the study. We describe a simple model that estimates the cloud-induced enhanced reflectances of cloud-free areas in the vicinity of clouds. The model assumes that the enhancement is due entirely to Rayleigh scattering and is therefore bigger at shorter wavelengths, thus creating a so-called apparent "bluing" of aerosols in remote sensing retrievals.

Aerosol processing in mixed-phase clouds in ECHAM5-HAM: Model description and comparison to observations

NASA Astrophysics Data System (ADS)

Hoose, C.; Lohmann, U.; Stier, P.; Verheggen, B.; Weingartner, E.

2008-04-01

The global aerosol-climate model ECHAM5-HAM has been extended by an explicit treatment of cloud-borne particles. Two additional modes for in-droplet and in-crystal particles are introduced, which are coupled to the number of cloud droplet and ice crystal concentrations simulated by the ECHAM5 double-moment cloud microphysics scheme. Transfer, production, and removal of cloud-borne aerosol number and mass by cloud droplet activation, collision scavenging, aqueous-phase sulfate production, freezing, melting, evaporation, sublimation, and precipitation formation are taken into account. The model performance is demonstrated and validated with observations of the evolution of total and interstitial aerosol concentrations and size distributions during three different mixed-phase cloud events at the alpine high-altitude research station Jungfraujoch (Switzerland). Although the single-column simulations cannot be compared one-to-one with the observations, the governing processes in the evolution of the cloud and aerosol parameters are captured qualitatively well. High scavenged fractions are found during the presence of liquid water, while the release of particles during the Bergeron-Findeisen process results in low scavenged fractions after cloud glaciation. The observed coexistence of liquid and ice, which might be related to cloud heterogeneity at subgrid scales, can only be simulated in the model when assuming nonequilibrium conditions.

Preparatory studies of zero-g cloud drop coalescence experiment

NASA Technical Reports Server (NTRS)

Telford, J. W.; Keck, T. S.

1979-01-01

Experiments to be performed in a weightless environment in order to study collision and coalescence processes of cloud droplets are described. Rain formation in warm clouds, formation of larger cloud drops, ice and water collision processes, and precipitation in supercooled clouds are among the topics covered.

Dust in brown dwarfs and extrasolar planets. V. Cloud formation in carbon- and oxygen-rich environments

NASA Astrophysics Data System (ADS)

Helling, Ch.; Tootill, D.; Woitke, P.; Lee, G.

2017-07-01

Context. Recent observations indicate potentially carbon-rich (C/O > 1) exoplanet atmospheres. Spectral fitting methods for brown dwarfs and exoplanets have invoked the C/O ratio as additional parameter but carbon-rich cloud formation modeling is a challenge for the models applied. The determination of the habitable zone for exoplanets requires the treatment of cloud formation in chemically different regimes. Aims: We aim to model cloud formation processes for carbon-rich exoplanetary atmospheres. Disk models show that carbon-rich or near-carbon-rich niches may emerge and cool carbon planets may trace these particular stages of planetary evolution. Methods: We extended our kinetic cloud formation model by including carbon seed formation and the formation of C[s], TiC[s], SiC[s], KCl[s], and MgS[s] by gas-surface reactions. We solved a system of dust moment equations and element conservation for a prescribed Drift-Phoenixatmosphere structure to study how a cloud structure would change with changing initial C/O0 = 0.43...10.0. Results: The seed formation efficiency is lower in carbon-rich atmospheres than in oxygen-rich gases because carbon is a very effective growth species. The consequence is that fewer particles make up a cloud if C/O0 > 1. The cloud particles are smaller in size than in an oxygen-rich atmosphere. An increasing initial C/O ratio does not revert this trend because a much greater abundance of condensible gas species exists in a carbon-rich environment. Cloud particles are generally made of a mix of materials: carbon dominates if C/O0 > 1 and silicates dominate if C/O0 < 1. A carbon content of 80-90% carbon is reached only in extreme cases where C/O0 = 3.0 or 10.0. Conclusions: Carbon-rich atmospheres form clouds that are made of particles of height-dependent mixed compositions, sizes and numbers. The remaining gas phase is far less depleted than in an oxygen-rich atmosphere. Typical tracer molecules are HCN and C2H2 in combination with a featureless, smooth continuum due to a carbonaceous cloud cover, unless the cloud particles become crystalline.

Cloud water composition during HCCT-2010: Scavenging efficiencies, solute concentrations, and droplet size dependence of inorganic ions and dissolved organic carbon

NASA Astrophysics Data System (ADS)

van Pinxteren, Dominik; Wadinga Fomba, Khanneh; Mertes, Stephan; Müller, Konrad; Spindler, Gerald; Schneider, Johannes; Lee, Taehyoung; Collett, Jeffrey L.; Herrmann, Hartmut

2016-03-01

Cloud water samples were taken in September/October 2010 at Mt. Schmücke in a rural, forested area in Germany during the Lagrange-type Hill Cap Cloud Thuringia 2010 (HCCT-2010) cloud experiment. Besides bulk collectors, a three-stage and a five-stage collector were applied and samples were analysed for inorganic ions (SO42-,NO3-, NH4+, Cl-, Na+, Mg2+, Ca2+, K+), H2O2 (aq), S(IV), and dissolved organic carbon (DOC). Campaign volume-weighted mean concentrations were 191, 142, and 39 µmol L-1 for ammonium, nitrate, and sulfate respectively, between 4 and 27 µmol L-1 for minor ions, 5.4 µmol L-1 for H2O2 (aq), 1.9 µmol L-1 for S(IV), and 3.9 mgC L-1 for DOC. The concentrations compare well to more recent European cloud water data from similar sites. On a mass basis, organic material (as DOC × 1.8) contributed 20-40 % (event means) to total solute concentrations and was found to have non-negligible impact on cloud water acidity. Relative standard deviations of major ions were 60-66 % for solute concentrations and 52-80 % for cloud water loadings (CWLs). The similar variability of solute concentrations and CWLs together with the results of back-trajectory analysis and principal component analysis, suggests that concentrations in incoming air masses (i.e. air mass history), rather than cloud liquid water content (LWC), were the main factor controlling bulk solute concentrations for the cloud studied. Droplet effective radius was found to be a somewhat better predictor for cloud water total ionic content (TIC) than LWC, even though no single explanatory variable can fully describe TIC (or solute concentration) variations in a simple functional relation due to the complex processes involved. Bulk concentrations typically agreed within a factor of 2 with co-located measurements of residual particle concentrations sampled by a counterflow virtual impactor (CVI) and analysed by an aerosol mass spectrometer (AMS), with the deviations being mainly caused by systematic differences and limitations of the approaches (such as outgassing of dissolved gases during residual particle sampling). Scavenging efficiencies (SEs) of aerosol constituents were 0.56-0.94, 0.79-0.99, 0.71-98, and 0.67-0.92 for SO42-, NO3-, NH4+, and DOC respectively when calculated as event means with in-cloud data only. SEs estimated using data from an upwind site were substantially different in many cases, revealing the impact of gas-phase uptake (for volatile constituents) and mass losses across Mt. Schmücke likely due to physical processes such as droplet scavenging by trees and/or entrainment. Drop size-resolved cloud water concentrations of major ions SO42-, NO3-, and NH4+ revealed two main profiles: decreasing concentrations with increasing droplet size and "U" shapes. In contrast, profiles of typical coarse particle mode minor ions were often increasing with increasing drop size, highlighting the importance of a species' particle concentration size distribution for the development of size-resolved solute concentration patterns. Concentration differences between droplet size classes were typically < 2 for major ions from the three-stage collector and somewhat more pronounced from the five-stage collector, while they were much larger for minor ions. Due to a better separation of droplet populations, the five-stage collector was capable of resolving some features of solute size dependencies not seen in the three-stage data, especially sharp concentration increases (up to a factor of 5-10) in the smallest droplets for many solutes.

Numerical Simulation of Interacting Magnetic Flux Ropes

NASA Astrophysics Data System (ADS)

Odstrcil, Dusan; Vandas, Marek; Pizzo, Victor J.; MacNeice, Peter

2003-09-01

A 212-D MHD numerical model is used to investigate the dynamic interaction between two flux ropes (clouds) in a homogeneous magnetized plasma. One cloud is set into motion while the other is initially at rest. The moving cloud generates a shock which interacts with the second cloud. Two cases with different characteristic speeds within the second cloud are presented. The shock front is significantly distorted when it propagates faster (slower) in the cloud with larger (smaller) characteristic speed. Correspondingly, the density behind the shock front becomes smaller (larger). Later, the clouds approach each other and by a momentum exchange they come to a common speed. The oppositely directed magnetic fields are pushed together, a driven magnetic reconnection takes a place, and the two flux ropes gradually coalescence into a single flux rope.

Deriving the concentration of airborne ash with a CAS-DPOL instrument: assessing uncertainties introduced by the instrument design

NASA Astrophysics Data System (ADS)

Spanu, Antonio; Weinzierl, Bernadett; Freudenthaler, Volker; Sauer, Daniel; Gasteiger, Josef

2016-04-01

Explosive volcanic eruptions inject large amounts of gas and particles into the atmosphere resulting in strong impacts on anthropic systems and climate. Fine ash particles in suspension, even if at low concentrations, are a serious aviation safety hazard. A key point to predict the dispersion and deposition of volcanic ash is the knowledge of emitted mass and its particle size distribution. Usually the deposit is used to characterize the source but a large uncertainty is present for fine and very fine ash particles which are usually not well preserved. Conversely, satellite observations provide only column-integrated information and are strongly sensitive to cloud conditions above the ash plumes. Consequently, in situ measurements are fundamental to extend our knowledge on ash clouds, their properties, and interactions over the vertical extent of the atmosphere. Different in-situ instruments are available covering different particle size ranges using a variety of measurement techniques. Depending on the measurement technique, artefacts due to instrument setup and ambient conditions can strongly modify the measured number concentration and size distribution of the airborne particles. It is fundamental to correct for those effects to quantify the uncertainty associated with the measurement. Here we evaluate the potential of our optical light-scattering spectrometer CAS-DPOL to detect airborne mineral dust and volcanic ash (in the size range between 0.7μm and 50μm) and to provide a reliable estimation of the mass concentration, investigating the associate uncertainty. The CAS-DPOL instrument sizes particles by detecting the light scattered off the particle into a defined angle. The associated uncertainty depends on the optical instrument design and on unknown particles characteristics such as shape and material. Indirect measurements of mass concentrations are statistically reconstructed using the air flow velocity. Therefore, the detected concentration is strongly sensitive to the sample flow and on the mechanical instrument design. Using a fluid dynamics model coupled with an optical model we analyze the effects of instrument design on the measurement, identify measurement uncertainties and recommend strategies to reduce the uncertainties. The two main results are that the optical design of the CAS-DPOL aerosol spectrometer can lead to an under-counting bias of up to 40% for larger particles and an over-counting bias of 20%-30% for smaller particles. Secondly, depending on how the instrument is mounted on the plane, the sampling can be subject to a significantly larger size selection bias than typically recognized, especially if the mounting leads to irregular sampling conditions. To correct both problems a new correction algorithm is described generalizing the results also to other optical particle counters. Finally, a comparison study is presented showing the effects on mass estimation and radiative forcing for uncorrected and corrected data also stating the resulting uncertainty.

Coaxial digital holography measures particular matter in cloud and ambient atmosphere

NASA Astrophysics Data System (ADS)

Li, Baosheng; Yu, Haonan; Jia, Yizhen; Tao, Xiaojie; Zhang, Yang

2018-02-01

In the artificially affected weather, the detection of cloud droplets particles provides an important reference for the effective impact of artificial weather. Digital holography has the unique advantages of full-field, non-contact, no damage, real-time and quantification. In this paper, coaxial digital holography is used to record the polyethylene standard particles and aluminum scrap, and some important parameters, such as three-dimensional coordinate spatial distribution and particle size, will be obtained by the means of analyzing the digital hologram of the particle. The experimental results verify the feasibility of the coaxial digital holographic device applied to the measurement of the cloud parameters, and complete the construction of the coaxial digital holographic system and the measurement of the particles.

Evaluation of Multilayer Cloud Detection Using a MODIS CO2-Slicing Algorithm With CALIPSO-CloudSat Measurements

NASA Technical Reports Server (NTRS)

Viudez-Mora, Antonio; Kato, Seiji

2015-01-01

This work evaluates the multilayer cloud (MCF) algorithm based on CO2-slicing techniques against CALISPO-CloudSat (CLCS) measurement. This evaluation showed that the MCF underestimates the presence of multilayered clouds compared with CLCS and are retrained to cloud emissivities below 0.8 and cloud optical septs no larger than 0.3.

Aerosol Enhancements in the Upper Troposphere Over The Amazon Forest: Do Amazonian Clouds Produce Aerosols?

NASA Astrophysics Data System (ADS)

Andreae, M. O.; Afchine, A.; Albrecht, R. I.; Artaxo, P.; Borrmann, S.; Cecchini, M. A.; Costa, A.; Dollner, M.; Fütterer, D.; Järvinen, E.; Klimach, T.; Konemann, T.; Kraemer, M.; Krüger, M. L.; Machado, L.; Mertes, S.; Pöhlker, C.; Poeschl, U.; Sauer, D. N.; Schnaiter, M.; Schneider, J.; Schulz, C.; Spanu, A.; Walser, A.; Weinzierl, B.; Wendisch, M.

2015-12-01

The German-Brazilian cooperative aircraft campaign ACRIDICON-CHUVA (Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems) on the German research aircraft HALO took place over the Amazon Basin in September/October 2014, with the objective of studying tropical deep convective clouds over the Amazon rainforest and their interactions with trace gases, aerosol particles, and atmospheric radiation. The aircraft was equipped with about 30 remote sensing and in-situ instruments for meteorological, trace gas, aerosol, cloud, precipitation, and solar radiation measurements. Fourteen research flights were conducted during this campaign. Observations during ACRIDICON-CHUVA showed high aerosol concentrations in the upper troposphere (UT) over the Amazon Basin, with concentrations after normalization to standard conditions often exceeding those in the boundary layer (BL). This behavior was consistent between several aerosol metrics, including condensation nuclei (CN), cloud condensation nuclei (CCN), and chemical species mass concentrations. These UT aerosols were different in their composition and size distribution from the aerosol in the BL, making convective transport of particles unlikely as a source. The regions in the immediate outflow of deep convective clouds were found to be depleted in aerosol particles, whereas enhanced aerosol number and mass concentrations were found in UT regions that had experienced outflow from deep convection in the preceding 24-48 hours. This suggests that aerosol production takes place in the UT based on volatile and condensable material brought up by deep convection. Subsequently, downward mixing and transport of upper tropospheric aerosol may be a source of particles to the BL, where they increase in size by the condensation of biogenic volatile organic carbon (BVOC) oxidation products. This may be an important source of aerosol particles in the Amazonian BL, where aerosol nucleation and new particle formation has not been observed.

A Condensation–coalescence Cloud Model for Exoplanetary Atmospheres: Formulation and Test Applications to Terrestrial and Jovian Clouds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ohno, Kazumasa; Okuzumi, Satoshi

A number of transiting exoplanets have featureless transmission spectra that might suggest the presence of clouds at high altitudes. A realistic cloud model is necessary to understand the atmospheric conditions under which such high-altitude clouds can form. In this study, we present a new cloud model that takes into account the microphysics of both condensation and coalescence. Our model provides the vertical profiles of the size and density of cloud and rain particles in an updraft for a given set of physical parameters, including the updraft velocity and the number density of cloud condensation nuclei (CCNs). We test our modelmore » by comparing with observations of trade-wind cumuli on Earth and ammonia ice clouds in Jupiter. For trade-wind cumuli, the model including both condensation and coalescence gives predictions that are consistent with observations, while the model including only condensation overestimates the mass density of cloud droplets by up to an order of magnitude. For Jovian ammonia clouds, the condensation–coalescence model simultaneously reproduces the effective particle radius, cloud optical thickness, and cloud geometric thickness inferred from Voyager observations if the updraft velocity and CCN number density are taken to be consistent with the results of moist convection simulations and Galileo probe measurements, respectively. These results suggest that the coalescence of condensate particles is important not only in terrestrial water clouds but also in Jovian ice clouds. Our model will be useful to understand how the dynamics, compositions, and nucleation processes in exoplanetary atmospheres affect the vertical extent and optical thickness of exoplanetary clouds via cloud microphysics.« less

Aqueous Processing of Atmospheric Organic Particles in Cloud Water Collected via Aircraft Sampling.

PubMed

Boone, Eric J; Laskin, Alexander; Laskin, Julia; Wirth, Christopher; Shepson, Paul B; Stirm, Brian H; Pratt, Kerri A

2015-07-21

Cloudwater and below-cloud atmospheric particle samples were collected onboard a research aircraft during the Southern Oxidant and Aerosol Study (SOAS) over a forested region of Alabama in June 2013. The organic molecular composition of the samples was studied to gain insights into the aqueous-phase processing of organic compounds within cloud droplets. High resolution mass spectrometry (HRMS) with nanospray desorption electrospray ionization (nano-DESI) and direct infusion electrospray ionization (ESI) were utilized to compare the organic composition of the particle and cloudwater samples, respectively. Isoprene and monoterpene-derived organosulfates and oligomers were identified in both the particles and cloudwater, showing the significant influence of biogenic volatile organic compound oxidation above the forested region. While the average O:C ratios of the organic compounds were similar between the atmospheric particle and cloudwater samples, the chemical composition of these samples was quite different. Specifically, hydrolysis of organosulfates and formation of nitrogen-containing compounds were observed for the cloudwater when compared to the atmospheric particle samples, demonstrating that cloud processing changes the composition of organic aerosol.

A new chemistry option in WRF-Chem v. 3.4 for the simulation of direct and indirect aerosol effects using VBS: evaluation against IMPACT-EUCAARI data

NASA Astrophysics Data System (ADS)

Tuccella, P.; Curci, G.; Grell, G. A.; Visconti, G.; Crumeyrolle, S.; Schwarzenboeck, A.; Mensah, A. A.

2015-09-01

A parameterization for secondary organic aerosol (SOA) production based on the volatility basis set (VBS) approach has been coupled with microphysics and radiative schemes in the Weather Research and Forecasting model with Chemistry (WRF-Chem) model. The new chemistry option called "RACM-MADE-VBS-AQCHEM" was evaluated on a cloud resolving scale against ground-based and aircraft measurements collected during the IMPACT-EUCAARI (Intensive Cloud Aerosol Measurement Campaign - European Integrated project on Aerosol Cloud Climate and Air quality interaction) campaign, and complemented with satellite data from MODIS. The day-to-day variability and the diurnal cycle of ozone (O3) and nitrogen oxides (NOx) at the surface are captured by the model. Surface aerosol mass concentrations of sulfate (SO4), nitrate (NO3), ammonium (NH4), and organic matter (OM) are simulated with correlations larger than 0.55. WRF-Chem captures the vertical profile of the aerosol mass concentration in both the planetary boundary layer (PBL) and free troposphere (FT) as a function of the synoptic condition, but the model does not capture the full range of the measured concentrations. Predicted OM concentration is at the lower end of the observed mass concentrations. The bias may be attributable to the missing aqueous chemistry processes of organic compounds and to uncertainties in meteorological fields. A key role could be played by assumptions on the VBS approach such as the SOA formation pathways, oxidation rate, and dry deposition velocity of organic condensable vapours. Another source of error in simulating SOA is the uncertainties in the anthropogenic emissions of primary organic carbon. Aerosol particle number concentration (condensation nuclei, CN) is overestimated by a factor of 1.4 and 1.7 within the PBL and FT, respectively. Model bias is most likely attributable to the uncertainties of primary particle emissions (mostly in the PBL) and to the nucleation rate. Simulated cloud condensation nuclei (CCN) are also overestimated, but the bias is more contained with respect to that of CN. The CCN efficiency, which is a characterization of the ability of aerosol particles to nucleate cloud droplets, is underestimated by a factor of 1.5 and 3.8 in the PBL and FT, respectively. The comparison with MODIS data shows that the model overestimates the aerosol optical thickness (AOT). The domain averages (for 1 day) are 0.38 ± 0.12 and 0.42 ± 0.10 for MODIS and WRF-Chem data, respectively. The droplet effective radius (Re) in liquid-phase clouds is underestimated by a factor of 1.5; the cloud liquid water path (LWP) is overestimated by a factor of 1.1-1.6. The consequence is the overestimation of average liquid cloud optical thickness (COT) from a few percent up to 42 %. The predicted cloud water path (CWP) in all phases displays a bias in the range +41-80 %, whereas the bias of COT is about 15 %. In sensitivity tests where we excluded SOA, the skills of the model in reproducing the observed patterns and average values of the microphysical and optical properties of liquid and all phase clouds decreases. Moreover, the run without SOA (NOSOA) shows convective clouds with an enhanced content of liquid and frozen hydrometers, and stronger updrafts and downdrafts. Considering that the previous version of WRF-Chem coupled with a modal aerosol module predicted very low SOA content (secondary organic aerosol model (SORGAM) mechanism) the new proposed option may lead to a better characterization of aerosol-cloud feedbacks.

A global view of atmospheric ice particle complexity

NASA Astrophysics Data System (ADS)

Schmitt, Carl G.; Heymsfield, Andrew J.; Connolly, Paul; Järvinen, Emma; Schnaiter, Martin

2016-11-01

Atmospheric ice particles exist in a variety of shapes and sizes. Single hexagonal crystals like common hexagonal plates and columns are possible, but more frequently, atmospheric ice particles are much more complex. Ice particle shapes have a substantial impact on many atmospheric processes through fall speed, affecting cloud lifetime, to radiative properties, affecting energy balance to name a few. This publication builds on earlier work where a technique was demonstrated to separate single crystals and aggregates of crystals using particle imagery data from aircraft field campaigns. Here data from 10 field programs have been analyzed and ice particle complexity parameterized by cloud temperature for arctic, midlatitude (summer and frontal), and tropical cloud systems. Results show that the transition from simple to complex particles can be as small as 80 µm or as large as 400 µm depending on conditions. All regimes show trends of decreasing transition size with decreasing temperature.

A Numerical Study of Convection in a Condensing CO2 Atmosphere under Early Mars-Like Conditions

NASA Astrophysics Data System (ADS)

Nakajima, Kensuke; Yamashita, Tatsuya; Odaka, Masatsugu; Sugiyama, Ko-ichiro; Ishiwatari, Masaki; Nishizawa, Seiya; Takahashi, Yoshiyuki O.; Hayashi, Yoshi-Yuki

2017-10-01

Cloud convection of a CO2 atmosphere where the major constituent condenses is numerically investigated under a setup idealizing a possible warm atmosphere of early Mars, utilizing a two-dimensional cloud-resolving model forced by a fixed cooling profile as a substitute for a radiative process. The authors compare two cases with different critical saturation ratios as condensation criteria and also examine sensitivity to number mixing ratio of condensed particles given externally.When supersaturation is not necessary for condensation, the entire horizontal domain above the condensation level is continuously covered by clouds irrespective of number mixing ratio of condensed particles. Horizontal-mean cloud mass density decreases exponentially with height. The circulations below and above the condensation level are dominated by dry cellular convection and buoyancy waves, respectively.When 1.35 is adopted as the critical saturation ratio, clouds appear exclusively as intense, short-lived, quasi-periodic events. Clouds start just above the condensation level and develop upward, but intense updrafts exist only around the cloud top; they do not extend to the bottom of the condensation layer. The cloud layer is rapidly warmed by latent heat during the cloud events, and then the layer is slowly cooled by the specified thermal forcing, and supersaturation gradually develops leading to the next cloud event. The periodic appearance of cloud events does not occur when number mixing ratio of condensed particles is large.

Parameterization of Shortwave Cloud Optical Properties for a Mixture of Ice Particle Habits for use in Atmospheric Models

NASA Technical Reports Server (NTRS)

Chou, Ming-Dah; Lee, Kyu-Tae; Yang, Ping; Lau, William K. M. (Technical Monitor)

2002-01-01

Based on the single-scattering optical properties pre-computed with an improved geometric optics method, the bulk absorption coefficient, single-scattering albedo, and asymmetry factor of ice particles have been parameterized as a function of the effective particle size of a mixture of ice habits, the ice water amount, and spectral band. The parameterization has been applied to computing fluxes for sample clouds with various particle size distributions and assumed mixtures of particle habits. It is found that flux calculations are not overly sensitive to the assumed particle habits if the definition of the effective particle size is consistent with the particle habits that the parameterization is based. Otherwise, the error in the flux calculations could reach a magnitude unacceptable for climate studies. Different from many previous studies, the parameterization requires only an effective particle size representing all ice habits in a cloud layer, but not the effective size of individual ice habits.

Collocated observations of cloud condensation nuclei, particle size distributions, and chemical composition

PubMed Central

Schmale, Julia; Henning, Silvia; Henzing, Bas; Keskinen, Helmi; Sellegri, Karine; Ovadnevaite, Jurgita; Bougiatioti, Aikaterini; Kalivitis, Nikos; Stavroulas, Iasonas; Jefferson, Anne; Park, Minsu; Schlag, Patrick; Kristensson, Adam; Iwamoto, Yoko; Pringle, Kirsty; Reddington, Carly; Aalto, Pasi; Äijälä, Mikko; Baltensperger, Urs; Bialek, Jakub; Birmili, Wolfram; Bukowiecki, Nicolas; Ehn, Mikael; Fjæraa, Ann Mari; Fiebig, Markus; Frank, Göran; Fröhlich, Roman; Frumau, Arnoud; Furuya, Masaki; Hammer, Emanuel; Heikkinen, Liine; Herrmann, Erik; Holzinger, Rupert; Hyono, Hiroyuki; Kanakidou, Maria; Kiendler-Scharr, Astrid; Kinouchi, Kento; Kos, Gerard; Kulmala, Markku; Mihalopoulos, Nikolaos; Motos, Ghislain; Nenes, Athanasios; O’Dowd, Colin; Paramonov, Mikhail; Petäjä, Tuukka; Picard, David; Poulain, Laurent; Prévôt, André Stephan Henry; Slowik, Jay; Sonntag, Andre; Swietlicki, Erik; Svenningsson, Birgitta; Tsurumaru, Hiroshi; Wiedensohler, Alfred; Wittbom, Cerina; Ogren, John A.; Matsuki, Atsushi; Yum, Seong Soo; Myhre, Cathrine Lund; Carslaw, Ken; Stratmann, Frank; Gysel, Martin

2017-01-01

Cloud condensation nuclei (CCN) number concentrations alongside with submicrometer particle number size distributions and particle chemical composition have been measured at atmospheric observatories of the Aerosols, Clouds, and Trace gases Research InfraStructure (ACTRIS) as well as other international sites over multiple years. Here, harmonized data records from 11 observatories are summarized, spanning 98,677 instrument hours for CCN data, 157,880 for particle number size distributions, and 70,817 for chemical composition data. The observatories represent nine different environments, e.g., Arctic, Atlantic, Pacific and Mediterranean maritime, boreal forest, or high alpine atmospheric conditions. This is a unique collection of aerosol particle properties most relevant for studying aerosol-cloud interactions which constitute the largest uncertainty in anthropogenic radiative forcing of the climate. The dataset is appropriate for comprehensive aerosol characterization (e.g., closure studies of CCN), model-measurement intercomparison and satellite retrieval method evaluation, among others. Data have been acquired and processed following international recommendations for quality assurance and have undergone multiple stages of quality assessment. PMID:28291234

Collocated observations of cloud condensation nuclei, particle size distributions, and chemical composition

NASA Astrophysics Data System (ADS)

Schmale, Julia; Henning, Silvia; Henzing, Bas; Keskinen, Helmi; Sellegri, Karine; Ovadnevaite, Jurgita; Bougiatioti, Aikaterini; Kalivitis, Nikos; Stavroulas, Iasonas; Jefferson, Anne; Park, Minsu; Schlag, Patrick; Kristensson, Adam; Iwamoto, Yoko; Pringle, Kirsty; Reddington, Carly; Aalto, Pasi; Äijälä, Mikko; Baltensperger, Urs; Bialek, Jakub; Birmili, Wolfram; Bukowiecki, Nicolas; Ehn, Mikael; Fjæraa, Ann Mari; Fiebig, Markus; Frank, Göran; Fröhlich, Roman; Frumau, Arnoud; Furuya, Masaki; Hammer, Emanuel; Heikkinen, Liine; Herrmann, Erik; Holzinger, Rupert; Hyono, Hiroyuki; Kanakidou, Maria; Kiendler-Scharr, Astrid; Kinouchi, Kento; Kos, Gerard; Kulmala, Markku; Mihalopoulos, Nikolaos; Motos, Ghislain; Nenes, Athanasios; O'Dowd, Colin; Paramonov, Mikhail; Petäjä, Tuukka; Picard, David; Poulain, Laurent; Prévôt, André Stephan Henry; Slowik, Jay; Sonntag, Andre; Swietlicki, Erik; Svenningsson, Birgitta; Tsurumaru, Hiroshi; Wiedensohler, Alfred; Wittbom, Cerina; Ogren, John A.; Matsuki, Atsushi; Yum, Seong Soo; Myhre, Cathrine Lund; Carslaw, Ken; Stratmann, Frank; Gysel, Martin

2017-03-01

Cloud condensation nuclei (CCN) number concentrations alongside with submicrometer particle number size distributions and particle chemical composition have been measured at atmospheric observatories of the Aerosols, Clouds, and Trace gases Research InfraStructure (ACTRIS) as well as other international sites over multiple years. Here, harmonized data records from 11 observatories are summarized, spanning 98,677 instrument hours for CCN data, 157,880 for particle number size distributions, and 70,817 for chemical composition data. The observatories represent nine different environments, e.g., Arctic, Atlantic, Pacific and Mediterranean maritime, boreal forest, or high alpine atmospheric conditions. This is a unique collection of aerosol particle properties most relevant for studying aerosol-cloud interactions which constitute the largest uncertainty in anthropogenic radiative forcing of the climate. The dataset is appropriate for comprehensive aerosol characterization (e.g., closure studies of CCN), model-measurement intercomparison and satellite retrieval method evaluation, among others. Data have been acquired and processed following international recommendations for quality assurance and have undergone multiple stages of quality assessment.

Contribution of Arctic seabird-colony ammonia to atmospheric particles and cloud-albedo radiative effect

NASA Astrophysics Data System (ADS)

Croft, B.; Wentworth, G. R.; Martin, R. V.; Leaitch, W. R.; Murphy, J. G.; Murphy, B. N.; Kodros, J. K.; Abbatt, J. P. D.; Pierce, J. R.

2016-11-01

The Arctic region is vulnerable to climate change and able to affect global climate. The summertime Arctic atmosphere is pristine and strongly influenced by natural regional emissions, which have poorly understood climate impacts related to atmospheric particles and clouds. Here we show that ammonia from seabird-colony guano is a key factor contributing to bursts of newly formed particles, which are observed every summer in the near-surface atmosphere at Alert, Nunavut, Canada. Our chemical-transport model simulations indicate that the pan-Arctic seabird-influenced particles can grow by sulfuric acid and organic vapour condensation to diameters sufficiently large to promote pan-Arctic cloud-droplet formation in the clean Arctic summertime. We calculate that the resultant cooling tendencies could be large (about -0.5 W m-2 pan-Arctic-mean cooling), exceeding -1 W m-2 near the largest seabird colonies due to the effects of seabird-influenced particles on cloud albedo. These coupled ecological-chemical processes may be susceptible to Arctic warming and industrialization.

Contribution of Arctic seabird-colony ammonia to atmospheric particles and cloud-albedo radiative effect.

PubMed

Croft, B; Wentworth, G R; Martin, R V; Leaitch, W R; Murphy, J G; Murphy, B N; Kodros, J K; Abbatt, J P D; Pierce, J R

2016-11-15

The Arctic region is vulnerable to climate change and able to affect global climate. The summertime Arctic atmosphere is pristine and strongly influenced by natural regional emissions, which have poorly understood climate impacts related to atmospheric particles and clouds. Here we show that ammonia from seabird-colony guano is a key factor contributing to bursts of newly formed particles, which are observed every summer in the near-surface atmosphere at Alert, Nunavut, Canada. Our chemical-transport model simulations indicate that the pan-Arctic seabird-influenced particles can grow by sulfuric acid and organic vapour condensation to diameters sufficiently large to promote pan-Arctic cloud-droplet formation in the clean Arctic summertime. We calculate that the resultant cooling tendencies could be large (about -0.5 W m -2 pan-Arctic-mean cooling), exceeding -1 W m -2 near the largest seabird colonies due to the effects of seabird-influenced particles on cloud albedo. These coupled ecological-chemical processes may be susceptible to Arctic warming and industrialization.

Fine-scale application of WRF-CAM5 during a dust storm episode over East Asia: Sensitivity to grid resolutions and aerosol activation parameterizations

NASA Astrophysics Data System (ADS)

Wang, Kai; Zhang, Yang; Zhang, Xin; Fan, Jiwen; Leung, L. Ruby; Zheng, Bo; Zhang, Qiang; He, Kebin

2018-03-01

An advanced online-coupled meteorology and chemistry model WRF-CAM5 has been applied to East Asia using triple-nested domains at different grid resolutions (i.e., 36-, 12-, and 4-km) to simulate a severe dust storm period in spring 2010. Analyses are performed to evaluate the model performance and investigate model sensitivity to different horizontal grid sizes and aerosol activation parameterizations and to examine aerosol-cloud interactions and their impacts on the air quality. A comprehensive model evaluation of the baseline simulations using the default Abdul-Razzak and Ghan (AG) aerosol activation scheme shows that the model can well predict major meteorological variables such as 2-m temperature (T2), water vapor mixing ratio (Q2), 10-m wind speed (WS10) and wind direction (WD10), and shortwave and longwave radiation across different resolutions with domain-average normalized mean biases typically within ±15%. The baseline simulations also show moderate biases for precipitation and moderate-to-large underpredictions for other major variables associated with aerosol-cloud interactions such as cloud droplet number concentration (CDNC), cloud optical thickness (COT), and cloud liquid water path (LWP) due to uncertainties or limitations in the aerosol-cloud treatments. The model performance is sensitive to grid resolutions, especially for surface meteorological variables such as T2, Q2, WS10, and WD10, with the performance generally improving at finer grid resolutions for those variables. Comparison of the sensitivity simulations with an alternative (i.e., the Fountoukis and Nenes (FN) series scheme) and the default (i.e., AG scheme) aerosol activation scheme shows that the former predicts larger values for cloud variables such as CDNC and COT across all grid resolutions and improves the overall domain-average model performance for many cloud/radiation variables and precipitation. Sensitivity simulations using the FN series scheme also have large impacts on radiations, T2, precipitation, and air quality (e.g., decreasing O3) through complex aerosol-radiation-cloud-chemistry feedbacks. The inclusion of adsorptive activation of dust particles in the FN series scheme has similar impacts on the meteorology and air quality but to lesser extent as compared to differences between the FN series and AG schemes. Compared to the overall differences between the FN series and AG schemes, impacts of adsorptive activation of dust particles can contribute significantly to the increase of total CDNC (∼45%) during dust storm events and indicate their importance in modulating regional climate over East Asia.

Ship Tracks

Atmospheric Science Data Center

2013-04-19

... into a moist layer of atmosphere. The particles become cloud condensation nuclei (CCN), which may either produce new cloud particles where ... visualization of the vertical structure of the condensation trails. It was created using a combination of red band data from ...

Investigation of unsteadiness in Shock-particle cloud interaction: Fully resolved two-dimensional simulation and one-dimensional modeling

NASA Astrophysics Data System (ADS)

Hosseinzadeh-Nik, Zahra; Regele, Jonathan D.

2015-11-01

Dense compressible particle-laden flow, which has a complex nature, exists in various engineering applications. Shock waves impacting a particle cloud is a canonical problem to investigate this type of flow. It has been demonstrated that large flow unsteadiness is generated inside the particle cloud from the flow induced by the shock passage. It is desirable to develop models for the Reynolds stress to capture the energy contained in vortical structures so that volume-averaged models with point particles can be simulated accurately. However, the previous work used Euler equations, which makes the prediction of vorticity generation and propagation innacurate. In this work, a fully resolved two dimensional (2D) simulation using the compressible Navier-Stokes equations with a volume penalization method to model the particles has been performed with the parallel adaptive wavelet-collocation method. The results still show large unsteadiness inside and downstream of the particle cloud. A 1D model is created for the unclosed terms based upon these 2D results. The 1D model uses a two-phase simple low dissipation AUSM scheme (TSLAU) developed by coupled with the compressible two phase kinetic energy equation.

Clouds and aerosols in Puerto Rico - a new evaluation

NASA Astrophysics Data System (ADS)

Allan, J. D.; Baumgardner, D.; Raga, G. B.; Mayol-Bracero, O. L.; Morales-García, F.; García-García, F.; Montero-Martínez, G.; Borrmann, S.; Schneider, J.; Mertes, S.; Walter, S.; Gysel, M.; Dusek, U.; Frank, G. P.; Krämer, M.

2007-08-01

The influence of aerosols, both natural and anthropogenic, remains a major area of uncertainty when predicting the properties and behaviour of clouds and their influence on climate. In an attempt to better understand warm cloud formation in a tropical marine environment, a period of intensive measurements using some of the latest developments in online instrumentation took place in December 2004 in Puerto Rico. Simultaneous online measurements of aerosol size distributions, composition, hygroscopicity and optical properties were made near the lighthouse of Cape San Juan in the north-eastern corner of the island and at the top of East Peak mountain (1040 m a.s.l.), the two sites separated by 17 km. Additional measurements of the cloud droplet residual and interstitial aerosol properties were made at the mountain site, accompanied by measurements of cloud droplet size distributions, liquid water content and the chemical composition of cloud and rain water samples. Both aerosol composition and cloud properties were found to be sensitive to wind sector. Air from the east-northeast (ENE) was mostly free of anthropogenic influences, the submircron fraction being mainly composed of non-sea salt sulphate, while that from the east-southeast (ESE) was found to be moderately influenced by populated islands upwind, adding smaller (<100 nm), externally mixed, carbonaceous particles to the aerosol that increased the number concentrations by over a factor of 3. This change in composition was also accompanied with a reduction in the measured hygroscopicity and fractional cloud activation potential of the aerosol. At the mountain site, the average cloud droplet concentrations increased from 193 to 519 cm-3, median volume diameter decreased from 20 to 14 μm and the liquid water content increased from 0.24 to 0.31 g m-3 when the winds shifted from the ENE to ESE. Larger numbers of interstitial particles were recorded, most notably at sizes greater than 100 nm, which were absent during clean conditions. The average size of the residual particles and concentrations of cloudwater nitrate, sulphate and insoluble material increased during polluted conditions. Previous studies in Puerto Rico had reported the presence of a significant non-anthropogenic organic fraction in the aerosols measured and concluded that this was a factor controlling the in situ cloud properties. However, this was not observed in our case. In contrast to the 1.00±0.14 μg m-3 of organic carbon measured in 1992 and 1995, the organic matter measured in the current study of 0.17±0.35 μg m-3 is many times lower, most of which can be attributed to anthropogenic sources. During clean conditions, the submicron aerosol was observed to be almost entirely inorganic, an observation supported by the hygroscopicity measurements. This suggests that organic aerosols from marine sources may not be completely ubiquitous (either spatially or temporally) in this environment and requires further investigation to quantify their true extent and implications, with more extensive, longer-term sampling in conjunction with back trajectory analyses.

Cloud-Resolving Model Simulations of Aerosol-Cloud Interactions Triggered by Strong Aerosol Emissions in the Arctic

NASA Astrophysics Data System (ADS)

Wang, H.; Kravitz, B.; Rasch, P. J.; Morrison, H.; Solomon, A.

2014-12-01

Previous process-oriented modeling studies have highlighted the dependence of effectiveness of cloud brightening by aerosols on cloud regimes in warm marine boundary layer. Cloud microphysical processes in clouds that contain ice, and hence the mechanisms that drive aerosol-cloud interactions, are more complicated than in warm clouds. Interactions between ice particles and liquid drops add additional levels of complexity to aerosol effects. A cloud-resolving model is used to study aerosol-cloud interactions in the Arctic triggered by strong aerosol emissions, through either geoengineering injection or concentrated sources such as shipping and fires. An updated cloud microphysical scheme with prognostic aerosol and cloud particle numbers is employed. Model simulations are performed in pure super-cooled liquid and mixed-phase clouds, separately, with or without an injection of aerosols into either a clean or a more polluted Arctic boundary layer. Vertical mixing and cloud scavenging of particles injected from the surface is still quite efficient in the less turbulent cold environment. Overall, the injection of aerosols into the Arctic boundary layer can delay the collapse of the boundary layer and increase low-cloud albedo. The pure liquid clouds are more susceptible to the increase in aerosol number concentration than the mixed-phase clouds. Rain production processes are more effectively suppressed by aerosol injection, whereas ice precipitation (snow) is affected less; thus the effectiveness of brightening mixed-phase clouds is lower than for liquid-only clouds. Aerosol injection into a clean boundary layer results in a greater cloud albedo increase than injection into a polluted one, consistent with current knowledge about aerosol-cloud interactions. Unlike previous studies investigating warm clouds, the impact of dynamical feedback due to precipitation changes is small. According to these results, which are dependent upon the representation of ice nucleation processes in the employed microphysical scheme, Arctic geoengineering/shipping could have substantial local radiative effects, but is unlikely to be effective as the sole means of counterbalancing warming due to climate change.

Design evaluations for a flight cloud physics holocamera. [holographic/photographic camera for low-g Atmospheric Cloud Physics Laboratory

NASA Technical Reports Server (NTRS)

Moore, W. W., Jr.; Kurtz, R. L.; Lemons, J. F.

1976-01-01

The paper describes a holographic/photographic camera to be used with the zero-g or low-g Atmospheric Cloud Physics Laboratory. The flight prototype holocamera is intended to record particles from 0.01 to 5 microns for an optimum two-dimensional plane only in the microscopic photography mode, particles on a volume basis in the in-line holography mode from 5 microns up, and all particle sizes possible on a volume basis in the acute sideband holography mode.

Scattering by randomly oriented ellipsoids: Application to aerosol and cloud problems

NASA Technical Reports Server (NTRS)

Asano, S.; Sato, M.; Hansen, J. E.

1979-01-01

A program was developed for computing the scattering and absorption by arbitrarily oriented and randomly oriented prolate and oblate spheroids. This permits examination of the effect of particle shape for cases ranging from needles through spheres to platelets. Applications of this capability to aerosol and cloud problems are discussed. Initial results suggest that the effect of nonspherical particle shape on transfer of radiation through aerosol layers and cirrus clouds, as required for many climate studies, can be readily accounted for by defining an appropriate effective spherical particle radius.

Some Technical Aspects of a CALIOP and MODIS Data Analysis that Examines Near-Cloud Aerosol Properties as a Function of Cloud Fraction

NASA Technical Reports Server (NTRS)

Varnai, Tamas; Yang, Weidong; Marshak, Alexander

2016-01-01

CALIOP shows stronger near-cloud changes in aerosol properties at higher cloud fractions. Cloud fraction variations explain a third of near-cloud changes in overall aerosol statistics. Cloud fraction and aerosol particle size distribution have a complex relationship.

Effect of acidification on carrot (Daucus carota) juice cloud stability.

PubMed

Schultz, Alison K; Barrett, Diane M; Dungan, Stephanie R

2014-11-26

Effects of acidity on cloud stability in pasteurized carrot juice were examined over the pH range of 3.5-6.2. Cloud sedimentation, particle diameter, and ζ potential were measured at each pH condition to quantify juice cloud stability and clarification during 3 days of storage. Acidification below pH 4.9 resulted in a less negative ζ potential, an increased particle size, and an unstable cloud, leading to juice clarification. As the acidity increased, clarification occurred more rapidly and to a greater extent. Only a weak effect of ionic strength was observed when sodium salts were added to the juice, but the addition of calcium salts significantly reduced the cloud stability.

A multi-sensor study of the impact of ground-based glaciogenic seeding on clouds and precipitation over mountains in Wyoming. Part II: Seeding impact analysis

NASA Astrophysics Data System (ADS)

Pokharel, Binod; Geerts, Bart; Jing, Xiaoqin; Friedrich, Katja; Ikeda, Kyoko; Rasmussen, Roy

2017-01-01

The AgI Seeding Cloud Impact Investigation (ASCII) campaign, conducted in early 2012 and 2013 over two mountain ranges in southern Wyoming, was designed to examine the impact of ground-based glaciogenic seeding on snow growth in winter orographic clouds. Part I of this study (Pokharel and Geerts, 2016) describes the project design, instrumentation, as well as the ambient atmospheric conditions and macrophysical and microphysical properties of the clouds sampled in ASCII. This paper (Part II) explores how the silver iodide (AgI) seeding affects snow growth in these orographic clouds in up to 27 intensive operation periods (IOPs), depending on the instrument used. In most cases, 2 h without seeding (NOSEED) were followed by 2 h of seeding (SEED). In situ data at flight level (2D-probes) indicate higher concentrations of small snow particles during SEED in convective clouds. The double difference of radar reflectivity Z (SEED - NOSEED in the target region, compared to the same trend in the control region) indicates an increase in Z for the composite of ASCII cases, over either mountain range, and for any of the three radar systems (WCR, MRR, and DOW), each with their own control and target regions, and for an array of snow gauges. But this double difference varies significantly from case to case, which is attributed to uncertainties related to sampling representativeness and to differences in natural trends between control and target regions. We conclude that a sample much larger than ASCII's sample is needed for clear observational evidence regarding the sensitivity of seeding efficacy to atmospheric and cloud conditions.

Assessment of the first indirect radiative effect of ammonium-sulfate-nitrate aerosols in East Asia

NASA Astrophysics Data System (ADS)

Han, Xiao; Zhang, Meigen; Skorokhod, Andrei

2017-11-01

A physically based cloud nucleation parameterization was introduced into an optical properties/radiative transfer module incorporated with the off-line air quality modeling system Regional Atmospheric Modeling System (RAMS)-Models-3 Community Multi Scale Air Quality (CMAQ) to investigate the distribution features of the first indirect radiative effects of sulfate, nitrate, and ammonium-sulfate-nitrate (ASN) over East Asia for the years of 2005, 2010, and 2013. The relationship between aerosol particles and cloud droplet number concentration could be properly described by this parameterization because the simulated cloud fraction and cloud liquid water path were generally reliable compared with Moderate Resolution Imaging Spectroradiometer (MODIS) retrieved data. Simulation results showed that the strong effect of indirect forcing was mainly concentrated in Southeast China, the East China Sea, the Yellow Sea, and the Sea of Japan. The highest indirect radiative forcing of ASN reached -3.47 W m-2 over Southeast China and was obviously larger than the global mean of the indirect forcing of all anthropogenic aerosols. In addition, sulfate provided about half of the contribution to the ASN indirect forcing effect. However, the effect caused by nitrate was weak because the mass burden of nitrate was very low during summer, whereas the cloud fraction was the highest. The analysis indicated that even though the interannual variation of indirect forcing magnitude generally followed the trend of aerosol mass burden from 2005 to 2013, the cloud fraction was an important factor that determined the distribution pattern of indirect forcing. The heaviest aerosol loading in North China did not cause a strong radiative effect because of the low cloud fraction over this region.

Coupling of the microphysical and optical properties of an Arctic nimbostratus cloud during the ASTAR 2004 experiment: Implications for light-scattering modeling

NASA Astrophysics Data System (ADS)

Jourdan, Olivier; Mioche, Guillaume; Garrett, Timothy J.; SchwarzenböCk, Alfons; Vidot, JéRôMe; Xie, Yu; Shcherbakov, Valery; Yang, Ping; Gayet, Jean-FrançOis

2010-12-01

Airborne measurements in an Arctic mixed-phase nimbostratus cloud were conducted in Spitsbergen on 21 May 2004 during the international Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR) campaign. The in situ instrument suite aboard the Alfred Wegener Institute Polar 2 aircraft included a polar nephelometer (PN), a cloud particle imager (CPI), a Nevzorov probe, and a standard PMS 2DC probe to measure the cloud particle single-scattering properties (at a wavelength of 0.8 μm), and the particle morphology and size, as well as the in-cloud partitioning of ice/water content. The main objective of this work is to present a technique based on principal component analysis and light-scattering modeling to link the microphysical properties of cloud particles to their optical characteristics. The technique is applied to the data collected during the 21 May case study where a wide variety of ice crystal shapes and liquid water fractions were observed at temperatures ranging from -1°C to -12°C. CPI measurements highlight the presence of large supercooled water droplets with diameters close to 500 μm. Although the majority of ice particles were found to have irregular shapes, columns and needles were the prevailing regular habits between -3°C and -6°C while stellars and plates were observed at temperatures below -8°C. The implementation of the principal component analysis of the PN scattering phase function measurements revealed representative optical patterns that were consistent with the particle habit classification derived from the CPI. This indicates that the synergy between the CPI and the PN can be exploited to link the microphysical and shape properties of cloud particles to their single-scattering characteristics. Using light-scattering modeling, we have established equivalent microphysical models based on a limited set of free parameters (roughness, mixture of idealized particle habits, and aspect ratio of ice crystals) that reproduce the main optical features assessed for cloud regions with different particle geometries and liquid water fractions. However, the retrieved bulk microphysical parameters can substantially differ from the measurements (by several times for the effective size and up to 3 orders of magnitude for the number concentration). Several possible explanations for these discrepancies are discussed. The retrievals show that the optical contribution of small particles with sizes lower than 50 μm (droplets and ice crystals) is significant, always exceeding 50% of the total scattering signal, and thus needs to be more accurately quantified. The shattering of large ice crystals on the shrouded inlet of the PN could also strongly affect the retrieved microphysical parameters.

Stable water isotopologue ratios in fog and cloud droplets of liquid clouds are not size-dependent

USGS Publications Warehouse

Spiegel, J.K.; Aemisegger, F.; Scholl, M.; Wienhold, F.G.; Collett, J.L.; Lee, T.; van Pinxteren, D.; Mertes, S.; Tilgner, A.; Herrmann, H.; Werner, Roland A.; Buchmann, N.; Eugster, W.

2012-01-01

In this work, we present the first observations of stable water isotopologue ratios in cloud droplets of different sizes collected simultaneously. We address the question whether the isotope ratio of droplets in a liquid cloud varies as a function of droplet size. Samples were collected from a ground intercepted cloud (= fog) during the Hill Cap Cloud Thuringia 2010 campaign (HCCT-2010) using a three-stage Caltech Active Strand Cloud water Collector (CASCC). An instrument test revealed that no artificial isotopic fractionation occurs during sample collection with the CASCC. Furthermore, we could experimentally confirm the hypothesis that the δ values of cloud droplets of the relevant droplet sizes (μm-range) were not significantly different and thus can be assumed to be in isotopic equilibrium immediately with the surrounding water vapor. However, during the dissolution period of the cloud, when the supersaturation inside the cloud decreased and the cloud began to clear, differences in isotope ratios of the different droplet sizes tended to be larger. This is likely to result from the cloud's heterogeneity, implying that larger and smaller cloud droplets have been collected at different moments in time, delivering isotope ratios from different collection times.

An aircraft-based case study of new particle formation and growth in the summertime Arctic

NASA Astrophysics Data System (ADS)

Willis, M. D.; Abbatt, J.; Burkart, J.; Bozem, H.; Koellner, F.; Schneider, J.; Hoor, P. M.; Herber, A. B.; Leaitch, W. R.

2015-12-01

Motivated by the changing climate of the Arctic and decreasing summer sea-ice extent, we aim to better understand how atmospheric composition will impact, or be impacted by, climate and environmental change in this region. Much attention has been paid to springtime Arctic aerosol owing to significant anthropogenic influence on this remote environment, but the cleaner, more locally influenced summertime Arctic is not well characterized. We present results of vertically resolved, particle number, aerosol size distributions, submicron aerosol composition from an aerosol mass spectrometer (AMS), and cloud condensation nuclei (CCN) concentrations from the NETCARE 2014 Polar 6 aircraft campaign. The campaign was based in the high Arctic, at Resolute Bay, Nunavut, Canada (74°N, 94°W), allowing measurements from 60 to 2900 meters over ice, open water and near the ice-edge. The focus of this case study is a new particle formation and growth event observed at the eastern end of Lancaster Sound (74°N, 81°W) on July 12, 2014 under clear sky conditions. During this flight Polar 6 travelled to the end of Lancaster Sound at 2900 m and subsequently descended to 60-70 m above the surface heading due west, with winds from the west. At the lowest altitude we observed a significant increase in particles > 4 nm, between 20 - 100 nm, and > 100 nm, indicating the presence of small particles between 4 - 20 nm and growth to larger sizes. In addition, CCN concentrations were enhanced up to ~ 200/cm3 from background levels of ≤ 100/cm3. Concurrently, the AMS indicated enhanced levels of methane sulfonic acid (MSA) and marine-like organic aerosol (OA) correlated in time with the presence of larger particles, as well as an iodide signal which correlated with the presence of small particles. These observations suggest that iodine oxides could be one contributor to particle formation, and that marine-like OA and MSA could contribute to particle growth in the summertime Arctic.

Climate Responses to Changes in Land-surface Properties due to Wildfires

NASA Astrophysics Data System (ADS)

Liu, Y.; Hao, X.; Qu, J. J.

2015-12-01

Wildfires can feedback the atmosphere by impacting atmospheric radiation transfer and cloud microphysics through emitting smoke particles and the land-air heat and water fluxes through modifying land-surface properties. While the impacts through smoke particles have been extensively investigated recently, very few studies have been conducted to examine the impacts through land-surface property change. This study is to fill this gap by examining the climate responses to the changes in land-surface properties induced by several large wildfires in the United States. Satellite remote sensing tools including MODIS and Landsat are used to quantitatively evaluate the land-surface changes characterized by reduced vegetation coverage and increased albedo over long post-fire periods. Variations in air and soil temperature and moisture of the burned areas are also monitored. Climate modeling is conducted to simulate climate responses and understand the related physical processes and interactions. The preliminary results indicate noticeable changes in water and heat transfers from the ground to the atmosphere through several mechanisms. Larger albedo reduces solar radiation absorbed on the ground, leading to less energy for latent and sensible heat fluxes. With smaller vegetation coverage, water transfer from the soil to the atmosphere through transpiration is reduced. Meanwhile, the Bowen ratio becomes larger after burning and therefore more solar energy absorbed on the ground is converted into sensible heat instead of being used as latent energy for water phase change. In addition, reduced vegetation coverage reduces roughness and increases wind speed, which modify dynamic resistances to water and heat movements. As a result of the changes in the land-air heat and water fluxes, clouds and precipitation as well as other atmospheric processes are affected by wildfires.

Toward the Characterization of Mixed-Phase Clouds Using Remote Sensing

NASA Astrophysics Data System (ADS)

Andronache, C.

2015-12-01

Mixed-phase clouds consist of a mixture of ice particles and liquid droplets at temperatures below 0 deg C. They are present in all seasons in many regions of the world, account for about 30% of the global cloud coverage, and are linked to cloud electrification and aircraft icing. The mix of ice particles, liquid droplets, and water vapor is unstable, and such clouds are thought to have a short lifetime. A characteristic parameter is the phase composition of mixed-phase clouds. It affects the cloud life cycle and the rate of precipitation. This parameter is important for cloud parameters retrievals by radar, lidar, and satellite and is relevant for climate modeling. The phase transformation includes the remarkable Wegener-Bergeron-Findeisen (WBF) process. The direction and the rate of the phase transformations depend on the local thermodynamic and microphysical properties. Cloud condensation nuclei (CCN) and ice nuclei (IN) particles determine to a large extent cloud microstructure and the dynamic response of clouds to aerosols. The complexity of dynamics and microphysics involved in mixed-phase clouds requires a set of observational and modeling tools that continue to be refined. Among these techniques, the remote sensing methods provide an increasing number of parameters, covering large regions of the world. Thus, a series of studies were dedicated to stratiform mixed-phase clouds revealing longer lifetime than previously thought. Satellite data and aircraft in situ measurements in deep convective clouds suggest that highly supercooled water often occurs in vigorous continental convective storms. In this study, we use cases of convective clouds to discuss the feasibility of mixed-phase clouds characterization and potential advantages of remote sensing.

Peltier-based cloud chamber

NASA Astrophysics Data System (ADS)

Nar, Sevda Yeliz; Cakir, Altan

2018-02-01

Particles produced by nuclear decay, cosmic radiation and reactions can be identified through various methods. One of these methods that has been effective in the last century is the cloud chamber. The chamber makes visible cosmic particles that we are exposed to radiation per second. Diffusion cloud chamber is a kind of cloud chamber that is cooled by dry ice. This traditional model has some application difficulties. In this work, Peltier-based cloud chamber cooled by thermoelectric modules is studied. The new model provided uniformly cooled base of the chamber, moreover, it has longer lifetime than the traditional chamber in terms of observation time. This gain has reduced the costs which spent each time for cosmic particle observation. The chamber is an easy-to-use system according to traditional diffusion cloud chamber. The new model is portable, easier to make, and can be used in the nuclear physics experiments. In addition, it would be very useful to observe Muons which are the direct evidence for Lorentz contraction and time expansion predicted by Einsteins special relativity principle.

A study of an expanding interplanatary magnetic cloud and its interaction with the earth's magnetosphere - The interplanetary aspect

NASA Technical Reports Server (NTRS)

Farrugia, C. J.; Burlaga, L. F.; Osherovich, V. A.; Richardson, I. G.; Freeman, M. P.; Lepping, R. P.; Lazarus, A. J.

1993-01-01

High time resolution interplanetary magnetic field and plasma measurements of an interplanetary magnetic cloud and its interaction with the earth's magnetosphere on January 14/15, 1988 are interpreted and discussed. It is argued that the data are consistent with the theoretical model of magnetic clouds as flux ropes of local straight cylindrical geometry. The data also suggest that this cloud is aligned with its axis in the ecliptic plane and pointing in the east-west direction. Evidence consisting of the intensity and directional distribution of energetic particle in the magnetic cloud argues in favor of the connectedness of the magnetic field lines to the sun's surface. The intensities of about 0.5 MeV ions is rapidly enhanced and the particles stream in a collimated beam along the magnetic field preferentially from the west of the sun. The particles travel form a flare site along the cloud magnetic field lines, which are thus presumably still attached to the sun.

Impact of mixing state and hygroscopicity on CCN activity of biomass burning aerosol in Amazonia

NASA Astrophysics Data System (ADS)

Sánchez Gácita, Madeleine; Longo, Karla M.; Freire, Julliana L. M.; Freitas, Saulo R.; Martin, Scot T.

2017-02-01

Smoke aerosols prevail throughout Amazonia because of widespread biomass burning during the dry season, and external mixing, low variability in the particle size distribution and low particle hygroscopicity are typical. There can be profound effects on cloud properties. This study uses an adiabatic cloud model to simulate the activation of smoke particles as cloud condensation nuclei (CCN) for three hypothetical case studies, chosen as to resemble biomass burning aerosol observations in Amazonia. The relative importance of variability in hygroscopicity, mixing state, and activation kinetics for the activated fraction and maximum supersaturation is assessed. For a population with κp = 0.04, an overestimation of the cloud droplet number concentration Nd for the three selected case studies between 22.4 ± 1.4 and 54.3 ± 3.7 % was obtained when assuming a hygroscopicity parameter κp = 0.20. Assuming internal mixing of the aerosol population led to overestimations of up to 20 % of Nd when a group of particles with medium hygroscopicity was present in the externally mixed population cases. However, the overestimations were below 10 % for external mixtures between very low and low-hygroscopicity particles, as seems to be the case for Amazon smoke particles. Kinetic limitations were significant for medium- and high-hygroscopicity particles, and much lower for very low and low-hygroscopicity particles. When particles were assumed to be at equilibrium and to respond instantly to changes in the air parcel supersaturation, the overestimation of the droplet concentration was up to ˜ 100 % in internally mixed populations, and up to ˜ 250 % in externally mixed ones, being larger for the higher values of hygroscopicity. In addition, a perceptible delay between the times when maximum supersaturation and maximum aerosol activated fraction are reached was noticed and, for aerosol populations with effective hygroscopicity κpeff higher than a certain threshold value, the delay in particle activation was such that no particles were activated at the time of maximum supersaturation. Considering internally mixed populations, for an updraft velocity W = 0.5 m s-1 this threshold of no activation varied between κpeff = 0.35 and κpeff = 0.5 for the different case studies. However, for low hygroscopicity, kinetic limitations played a weaker role for CCN activation of particles, even when taking into account the large aerosol mass and number concentrations. For the very low range of hygroscopicities, the overestimation of the droplet concentration due to the equilibrium assumption was lowest and the delay between the times when maximum supersaturation and maximum activated fraction were reached was greatly reduced or no longer observed (depending on the case study). These findings on uncertainties and sensitivities provide guidance on appropriate simplifications that can be used for modeling of smoke aerosols within general circulation models. The use of medium values of hygroscopicity representative of smoke aerosols for other biomass burning regions on Earth can lead to significant errors compared to the use of low hygroscopicity for Amazonia (between 0.05 and 0.13, according to available observations). Also in this region, consideration of the biomass burning population as internally mixed will lead to small errors in the droplet concentration, while significantly increasing the computational burden. Regardless of the large smoke aerosol loads in the region during the dry season, kinetic limitations are expected to be low.

The Particle Habit Imaging and Polar Scattering probe PHIPS: First Stereo-Imaging and Polar Scattering Function Measurements of Ice Particles

NASA Astrophysics Data System (ADS)

Abdelmonem, A.; Schnaiter, M.; Schön, R.; Leisner, T.

2009-04-01

Cirrus clouds impact climate by their influence on the water vapour distribution in the upper troposphere. Moreover, they directly affect the radiative balance of the Earth's atmosphere by the scattering of incoming solar radiation and the absorption of outgoing thermal emission. The link between the microphysical properties of ice cloud particles and the radiative forcing of the clouds is not as yet well understood and the influence of the shapes of ice crystals on the radiative budget of cirrus clouds is currently under debate. PHIPS is a new experimental device for the stereo-imaging of individual cloud particles and the simultaneous measurement of the polar scattering function of the same particle. PHIPS uses an automated particle event triggering system that ensures that only those particles are captured which are located in the field of view - depth of field volume of the microscope unit. Efforts were made to improve the resolution power of the microscope unit down to about 3 µm and to facilitate a 3D morphology impression of the ice crystals. This is realised by a stereo-imaging set up composed of two identical microscopes which image the same particle under an angular viewing distance of 30°. The scattering part of PHIPS enables the measurement of the polar light scattering function of cloud particles with an angular resolution of 1° for forward scattering directions (from 1° to 10°) and 8° for side and backscattering directions (from 18° to 170°). For each particle the light scattering pulse per channel is stored either as integrated intensity or as time resolved intensity function which opens a new category of data analysis concerning details of the particle movement. PHIPS is the first step to PHIPS-HALO which is one of the in situ ice particle and water vapour instruments that are currently under development for the new German research aircraft HALO. The instrument was tested in the ice cloud characterisation campaign HALO-02 which was conducted in December 2008 at the AIDA cloud chamber in the temperature range from -5°C to -70°C. In a series of experiments small externally generated seed ice crystals were grown in AIDA at distinct temperature and saturation ratio conditions. For these experiments the long known ice morphology diagram with the temperature dependent morphology changes and the supersaturation dependent structural complexity could clearly be reproduced by PHIPS. Structural details like hollow crystals, crystals with inclusions, and crystals with stepped surfaces (Hopper crystals) could be resolved by PHIPS. Moreover, the advantage of stereo-imaging in terms of habit classification and particle orientation deduction could be demonstrated. The scattering function measurement reveals ice particle orientation dependent specular reflection peaks which might contain information about the surface roughness. The presentation will describe the instrument set up in detail and highlight some preliminary results.

Stereoscopic Retrieval of Smoke Plume Heights and Motion from Space-Based Multi-Angle Imaging, Using the MISR INteractive eXplorer(MINX)

NASA Technical Reports Server (NTRS)

Nelson, David L.; Kahn, Ralph A.

2014-01-01

Airborne particles desert dust, wildfire smoke, volcanic effluent, urban pollution affect Earth's climate as well as air quality and health. They are found in the atmosphere all over the planet, but vary immensely in amount and properties with season and location. Most aerosol particles are injected into the near-surface boundary layer, but some, especially wildfire smoke, desert dust and volcanic ash, can be injected higher into the atmosphere, where they can stay aloft longer, travel farther, produce larger climate effects, and possibly affect human and ecosystem health far downwind. So monitoring aerosol injection height globally can make important contributions to climate science and air quality studies. The Multi-angle Imaging Spectro-Radiometer (MISR) is a space borne instrument designed to study Earths clouds, aerosols, and surface. Since late February 2000 it has been retrieving aerosol particle amount and properties, as well as cloud height and wind data, globally, about once per week. The MINX visualization and analysis tool complements the operational MISR data products, enabling users to retrieve heights and winds locally for detailed studies of smoke plumes, at higher spatial resolution and with greater precision than the operational product and other space-based, passive remote sensing techniques. MINX software is being used to provide plume height statistics for climatological studies as well as to investigate the dynamics of individual plumes, and to provide parameterizations for climate modeling.

Snow precipitation on Mars driven by cloud-induced night-time convection

NASA Astrophysics Data System (ADS)

Spiga, Aymeric; Hinson, David P.; Madeleine, Jean-Baptiste; Navarro, Thomas; Millour, Ehouarn; Forget, François; Montmessin, Franck

2017-09-01

Although it contains less water vapour than Earth's atmosphere, the Martian atmosphere hosts clouds. These clouds, composed of water-ice particles, influence the global transport of water vapour and the seasonal variations of ice deposits. However, the influence of water-ice clouds on local weather is unclear: it is thought that Martian clouds are devoid of moist convective motions, and snow precipitation occurs only by the slow sedimentation of individual particles. Here we present numerical simulations of the meteorology in Martian cloudy regions that demonstrate that localized convective snowstorms can occur on Mars. We show that such snowstorms--or ice microbursts--can explain deep night-time mixing layers detected from orbit and precipitation signatures detected below water-ice clouds by the Phoenix lander. In our simulations, convective snowstorms occur only during the Martian night, and result from atmospheric instability due to radiative cooling of water-ice cloud particles. This triggers strong convective plumes within and below clouds, with fast snow precipitation resulting from the vigorous descending currents. Night-time convection in Martian water-ice clouds and the associated snow precipitation lead to transport of water both above and below the mixing layers, and thus would affect Mars' water cycle past and present, especially under the high-obliquity conditions associated with a more intense water cycle.

Modelling ice microphysics of mixed-phase clouds

NASA Astrophysics Data System (ADS)

Ahola, J.; Raatikainen, T.; Tonttila, J.; Romakkaniemi, S.; Kokkola, H.; Korhonen, H.

2017-12-01

The low-level Arctic mixed-phase clouds have a significant role for the Arctic climate due to their ability to absorb and reflect radiation. Since the climate change is amplified in polar areas, it is vital to apprehend the mixed-phase cloud processes. From a modelling point of view, this requires a high spatiotemporal resolution to capture turbulence and the relevant microphysical processes, which has shown to be difficult.In order to solve this problem about modelling mixed-phase clouds, a new ice microphysics description has been developed. The recently published large-eddy simulation cloud model UCLALES-SALSA offers a good base for a feasible solution (Tonttila et al., Geosci. Mod. Dev., 10:169-188, 2017). The model includes aerosol-cloud interactions described with a sectional SALSA module (Kokkola et al., Atmos. Chem. Phys., 8, 2469-2483, 2008), which represents a good compromise between detail and computational expense.Newly, the SALSA module has been upgraded to include also ice microphysics. The dynamical part of the model is based on well-known UCLA-LES model (Stevens et al., J. Atmos. Sci., 56, 3963-3984, 1999) which can be used to study cloud dynamics on a fine grid.The microphysical description of ice is sectional and the included processes consist of formation, growth and removal of ice and snow particles. Ice cloud particles are formed by parameterized homo- or heterogeneous nucleation. The growth mechanisms of ice particles and snow include coagulation and condensation of water vapor. Autoconversion from cloud ice particles to snow is parameterized. The removal of ice particles and snow happens by sedimentation and melting.The implementation of ice microphysics is tested by initializing the cloud simulation with atmospheric observations from the Indirect and Semi-Direct Aerosol Campaign (ISDAC). The results are compared to the model results shown in the paper of Ovchinnikov et al. (J. Adv. Model. Earth Syst., 6, 223-248, 2014) and they show a good match. One of the advantages of UCLALES-SALSA is that it can be used to quantify the effect of aerosol scavenging on cloud properties in a precise way.

Further evidence for particle nucleation in clear air adjacent to marine cumulus clouds

NASA Astrophysics Data System (ADS)

Perry, Kevin D.; Hobbs, Peter V.

1994-11-01

Observational evidence is presented for the nucleation of condensation nuclei (CN) in the clear air adjacent to an isolated, marine, cumulus cloud. Two separate regions of particle nucleation are identified: one located above the cloud top, and the second located downwind of the cloud near the level of the anvil outflow. The regions of high CN concentrations were located in extremely clean marine air, with unactivated aerosol surface area (excluding the nucleation mode) less than 2 sq micrometers/cu cm, air temperature -31 C, and higher relative humidities than the undisturbed environment. Vertical profile measurements downwind of the cloud showed that CN concentrations at the level of the anvil outflow (4.9 km) were 8 times greater than at any other level between the surface and 5.3 km. A conceptual model is formulated in which aerosol particles, sulfur dioxide (SO2), sulfuric acid vapor (H2SO4), dimethyl sulfide (DMS), and ozone (O3) from the boundary layer are entrained into the cumulus cloud. Total aerosol number concentrations and unactivated aerosol surface area decrease with height in the cloud due to Brownian diffusion and diffusiophoresis of cloud interstitial aerosol to hydrometeors, coalescence scavenging by cloud droplets, collisional scavenging by ice particles, and subsequent removal by precipitation. The air that is detrained from the cloud raises the relative humidity and vents the clean air, SO2, H2SO4, DMS, and O3 to the near-cloud environment. Hydroxyl radicals then oxidize the SO2 and DMS to H2SO4. Under the conditions of high relative humidity, low total aerosol surface area, low temperatures, and high SO2 concentrations near cloud top, significant concentrations of new particles can be produced by homogeneous-bimolecular nucleation of sulfuric acid solution droplets from H2SO4 and H2O vapor molecules. The concentration of CN as a function of time is calculated for the case described in this paper using a bimodal integral nucleation model. The model results show that significant numbers of CN could have been produced within a few hours by the homogeneous-bimolecular nucleation of sulfuric acid solution droplets under the observed conditions provided the concentration of SO2 near cloud top was enhanced by vertical transport.

Microsecond-scale electric field pulses in cloud lightning discharges

NASA Technical Reports Server (NTRS)

Villanueva, Y.; Rakov, V. A.; Uman, M. A.; Brook, M.

1994-01-01

From wideband electric field records acquired using a 12-bit digitizing system with a 500-ns sampling interval, microsecond-scale pulses in different stages of cloud flashes in Florida and New Mexico are analyzed. Pulse occurrence statistics and waveshape characteristics are presented. The larger pulses tend to occur early in the flash, confirming the results of Bils et al. (1988) and in contrast with the three-stage representation of cloud-discharge electric fields suggested by Kitagawa and Brook (1960). Possible explanations for the discrepancy are discussed. The tendency for the larger pulses to occur early in the cloud flash suggests that they are related to the initial in-cloud channel formation processes and contradicts the common view found in the atmospheric radio-noise literature that the main sources of VLF/LF electromagnetic radiation in cloud flashes are the K processes which occur in the final, or J type, part of the cloud discharge.

Microphysical Processes Affecting the Pinatubo Volcanic Plume

NASA Technical Reports Server (NTRS)

Hamill, Patrick; Houben, Howard; Young, Richard; Turco, Richard; Zhao, Jingxia

1996-01-01

In this paper we consider microphysical processes which affect the formation of sulfate particles and their size distribution in a dispersing cloud. A model for the dispersion of the Mt. Pinatubo volcanic cloud is described. We then consider a single point in the dispersing cloud and study the effects of nucleation, condensation and coagulation on the time evolution of the particle size distribution at that point.

When is an INP not an INP?

NASA Astrophysics Data System (ADS)

Simpson, Emma; Connolly, Paul; McFiggans, Gordon

2016-04-01

Processes such as precipitation and radiation depend on the concentration and size of different hydrometeors within clouds therefore it is important to accurately predict them in weather and climate models. A large fraction of clouds present in our atmosphere are mixed phase; contain both liquid and ice particles. The number of drops and ice crystals present in mixed phase clouds strongly depends on the size distribution of aerosols. Cloud condensation nuclei (CCN), a subset of atmospheric aerosol particles, are required for liquid drops to form in the atmosphere. These particles are ubiquitous in the atmosphere. To nucleate ice particles in mixed phase clouds ice nucleating particles (INP) are required. These particles are rarer than CCN. Here we investigate the case where CCN and INPs are in direct competition with each other for water vapour within a cloud. Focusing on the immersion and condensation modes of freezing (where an INP must be immersed within a liquid drop before it can freeze) we show that the presence of CCN can suppress the formation of ice. CCN are more hydrophilic than IN and as such are better able to compete for water vapour than, typically insoluble, INPs. Therefore water is more likely to condense onto a CCN than INP, leaving the INP without enough condensed water on it to be able to freeze in the immersion or condensation mode. The magnitude of this suppression effect strongly depends on a currently unconstrained quantity. Here we refer to this quantity as the critical mass of condensed water required for freezing, Mwc. Mwc is the threshold amount of water that must be condensed onto a INP before it can freeze in the immersion or condensation mode. Using the detailed cloud parcel model, Aerosol-Cloud-Precipiation-Interaction Model (ACPIM), developed at the University of Manchester we show that if only a small amount of water is required for freezing there is little suppression effect and if a large amount of water is required there is a large suppression effect. In this poster possible ways to constrain Mwc are discussed as well as conditions where the suppression effect is likely to be greatest. Key Words: Clouds, aerosol, CCN, IN, modelling

A Mechanistic Understanding of North American Monsoon and Microphysical Properties of Ice Particles

NASA Astrophysics Data System (ADS)

Erfani, Ehsan

A mechanistic understanding of the North American Monsoon (NAM) is suggested by incorporating local- and synoptic-scale processes. The local-scale mechanism describes the effect sea surface temperature (SST) in Gulf of California (GC) and how it contributes to the low-level moisture during the 2004 NAM. Before NAM onset, the strong low-level temperature inversion exists over the GC, but this inversion weakens with increasing GC SST and generally disappears once SSTs exceed 29.5°C, allowing the moist air, trapped in the MBL, to mix with free tropospheric air. This leads to a deep, moist layer that can be transported toward the NAM regions to produce thunderstorms. The synoptic scale mechanism is based on climatologies from 1983 to 2010 and explains that the warmest SSTs moving up the coast contributes to NAM convection and atmospheric heating, and consequently advancing the position of the anticyclone and the region of descent northward. In order to improve microphysical properties of ice clouds, this study develops self-consistent second order polynomial mass- and projected area-dimension (m-D and A-D) expressions that are valid over a much larger size range, compared to traditional power laws. Such expressions can easily be reduced to power laws for the size range of interest, in order to use in cloud and climate models. This was done by combining field measurements of individual ice particle m and D with airborne optical probe measurements of D, A and estimates of m. The resulting m-D and A-D expressions are functions of temperature and cloud type (synoptic vs. anvil), and are in good agreement with m-D power laws developed from recent field studies. These expressions also appear representative for heavily rimed dendrites occurring over the Sierra Nevada Mountains. By using the m-D field measurements of rimed and unrimed particles, and by developing theoretical methods, an approach was suggested for calculating rimed m and A, which has the benefit of accounting for the degree of riming, and therefore it produces a gradual and continuous growth from unrimed ice particles to graupel. The treatment for riming includes a parameterization for collision efficiency as a function of droplet size and ice particle size using the available numerical studies. A rimed snow growth model (RSGM) was developed based on the growth processes of vapor diffusion, aggregation, and riming. The RSGM uses a measured radar reflectivity at cloud top for initialization, and then predicts the vertical evolution of size spectra. The RSGM is based on the zeroth- and second- moment conservation equations with respect to mass, and thus conserves the number concentration and radar reflectivity, respectively. The size spectra predicted by the RSGM are in good agreement with observed spectra during Lagrangian spiral descents through frontal clouds. The snowfall rate with the inclusion of riming is significantly greater than that produced by the vapor deposition and aggregation alone. Snowfall rates are found to be sensitive to the cloud drop size distribution.

Laboratory, Computational and Theoretical Investigations of Ice Nucleation and its Implications for Mixed Phase Clouds

NASA Astrophysics Data System (ADS)

Yang, Fan

Ice particles in atmospheric clouds play an important role in determining cloud lifetime, precipitation and radiation. It is therefore important to understand the whole life cycle of ice particles in the atmosphere, e.g., where they come from (nucleation), how they evolve (growth), and where they go (precipitation). Ice nucleation is the crucial step for ice formation, and in this study, we will mainly focus on ice nucleation in the lab and its effect on mixed-phase stratiform clouds. In the first half of this study, we investigate the relevance of moving contact lines (i.e., the region where three or more phases meet) on the phenomenon of contact nucleation. High speed video is used to investigate heterogeneous ice nucleation in supercooled droplets resting on cold substrates under two different dynamic conditions: droplet electrowetting and droplet vibration. The results show that contact-line motion is not a sufficient condition to trigger ice nucleation, while locally curved contact lines that can result from contact-line motion are strongly related to ice nucleation. We propose that pressure perturbations due to locally curved contact lines can strongly enhance the ice nucleation rate, which gives another interpretation for the mechanism for contact nucleation. Corresponding theoretical results provide a quantitative connection between pressure perturbations and temperature, providing a useful tool for ice nucleation calculations in atmospheric models. In this second half of the study, we build a minimalist model for long lifetime mixed-phase stratiform clouds based on stochastic ice nucleation. Our result shows that there is a non-linear relationship between ice water contact and ice number concentration in the mixed-phase cloud, as long as the volume ice nucleation rate is constant. This statistical property may help identify the source of ice nuclei in mixed-phase clouds. In addition, results from Lagrangian ice particle tracking in time dependent fields show that long lifetime ice particles exist in mixed-phase stratiform clouds. We find that small ice particle can be trapped in eddy-like structures. Whether ice particles grow or sublimate depends on the thermodynamic field in the trapping region. This dynamic-thermodynamic coupling effect on the lifetime of ice particles might explain the fast phase-partition change observed in the mixed phase cloud.

Measurement and Modeling of Electromagnetic Scattering by Particles and Particle Groups. Chapter 3

NASA Technical Reports Server (NTRS)

Mishchenko, Michael I.

2015-01-01

Small particles forming clouds of interstellar and circumstellar dust, regolith surfaces of many solar system bodies, and cometary atmospheres have a strong and often controlling effect on many ambient physical and chemical processes. Similarly, aerosol and cloud particles exert a strong influence on the regional and global climates of the Earth, other planets of the solar system, and exoplanets. Therefore, detailed and accurate knowledge of physical and chemical characteristics of such particles has the utmost scientific importance.

Observed Aerosol Influence on Ice Water Content of Arctic Mixed-Phase Clouds

NASA Astrophysics Data System (ADS)

Norgren, M.; de Boer, G.; Shupe, M.

2016-12-01

The response of ice water content (IWC) in Arctic mixed-phase stratocumulus to atmospheric aerosols is observed. IWC retrievals from ground based radars operated by the Atmospheric Radiation Measurement (ARM) program in Barrow, Alaska are used to construct composite profiles of cloud IWC from a 9-year radar record starting in January of 2000. The IWC profiles for high (polluted) and low (clean) aerosol loadings are compared. Generally, we find that clean clouds exhibit statistically significant higher levels of IWC than do polluted clouds by a factor of 2-4 at cloud base. For springtime clouds, with a maximum relative humidity with respect to ice (RHI) above 110% in the cloud layer, the IWC at cloud base was a factor of 3.25 times higher in clean clouds than it was in polluted clouds. We infer that the aerosol loading of the cloud environment alters the liquid drop size distribution within the cloud, with larger drops being more frequent in clean clouds. Larger cloud drops promote riming within the cloud layer, which is one explanation for the higher IWC levels in clean clouds. The drop size distribution may also be a significant control of ice nucleation events within mixed-phase clouds. Whether the high IWC levels in clean clouds are due to increased riming or nucleation events is unclear at this time.

Laboratory Simulations of Haze Formation in the Atmospheres of Super-Earths and Mini-Neptunes: Particle Color and Size Distribution

NASA Astrophysics Data System (ADS)

He, Chao; Hörst, Sarah M.; Lewis, Nikole K.; Yu, Xinting; Moses, Julianne I.; Kempton, Eliza M.-R.; McGuiggan, Patricia; Morley, Caroline V.; Valenti, Jeff A.; Vuitton, Véronique

2018-03-01

Super-Earths and mini-Neptunes are the most abundant types of planets among the ∼3500 confirmed exoplanets, and are expected to exhibit a wide variety of atmospheric compositions. Recent transmission spectra of super-Earths and mini-Neptunes have demonstrated the possibility that exoplanets have haze/cloud layers at high altitudes in their atmospheres. However, the compositions, size distributions, and optical properties of these particles in exoplanet atmospheres are poorly understood. Here, we present the results of experimental laboratory investigations of photochemical haze formation within a range of planetary atmospheric conditions, as well as observations of the color and size of produced haze particles. We find that atmospheric temperature and metallicity strongly affect particle color and size, thus altering the particles’ optical properties (e.g., absorptivity, scattering, etc.); on a larger scale, this affects the atmospheric and surface temperature of the exoplanets, and their potential habitability. Our results provide constraints on haze formation and particle properties that can serve as critical inputs for exoplanet atmosphere modeling, and guide future observations of super-Earths and mini-Neptunes with the Transiting Exoplanet Survey Satellite, the James Webb Space Telescope, and the Wide-Field Infrared Survey Telescope.

Evidence of atmospheric nanoparticle formation from emissions of marine microorganisms

NASA Astrophysics Data System (ADS)

Sellegri, K.; Pey, J.; Rose, C.; Culot, A.; DeWitt, H. L.; Mas, S.; Schwier, A. N.; Temime-Roussel, B.; Charriere, B.; Saiz-Lopez, A.; Mahajan, A. S.; Parin, D.; Kukui, A.; Sempere, R.; D'Anna, B.; Marchand, N.

2016-06-01

Earth, as a whole, can be considered as a living organism emitting gases and particles into its atmosphere, in order to regulate its own temperature. In particular, oceans may respond to climate change by emitting particles that ultimately will influence cloud coverage. At the global scale, a large fraction of the aerosol number concentration is formed by nucleation of gas-phase species, but this process has never been directly observed above oceans. Here we present, using semicontrolled seawater-air enclosures, evidence that nucleation may occur from marine biological emissions in the atmosphere of the open ocean. We identify iodine-containing species as major precursors for new particle clusters' formation, while questioning the role of the commonly accepted dimethyl sulfide oxidation products, in forming new particle clusters in the region investigated and within a time scale on the order of an hour. We further show that amines would sustain the new particle formation process by growing the new clusters to larger sizes. Our results suggest that iodine-containing species and amines are correlated to different biological tracers. These observations, if generalized, would call for a substantial change of modeling approaches of the sea-to-air interactions.

A New Method Using Single-Particle Mass Spectrometry Data to Distinguish Mineral Dust and Biological Aerosols

NASA Astrophysics Data System (ADS)

Al-Mashat, H.; Kristensen, L.; Sultana, C. M.; Prather, K. A.

2016-12-01

The ability to distinguish types of particles present within a cloud is important for determining accurate inputs to climate models. The chemical composition of particles within cloud liquid droplets and ice crystals can have a significant impact on the timing, location, and amount of precipitation that falls. Precipitation efficiency is increased by the presence of ice crystals in clouds, and both mineral dust and biological aerosols have been shown to be effective ice nucleating particles (INPs) in the atmosphere. A current challenge in aerosol science is distinguishing mineral dust and biological material in the analysis of real-time, ambient, single-particle mass spectral data. Single-particle mass spectrometers are capable of measuring the size-resolved chemical composition of individual atmospheric particles. However, there is no consistent analytical method for distinguishing dust and biological aerosols. Sampling and characterization of control samples (i.e. of known identity) of mineral dust and bacteria were performed by the Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) as part of the Fifth Ice Nucleation (FIN01) Workshop at the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) facility in Karlsruhe, Germany. Using data collected by the ATOFMS of control samples, a new metric has been developed to classify single particles as dust or biological independent of spectral cluster analysis. This method, involving the use of a ratio of mass spectral peak areas for organic nitrogen and silicates, is easily reproducible and does not rely on extensive knowledge of particle chemistry or the ionization characteristics of mass spectrometers. This represents a step toward rapidly distinguishing particle types responsible for ice nucleation activity during real-time sampling in clouds. The ability to distinguish types of particles present within a cloud is important for determining accurate inputs to climate models. The chemical composition of particles within cloud liquid droplets and ice crystals can have a significant impact on the timing, location, and amount of precipitation that falls. Precipitation efficiency is increased by the presence of ice crystals in clouds, and both mineral dust and biological aerosols have been shown to be effective ice nucleating particles (INPs) in the atmosphere. A current challenge in aerosol science is distinguishing mineral dust and biological material in the analysis of real-time, ambient, single-particle mass spectral data. Single-particle mass spectrometers are capable of measuring the size-resolved chemical composition of individual atmospheric particles. However, there is no consistent analytical method for distinguishing dust and biological aerosols. Sampling and characterization of control samples (i.e. of known identity) of mineral dust and bacteria were performed by the Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) as part of the Fifth Ice Nucleation (FIN01) Workshop at the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) facility in Karlsruhe, Germany. Using data collected by the ATOFMS of control samples, a new metric has been developed to classify single particles as dust or biological independent of spectral cluster analysis. This method, involving the use of a ratio of mass spectral peak areas for organic nitrogen and silicates, is easily reproducible and does not rely on extensive knowledge of particle chemistry or the ionization characteristics of mass spectrometers. This represents a step toward rapidly distinguishing particle types responsible for ice nucleation activity during real-time sampling in clouds.

Ice particle morphology and microphysical properties of cirrus clouds inferred from combined CALIOP-IIR measurements

NASA Astrophysics Data System (ADS)

Saito, Masanori; Iwabuchi, Hironobu; Yang, Ping; Tang, Guanglin; King, Michael D.; Sekiguchi, Miho

2017-04-01

Ice particle morphology and microphysical properties of cirrus clouds are essential for assessing radiative forcing associated with these clouds. We develop an optimal estimation-based algorithm to infer cirrus cloud optical thickness (COT), cloud effective radius (CER), plate fraction including quasi-horizontally oriented plates (HOPs), and the degree of surface roughness from the Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) and the Infrared Imaging Radiometer (IIR) on the Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) platform. A simple but realistic ice particle model is used, and the relevant bulk optical properties are computed using state-of-the-art light-scattering computational capabilities. Rigorous estimation of uncertainties related to surface properties, atmospheric gases, and cloud heterogeneity is performed. The results based on the present method show that COTs are quite consistent with other satellite products and CERs essentially agree with the other counterparts. A 1 month global analysis for April 2007, in which CALIPSO off-nadir angle is 0.3°, shows that the HOP has significant temperature-dependence and is critical to the lidar ratio when cloud temperature is warmer than -40°C. The lidar ratio is calculated from the bulk optical properties based on the inferred parameters, showing robust temperature dependence. The median lidar ratio of cirrus clouds is 27-31 sr over the globe.

Aerosol properties in the upper clouds of Venus from glory observations by the Venus Monitoring Camera (Venus Express mission)

NASA Astrophysics Data System (ADS)

Markiewicz, Wojciech J.; Petrova, Elena V.; Shalygina, Oksana S.

2018-01-01

From the angular positions of the glory features observed on the upper cloud deck of Venus in three VMC channels (at 0.365, 0.513, and 0.965 μm), the dominating sizes of cloud particles and their refractive indices have been retrieved, and their spatial and temporal variations have been analyzed. For this, the phase profiles of brightness were compared to the single-scattering phase functions of particles of different sizes, since diffuse multiple scattering in the clouds does not move the angular positions of the glory, which is produced by the single scattering by cloud particles, but only makes them less pronounced. We presented the measured phase profiles in two ways: they were built for individual images and for individual small regions observed in series of successive images. The analysis of the data of both types has yielded consistent results. The presently retrieved radii of cloud particle average approximately 1.0-1.2 μm (though some values reach 1.4 μm) and demonstrate a variable pattern versus latitude and local solar time (LST). The decrease of particle sizes at high latitudes (down to 0.6 μm at 60°S) earlier found from the 0.965-μm and partly 0.365-μm data has been definitely confirmed in the analysis of the data of all three channels considered. To obtain the consistent estimates of particle sizes from the UV glory maximum and minimum positions, we have to vary the effective variance of the particle sizes, while it was fixed constant in our previous studies. The twofold increase of this parameter (from 0.07 to 0.14) diminishes the estimates of particle sizes by 10-15%, while the effect on the retrieved refractive index is negligible. The obtained estimates of the refractive index are more or less uniformly distributed over the covered latitude and LST ranges, and most of them are higher than those of concentrated sulfuric acid solution. This confirms our previous result obtained only at 0.965 μm, and now we may state that the cases of a relatively high real part of the refractive index are often observed for the 1-μm mode of cloud particles on Venus. Consequently, an additional component with a high value of the refractive index is required to be present in the cloud droplets. We suggest that this component is in small submicron particles; during the condensation process, they become incorporated into sulfuric acid droplets, which results in forming the complex UV absorbing particles with an increased refractive index. We suppose that this material can be ferric chloride that is one of the candidates for the so-called unknown UV absorber in the upper clouds of Venus.

Mixing state of regionally transported soot particles and the coating effect on their size and shape at a mountain site in Japan

NASA Astrophysics Data System (ADS)

Adachi, Kouji; Zaizen, Yuji; Kajino, Mizuo; Igarashi, Yasuhito

2014-05-01

Soot particles influence the global climate through interactions with sunlight. A coating on soot particles increases their light absorption by increasing their absorption cross section and cloud condensation nuclei activity when mixed with other hygroscopic aerosol components. Therefore, it is important to understand how soot internally mixes with other materials to accurately simulate its effects in climate models. In this study, we used a transmission electron microscope (TEM) with an auto particle analysis system, which enables more particles to be analyzed than a conventional TEM. Using the TEM, soot particle size and shape (shape factor) were determined with and without coating from samples collected at a remote mountain site in Japan. The results indicate that ~10% of aerosol particles between 60 and 350 nm in aerodynamic diameters contain or consist of soot particles and ~75% of soot particles were internally mixed with nonvolatile ammonium sulfate or other materials. In contrast to an assumption that coatings change soot shape, both internally and externally mixed soot particles had similar shape and size distributions. Larger aerosol particles had higher soot mixing ratios, i.e., more than 40% of aerosol particles with diameters >1 µm had soot inclusions, whereas <20% of aerosol particles with diameters <1 µm included soot. Our results suggest that climate models may use the same size distributions and shapes for both internally and externally mixed soot; however, changing the soot mixing ratios in the different aerosol size bins is necessary.

Quantifying Uncertainties in Mass-Dimensional Relationships Through a Comparison Between CloudSat and SPartICus Reflectivity Factors

NASA Astrophysics Data System (ADS)

Mascio, J.; Mace, G. G.

2015-12-01

CloudSat and CALIPSO, two of the satellites in the A-Train constellation, use algorithms to calculate the scattering properties of small cloud particles, such as the T-matrix method. Ice clouds (i.e. cirrus) cause problems with these cloud property retrieval algorithms because of their variability in ice mass as a function of particle size. Assumptions regarding the microphysical properties, such as mass-dimensional (m-D) relationships, are often necessary in retrieval algorithms for simplification, but these assumptions create uncertainties of their own. Therefore, ice cloud property retrieval uncertainties can be substantial and are often not well known. To investigate these uncertainties, reflectivity factors measured by CloudSat are compared to those calculated from particle size distributions (PSDs) to which different m-D relationships are applied. These PSDs are from data collected in situ during three flights of the Small Particles in Cirrus (SPartICus) campaign. We find that no specific habit emerges as preferred and instead we conclude that the microphysical characteristics of ice crystal populations tend to be distributed over a continuum and, therefore, cannot be categorized easily. To quantify the uncertainties in the mass-dimensional relationships, an optimal estimation inversion was run to retrieve the m-D relationship per SPartICus flight, as well as to calculate uncertainties of the m-D power law.

Secondary organic aerosol production from pinanediol, a semi-volatile surrogate for first-generation oxidation products of monoterpenes

NASA Astrophysics Data System (ADS)

Ye, Penglin; Zhao, Yunliang; Chuang, Wayne K.; Robinson, Allen L.; Donahue, Neil M.

2018-05-01

We have investigated the production of secondary organic aerosol (SOA) from pinanediol (PD), a precursor chosen as a semi-volatile surrogate for first-generation oxidation products of monoterpenes. Observations at the CLOUD facility at CERN have shown that oxidation of organic compounds such as PD can be an important contributor to new-particle formation. Here we focus on SOA mass yields and chemical composition from PD photo-oxidation in the CMU smog chamber. To determine the SOA mass yields from this semi-volatile precursor, we had to address partitioning of both the PD and its oxidation products to the chamber walls. After correcting for these losses, we found OA loading dependent SOA mass yields from PD oxidation that ranged between 0.1 and 0.9 for SOA concentrations between 0.02 and 20 µg m-3, these mass yields are 2-3 times larger than typical of much more volatile monoterpenes. The average carbon oxidation state measured with an aerosol mass spectrometer was around -0.7. We modeled the chamber data using a dynamical two-dimensional volatility basis set and found that a significant fraction of the SOA comprises low-volatility organic compounds that could drive new-particle formation and growth, which is consistent with the CLOUD observations.

Comparison of Ice Cloud Particle Sizes Retrieved From Satellite Data Derived From In Situ Measurements

NASA Technical Reports Server (NTRS)

Han, Qingyuan; Rossow, William B.; Chou, Joyce; Welch, Ronald M.

1997-01-01

Cloud microphysical parameterizations have attracted a great deal of attention in recent years due to their effect on cloud radiative properties and cloud-related hydrological processes in large-scale models. The parameterization of cirrus particle size has been demonstrated as an indispensable component in the climate feedback analysis. Therefore, global-scale, long-term observations of cirrus particle sizes are required both as a basis of and as a validation of parameterizations for climate models. While there is a global scale, long-term survey of water cloud droplet sizes (Han et al. 1994), there is no comparable study for cirrus ice crystals. In this paper a near-global survey of cirrus ice crystal sizes is conducted using ISCCP satellite data analysis. The retrieval scheme uses phase functions based upon hexagonal crystals calculated by a ray tracing technique. The results show that global mean values of D(e) are about 60 micro-m. This study also investigates the possible reasons for the significant difference between satellite retrieved effective radii (approx. 60 micro-m) and aircraft measured particle sizes (approx. 200 micro-m) during the FIRE I IFO experiment. They are (1) vertical inhomogeneity of cirrus particle sizes; (2) lower limit of the instrument used in aircraft measurements; (3) different definitions of effective particle sizes; and (4) possible inappropriate phase functions used in satellite retrieval.

International Workshop on Comparing Ice Nucleation Measuring Systems 2014

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cziczo, Daniel

The relationship of ambient aerosol particles to the formation of ice-containing clouds is one of the largest uncertainties in understanding the Earth’s climate. The uncertainty is due to several poorly understood processes and measurements including, but not limited to: (1) the microphysics of how particles nucleate ice, (2) the number of ice forming particles as a function of atmospheric properties such as temperature and relative humidity, (3) the atmospheric distribution of ice forming particles and (4) the role of anthropogenic activities in producing or changing the behavior of ice forming particles. The ways in which ice forming particles can impactmore » climate is also multi-faceted. More ice forming particles can lead to clouds with more ice crystals and different optical properties than clouds with less ice forming particles. More effective ice forming particles can lead to ice at higher temperature and/or lower saturation, resulting in clouds at lower altitude or latitude which also changes the Earth’s radiative balance. Ice nucleation also initiates most of the Earth’s precipitation, even in the mid- and low-latitudes, since cloud-top temperatures are often below freezing. The limited measurements and lack of understanding directly translates to restrictions in our ability to model atmospheric ice formation and project changes into the future. The importance of ice nucleation research is further exemplified by Figure 1 which shows the publications per decade and citations per year on the topic of ice nucleation [DeMott et al., 2011]. After a lull at the end of the last century, there has been a dramatic increase in both publications and citations related to ice nucleation; this directly corresponds to the importance of ice nucleation on the Earth’s climate and the uncertainty in this area noted by the Solomon [2007].« less

Ice formation and development in aged, wintertime cumulus over the UK : observations and modelling

NASA Astrophysics Data System (ADS)

Crawford, I.; Bower, K. N.; Choularton, T. W.; Dearden, C.; Crosier, J.; Westbrook, C.; Capes, G.; Coe, H.; Connolly, P.; Dorsey, J. R.; Gallagher, M. W.; Williams, P.; Trembath, J.; Cui, Z.; Blyth, A.

2011-11-01

In-situ high resolution aircraft measurements of cloud microphysical properties were made in coordination with ground based remote sensing observations of Radar and Lidar as part of the Aerosol Properties, PRocesses And InfluenceS on the Earth's climate (APPRAISE) project. A narrow but extensive line (~100 km long) of shallow convective clouds over the southern UK was studied. Cloud top temperatures were observed to be higher than ~-8 °C, but the clouds were seen to consist of supercooled droplets and varying concentrations of ice particles. No ice particles were observed to be falling into the cloud tops from above. Current parameterisations of ice nuclei (IN) numbers predict too few particles will be active as ice nuclei to account for ice particle concentrations at the observed near cloud top temperatures (~-7 °C). The role of biological particles, consistent with concentrations observed near the surface, acting as potential efficient high temperature IN is considered important in this case. It was found that very high concentrations of ice particles (up to 100 L-1) could be produced by powerful secondary ice particle production emphasising the importance of understanding primary ice formation in slightly supercooled clouds. Aircraft penetrations at -3.5 °C, showed peak ice crystal concentrations of up to 100 L-1 which together with the characteristic ice crystal habits observed (generally rimed ice particles and columns) suggested secondary ice production had occurred. To investigate whether the Hallett-Mossop (HM) secondary ice production process could account for these observations, ice splinter production rates were calculated. These calculated rates and observations could only be reconciled provided the constraint that only droplets >24 μm in diameter could lead to splinter production, was relaxed slightly by 2 μm. Model simulations of the case study were also performed with the WRF (Weather, Research and Forecasting) model and ACPIM (Aerosol Cloud and Precipitation Interactions Model) to investigate the likely origins of the ice phase in these slightly supercooled clouds and to assess the role played by the HM process in this and in controlling precipitation formation under these conditions. WRF results showed that while HM does act to increase the mass and number concentration of ice particles produced in the model simulations, in the absence of HM, the ice number concentration arising from primary ice nucleation alone (several L-1) was apparently sufficient to sustain precipitation although the distribution of the precipitation was changed. Thus in the WRF model the HM process was shown to be non-critical for the formation of precipitation in this particular case. However, this result is seen to be subject to an important caveat concerning the simulation of the cloud macrostructure. The model was unable to capture a sharp temperature inversion seen in the radiosonde profiles at 2 km, and consequently the cloud top temperature in the model was able to reach lower values than observed in-situ or obtained from satellite data. ACPIM simulations confirmed the HM process to be a very powerful mechanism for producing the observed high ice concentrations, provided that primary nucleation occured to initiate the ice formation, and large droplets were present which then fell collecting the primary ice particles to form instant rimer particles. However, the time to generate the observed peak ice concentrations was found to be dependant on the number of primary IN present (decreasing with increasing IN number). This became realistic (around 20 min) only when the temperature input to the existing IN parameterisation was 6 °C lower than observed at cloud top, highlighting the requirement to improve basic knowledge of the number and type of IN active at these high temperatures. In simulations where cloud droplet numbers were realistic the precipitation rate was found to be unaffected by HM, with warm rain processes dominating precipitation development in this instance.

Laboratory and Cloud Chamber Studies of Formation Processes and Properties of Atmospheric Ice Particles

NASA Astrophysics Data System (ADS)

Leisner, T.; Abdelmonem, A.; Benz, S.; Brinkmann, M.; Möhler, O.; Rzesanke, D.; Saathoff, H.; Schnaiter, M.; Wagner, R.

2009-04-01

The formation of ice in tropospheric clouds controls the evolution of precipitation and thereby influences climate and weather via a complex network of dynamical and microphysical processes. At higher altitudes, ice particles in cirrus clouds or contrails modify the radiative energy budget by direct interaction with the shortwave and longwave radiation. In order to improve the parameterisation of the complex microphysical and dynamical processes leading to and controlling the evolution of tropospheric ice, laboratory experiments are performed at the IMK Karlsruhe both on a single particle level and in the aerosol and cloud chamber AIDA. Single particle experiments in electrodynamic levitation lend themselves to the study of the interaction between cloud droplets and aerosol particles under extremely well characterized and static conditions in order to obtain microphysical parameters as freezing nucleation rates for homogeneous and heterogeneous ice formation. They also allow the observation of the freezing dynamics and of secondary ice formation and multiplication processes under controlled conditions and with very high spatial and temporal resolution. The inherent droplet charge in these experiments can be varied over a wide range in order to assess the influence of the electrical state of the cloud on its microphysics. In the AIDA chamber on the other hand, these processes are observable under the realistic dynamic conditions of an expanding and cooling cloud- parcel with interacting particles and are probed simultaneously by a comprehensive set of analytical instruments. By this means, microphysical processes can be studied in their complex interplay with dynamical processes as for example coagulation or particle evaporation and growth via the Bergeron - Findeisen process. Shortwave scattering and longwave absorption properties of the nucleating and growing ice crystals are probed by in situ polarised laser light scattering measurements and infrared extinction spectroscopy. In conjunction with ex situ single particle imaging and light scattering measurements the relation between the overall extinction and depolarization properties of the ice clouds and the morphological details of the constituent ice crystals are investigated. In our contribution we will concentrate on the parameterization of homogeneous and heterogeneous ice formation processes under various atmospheric conditions and on the optical properties of the ice crystals produced under these conditions. First attempts to parameterize the observations will be presented.

A new chemistry option in WRF/Chem v. 3.4 for the simulation of direct and indirect aerosol effects using VBS: evaluation against IMPACT-EUCAARI data

NASA Astrophysics Data System (ADS)

Tuccella, P.; Curci, G.; Grell, G. A.; Visconti, G.; Crumeroylle, S.; Schwarzenboeck, A.; Mensah, A. A.

2015-02-01

A parameterization for secondary organic aerosol (SOA) production based on the volatility basis set (VBS) approach has been coupled with microphysics and radiative scheme in WRF/Chem model. The new chemistry option called "RACM/MADE/VBS" was evaluated on a cloud resolving scale against ground-based and aircraft measurements collected during the IMPACT-EUCAARI campaign, and complemented with satellite data from MODIS. The day-to-day variability and the diurnal cycle of ozone (O3) and nitrogen oxides (NOx) at the surface is captured by the model. Surface aerosol mass of sulphate (SO4), nitrate (NO3), ammonium (NH4), and organic matter (OM) is simulated with a correlation larger than 0.55. WRF/Chem captures the vertical profile of the aerosol mass in both the planetary boundary layer (PBL) and free troposphere (FT) as a function of the synoptic condition, but the model does not capture the full range of the measured concentrations. Predicted OM concentration is at the lower end of the observed mass. The bias may be attributable to the missing aqueous chemistry processes of organic compounds, the uncertainties in meteorological fields, the assumption on the deposition velocity of condensable organic vapours, and the uncertainties in the anthropogenic emissions of primary organic carbon. Aerosol particle number concentration (condensation nuclei, CN) is overestimated by a factor 1.4 and 1.7 within PBL and FT, respectively. Model bias is most likely attributable to the uncertainties of primary particle emissions (mostly in the PBL) and to the nucleation rate. The overestimation of simulated cloud condensation nuclei (CCN) is more contained with respect to that of CN. The CCN efficiency, which is a measure of the ability of aerosol particles to nucleate cloud droplets, is underestimated by a factor of 1.5 and 3.8 in the PBL and FT, respectively. The comparison with MODIS data shows that the model overestimates the aerosol optical thickness (AOT). The domain averages (for one day) are 0.38 ± 0.12 and 0.42 ± 0.10 for MODIS and WRF/Chem data, respectively. Cloud water path (CWP) is overestimated on average by a factor of 1.7, whereas modelled cloud optical thickness (COT) agrees with observations within 10%. In a sensitivity test where the SOA was not included, simulated CWP is reduced by 40%, and its distribution function shifts toward lower values with respect to the reference run with SOA. The sensitivity test exhibits also 10% more optically thin clouds (COT < 40) and an average COT roughly halved. Moreover, the run with SOA shows convective clouds with an enhanced content of liquid and frozen hydrometers, and stronger updrafts and downdrafts. Considering that the previous version of WRF/Chem coupled with a modal aerosol module predicted very low SOA content (SORGAM mechanism) the new proposed option may lead to a better characterization of aerosol-cloud feedbacks.

Aerosol Radiative Forcing in Asian Continental Outflow

NASA Technical Reports Server (NTRS)

Pueschel, R.; Kinne, S.; Redemann, J.; Gore, Warren J. (Technical Monitor)

2000-01-01

Aerosols in elevated layers were sampled with FSSP-probes and wire impactors over the Pacific ocean aboard the NASA DC-8 aircraft. Analyses of particle size and morphology identifies two distinctly different aerosol types for cases when the mid-visible extinctions exceed 0.2/km. Smaller sizes (effective radii of 0.2 um) and moderate absorption (mid-visible single scattering albedo of.935) are typical for urban-industrial pollution. Larger sizes (effective radii of 0.7 um) and weak absorption (mid-visible single scattering albedo of 0.985) identify dust. This aerosol classification is in agreement with its origin as determined by airmass back trajectory analysis. Based on lidar vertical profiling, aerosol dominated by dust and urban-industrial pollution above 3km were assigned mid-visible optical depths of 0.50 and 0.27, respectively. Radiative transfer simulations, considering a 50% cloud-cover below the aerosol layers, suggest (on a daily tP C)C> basis) small reductions (-4W/m2) to the energy budget at the top of the atmosphere for both aerosol types. For c' 0 dust, more backscattering of sunlight (weaker solar absorption) is compensated by a stronger greenhouse effect due to larger sizes. Forced reductions to the energy budget at the surface are 12W/m2 for both aerosol types. In contrast, impacts on heating rates within the aerosol layers are quite different: While urban-industrial aerosol warms the layer (at +0.6K/day as solar heating dominates), dust cools (at -0.5K/day as infrared cooling dominates). Sensitivity tests show the dependence of the aerosol climatic impact on the optical depth, particle size, absorptivity, and altitude of the layers, as well as clouds and surface properties. Climatic cooling can be eliminated (1) for the urban-industrial aerosol if absorption is increased to yield a mid-visible single scattering albedo of 0.89, or if the ocean is replaced by a land surface; (2) for the dust aerosol if the effective radius is increased from 0.7 to 1.2 um. The removal of low-level clouds doubles the cooling at the top of the atmosphere to about -8W/m2.

Cloud water composition during HCCT-2010: Scavenging efficiencies, solute concentrations, and droplet size dependence of inorganic ions and dissolved organic carbon

NASA Astrophysics Data System (ADS)

van Pinxteren, D.; Fomba, K. W.; Mertes, S.; Müller, K.; Spindler, G.; Schneider, J.; Lee, T.; Collett, J.; Herrmann, H.

2015-09-01

Cloud water samples were taken in September/October 2010 at Mt. Schmücke in a rural, forested area in Germany during the Lagrange-type Hill Cap Cloud Thuringia 2010 (HCCT-2010) cloud experiment. Besides bulk collectors, a 3-stage and a 5-stage collector were applied and samples were analysed for inorganic ions (SO42-, NO3-, NH4+, Cl-, Na+, Mg2+, Ca2+, K+), H2O2 (aq), S(IV), and dissolved organic carbon (DOC). Campaign volume-weighted mean concentrations were 191, 142, and 39 μmol L-1 for ammonium, nitrate, and sulfate, respectively, between 4 and 27 μmol L-1 for minor ions, 5.4 μmol L-1 for H2O2 (aq), 1.9 μmol L-1 for S(IV), and 3.9 mgC L-1 for DOC. The concentrations compare well to more recent European cloud water data from similar sites. On a mass basis, organic material (as DOC · 1.8) contributed 20-40 % (event means) to total solute concentrations and was found to have non-negligible impact on cloud water acidity. Relative standard deviations of major ions were 60-66 % for solute concentrations and 52-80 % for cloud water loadings (CWLs). Contrary to some earlier suggestions, the similar variability of solute concentrations and CWLs together with the results of back trajectory analysis and principal component analysis, suggests that concentrations in incoming air masses (i.e. air mass history), rather than cloud liquid water content (LWC) was the main factor controlling bulk solute concentrations at Mt. Schmücke. Droplet effective radius was found to be a somewhat better predictor for cloud water total ionic content (TIC) than LWC, even though no single explanatory variable can fully describe TIC (or solute concentration) variations in a simple functional relation due to the complex processes involved. Bulk concentrations typically agreed within a factor of 2 with co-located measurements of residual particle concentrations sampled by a counterflow virtual impactor (CV) and analysed by an aerosol mass spectrometer (AMS), with the deviations being mainly caused by systematic differences and limitations of the approaches (such as outgassing of dissolved gases during residual particle sampling). Scavenging efficiencies (SEs) of aerosol constituents were 0.56-0.94, 0.79-0.99, 0.71-98, and 0.67-0.92 for SO42-, NO3-, NH4+, and DOC, respectively, when calculated as event means with in-cloud data only. SEs estimated using data from an upwind site were substantially different in many cases, revealing the impact of gas-phase uptake (for volatile constituents) and mass losses across Mt. Schmücke likely due to physical processes such as droplet scavenging by trees and/or entrainment. Drop size-resolved cloud water concentrations of major ions SO42-, NO3-, and NH4+ revealed two main profiles: decreasing concentrations with increasing droplet size and "U"-shapes. In contrast, profiles of typical coarse particle mode minor ions were often increasing with increasing drop size, highlighting the importance of a species' particle concentration size distribution for the development of size-resolved solute concentration patterns. Concentration differences between droplet size classes were typically < 2 for major ions from the 3-stage collector and somewhat more pronounced from the 5-stage collector, while they were much larger for minor ions. Due to a better separation of droplet populations, the 5-stage collector was capable of resolving some features of solute size dependencies not seen in the 3-stage data, especially sharp concentration increases (up to a factor of 5-10) in the smallest droplets for many solutes.

Identification of possible sources of particulate matter in the personal cloud using SEM/EDX

NASA Astrophysics Data System (ADS)

Conner, Teri L.; Williams, Ronald W.

2004-10-01

The United States Environmental Protection Agency (US EPA) conducted the Baltimore Particulate Matter (PM) Epidemiology-Exposure Study of the Elderly during the summer of 1998. The study design included PM2.5 samples obtained from elderly (65+ years of age) retirement facility residents using personal exposure sampling devices. These sampling devices were also used to obtain PM2.5 samples at fixed locations within the personal monitoring subjects' apartments. Selected personal and apartment samples were examined using scanning electron microscopy with individual-particle X-ray analysis (SEM/EDX), providing a qualitative assessment of the chemical and physical characteristics of geological and trace element particles collected within these micro-environments at the retirement facility. This information was used to identify possible indoor source particles. The manual surveys of the personal samples revealed that some particles larger than 2.5 μm reached the filter surface. Using SEM/EDX, several particle types with possible indoor origins were identified. The Al-Zr-Cl particle is likely to have originated from a personal antiperspirant product. Particles with a talc or alumino-silicate composition point to cosmetics as a possible source. Large cadmium-containing particles were also found, which may indicate the use of art pigments or ceramic glazes, or emissions from television screen phosphors. A greater variety of particles was observed in a personal sample compared with its corresponding fixed-location apartment sample.

Waves on Ice

Atmospheric Science Data Center

2013-04-16

article title:  Waves on White: Ice or Clouds?     View Larger ... like a wavy cloud pattern was actually a wavy pattern on the ice surface. One of MISR's cloud classification products, the Angular Signature ...

Vertical profiling of aerosol particles and trace gases over the central Arctic Ocean during summer

NASA Astrophysics Data System (ADS)

Kupiszewski, P.; Leck, C.; Tjernström, M.; Sjogren, S.; Sedlar, J.; Graus, M.; Müller, M.; Brooks, B.; Swietlicki, E.; Norris, S.; Hansel, A.

2013-04-01

Unique measurements of vertical size resolved aerosol particle concentrations, trace gas concentrations and meteorological data were obtained during the Arctic Summer Cloud Ocean Study (ASCOS, http://www.ascos.se), an International Polar Year project aimed at establishing the processes responsible for formation and evolution of low-level clouds over the high Arctic summer pack ice. The experiment was conducted from onboard the Swedish icebreaker Oden, and provided both ship- and helicopter-based measurements. This study focuses on the vertical helicopter profiles and onboard measurements obtained during a three-week period when Oden was anchored to a drifting ice floe, and sheds light on the characteristics of Arctic aerosol particles and their distribution throughout the lower atmosphere. Distinct differences in aerosol particle characteristics within defined atmospheric layers are identified. Near the surface (lowermost couple hundred meters), transport from the marginal ice zone (MIZ), if sufficiently short (less than ca. 2 days), condensational growth and cloud-processing develop the aerosol population. During two of the four representative periods defined in this study, such influence is shown. At altitudes above about 1 km, long-range transport occurs frequently. However, only infrequently does large-scale subsidence descend such air masses to become entrained into the mixed layer in the high Arctic, and therefore they are unlikely to directly influence low-level stratiform cloud formation. Nonetheless, long-range transport plumes can influence the radiative balance of the PBL by influencing formation and evolution of higher clouds, as well as through precipitation transport of particles downwards. New particle formation was occasionally observed, particularly in the near-surface layer. We hypothesize that the origin of these ultrafine particles can be from biological processes, both primary and secondary, within the open leads between the pack ice and/or along the MIZ. In general, local sources, in combination with upstream boundary layer transport of precursor gases from the MIZ, are suggested to constitute the origin of CCN particles and thus be of importance for the formation of interior Arctic low level clouds during summer, and subsequently, through cloud influences, on the melting and freezing of sea ice.

Use of the ARM Measurement of Spectral Zenith Radiance For Better Understanding Of 3D Cloud-Radiation Processes and Aerosol-Cloud Interaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chiu, Jui-Yuan

2010-10-19

Our proposal focuses on cloud-radiation processes in a general 3D cloud situation, with particular emphasis on cloud optical depth and effective particle size. We also focus on zenith radiance measurements, both active and passive. The proposal has three main parts. Part One exploits the "solar-background" mode of ARM lidars to allow them to retrieve cloud optical depth not just for thin clouds but for all clouds. This also enables the study of aerosol cloud interactions with a single instrument. Part Two exploits the large number of new wavelengths offered by ARM's zenith-pointing ShortWave Spectrometer (SWS), especially during CLASIC, to developmore » better retrievals not only of cloud optical depth but also of cloud particle size. We also propose to take advantage of the SWS's 1 Hz sampling to study the "twilight zone" around clouds where strong aerosol-cloud interactions are taking place. Part Three involves continuing our cloud optical depth and cloud fraction retrieval research with ARM's 2NFOV instrument by, first, analyzing its data from the AMF-COPS/CLOWD deployment, and second, making our algorithms part of ARM's operational data processing.« less

The relevance of nanoscale biological fragments for ice nucleation in clouds

NASA Astrophysics Data System (ADS)

O‧Sullivan, D.; Murray, B. J.; Ross, J. F.; Whale, T. F.; Price, H. C.; Atkinson, J. D.; Umo, N. S.; Webb, M. E.

2015-01-01

Most studies of the role of biological entities as atmospheric ice-nucleating particles have focused on relatively rare supermicron particles such as bacterial cells, fungal spores and pollen grains. However, it is not clear that there are sufficient numbers of these particles in the atmosphere to strongly influence clouds. Here we show that the ice-nucleating activity of a fungus from the ubiquitous genus Fusarium is related to the presence of nanometre-scale particles which are far more numerous, and therefore potentially far more important for cloud glaciation than whole intact spores or hyphae. In addition, we quantify the ice-nucleating activity of nano-ice nucleating particles (nano-INPs) washed off pollen and also show that nano-INPs are present in a soil sample. Based on these results, we suggest that there is a reservoir of biological nano-INPs present in the environment which may, for example, become aerosolised in association with fertile soil dust particles.

The relevance of nanoscale biological fragments for ice nucleation in clouds.

PubMed

O'Sullivan, D; Murray, B J; Ross, J F; Whale, T F; Price, H C; Atkinson, J D; Umo, N S; Webb, M E

2015-01-28

Most studies of the role of biological entities as atmospheric ice-nucleating particles have focused on relatively rare supermicron particles such as bacterial cells, fungal spores and pollen grains. However, it is not clear that there are sufficient numbers of these particles in the atmosphere to strongly influence clouds. Here we show that the ice-nucleating activity of a fungus from the ubiquitous genus Fusarium is related to the presence of nanometre-scale particles which are far more numerous, and therefore potentially far more important for cloud glaciation than whole intact spores or hyphae. In addition, we quantify the ice-nucleating activity of nano-ice nucleating particles (nano-INPs) washed off pollen and also show that nano-INPs are present in a soil sample. Based on these results, we suggest that there is a reservoir of biological nano-INPs present in the environment which may, for example, become aerosolised in association with fertile soil dust particles.

Exploiting Cloud Radar Doppler Spectra of Mixed-Phase Clouds during ACCEPT Field Experiment to Identify Microphysical Processes

NASA Astrophysics Data System (ADS)

Kalesse, H.; Myagkov, A.; Seifert, P.; Buehl, J.

2015-12-01

Cloud radar Doppler spectra offer much information about cloud processes. By analyzing millimeter radar Doppler spectra from cloud-top to -base in mixed-phase clouds in which super-cooled liquid-layers are present we try to tell the microphysical evolution story of particles that are present by disentangling the contributions of the solid and liquid particles to the total radar returns. Instead of considering vertical profiles, dynamical effects are taken into account by following the particle population evolution along slanted paths which are caused by horizontal advection of the cloud. The goal is to identify regions in which different microphysical processes such as new particle formation (nucleation), water vapor deposition, aggregation, riming, or sublimation occurr. Cloud radar measurements are supplemented by Doppler lidar and Raman lidar observations as well as observations with MWR, wind profiler, and radio sondes. The presence of super-cooled liquid layers is identified by positive liquid water paths in MWR measurements, the vertical location of liquid layers (in non-raining systems and below lidar extinction) is derived from regions of high-backscatter and low depolarization in Raman lidar observations. In collocated cloud radar measurements, we try to identify cloud phase in the cloud radar Doppler spectrum via location of the Doppler peak(s), the existence of multi-modalities or the spectral skewness. Additionally, within the super-cooled liquid layers, the radar-identified liquid droplets are used as air motion tracer to correct the radar Doppler spectrum for vertical air motion w. These radar-derived estimates of w are validated by independent estimates of w from collocated Doppler lidar measurements. A 35 GHz vertically pointing cloud Doppler radar (METEK MIRA-35) in linear depolarization (LDR) mode is used. Data is from the deployment of the Leipzig Aerosol and Cloud Remote Observations System (LACROS) during the Analysis of the Composition of Clouds with Extended Polarization Techniques (ACCEPT) field experiment in Cabauw, Netherlands in Fall 2014. There, another MIRA-35 was operated in simultaneous transmission and simultaneous reception (STSR) mode for obtaining measurements of differential reflectivity (ZDR) and correlation coefficient ρhv.

On The Cloud Processing of Aerosol Particles: An Entraining Air Parcel Model With Two-dimensional Spectral Cloud Microphysics and A New Formulation of The Collection Kernel

NASA Astrophysics Data System (ADS)

Bott, Andreas; Kerkweg, Astrid; Wurzler, Sabine

A study has been made of the modification of aerosol spectra due to cloud pro- cesses and the impact of the modified aerosols on the microphysical structure of future clouds. For this purpose an entraining air parcel model with two-dimensional spectral cloud microphysics has been used. In order to treat collision/coalescence processes in the two-dimensional microphysical module, a new realistic and continuous formu- lation of the collection kernel has been developed. Based on experimental data, the kernel covers the entire investigated size range of aerosols, cloud and rain drops, that is the kernel combines all important coalescence processes such as the collision of cloud drops as well as the impaction scavenging of small aerosols by big raindrops. Since chemical reactions in the gas phase and in cloud drops have an important impact on the physico-chemical properties of aerosol particles, the parcel model has been extended by a chemical module describing gas phase and aqueous phase chemical reactions. However, it will be shown that in the numerical case studies presented in this paper the modification of aerosols by chemical reactions has a minor influence on the microphysical structure of future clouds. The major process yielding in a second cloud event an enhanced formation of rain is the production of large aerosol particles by collision/coalescence processes in the first cloud.