Science.gov

Sample records for ice cloud formation

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. Observations of cloud microphysics and ice formation during COPE

    NASA Astrophysics Data System (ADS)

    Taylor, J. W.; Choularton, T. W.; Blyth, A. M.; Liu, Z.; Bower, K. N.; Crosier, J.; Gallagher, M. W.; Williams, P. I.; Dorsey, J. R.; Flynn, M. J.; Bennett, L. J.; Huang, Y.; French, J.; Korolev, A.; Brown, P. R. A.

    2016-01-01

    We present microphysical observations of cumulus clouds measured over the southwest peninsula of the UK during the COnvective Precipitation Experiment (COPE) in August 2013, which are framed into a wider context using ground-based and airborne radar measurements. Two lines of cumulus clouds formed in the early afternoon along convergence lines aligned with the peninsula. The lines became longer and broader during the afternoon due to new cell formation and stratiform regions forming downwind of the convective cells. Ice concentrations up to 350 L-1, well in excess of the expected ice nuclei (IN) concentrations, were measured in the mature stratiform regions, suggesting that secondary ice production was active. Detailed sampling focused on an isolated liquid cloud that glaciated as it matured to merge with a band of cloud downwind. In the initial cell, drizzle concentrations increased from ˜ 0.5 to ˜ 20 L-1 in around 20 min. Ice concentrations developed up to a few per litre, which is around the level expected of primary IN. The ice images were most consistent with freezing drizzle, rather than smaller cloud drops or interstitial IN forming the first ice. As new cells emerged in and around the cloud, ice concentrations up to 2 orders of magnitude higher than the predicted IN concentrations developed, and the cloud glaciated over a period of 12-15 min. Almost all of the first ice particles to be observed were frozen drops, while vapour-grown ice crystals were dominant in the latter stages. Our observations are consistent with the production of large numbers of small secondary ice crystals/fragments, by a mechanism such as Hallett-Mossop or droplets shattering upon freezing. Some of the small ice froze drizzle drops on contact, while others grew more slowly by vapour deposition. Graupel and columns were seen in cloud penetrations up to the -12 °C level, though many ice particles were mixed habit due to riming and growth by vapour deposition at multiple temperatures

  6. An improved ice cloud formation parameterization in the EMAC model

    NASA Astrophysics Data System (ADS)

    Bacer, Sara; Pozzer, Andrea; Karydis, Vlassis; Tsimpidi, Alexandra; Tost, Holger; Sullivan, Sylvia; Nenes, Athanasios; Barahona, Donifan; Lelieveld, Jos

    2017-04-01

    Cirrus clouds cover about 30% of the Earth's surface and are an important modulator of the radiative energy budget of the atmosphere. Despite their importance in the global climate system, there are still large uncertainties in understanding the microphysical properties and interactions with aerosols. Ice crystal formation is quite complex and a variety of mechanisms exists for ice nucleation, depending on aerosol characteristics and environmental conditions. Ice crystals can be formed via homogeneous nucleation or heterogeneous nucleation of ice-nucleating particles in different ways (contact, immersion, condensation, deposition). We have implemented the computationally efficient cirrus cloud formation parameterization by Barahona and Nenes (2009) into the EMAC (ECHAM5/MESSy Atmospheric Chemistry) model in order to improve the representation of ice clouds and aerosol-cloud interactions. The parameterization computes the ice crystal number concentration from precursor aerosols and ice-nucleating particles accounting for the competition between homogeneous and heterogeneous nucleation and among different freezing modes. Our work shows the differences and the improvements obtained after the implementation with respect to the previous version of EMAC.

  7. Ice Nuclei Variability and Ice Formation in Mixed-phase Clouds

    NASA Astrophysics Data System (ADS)

    Demott, P. J.; Twohy, C. H.; Prenni, A. J.; Kreidenweis, S. M.; Brooks, S. D.; Rogers, D. C.

    2005-12-01

    While it is expected that ice nuclei impose a critical role in ice initiation in clouds, there are relatively few validations of direct relations between ice nuclei concentrations and ice crystal concentrations. Further, very little is known about the spatial and temporal distribution of ice nuclei, let alone their sources. Such knowledge is critical for understanding precipitation formation, cloud lifetimes, the existence of aircraft icing hazards, and the impacts of changing atmospheric aerosol particle concentrations and compositions on cold cloud processes. In this study, we document measurements of ice nuclei in relation to the presence and concentrations of ice crystals in modestly supercooled clouds and also consider the implications of differences in ice nuclei concentrations measured at different locations and times during several studies. In the first part of this presentation, we show results from measurements made in the Alliance Icing Research Study II, conducted in late Fall 2003 over the Northeast U.S. and Eastern Canada. A counterflow virtual impactor was used for selectively sampling cloud particles during aircraft measurements of clouds. Measurements were made on the evaporated residual aerosol particles, including re-processing at controlled temperatures and relative humidities to determine their ice nucleating behavior for conditions of direct relevance to the clouds using a continuous flow ice-thermal diffusion chamber (CFDC). Comparing to measurements of ice crystals in clouds, a clear correlation between the presence or absence of ice nuclei and ice crystals was demonstrated in some cases. However, the concentrations of the two populations did not correlate as well. Reasons for this may reflect different (or not assessed) ice formation processes, redistribution of ice in clouds, and potential artifacts of the sampling procedure. Since these results and those of Prenni et al. (this meeting), describing the vital role of ice nuclei in affecting

  8. Optically thin ice clouds in Arctic; Formation processes

    NASA Astrophysics Data System (ADS)

    Jouan, Caroline; Pelon, Jacques; Girard, Eric; Blanchet, Jean-Pierre; Wobrock, Wolfram; Gayet, Jean-Franćois; Schwarzenböck, Alfons; Gultepe, Ismail; Delanoë, Julien; Mioche, Guillaume

    2010-05-01

    Arctic ice cloud formation during winter is poorly understood mainly due to lack of observations and the remoteness of this region. Yet, their influence on Northern Hemisphere weather and climate is of paramount importance, and the modification of their properties, linked to aerosol-cloud interaction processes, needs to be better understood. Large concentration of aerosols in the Arctic during winter is associated to long-range transport of anthropogenic aerosols from the mid-latitudes to the Arctic. Observations show that sulphuric acid coats most of these aerosols. Laboratory and in-situ measurements show that at cold temperature (< -30°C), acidic coating lowers the freezing point and deactivates ice nuclei (IN). Therefore, the IN concentration is reduced in these regions and there is less competition for the same available moisture. As a result, large ice crystals form in relatively small concentrations. It is hypothesized that the observed low concentration of large ice crystals in thin ice clouds is linked to the acidification of aerosols. To check this, it is necessary to analyse cloud properties in the Arctic. Extensive measurements from ground-based sites and satellite remote sensing (CloudSat and CALIPSO) reveal the existence of two types of extended optically thin ice clouds (TICs) in the Arctic during the polar night and early spring. The first type (TIC-1) is seen only by the lidar, but not the radar, and is found in pristine environment whereas the second type (TIC-2) is detected by both sensors, and is associated with high concentration of aerosols, possibly anthropogenic. TIC-2 is characterized by a low concentration of ice crystals that are large enough to precipitate. To further investigate the interactions between TICs clouds and aerosols, in-situ, airborne and satellite measurements of specific cases observed during the POLARCAT and ISDAC field experiments are analyzed. These two field campaigns took place respectively over the North Slope of

  9. Optically thin ice clouds in Arctic : Formation processes

    NASA Astrophysics Data System (ADS)

    Jouan, C.; Girard, E.; Pelon, J.; Blanchet, J.; Wobrock, W.; Gultepe, I.; Gayet, J.; Delanoë, J.; Mioche, G.; Adam de Villiers, R.

    2010-12-01

    Arctic ice cloud formation during winter is poorly understood mainly due to lack of observations and the remoteness of this region. Their influence on Northern Hemisphere weather and climate is of paramount importance, and the modification of their properties, linked to aerosol-cloud interaction processes, needs to be better understood. Large concentration of aerosols in the Arctic during winter is associated to long-range transport of anthropogenic aerosols from the mid-latitudes to the Arctic. Observations show that sulphuric acid coats most of these aerosols. Laboratory and in-situ measurements show that at cold temperature (<-30°C), acidic coating lowers the freezing point and deactivates ice nuclei (IN). Therefore, the IN concentration is reduced in these regions and there is less competition for the same available moisture. As a result, large ice crystals form in relatively small concentrations. It is hypothesized that the observed low concentration of large ice crystals in thin ice clouds is linked to the acidification of aerosols. Extensive measurements from ground-based sites and satellite remote sensing (CloudSat and CALIPSO) reveal the existence of two types of extended optically thin ice clouds (TICs) in the Arctic during the polar night and early spring. The first type (TIC-1) is seen only by the lidar, but not the radar, and is found in pristine environment whereas the second type (TIC-2) is detected by both sensors, and is associated with high concentration of aerosols, possibly anthropogenic. TIC-2 is characterized by a low concentration of ice crystals that are large enough to precipitate. To further investigate the interactions between TICs clouds and aerosols, in-situ, airborne and satellite measurements of specific cases observed during the POLARCAT and ISDAC field experiments are analyzed. These two field campaigns took place respectively over the North Slope of Alaska and Northern part of Sweden in April 2008. Analysis of cloud type can be

  10. Ice nucleation by cellulose and its potential contribution to ice formation in clouds

    NASA Astrophysics Data System (ADS)

    Hiranuma, N.; Möhler, O.; Yamashita, K.; Tajiri, T.; Saito, A.; Kiselev, A.; Hoffmann, N.; Hoose, C.; Jantsch, E.; Koop, T.; Murakami, M.

    2015-04-01

    Ice particles in the atmosphere influence clouds, precipitation and climate, and often form with help from aerosols that serve as ice-nucleating particles. Biological particles, including non-proteinaceous ones, contribute to the diverse spectrum of ice-nucleating particles. However, little is known about their atmospheric abundance and ice nucleation efficiency, and their role in clouds and the climate system is poorly constrained. One biological particle type, cellulose, has been shown to exist in an airborne form that is prevalent throughout the year even at remote and elevated locations. Here we report experiments in a cloud simulation chamber to demonstrate that microcrystalline cellulose particles can act as efficient ice-nucleating particles in simulated supercooled clouds. In six immersion mode freezing experiments, we measured the ice nucleation active surface-site densities of aerosolized cellulose across a range of temperatures. Using these active surface-site densities, we developed parameters describing the ice nucleation ability of these particles and applied them to observed atmospheric cellulose and plant debris concentrations in a global aerosol model. We find that ice nucleation by cellulose becomes significant (>0.1 l-1) below about -21 °C, temperatures relevant to mixed-phase clouds. We conclude that the ability of cellulose to act as ice-nucleating particles requires a revised quantification of their role in cloud formation and precipitation.

  11. Importance of Chemical Composition of Ice Nuclei on the Formation of Arctic Ice Clouds

    NASA Astrophysics Data System (ADS)

    Keita, Setigui Aboubacar; Girard, Eric

    2016-09-01

    Ice clouds play an important role in the Arctic weather and climate system but interactions between aerosols, clouds and radiation remain poorly understood. Consequently, it is essential to fully understand their properties and especially their formation process. Extensive measurements from ground-based sites and satellite remote sensing reveal the existence of two Types of Ice Clouds (TICs) in the Arctic during the polar night and early spring. TICs-1 are composed by non-precipitating small (radar-unseen) ice crystals of less than 30 μm in diameter. The second type, TICs-2, are detected by radar and are characterized by a low concentration of large precipitating ice crystals ice crystals (>30 μm). To explain these differences, we hypothesized that TIC-2 formation is linked to the acidification of aerosols, which inhibits the ice nucleating properties of ice nuclei (IN). As a result, the IN concentration is reduced in these regions, resulting to a lower concentration of larger ice crystals. Water vapor available for deposition being the same, these crystals reach a larger size. Current weather and climate models cannot simulate these different types of ice clouds. This problem is partly due to the parameterizations implemented for ice nucleation. Over the past 10 years, several parameterizations of homogeneous and heterogeneous ice nucleation on IN of different chemical compositions have been developed. These parameterizations are based on two approaches: stochastic (that is nucleation is a probabilistic process, which is time dependent) and singular (that is nucleation occurs at fixed conditions of temperature and humidity and time-independent). The best approach remains unclear. This research aims to better understand the formation process of Arctic TICs using recently developed ice nucleation parameterizations. For this purpose, we have implemented these ice nucleation parameterizations into the Limited Area version of the Global Multiscale Environmental Model

  12. Cirrus cloud formation and the role of heterogeneous ice nuclei

    NASA Astrophysics Data System (ADS)

    Froyd, Karl D.; Cziczo, Daniel J.; Hoose, Corinna; Jensen, Eric J.; Diao, Minghui; Zondlo, Mark A.; Smith, Jessica B.; Twohy, Cynthia H.; Murphy, Daniel M.

    2013-05-01

    Composition, size, and phase are key properties that define the ability of an aerosol particle to initiate ice in cirrus clouds. Properties of cirrus ice nuclei (IN) have not been well constrained due to a lack of systematic measurements in the upper troposphere. We have analyzed the size and composition of sublimated cirrus particles sampled from a high altitude research aircraft using both in situ and offline techniques. Mineral dust and metallic particles are the most enhanced residue types relative to background aerosol. Using a combination of cirrus residue composition, relative humidity, and cirrus particle concentration measurements, we infer that heterogeneous nucleation is a dominant cirrus formation mechanism for the mid-latitude, subtropical, and tropical regions under study. Other proposed heterogeneous IN including biomass burning particles, elemental carbon, and biological material were not abundant in cirrus residuals.

  13. Solid ammonium sulfate aerosols as ice nuclei: a pathway for cirrus cloud formation.

    PubMed

    Abbatt, J P D; Benz, S; Cziczo, D J; Kanji, Z; Lohmann, U; Möhler, O

    2006-09-22

    Laboratory measurements support a cirrus cloud formation pathway involving heterogeneous ice nucleation by solid ammonium sulfate aerosols. Ice formation occurs at low ice-saturation ratios consistent with the formation of continental cirrus and an interhemispheric asymmetry observed for cloud onset. In a climate model, this mechanism provides a widespread source of ice nuclei and leads to fewer but larger ice crystals as compared with a homogeneous freezing scenario. This reduces both the cloud albedo and the longwave heating by cirrus. With the global ammonia budget dominated by agricultural practices, this pathway might further couple anthropogenic activity to the climate system.

  14. Numerical simulations of the formation and evolution of water ice clouds in the Martian atmosphere

    NASA Technical Reports Server (NTRS)

    Michelangeli, Diane V.; Toon, Owen B.; Haberle, Robert M.; Pollack, James B.

    1993-01-01

    A model of the formation, evolution, and description of Martian water ice clouds is developed which well reproduces the physical processes governing the microphysics of water ice cloud formation on Mars. The model is used to show that the cloud properties are most sensitive to the temperature profile, the number of days for which condensation previously occurred, the contact angle, and the presence of incoming meteoritic debris at the top of the atmosphere. The AM-PM differences in optical depths measured at the Viking Lander site were successfully simulated with the model, obtaining total column optical depths of ice of a few tenths in agreement with observations.

  15. Ice Formation and Growth in Orographically-Enhanced Mixed-Phase Clouds

    NASA Astrophysics Data System (ADS)

    David, Robert; Lowenthal, Douglas; Gannet Hallar, A.; McCubbin, Ian; Avallone, Linnea; Mace, Gerald; Wang, Zhien

    2015-04-01

    The formation and evolution of ice in mixed-phase clouds continues to be an active area of research due to the complex interactions between vapor, liquid and ice. Orographically-enhanced clouds are commonly mixed-phase during winter. An airborne study, the Colorado Airborne Mixed-Phase Cloud Study (CAMPS), and a ground-based field campaign, the Storm Peak Lab (SPL) Cloud Property Validation Experiment (StormVEx) were conducted in the Park Range of the Colorado Rockies. The CAMPS study utilized the University of Wyoming King Air (UWKA) to provide airborne cloud microphysical and meteorological data on 29 flights totaling 98 flight hours over the Park Range from December 15, 2010 to February 28, 2011. The UWKA was equipped with instruments that measured both cloud droplet and ice crystal size distributions, liquid water content, total water content (vapor, liquid, and ice), and 3-dimensional wind speed and direction. The Wyoming Cloud Radar and Lidar were also deployed during the campaign. These measurements are used to characterize cloud structure upwind and above the Park Range. StormVEx measured temperature, and cloud droplet and ice crystal size distributions at SPL. The observations from SPL are used to determine mountain top cloud microphysical properties at elevations lower than the UWKA was able to sample in-situ. Comparisons showed that cloud microphysics aloft and at the surface were consistent with respect to snow growth processes. Small ice crystal concentrations were routinely higher at the surface and a relationship between small ice crystal concentrations, large cloud droplet concentrations and temperature was observed, suggesting liquid-dependent ice nucleation near cloud base. Terrain flow effects on cloud microphysics and structure are considered.

  16. Modeling the relative contributions of secondary ice formation processes to ice crystal number concentrations within mixed-phase clouds

    NASA Astrophysics Data System (ADS)

    Sullivan, Sylvia; Hoose, Corinna; Nenes, Athanasios

    2016-04-01

    Measurements of in-cloud ice crystal number concentrations can be three or four orders of magnitude greater than the in-cloud ice nuclei number concentrations. This discrepancy can be explained by various secondary ice formation processes, which occur after initial ice nucleation, but the relative importance of these processes, and even the exact physics of each, is still unclear. A simple bin microphysics model (2IM) is constructed to investigate these knowledge gaps. 2IM extends the time-lag collision parameterization of Yano and Phillips, 2011 to include rime splintering, ice-ice aggregation, and droplet shattering and to incorporate the aspect ratio evolution as in Jensen and Harrington, 2015. The relative contribution of the secondary processes under various conditions are shown. In particular, temperature-dependent efficiencies are adjusted for ice-ice aggregation versus collision around -15°C, when rime splintering is no longer active, and the effect of aspect ratio on the process weighting is explored. The resulting simulations are intended to guide secondary ice formation parameterizations in larger-scale mixed-phase cloud schemes.

  17. Modeling studying on ice formation by bacteria in warm-based convective cloud

    NASA Astrophysics Data System (ADS)

    Sun, J.

    2005-12-01

    Bacteria have been recognized as cloud condensation nuclei (CCN), and certain bacteria, commonly found in plants, have exhibited capacity to act as ice nuclei (IN) at temperatures as warm as -2 °C. These ice nucleating bacteria are readily disseminated into the atmosphere and have been observed in clouds at altitudes of several kilometres. It is noteworthy that over 20 years ago, one assumed the possibility of bacterial transport and their importance into cloud formation process, rain and precipitation, as well as causing disease in plants and animal kingdom. We used a 1-D cumulus cloud model with the CCOPE 19th July 1981 case and the observed field profile of bacterial concentration, to simulate the significance of bacteria as IN through condensation freezing mechanism. In this paper, we will present our results on the role of bacteria as active ice nuclei in the developing stage of cumulus clouds, and their potential significance in atmospheric sciences.

  18. Seasonal and spatial variability of heterogeneous ice formation in stratiform clouds and its possible impact on precipitation formation

    NASA Astrophysics Data System (ADS)

    Seifert, P.; Ansmann, A.; Baars, H.; Buehl, J.; Kanitz, T.; Bohlmann, S.; Engelmann, R.; Kunz, C.

    2015-12-01

    Lidar observations of stratiform mid-level clouds were used to investigate the efficiency of heterogeneous ice nucleation as a function of cloud top temperature. The long-term lidar-based cloud datasets were collected in Germany (51°N,12°E), in southeastern China (22°N,112°E), Cape Verde (15°N,24°W), the Amazon Basin (1°N,60°W), South Africa (34°S,19°E), and southern Chile (53°S,71°W). They thus cover a variety of northern- and southern latitudinal belts from the midlatitudes to the tropics. Observations of the depolarization ratio were used to categorize the observed cloud layers into either ice-free (no depolarized signals observed) or ice-containing clouds (signals depolarized by scattering at ice crystals). Strong hemispheric and regional differences were observed in the heterogeneous ice formation efficiency at the different sites, especially in the high-temperature range between -20 and 0 °C. The fraction of ice containing clouds in this temperature range is highest at the northern-latitudinal sites of Germany and southeastern China. Over Leipzig, 50% of all clouds contain ice at -10 °C. In contrast, over southern Chile virtually no ice-containing clouds were observed between -20 and 0 °C. Seasonal differences in the ice-cloud fraction were found over Germany and the Amazon Basin. The observed regional, hemispheric and seasonal contrasts can be explained by differences in the aerosol concentration at cloud level above the different sites. Cloud vertical motion (observed with Doppler lidar), which also determine the microphysical cloud evolution, were found to be similar for all cloud layers. From combined observations of cloud radar and lidar at Leipzig it was in addition found that ice water contents of below approx. 10-6kg/m³ cannot be detected with lidar. Clouds classified as pure liquid from the lidar-only observations thus could contain ice water contents of below that threshold. Considering the hemispheric differences in heterogeneous

  19. Formation and characterization of simulated small droplet icing clouds

    NASA Technical Reports Server (NTRS)

    Ingebo, R. D.

    1986-01-01

    Two pneumatic two-fluid atomizers operating at high liquid and gas pressures produced water sprays that simulated small droplet clouds for use in studying icing effects on aircraft performance. To measure median volume diameter, MVD or D sub v.5, of small droplet water sprays, a scattered-light scanning instrument was developed. Drop size data agreed fairly well with calculated values at water and nitrogen pressures of 60 and 20 psig, respectively, and at water and nitrogen pressures of 250 and 100 psig, respectively, but not very well at intermediate values of water and nitrogen pressure. MVD data were correlated with D sub 0, W sub N, and W sub w, i.e., orifice diameter, nitrogen, and water flowrate, respectively, to give the expression for MVD in microns.

  20. Dependence of Ice Formation in Sierra Winter Orographic Clouds on the Mixing State of Aerosols Serving as Ice Nuclei

    NASA Astrophysics Data System (ADS)

    DeMott, P. J.; Prather, K. A.; Sullivan, R. C.; Suski, K.; Comstock, J. M.; Tomlinson, J. M.; Rosenfeld, D.; Prenni, A. J.; Cazorla, A.

    2011-12-01

    The CalWater study of February to March 2011 offered the opportunity for observations of aerosols from local, regional and long distance sources as they were integrated into clouds and precipitation in the Sierra Nevada. Single particle chemical analysis of cloud particle residual nuclei and surface precipitation, and their association with changes in cloud microphysical differences, suggest that ice initiation and precipitation formation were strongly affected by intrusions of Asian dust. This is consistent with coincident processing of aerosols present in ambient air and cloud particle residuals as ice nuclei. Elevated ice nuclei concentrations were associated with the presence of dust detected in cloud particle residuals, and dust particles dominated ice nuclei chemical compositions assessed by transmission electron microscopy x-ray analyses at these same times. Evidence of the role of Asian dust as ice nuclei during 2011 are consistent with back trajectory analyses and with recently published observational findings from CalWater Early Start data from 2009. The relative roles of aerosols from the marine boundary layer, biomass burning, and pollution as ice nuclei will also be discussed.

  1. High-resolution ice nucleation spectra of sea-ice bacteria: implications for cloud formation and life in frozen environments

    NASA Astrophysics Data System (ADS)

    Junge, K.; Swanson, B. D.

    2008-05-01

    Even though studies of Arctic ice forming particles suggest that a bacterial or viral source derived from open leads could be important for ice formation in Arctic clouds (Bigg and Leck, 2001), the ice nucleation potential of most polar marine psychrophiles or viruses has not been examined under conditions more closely resembling those in the atmosphere. In this paper, we examined the ice nucleation activity (INA) of several representative Arctic and Antarctic sea-ice bacterial isolates and a polar Colwellia phage virus. High-resolution ice nucleation spectra were obtained for droplets containing bacterial cells or virus particles using a free-fall freezing tube technique. The fraction of frozen droplets at a particular droplet temperature was determined by measuring the depolarized light scattering intensity from solution droplets in free-fall. Our experiments revealed that all sea-ice isolates and the virus nucleated ice at temperatures very close to the homogeneous nucleation temperature for the nucleation medium - which for artificial seawater was -42.2±0.3°C. Our results suggest that immersion freezing of these marine psychro-active bacteria and viruses would not be important for heterogeneous ice nucleation processes in polar clouds or to the formation of sea ice. These results also suggested that avoidance of ice formation in close proximity to cell surfaces might be one of the cold-adaptation and survival strategies for sea-ice bacteria. The fact that INA occurs at such low temperature could constitute one factor that explains the persistence of metabolic activities at temperatures far below the freezing point of seawater.

  2. 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.

  3. 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

  4. Heterogeneous formation of polar stratospheric clouds - Part 2: Nucleation of ice on synoptic scales

    NASA Astrophysics Data System (ADS)

    Engel, I.; Luo, B. P.; Pitts, M. C.; Poole, L. R.; Hoyle, C. R.; Grooß, J.-U.; Dörnbrack, A.; Peter, T.

    2013-04-01

    This paper provides unprecedented evidence for the importance of heterogeneous nucleation, likely on solid particles of meteoritic origin, and of small-scale temperature fluctuations, for the formation of ice particles in the Arctic stratosphere. During January 2010, ice PSCs (Polar Stratospheric Clouds) were shown by CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) to have occurred on a synoptic scale (~ 1000 km dimension). CALIPSO observations also showed widespread PSCs containing nitric acid trihydrate (NAT) particles in December 2009, prior to the occurrence of synoptic-scale regions of ice PSCs during mid-January 2010. We demonstrate by means of detailed microphysical modeling along air parcel trajectories that the formation of these PSCs is not readily reconciled with expectations from the conventional understanding of PSC nucleation mechanisms. The measurements are at odds with the previous laboratory-based understanding of PSC formation, which deemed direct heterogeneous nucleation of NAT and ice on preexisting solid particles unlikely. While a companion paper (Part 1) addresses the heterogeneous nucleation of NAT during December 2009, before the existence of ice PSCs, this paper shows that also the large-scale occurrence of stratospheric ice in January 2010 cannot be explained merely by homogeneous ice nucleation but requires the heterogeneous nucleation of ice, e.g. on meteoritic dust or preexisting NAT particles. The required efficiency of the ice nuclei is surprisingly high, namely comparable to that of known tropospheric ice nuclei such as mineral dust particles. To gain model agreement with the ice number densities inferred from observations, the presence of small-scale temperature fluctuations, with wavelengths unresolved by the numerical weather prediction models, is required. With the derived rate parameterization for heterogeneous ice nucleation we are able to explain and reproduce CALIPSO observations throughout the

  5. Heterogeneous formation of polar stratospheric clouds - Part 2: Nucleation of ice on synoptic scales

    NASA Astrophysics Data System (ADS)

    Engel, I.; Luo, B. P.; Pitts, M. C.; Poole, L. R.; Hoyle, C. R.; Grooß, J.-U.; Dörnbrack, A.; Peter, T.

    2013-11-01

    This paper provides compelling evidence for the importance of heterogeneous nucleation, likely on solid particles of meteoritic origin, and of small-scale temperature fluctuations, for the formation of ice particles in the Arctic stratosphere. During January 2010, ice PSCs (polar stratospheric clouds) were shown by CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) to have occurred on a synoptic scale (~1000 km dimension). CALIPSO observations also showed widespread PSCs containing NAT (nitric acid trihydrate) particles in December 2009, prior to the occurrence of synoptic-scale regions of ice PSCs during mid-January 2010. We demonstrate by means of detailed microphysical modeling along air parcel trajectories that the formation of these PSCs is not readily reconciled with expectations from the conventional understanding of PSC nucleation mechanisms. The measurements are at odds with the previous laboratory-based understanding of PSC formation, which deemed direct heterogeneous nucleation of NAT and ice on preexisting solid particles unlikely. While a companion paper (Part 1) addresses the heterogeneous nucleation of NAT during December 2009, before the existence of ice PSCs, this paper shows that also the large-scale occurrence of stratospheric ice in January 2010 cannot be explained merely by homogeneous ice nucleation but requires the heterogeneous nucleation of ice, e.g. on meteoritic dust or preexisting NAT particles. The required efficiency of the ice nuclei is surprisingly high, namely comparable to that of known tropospheric ice nuclei such as mineral dust particles. To gain model agreement with the ice number densities inferred from observations, the presence of small-scale temperature fluctuations, with wavelengths unresolved by the numerical weather prediction models, is required. With the derived rate parameterization for heterogeneous ice nucleation we are able to explain and reproduce CALIPSO observations throughout the

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    In cold high altitude cirrus clouds and anvils of high convective clouds in the tropics and mid-latitudes, ice partciles that are exposed 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. In this talk we will describe experiements that simulate the atmospheric freeze-drying cycle of aerosols. We find that aerosols with high organic content can form highly porous particles (HPA) with a larger diameter and a lower density than the initial homogenous aerosol following ice subliation. 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 follwoing ice sublimation. We find that the highly porous aerosol scatter solar light less efficiently than non-porous aerosol particles. A porous structure may explain the previously observed enhancement in ice nucleation efficiency of glassy organic particles. These observations may have implications for subsequent cloud formation cycles and aerosol albedo near cloud edges.

  7. Ice Clouds

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site]

    Heavy water ice clouds almost completely obscure the surface in Vastitas Borealis.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

    Image information: VIS instrument. Latitude 69.5, Longitude 283.6 East (76.4 West). 19 meter/pixel resolution.

  8. High-resolution ice nucleation spectra of sea-ice bacteria: implications for cloud formation and life in frozen environments

    NASA Astrophysics Data System (ADS)

    Junge, K.; Swanson, B. D.

    2007-11-01

    Even though studies of Arctic ice forming particles suggest that a bacterial or viral source derived from open leads could be important for cloud formation in the Arctic (Bigg and Leck, 2001), the ice nucleation potential of most polar marine psychrophiles or viruses has not been examined under conditions more closely resembling those in the atmosphere. In this paper, we examined the ice nucleation activity (INA) of several representative Arctic and Antarctic sea-ice bacterial isolates and a polar Colwellia phage virus. High-resolution ice nucleation spectra were obtained for droplets containing bacterial cells or virus particles using a free-fall freezing tube technique. The fraction of frozen droplets at a particular droplet temperature was determined by measuring the depolarized light scattering intensity from solution droplets in free-fall. Our experiments revealed that all sea-ice isolates and the virus nucleated ice at temperatures very close to the homogeneous nucleation temperature for the nucleation medium - which for artificial seawater was -42.2±0.3°C. Our results indicated that these marine psychro-active bacteria and viruses are not important for heterogeneous ice nucleation processes in sea ice or polar clouds. These results also suggested that avoidance of ice formation in close proximity to cell surfaces might be one of the cold-adaptation and survival strategies for sea-ice bacteria. The fact that INA occurs at such low temperature could constitute one factor that explains the persistence of metabolic activities at temperatures far below the freezing point of seawater.

  9. High-Resolution ice Nucleation Spectra of Sea-Ice Bacteria: Implications for Cloud Formation and Life in Frozen Environments

    NASA Astrophysics Data System (ADS)

    Junge, K.; Swanson, B.

    2007-12-01

    Even though studies of Arctic ice forming particles suggest that a bacterial or viral source derived from open leads could be important for cloud formation in the Arctic (Bigg and Leck, 2002), the ice nucleation potential of most polar marine psychrophiles or viruses has not been examined under conditions more closely resembling those in the atmosphere. In this paper, we examined the ice nucleation activity (INA) of several representative Arctic and Antarctic sea-ice bacterial isolates and a polar Colwellia phage virus. High-resolution ice nucleation spectra were obtained for droplets containing bacterial cells or virus particles using a free-fall freezing tube technique. The fraction of frozen droplets at a particular droplet temperature was determined by measuring the depolarized light scattering intensity from solution droplets in free-fall. Our experiments revealed that all sea-ice isolates and the virus nucleated ice at temperatures very close to the homogeneous nucleation temperature for the nucleation medium -- which for artificial seawater was - 42.2 degC (standdev. 0.3 degC). Our results indicated that these marine psychro-active bacteria and viruses are not important for heterogeneous ice nucleation processes in sea ice or polar clouds. These results also suggested that avoidance of ice formation in close proximity to cell surfaces might be one of the cold-adaptation and survival strategies for sea-ice bacteria. The fact that INA occurs at such low temperature could constitute one factor that explains the persistence of metabolic activities at temperatures far below the freezing point of seawater (Junge et al., 2006).

  10. On the Formation of Interstellar Water Ice: Constraints from a Search for Hydrogen Peroxide Ice in Molecular Clouds

    NASA Technical Reports Server (NTRS)

    Smith, R. G.; Charnely, S. B.; Pendleton, Y. J.; Wright, C. M.; Maldoni, M. M.; Robinson, G.

    2011-01-01

    Recent surface chemistry experiments have shown that the hydrogenation of molecular oxygen on interstellar dust grains is a plausible formation mechanism, via hydrogen peroxide (H2O2), for the production of water (H2O) ice mantles in the dense interstellar medium. Theoretical chemistry models also predict the formation of a significant abundance of H2O2 ice in grain mantles by this route. At their upper limits, the predicted and experimental abundances are sufficiently high that H2O2 should be detectable in molecular cloud ice spectra. To investigate this further, laboratory spectra have been obtained for H2O2/H2O ice films between 2.5 and 200 micron, from 10 to 180 K, containing 3%, 30%, and 97% H2O2 ice. Integrated absorbances for all the absorption features in low-temperature H2O2 ice have been derived from these spectra. For identifying H2O2 ice, the key results are the presence of unique features near 3.5, 7.0, and 11.3 micron. Comparing the laboratory spectra with the spectra of a group of 24 protostars and field stars, all of which have strong H2O ice absorption bands, no absorption features are found that can definitely be identified with H2O2 ice. In the absence of definite H2O2 features, the H2O2 abundance is constrained by its possible contribution to the weak absorption feature near 3.47 micron found on the long-wavelength wing of the 3 micron H2O ice band. This gives an average upper limit for H2O2, as a percentage of H2O, of 9% +/- 4%. This is a strong constraint on parameters for surface chemistry experiments and dense cloud chemistry models.

  11. On the Formation of Interstellar Water Ice: Constraints from a Search for Hydrogen Peroxide Ice in Molecular Clouds

    NASA Technical Reports Server (NTRS)

    Smith, R. G.; Charnely, S. B.; Pendleton, Y. J.; Wright, C. M.; Maldoni, M. M.; Robinson, G.

    2011-01-01

    Recent surface chemistry experiments have shown that the hydrogenation of molecular oxygen on interstellar dust grains is a plausible formation mechanism, via hydrogen peroxide (H2O2), for the production of water (H2O) ice mantles in the dense interstellar medium. Theoretical chemistry models also predict the formation of a significant abundance of H2O2 ice in grain mantles by this route. At their upper limits, the predicted and experimental abundances are sufficiently high that H2O2 should be detectable in molecular cloud ice spectra. To investigate this further, laboratory spectra have been obtained for H2O2/H2O ice films between 2.5 and 200 micron, from 10 to 180 K, containing 3%, 30%, and 97% H2O2 ice. Integrated absorbances for all the absorption features in low-temperature H2O2 ice have been derived from these spectra. For identifying H2O2 ice, the key results are the presence of unique features near 3.5, 7.0, and 11.3 micron. Comparing the laboratory spectra with the spectra of a group of 24 protostars and field stars, all of which have strong H2O ice absorption bands, no absorption features are found that can definitely be identified with H2O2 ice. In the absence of definite H2O2 features, the H2O2 abundance is constrained by its possible contribution to the weak absorption feature near 3.47 micron found on the long-wavelength wing of the 3 micron H2O ice band. This gives an average upper limit for H2O2, as a percentage of H2O, of 9% +/- 4%. This is a strong constraint on parameters for surface chemistry experiments and dense cloud chemistry models.

  12. Water ice cloud formation on Mars is more difficult than presumed: Laboratory studies of ice nucleation on surrogate materials

    NASA Astrophysics Data System (ADS)

    Iraci, Laura T.; Phebus, Bruce D.; Stone, Bradley M.; Colaprete, Anthony

    2010-12-01

    The role of water ice clouds in the martian water cycle and climate depends on cloud properties such as particle size and number distribution. These properties, in turn, depend on heterogeneous nucleation parameters which are poorly understood. Here we report laboratory experiments performed under martian temperature and water partial pressure conditions (158-185 K, 9 × 10 -7-1 × 10 -4 Torr H 2O) to determine the critical saturation ratio for ice onset, Scrit, as a function of temperature and dust composition. Using infrared spectroscopy to monitor ice nucleation and growth, we find a significant barrier to ice formation, with a pronounced temperature dependence. Even on clay minerals which show uptake of non-crystalline water before ice nucleation, we find a saturation ratio of 2.5 or more (RH ice > 250%) is needed to begin ice growth at temperatures near 160 K. These results could lead to changes of four orders of magnitude in the nucleation rate relative to the presumptions used currently in Mars microphysical models, which commonly set the contact parameter, m, to a single value of 0.95. Our results range from m = 0.84 to m = 0.98. For ice nucleation on Arizona Test Dust, the temperature dependence is described by m = 0.0046 * Tnucl + 0.1085, while m = 0.0055 * Tnucl + 0.0003 on a smectite-rich clay sample. Our findings suggest that cloud formation will be more difficult than previously thought, potentially leading to areas of increased near-surface humidity but generally drier conditions in the atmosphere of Mars, overall.

  13. Importance of Physico-Chemical Properties of Aerosols in the Formation of Arctic Ice Clouds

    NASA Astrophysics Data System (ADS)

    Keita, S. A.; Girard, E.

    2014-12-01

    Ice clouds play an important role in the Arctic weather and climate system but interactions between aerosols, clouds and radiation are poorly understood. Consequently, it is essential to fully understand their properties and especially their formation process. Extensive measurements from ground-based sites and satellite remote sensing reveal the existence of two Types of Ice Clouds (TICs) in the Arctic during the polar night and early spring. TIC-1 are composed by non-precipitating very small (radar-unseen) ice crystals whereas TIC-2 are detected by both sensors and are characterized by a low concentration of large precipitating ice crystals. It is hypothesized that TIC-2 formation is linked to the acidification of aerosols, which inhibit the ice nucleating properties of ice nuclei (IN). As a result, the IN concentration is reduced in these regions, resulting to a smaller concentration of larger ice crystals. Over the past 10 years, several parameterizations of homogeneous and heterogeneous ice nucleation have been developed to reflect the various physical and chemical properties of aerosols. These parameterizations are derived from laboratory studies on aerosols of different chemical compositions. The parameterizations are also developed according to two main approaches: stochastic (that nucleation is a probabilistic process, which is time dependent) and singular (that nucleation occurs at fixed conditions of temperature and humidity and time-independent). This research aims to better understand the formation process of TICs using a newly-developed ice nucleation parameterizations. For this purpose, we implement some parameterizations (2 approaches) into the Limited Area version of the Global Multiscale Environmental Model (GEM-LAM) and use them to simulate ice clouds observed during the Indirect and Semi-Direct Arctic Cloud (ISDAC) in Alaska. We use both approaches but special attention is focused on the new parameterizations of the singular approach. Simulation

  14. ON THE FORMATION OF INTERSTELLAR WATER ICE: CONSTRAINTS FROM A SEARCH FOR HYDROGEN PEROXIDE ICE IN MOLECULAR CLOUDS

    SciTech Connect

    Smith, R. G.; Wright, C. M.; Robinson, G.; Charnley, S. B.; Pendleton, Y. J.; Maldoni, M. M. E-mail: c.wright@adfa.edu.au E-mail: Steven.B.Charnley@nasa.gov

    2011-12-20

    Recent surface chemistry experiments have shown that the hydrogenation of molecular oxygen on interstellar dust grains is a plausible formation mechanism, via hydrogen peroxide (H{sub 2}O{sub 2}), for the production of water (H{sub 2}O) ice mantles in the dense interstellar medium. Theoretical chemistry models also predict the formation of a significant abundance of H{sub 2}O{sub 2} ice in grain mantles by this route. At their upper limits, the predicted and experimental abundances are sufficiently high that H{sub 2}O{sub 2} should be detectable in molecular cloud ice spectra. To investigate this further, laboratory spectra have been obtained for H{sub 2}O{sub 2}/H{sub 2}O ice films between 2.5 and 200 {mu}m, from 10 to 180 K, containing 3%, 30%, and 97% H{sub 2}O{sub 2} ice. Integrated absorbances for all the absorption features in low-temperature H{sub 2}O{sub 2} ice have been derived from these spectra. For identifying H{sub 2}O{sub 2} ice, the key results are the presence of unique features near 3.5, 7.0, and 11.3 {mu}m. Comparing the laboratory spectra with the spectra of a group of 24 protostars and field stars, all of which have strong H{sub 2}O ice absorption bands, no absorption features are found that can definitely be identified with H{sub 2}O{sub 2} ice. In the absence of definite H{sub 2}O{sub 2} features, the H{sub 2}O{sub 2} abundance is constrained by its possible contribution to the weak absorption feature near 3.47 {mu}m found on the long-wavelength wing of the 3 {mu}m H{sub 2}O ice band. This gives an average upper limit for H{sub 2}O{sub 2}, as a percentage of H{sub 2}O, of 9% {+-} 4%. This is a strong constraint on parameters for surface chemistry experiments and dense cloud chemistry models.

  15. Effects of Deep Convection on Upper Tropospheric Outflow Ice Supersaturation and Cirrus Cloud Formation

    NASA Astrophysics Data System (ADS)

    DiGangi, J. P.; O'Brien, A.; Diao, M.; Beaton, S. P.; Zondlo, M. A.

    2013-12-01

    A barrier in constraining the Earth's radiative forcing budget stems from the large uncertainties associated with cloud formation and dynamics. Recent work* has shown that small scale dynamics play a significant role in controlling the relative humidity of the upper troposphere and, in turn, the microphysics of cirrus clouds. While there has been significant discussion of the long-term transport effects of ground level trace gases and aerosols, only recently have datasets become available which examine the effects of fast convective transport on the relatively pristine upper troposphere. During the NSF Deep Convective Clouds and Chemistry (DC3) Experiment in May-June 2012, multiple aircraft, each with a large suite of chemical, aerosol and, cloud physics payloads, were utilized to characterize both the inflow and outflow of deep convective storms over the continental US. We have used data from 10 storms during DC3 as case studies to illustrate the influence of trace gases and aerosols, transported by deep convection to the upper troposphere, on ice supersaturation regions and cirrus cloud formation. Ice supersaturation regions (ISSR), defined as regions with relative humidity greater than 100% at temperatures below -40°C, in the outflow region of each storm are identified using humidity data from the NSF/NCAR VCSEL hygrometer on the NSF G-V. The ISSR intensity of the outflow of a storm is defined as the aggregate mean of the maximum relative humidity encountered in each individual ISSR in this region, a quantity that is observed to increase with ISSR length scales. Coordinated sampling of the inflow region of each storm, determined from NEXRAD radar measurements and flight tracks combined with notes from the flight summaries, by the NASA DC-8 provide a characterization of the chemical and particulate composition at the base of the storm. Mineral and nitrate particulate in the storm inflow are observed to have strong positive correlations with the ISSR intensity in

  16. Identification of Dust and Ice Cloud Formation from A-Train Datasets

    NASA Astrophysics Data System (ADS)

    Russell, D. S.; Liou, K. N.

    2014-12-01

    Dust aerosols are effective ice nuclei for clouds and instances of nucleation have been well studied in laboratory experiments. We used CALIOP/CALIPSO, MODIS/Aqua, and CloudSat on the A-Train to find collocated instances of clouds characterized as water by MODIS, but contain ice water as indicated by CloudSat. The vertical profiles of CALIPSO detect the presence of dust and polluted dust near clouds. This study concentrates on high dust aerosol areas including the regions surrounding the Sahara Desert as well as South Asia including the Tibetan Plateau. These cases display the effects of dust acting as ice nuclei in the time frame between MODIS overpass and CloudSat overpass (~45 seconds). Utilizing available datasets, we then carried out radiative transfer calculations to understand spectral radiative forcing differences between water and ice clouds, particularly over snow surfaces at the Tibetan Plateau.

  17. Ice nucleation in sulfuric acid/organic aerosols: implications for cirrus cloud formation

    NASA Astrophysics Data System (ADS)

    Beaver, M. R.; Elrod, M. J.; Garland, R. M.; Tolbert, M. A.

    2006-08-01

    Using an aerosol flow tube apparatus, we have studied the effects of aliphatic aldehydes (C3 to C10) and ketones (C3 and C9) on ice nucleation in sulfuric acid aerosols. Mixed aerosols were prepared by combining an organic vapor flow with a flow of sulfuric acid aerosols over a small mixing time (~60 s) at room temperature. No acid-catalyzed reactions were observed under these conditions, and physical uptake was responsible for the organic content of the sulfuric acid aerosols. In these experiments, aerosol organic content, determined by a Mie scattering analysis, was found to vary with the partial pressure of organic, the flow tube temperature, and the identity of the organic compound. The physical properties of the organic compounds (primarily the solubility and melting point) were found to play a dominant role in determining the inferred mode of nucleation (homogenous or heterogeneous) and the specific freezing temperatures observed. Overall, very soluble, low-melting organics, such as acetone and propanal, caused a decrease in aerosol ice nucleation temperatures when compared with aqueous sulfuric acid aerosol. In contrast, sulfuric acid particles exposed to organic compounds of eight carbons and greater, of much lower solubility and higher melting temperatures, nucleate ice at temperatures above aqueous sulfuric acid aerosols. Organic compounds of intermediate carbon chain length, C4-C7, (of intermediate solubility and melting temperatures) nucleated ice at the same temperature as aqueous sulfuric acid aerosols. Interpretations and implications of these results for cirrus cloud formation are discussed.

  18. Ice nucleation in sulfuric acid/organic aerosols: implications for cirrus cloud formation

    NASA Astrophysics Data System (ADS)

    Beaver, M. R.; Elrod, M. J.; Garland, R. M.; Tolbert, M. A.

    2006-03-01

    Using an aerosol flow tube apparatus, we have studied the effects of aliphatic aldehydes (C3 to C10) and ketones (C3 and C9) on ice nucleation in sulfuric acid aerosols. Mixed aerosols were prepared by combining an organic vapor flow with a flow of sulfuric acid aerosols over a small mixing time (~60 s) at room temperature. No acid-catalyzed reactions were observed under these conditions, and physical uptake was responsible for the organic content of the sulfuric acid aerosols. In these experiments, aerosol organic content, determined by a Mie scattering analysis, was found to vary with the partial pressure of organic, the flow tube temperature, and the identity of the organic compound. The physical properties of the organic compounds (primarily the solubility and melting point) were found to play a dominant role in determining the mode of nucleation (homogenous or heterogeneous) and the specific freezing temperatures observed. Overall, very soluble, low-melting organics, such as acetone and propanal, caused a decrease in aerosol ice nucleation temperatures when compared with aqueous sulfuric acid aerosol. In contrast, sulfuric acid particles exposed to organic compounds of eight carbons and greater, of much lower solubility and higher melting temperatures, nucleate ice at temperatures above aqueous sulfuric acid aerosols. Organic compounds of intermediate carbon chain length, C4-C7, (of intermediate solubility and melting temperatures) nucleated ice at the same temperature as aqueous sulfuric acid aerosols. Interpretations and implications of these results for cirrus cloud formation are discussed.

  19. Solid-State Photochemistry as a Formation Mechanism for Titan's Stratospheric C4N2 Ice Clouds

    NASA Technical Reports Server (NTRS)

    Anderson, C. M.; Samuelson, R. E.; Yung, Y. L.; McLain, J. L.

    2016-01-01

    We propose that C4N2 ice clouds observed in Titan's springtime polar stratosphere arise due to solid-state photochemistry occurring within extant ice cloud particles of HCN-HC3N mixtures. This formation process resembles the halogen-induced ice particle surface chemistry that leads to condensed nitric acid trihydrate (NAT) particles and ozone depletion in Earth's polar stratosphere. As our analysis of the Cassini Composite Infrared Spectrometer 478 per centimeter ice emission feature demonstrates, this solid-state photochemistry mechanism eliminates the need for the relatively high C4N2 saturation vapor pressures required (even though they are not observed) when the ice is produced through the usual procedure of direct condensation from the vapor.

  20. Solid-State Photochemistry as a Formation Mechanism for Titan's Stratospheric C4N2 Ice Clouds

    NASA Technical Reports Server (NTRS)

    Anderson, C. M.; Samuelson, R. E.; Yung, Y. L.; McLain, J. L.

    2016-01-01

    We propose that C4N2 ice clouds observed in Titan's springtime polar stratosphere arise due to solid-state photochemistry occurring within extant ice cloud particles of HCN-HC3N mixtures. This formation process resembles the halogen-induced ice particle surface chemistry that leads to condensed nitric acid trihydrate (NAT) particles and ozone depletion in Earth's polar stratosphere. As our analysis of the Cassini Composite Infrared Spectrometer 478 per centimeter ice emission feature demonstrates, this solid-state photochemistry mechanism eliminates the need for the relatively high C4N2 saturation vapor pressures required (even though they are not observed) when the ice is produced through the usual procedure of direct condensation from the vapor.

  1. Solid-state photochemistry as a formation mechanism for Titan's stratospheric C4N2 ice clouds

    NASA Astrophysics Data System (ADS)

    Anderson, C. M.; Samuelson, R. E.; Yung, Y. L.; McLain, J. L.

    2016-04-01

    We propose that C4N2 ice clouds observed in Titan's springtime polar stratosphere arise due to solid-state photochemistry occurring within extant ice cloud particles of HCN-HC3N mixtures. This formation process resembles the halogen-induced ice particle surface chemistry that leads to condensed nitric acid trihydrate (NAT) particles and ozone depletion in Earth's polar stratosphere. As our analysis of the Cassini Composite Infrared Spectrometer 478 cm-1 ice emission feature demonstrates, this solid-state photochemistry mechanism eliminates the need for the relatively high C4N2 saturation vapor pressures required (even though they are not observed) when the ice is produced through the usual procedure of direct condensation from the vapor.

  2. Cloud Formation

    NASA Astrophysics Data System (ADS)

    Graham, Mark Talmage

    2004-05-01

    Cloud formation is crucial to the heritage of modern physics, and there is a rich literature on this important topic. In 1927, Charles T.R. Wilson was awarded the Nobel Prize in physics for applications of the cloud chamber.2 Wilson was inspired to study cloud formation after working at a meteorological observatory on top of the highest mountain in Scotland, Ben Nevis, and testified near the end of his life, "The whole of my scientific work undoubtedly developed from the experiments I was led to make by what I saw during my fortnight on Ben Nevis in September 1894."3 To form clouds, Wilson used the sudden expansion of humid air.4 Any structure the cloud may have is spoiled by turbulence in the sudden expansion, but in 1912 Wilson got ion tracks to show up by using strobe photography of the chamber immediately upon expansion.5 In the interim, Millikan's study in 1909 of the formation of cloud droplets around individual ions was the first in which the electron charge was isolated. This study led to his famous oil drop experiment.6 To Millikan, as to Wilson, meteorology and physics were professionally indistinct. With his meteorological physics expertise, in WWI Millikan commanded perhaps the first meteorological observation and forecasting team essential to military operation in history.7 But even during peacetime meteorology is so much of a concern to everyone that a regular news segment is dedicated to it. Weather is the universal conversation topic, and life on land could not exist as we know it without clouds. One wonders then, why cloud formation is never covered in physics texts.

  3. Formation of mixed-phase particles during the freezing of polar stratospheric ice clouds.

    PubMed

    Bogdan, Anatoli; Molina, Mario J; Tenhu, Heikki; Mayer, Erwin; Loerting, Thomas

    2010-03-01

    Polar stratospheric clouds (PSCs) are extremely efficient at catalysing the transformation of photostable chlorine reservoirs into photolabile species, which are actively involved in springtime ozone-depletion events. Why PSCs are such efficient catalysts, however, is not well understood. Here, we investigate the freezing behaviour of ternary HNO₃-H₂SO₄-H₂O droplets of micrometric size, which form type II PSC ice particles. We show that on freezing, a phase separation into pure ice and a residual solution coating occurs; this coating does not freeze but transforms into glass below ∼150 K. We find that the coating, which is thicker around young ice crystals, can still be approximately 30 nm around older ice crystals of diameter about 10 µm. These results affect our understanding of PSC microphysics and chemistry and suggest that chlorine-activation reactions are better studied on supercooled HNO₃-H₂SO₄-H₂O solutions rather than on a pure ice surface.

  4. Comet formation in collapsing pebble clouds. What cometary bulk density implies for the cloud mass and dust-to-ice ratio

    NASA Astrophysics Data System (ADS)

    Lorek, S.; Gundlach, B.; Lacerda, P.; Blum, J.

    2016-03-01

    Context. Comets are remnants of the icy planetesimals that formed beyond the ice line in the solar nebula. Growing from μm-sized dust and ice particles to km-sized objects is, however, difficult because of growth barriers and time scale constraints. The gravitational collapse of pebble clouds that formed through the streaming instability may provide a suitable mechanism for comet formation. Aims: We study the collisional compression of silica, ice, and silica/ice-mixed pebbles during gravitational collapse of pebble clouds. Using the initial volume-filling factor and the dust-to-ice ratio of the pebbles as free parameters, we constrain the dust-to-ice mass ratio of the formed comet and the resulting volume-filling factor of the pebbles, depending on the cloud mass. Methods: We use the representative particle approach, which is a Monte Carlo method, to follow cloud collapse and collisional evolution of an ensemble of ice, silica, and silica/ice-mixed pebbles. Therefore, we developed a collision model which takes the various collision properties of dust and ice into account. We study pebbles with a compact size of 1 cm and vary the initial volume-filling factors, φ0, ranging from 0.001 to 0.4. We consider mixed pebbles as having dust-to-ice ratios between 0.5 and 10. We investigate four typical cloud masses, M, between 2.6 × 1014 (very low) and 2.6 × 1023 g (high). Results: Except for the very low-mass cloud (M = 2.6 × 1014 g), silica pebbles are always compressed during the collapse and attain volume-filling factors in the range from ⟨ φ ⟩ V ≈ 0.22 to 0.43, regardless of φ0. Ice pebbles experience no significant compression in very low-mass clouds. They are compressed to values in the range ⟨ φ ⟩ V ≈ 0.11 to 0.17 in low- and intermediate-mass clouds (M = 2.6 × 1017-2.6 × 1020 g); in high-mass clouds (M = 2.6 × 1023 g), ice pebbles end up with ⟨ φ ⟩ V ≈ 0.23. Mixed pebbles obtain filling factors in between the values for pure ice and

  5. Ice Crystal Cloud Research

    NASA Image and Video Library

    2016-07-11

    NASA Glenn’s Propulsion Systems Lab (PSL) is conducting research to characterize ice crystal clouds that can create a hazard to aircraft engines under certain conditions. The isokinetic probe (in gold) samples particles and another series of probes can measure everything from humidity to air pressure.

  6. Determining the necessary conditions for Martian cloud formation: Ice nucleation in an electrodynamic balance (EDB)

    NASA Astrophysics Data System (ADS)

    Berlin, S.; Bauer, A. J.; Cziczo, D. J.

    2013-12-01

    The Martian atmosphere contains water ice clouds similar to Earth's cirrus clouds. These clouds influence the atmospheric temperature profile, alter the balance of incoming and outgoing radiation, and vertically redistribute water and mineral dust. Extrapolations of classical heterogeneous nucleation theory from Earth-like conditions to colder temperature and lower pressure regimes present in extraterrestrial atmospheres may be inaccurate, and thus hydrological models describing these regimes could lack physical meaning. In this project, we use an electrodynamic balance (EDB) to levitate individual aerosol particles and study their freezing properties. We test previously characterized aerosols such as Arizona Test Dust (ATD) and sodium chloride (NaCl). Then, we examine the less well-studied Mojave Mars Simulant (MMS) dust, which mimics the composition and size of dust particles found in the Martian atmosphere. A relative humidity, temperature, and inert atmosphere are utilized to emulate conditions found in the Martian atmosphere. We will discuss the supersaturations under which heterogeneous ice nucleation occurs on surrogate Martian ice nuclei at various temperatures.

  7. Physical processes in polar stratospheric ice clouds

    NASA Technical Reports Server (NTRS)

    Toon, Owen B.; Turco, Richard; Jordan, Joseph

    1988-01-01

    A one dimensional model of cloud microphysics was used to simulate the formation and evolution of polar stratospheric ice clouds. Some of the processes which are included in the model are outlined. It is found that the clouds must undergo preferential nucleation upon the existing aerosols just as do tropospheric cirrus clouds. Therefore, there is an energy barrier between stratospheric nitric acid particles and ice particles implying that nitric acid does not form a continuous set of solutions between the trihydrate and ice. The Kelvin barrier is not significant in controlling the rate of formation of ice particles. It was found that the cloud properties are sensitive to the rate at which the air parcels cool. In wave clouds, with cooling rates of hundreds of degrees per day, most of the existing aerosols nucleate and become ice particles. Such clouds have particles with sizes on the order of a few microns, optical depths on order of unity and are probably not efficient at removing materials from the stratosphere. In clouds which form with cooling rates of a few degrees per day or less, only a small fraction of the aerosols become cloud particles. In such clouds the particle radius is larger than 10 microns, the optical depths are low and water vapor is efficiently removed. Seasonal simulations show that the lowest water vapor mixing ratio is determined by the lowest temperature reached, and that the time when clouds disappear is controlled by the time when temperatures begin to rise above the minimum values.

  8. Effects of ice-crystal structure on halo formation: cirrus cloud experimental and ray-tracing modeling studies.

    PubMed

    Sassen, K; Knight, N C; Takano, Y; Heymsfield, A J

    1994-07-20

    During the 1986 Project FIRE (First International Satellite Cloud Climatology Project Regional Experiment) field campaign, four 22° halo-producing cirrus clouds were studied jointly from a groundbased polarization lidar and an instrumented aircraft. The lidar data show the vertical cloud structure and the relative position of the aircraft, which collected a total of 84 slides by impaction, preserving the ice crystals for later microscopic examination. Although many particles were too fragile to survive impaction intact, a large fraction of the identifiable crystals were columns and radial bullet rosettes, with both displaying internal cavitations, and radial plate-column combinations. Particles that were solid or displayed only a slight amount of internal structure were relatively rare, which shows that the usual model postulated by halo theorists, i.e., the randomly oriented, solid hexagonal crystal, is inappropriate for typical cirrus clouds. With the aid of new ray-tracing simulations for hexagonal hollow ended column and bullet-rosette models, we evaluate the effects of more realistic ice-crystal structures on halo formation and lidar depolarization and consider why the common halo is not more common in cirrus clouds.

  9. Effects of Ice-Crystal Structure on Halo Formation: Cirrus Cloud Experimental and Ray-Tracing Modeling Studies

    NASA Technical Reports Server (NTRS)

    Sassen, Kenneth; Knight, Nancy C.; Takano, Yoshihide; Heymsfield, Andrew J.

    1994-01-01

    During the 1986 Project FIRE (First International Satellite Cloud Climatology Project Regional Experiment) field campaign, four 22 deg halo-producing cirrus clouds were studied jointly from a ground-based polarization lidar and an instrumented aircraft. The lidar data show the vertical cloud structure and the relative position of the aircraft, which collected a total of 84 slides by impaction, preserving the ice crystals for later microscopic examination. Although many particles were too fragile to survive impaction intact, a large fraction of the identifiable crystals were columns and radial bullet rosettes, with both displaying internal cavitations and radial plate-column combinations. Particles that were solid or displayed only a slight amount of internal structure were relatively rare, which shows that the usual model postulated by halo theorists, i.e., the randomly oriented, solid hexagonal crystal, is inappropriate for typical cirrus clouds. With the aid of new ray-tracing simulations for hexagonal hollow-ended column and bullet-rosette models, we evaluate the effects of more realistic ice-crystal structures on halo formation and lidar depolarization and consider why the common halo is not more common in cirrus clouds.

  10. Meteorology: dusty ice clouds over Alaska.

    PubMed

    Sassen, Kenneth

    2005-03-24

    Particles lofted into the atmosphere by desert dust storms can disperse widely and affect climate directly through aerosol scattering and absorption. They can also affect it indirectly by changing the scattering properties of clouds and, because desert dusts are particularly active ice-forming agents, by affecting the formation and thermodynamic phase of clouds. Here I show that dust storms that occurred in Asia early in 2004 created unusual ice clouds over Alaska at temperatures far warmer than those expected for normal cirrus-cloud formation.

  11. Ross Ice Shelf, Antarctic Ice and Clouds

    NASA Technical Reports Server (NTRS)

    1991-01-01

    In this view of Antarctic ice and clouds, (56.5S, 152.0W), the Ross Ice Shelf of Antarctica is almost totally clear, showing stress cracks in the ice surface caused by wind and tidal drift. Clouds on the eastern edge of the picture are associated with an Antarctic cyclone. Winds stirred up these storms have been known to reach hurricane force.

  12. Ice cloud formation potential by free tropospheric particles from long-range transport over the Northern Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    China, Swarup; Alpert, Peter A.; Zhang, Bo; Schum, Simeon; Dzepina, Katja; Wright, Kendra; Owen, R. Chris; Fialho, Paulo; Mazzoleni, Lynn R.; Mazzoleni, Claudio; Knopf, Daniel A.

    2017-03-01

    Long-range transported free tropospheric particles can play a significant role on heterogeneous ice nucleation. Using optical and electron microscopy we examine the physicochemical characteristics of ice nucleating particles (INPs). Particles were collected on substrates from the free troposphere at the remote Pico Mountain Observatory in the Azores Islands, after long-range transport and aging over the Atlantic Ocean. We investigate four specific events to study the ice formation potential by the collected particles with different ages and transport patterns. We use single-particle analysis, as well as bulk analysis to characterize particle populations. Both analyses show substantial differences in particle composition between samples from the four events; in addition, single-particle microscopy analysis indicates that most particles are coated by organic material. The identified INPs contained mixtures of dust, aged sea salt and soot, and organic material acquired either at the source or during transport. The temperature and relative humidity (RH) at which ice formed, varied only by 5% between samples, despite differences in particle composition, sources, and transport patterns. We hypothesize that this small variation in the onset RH may be due to the coating material on the particles. This study underscores and motivates the need to further investigate how long-range transported and atmospherically aged free tropospheric particles impact ice cloud formation.

  13. Ice cloud formation potential by free tropospheric particles from long-range transport over the Northern Atlantic Ocean

    DOE PAGES

    China, Swarup; Alpert, Peter A.; Zhang, Bo; ...

    2017-02-27

    Long-range transported free tropospheric particles can play a significant role on heterogeneous ice nucleation. Using optical and electron microscopy we examine the physicochemical characteristics of ice nucleating particles (INPs). Particles were collected on substrates from the free troposphere at the remote Pico Mountain Observatory in the Azores Islands, after long-range transport and aging over the Atlantic Ocean. We investigate four specific events to study the ice formation potential by the collected particles with different ages and transport patterns. We use single-particle analysis, as well as bulk analysis to characterize particle populations. Both analyses show substantial differences in particle composition betweenmore » samples from the four events; in addition, single-particle microscopy analysis indicates that most particles are coated by organic material. The identified INPs contained mixtures of dust, aged sea salt and soot, and organic material acquired either at the source or during transport. The temperature and relative humidity (RH) at which ice formed, varied only by 5% between samples, despite differences in particle composition, sources, and transport patterns. We hypothesize that this small variation in the onset RH may be due to the coating material on the particles. Finally, this study underscores and motivates the need to further investigate how long-range transported and atmospherically aged free tropospheric particles impact ice cloud formation.« less

  14. What Determines the Ice Polymorph in Clouds?

    PubMed

    Hudait, Arpa; Molinero, Valeria

    2016-07-20

    Ice crystals in the atmosphere nucleate from supercooled liquid water and grow by vapor uptake. The structure of the ice polymorph grown has strong impact on the morphology and light scattering of the ice crystals, modulates the amount of water vapor in ice clouds, and can impact the molecular uptake and reactivity of atmospheric aerosols. Experiments and molecular simulations indicate that ice nucleated and grown from deeply supercooled liquid water is metastable stacking disordered ice. The ice polymorph grown from vapor has not yet been determined. Here we use large-scale molecular simulations to determine the structure of ice that grows as a result of uptake of water vapor in the temperature range relevant to cirrus and mixed-phase clouds, elucidate the molecular mechanism of the formation of ice at the vapor interface, and compute the free energy difference between cubic and hexagonal ice interfaces with vapor. We find that vapor deposition results in growth of stacking disordered ice only under conditions of extreme supersaturation, for which a nonequilibrium liquid layer completely wets the surface of ice. Such extreme conditions have been used to produce stacking disordered frost ice in experiments and may be plausible in the summer polar mesosphere. Growth of ice from vapor at moderate supersaturations in the temperature range relevant to cirrus and mixed-phase clouds, from 200 to 260 K, produces exclusively the stable hexagonal ice polymorph. Cubic ice is disfavored with respect to hexagonal ice not only by a small penalty in the bulk free energy (3.6 ± 1.5 J mol(-1) at 260 K) but also by a large free energy penalty at the ice-vapor interface (89.7 ± 12.8 J mol(-1) at 260 K). The latter originates in higher vibrational entropy of the hexagonal-terminated ice-vapor interface. We predict that the free energy penalty against the cubic ice interface should decrease strongly with temperature, resulting in some degree of stacking disorder in ice grown from

  15. How important are glassy SOA ice nuclei for the formation of cirrus clouds?

    NASA Astrophysics Data System (ADS)

    Zhou, C.; Penner, J. E.; Lin, G.; Liu, X.; Wang, M.

    2014-12-01

    Extremely low ice numbers (i.e. 5 - 100 / L) have been observed in the tropical troposphere layer (TTL) in a variety of field campaigns. Various mechanisms have been proposed to explain these low numbers, including the effect of glassy secondary organic aerosol acting as heterogeneous ice nuclei (IN). In this study, we explored these effects using the CAM5.3 model. SOA fields were provided by an offline version of the University of Michigan-IMPACT model, which has a detailed process-based mechanism that describes aerosol microphysics and SOA formation through both gas phase and multiphase reactions. The transition criterion of SOA to glassy heterogeneous IN follows the parameterization developed by Wang et al. 2012. With this parameterization, glassy SOA IN form mainly when the temperature (T) is lower than 210K. In the default CAM5.3 set-up in which only the fraction of Aitken mode sulfate aerosols with diameter larger than 100nm participate in the ice nucleation (Liu and Penner 2005 parameterization), glassy SOA IN are shown to decrease the ice number (Ni) by suppressing some of the homogeneous freezing at low temperatures thereby leading to an improved representation of the relationship between Ni and T compared to the observations summarized by Kramer et al. 2009. However, when we allow the total number of the Aitken mode sulfate particles to participate in homogeneous freezing, glassy SOA IN have only a small impact on the relationship between Ni and T. If the subgrid updraft velocity is decreased to 0.1 m/s (compared to 0.2 m/s in the default set-up), there is a large decrease of Ni, since homogeneous freezing is more easily suppressed by glassy SOA IN at these updrafts. We also present the effects of glassy SOA IN using an alternative ice nucleation scheme (Barahona and Nenes, 2009).

  16. Metastable Nitric Acid Trihydrate in Ice Clouds

    PubMed Central

    Weiss, Fabian; Kubel, Frank; Gálvez, Óscar; Hoelzel, Markus; Parker, Stewart F.; Baloh, Philipp; Iannarelli, Riccardo; Rossi, Michel J.

    2016-01-01

    Abstract The composition of high‐altitude ice clouds is still a matter of intense discussion. The constituents in question are ice and nitric acid hydrates, but the exact phase composition of clouds and its formation mechanisms are still unknown. In this work, conclusive evidence for a long‐predicted phase, alpha‐nitric acid trihydrate (alpha‐NAT), is presented. This phase was characterized by a combination of X‐ray and neutron diffraction experiments, allowing a convincing structure solution. Furthermore, vibrational spectra (infrared and inelastic neutron scattering) were recorded and compared with theoretical calculations. A strong interaction between water ice and alpha‐NAT was found, which explains the experimental spectra and the phase‐transition kinetics. On the basis of these results, we propose a new three‐step mechanism for NAT formation in high‐altitude ice clouds. PMID:26879259

  17. Metastable Nitric Acid Trihydrate in Ice Clouds.

    PubMed

    Weiss, Fabian; Kubel, Frank; Gálvez, Óscar; Hoelzel, Markus; Parker, Stewart F; Baloh, Philipp; Iannarelli, Riccardo; Rossi, Michel J; Grothe, Hinrich

    2016-03-01

    The composition of high-altitude ice clouds is still a matter of intense discussion. The constituents in question are ice and nitric acid hydrates, but the exact phase composition of clouds and its formation mechanisms are still unknown. In this work, conclusive evidence for a long-predicted phase, alpha-nitric acid trihydrate (alpha-NAT), is presented. This phase was characterized by a combination of X-ray and neutron diffraction experiments, allowing a convincing structure solution. Furthermore, vibrational spectra (infrared and inelastic neutron scattering) were recorded and compared with theoretical calculations. A strong interaction between water ice and alpha-NAT was found, which explains the experimental spectra and the phase-transition kinetics. On the basis of these results, we propose a new three-step mechanism for NAT formation in high-altitude ice clouds. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. INFRARED SPECTROSCOPIC SURVEY OF THE QUIESCENT MEDIUM OF NEARBY CLOUDS. I. ICE FORMATION AND GRAIN GROWTH IN LUPUS

    SciTech Connect

    Boogert, A. C. A.; Chiar, J. E.; Knez, C.; Mundy, L. G.; Öberg, K. I.; Pendleton, Y. J.; Tielens, A. G. G. M.; Van Dishoeck, E. F.

    2013-11-01

    Infrared photometry and spectroscopy (1-25 μm) of background stars reddened by the Lupus molecular cloud complex are used to determine the properties of grains and the composition of ices before they are incorporated into circumstellar envelopes and disks. H{sub 2}O ices form at extinctions of A{sub K} = 0.25 ± 0.07 mag (A{sub V} = 2.1 ± 0.6). Such a low ice formation threshold is consistent with the absence of nearby hot stars. Overall, the Lupus clouds are in an early chemical phase. The abundance of H{sub 2}O ice (2.3 ± 0.1 × 10{sup –5} relative to N{sub H}) is typical for quiescent regions, but lower by a factor of three to four compared to dense envelopes of young stellar objects. The low solid CH{sub 3}OH abundance (<3%-8% relative to H{sub 2}O) indicates a low gas phase H/CO ratio, which is consistent with the observed incomplete CO freeze out. Furthermore it is found that the grains in Lupus experienced growth by coagulation. The mid-infrared (>5 μm) continuum extinction relative to A{sub K} increases as a function of A{sub K}. Most Lupus lines of sight are well fitted with empirically derived extinction curves corresponding to R{sub V} ∼ 3.5 (A{sub K} = 0.71) and R{sub V} ∼ 5.0 (A{sub K} = 1.47). For lines of sight with A{sub K} > 1.0 mag, the τ{sub 9.7}/A{sub K} ratio is a factor of two lower compared to the diffuse medium. Below 1.0 mag, values scatter between the dense and diffuse medium ratios. The absence of a gradual transition between diffuse and dense medium-type dust indicates that local conditions matter in the process that sets the τ{sub 9.7}/A{sub K} ratio. This process is likely related to grain growth by coagulation, as traced by the A{sub 7.4}/A{sub K} continuum extinction ratio, but not to ice mantle formation. Conversely, grains acquire ice mantles before the process of coagulation starts.

  19. Metastable Phases in Ice Clouds

    NASA Astrophysics Data System (ADS)

    Weiss, Fabian; Baloh, Philipp; Kubel, Frank; Hoelzel, Markus; Parker, Stewart; Grothe, Hinrich

    2014-05-01

    Polar Stratospheric Clouds and Cirrus Clouds contain both, pure water ice and phases of nitric acid hydrates. Preferentially for the latter, the thermodynamically stable phases have intensively been investigated in the past (e.g. nitric acid trihydrate, beta-NAT). As shown by Peter et al. [1] the water activity inside clouds is higher than expected, which might be explained by the presence of metastable stable phases (e.g. cubic ice). However, also metastable nitric acid hydrates might be important due to the inherent non-equilibrium freezing conditions in the upper atmosphere. The delta ice theory of Gao et al. [2] presents a model approach to solve this problem by involving both metastable ice and NAT as well. So it is of high interest to investigate the metastable phase of NAT (i.e. alpha-NAT), the structure of which was unknown up to the presence. In our laboratory a production procedure for metastable alpha-NAT has been developed, which gives access to neutron diffraction and X-ray diffraction measurements, where sample quantities of several Gramm are required. The diffraction techniques were used to solve the unknown crystalline structure of metastable alpha-NAT, which in turn allows the calculation of the vibrational spectra, which have also been recorded by us in the past. Rerefences [1] Peter, T., C. Marcolli, P. Spichtinger, T. Corti, M. B. Baker, and T. Koop. When dry air is too humid. Science, 314:1399-1402, 2006. [2] Gao, R., P. Popp, D. Fahey, T. Marcy, R. L. Herman, E. Weinstock, D. Baumgardener, T. Garrett, K. Rosenlof, T. Thompson, T. P. Bui, B. Ridley, S. C. Wofsy, O. B. Toon, M. Tolbert, B. Kärcher, Th. Peter, P. K. Hudson, A. Weinheimer, and A. Heymsfield. Evidence That Nitric Acid Increases Relative Humidity in Low-Temperature Cirrus Clouds, Science, 303:516-520, 2004. [3] Tizek, H., E. Knözinger, and H. Grothe. Formation and phase distribution of nitric acid hydrates in the mole fraction range xHNO3<0.25: A combined XRD and IR study, PCCP, 6

  20. Identifying Dynamical Forcing and Cloud-Radiative Feedbacks Critical to the Formation of Extreme Arctic Sea-Ice Extent in the Summers of 2007 and 1996

    NASA Astrophysics Data System (ADS)

    Dong, X.; Zib, B. J.; Xi, B.; Deng, Y.; Zhang, X.; Lin, B.; Long, C. N.

    2014-12-01

    Along with significant changes in Arctic climate system, the largest year-to-year variation in sea-ice extent has occurred in the Laptev, East Siberian, and Chukchi seas (define it here as the Area Of Focus, AOF), where two extremes of opposite signs were observed in the summers of 2007 and 1996. To untangle underlying forcing and feedbacks critical to the formation of the minimum (maximum) Arctic sea-ice extent of 2007 (1996), we examined in details the corresponding 2007 and 1996 anomalies of the large-scale atmospheric circulation and atmospheric physical parameters relevant to sea-ice variation utilizing satellite-derived sea-ice products and the NASA MERRA reanalysis. Our results indicate that, in addition to a triggering role of spring large-scale atmospheric circulation anomaly, a positive cloud-radiation-precipitable water vapor (PWV) feedback played the most important role in driving the sea-ice extent to a record low in the summer of 2007. Specially, atmospheric circulation change in spring induced anomalous southerly winds from the North Pacific not only advected more warm air, but also brought more water vapor to the AOF and formed more clouds. When cloud fraction (CF) was high and Arctic surfaces were covered by snow and ice, particularly during the onset of sea-ice melting (May-June), the cloud-greenhouse (LW) effect overwhelmed the cloud-albedo (SW) effect, producing a positive cloud radiative effect on surface radiation budget. Rising surface temperature subsequently enhanced evaporation and elevated atmospheric PWV, which drastically increased downwelling LW flux activating another positive feedback to the surface temperature. As sea-ice melting continued, additional SW (and LW) radiation was absorbed by open seas to increase surface temperature, and more water vapor evaporated to form more clouds, further accelerating sea-ice retreat through the positive cloud-radiation-PWV feedback. By contrast, when sea-ice reached an anomalously high extent in

  1. Ice Formation on Wings

    NASA Technical Reports Server (NTRS)

    Ritz, L

    1939-01-01

    This report makes use of the results obtained in the Gottingen ice tunnel in which the atmospheric conditions are simulated and the process of ice formation photographed. The effect of ice formation is threefold: 1) added weight to the airplane; 2) a change in the lift and drag forces; 3) a change in the stability characteristics.

  2. Physical processes in polar stratospheric ice clouds

    NASA Technical Reports Server (NTRS)

    Toon, Owen B.; Ferry, G.; Turco, R. P.; Jordan, J.; Goodman, J.

    1989-01-01

    The formulation and evolution of polar stratospheric ice clouds are simulated using a one-dimensional model of cloud microphysics. It is found that the optical thickness and particle size of ice clouds depend on the cooling rate of the air in which the cloud formed. It is necessary that there be an energy barrier to ice nucleation upon the preexisting aerosols in order to account for the cooling rate dependence of the cloud properties.

  3. Icing Cloud Calibration of the NASA Glenn Icing Research Tunnel

    NASA Technical Reports Server (NTRS)

    Ide, Robert F.; Oldenburg, John R.

    2001-01-01

    The icing research tunnel at the NASA Glenn Research Center underwent a major rehabilitation in 1999, necessitating recalibration of the icing clouds. This report describes the methods used in the recalibration, including the procedure used to establish a uniform icing cloud and the use of a standard icing blade technique for measurement of liquid water content. The instruments and methods used to perform the droplet size calibration are also described. The liquid water content/droplet size operating envelopes of the icing tunnel are shown for a range of airspeeds and compared to the FAA icing certification criteria. The capabilities of the IRT to produce large droplet icing clouds is also detailed.

  4. Radiative properties of ice clouds

    SciTech Connect

    Mitchell, D.L.; Koracin, D.; Carter, E.

    1996-04-01

    A new treatment of cirrus cloud radiative properties has been developed, based on anomalous diffraction theory (ADT), which does not parameterize size distributions in terms of an effective radius. Rather, is uses the size distribution parameters directly, and explicitly considers the ice particle shapes. There are three fundamental features which characterize this treatment: (1) the ice path radiation experiences as it travels through an ice crystal is parameterized, (2) only determines the amount of radiation scattered and absorbed, and (3) as in other treatments, the projected area of the size distribution is conserved. The first two features are unique to this treatment, since it does not convert the ice particles into equivalent volume or area spheres in order to apply Mie theory.

  5. Ammonia Ice Clouds on Jupiter

    NASA Technical Reports Server (NTRS)

    2007-01-01

    The top cloud layer on Jupiter is thought to consist of ammonia ice, but most of that ammonia 'hides' from spectrometers. It does not absorb light in the same way ammonia does. To many scientists, this implies that ammonia churned up from lower layers of the atmosphere 'ages' in some way after it condenses, possibly by being covered with a photochemically generated hydrocarbon mixture. The New Horizons Linear Etalon Imaging Spectral Array (LEISA), the half of the Ralph instrument that is able to 'see' in infrared wavelengths that are absorbed by ammonia ice, spotted these clouds and watched them evolve over five Jupiter days (about 40 Earth hours). In these images, spectroscopically identified fresh ammonia clouds are shown in bright blue. The largest cloud appeared as a localized source on day 1, intensified and broadened on day 2, became more diffuse on days 3 and 4, and disappeared on day 5. The diffusion seemed to follow the movement of a dark spot along the boundary of the oval region. Because the source of this ammonia lies deeper than the cloud, images like these can tell scientists much about the dynamics and heat conduction in Jupiter's lower atmosphere.

  6. Ammonia Ice Clouds on Jupiter

    NASA Technical Reports Server (NTRS)

    2007-01-01

    The top cloud layer on Jupiter is thought to consist of ammonia ice, but most of that ammonia 'hides' from spectrometers. It does not absorb light in the same way ammonia does. To many scientists, this implies that ammonia churned up from lower layers of the atmosphere 'ages' in some way after it condenses, possibly by being covered with a photochemically generated hydrocarbon mixture. The New Horizons Linear Etalon Imaging Spectral Array (LEISA), the half of the Ralph instrument that is able to 'see' in infrared wavelengths that are absorbed by ammonia ice, spotted these clouds and watched them evolve over five Jupiter days (about 40 Earth hours). In these images, spectroscopically identified fresh ammonia clouds are shown in bright blue. The largest cloud appeared as a localized source on day 1, intensified and broadened on day 2, became more diffuse on days 3 and 4, and disappeared on day 5. The diffusion seemed to follow the movement of a dark spot along the boundary of the oval region. Because the source of this ammonia lies deeper than the cloud, images like these can tell scientists much about the dynamics and heat conduction in Jupiter's lower atmosphere.

  7. Laser-induced plasma cloud interaction and ice multiplication under cirrus cloud conditions.

    PubMed

    Leisner, Thomas; Duft, Denis; Möhler, Ottmar; Saathoff, Harald; Schnaiter, Martin; Henin, Stefano; Stelmaszczyk, Kamil; Petrarca, Massimo; Delagrange, Raphaëlle; Hao, Zuoqiang; Lüder, Johannes; Petit, Yannick; Rohwetter, Philipp; Kasparian, Jérôme; Wolf, Jean-Pierre; Wöste, Ludger

    2013-06-18

    Potential impacts of lightning-induced plasma on cloud ice formation and precipitation have been a subject of debate for decades. Here, we report on the interaction of laser-generated plasma channels with water and ice clouds observed in a large cloud simulation chamber. Under the conditions of a typical storm cloud, in which ice and supercooled water coexist, no direct influence of the plasma channels on ice formation or precipitation processes could be detected. Under conditions typical for thin cirrus ice clouds, however, the plasma channels induced a surprisingly strong effect of ice multiplication. Within a few minutes, the laser action led to a strong enhancement of the total ice particle number density in the chamber by up to a factor of 100, even though only a 10(-9) fraction of the chamber volume was exposed to the plasma channels. The newly formed ice particles quickly reduced the water vapor pressure to ice saturation, thereby increasing the cloud optical thickness by up to three orders of magnitude. A model relying on the complete vaporization of ice particles in the laser filament and the condensation of the resulting water vapor on plasma ions reproduces our experimental findings. This surprising effect might open new perspectives for remote sensing of water vapor and ice in the upper troposphere.

  8. Laser-induced plasma cloud interaction and ice multiplication under cirrus cloud conditions

    PubMed Central

    Leisner, Thomas; Duft, Denis; Möhler, Ottmar; Saathoff, Harald; Schnaiter, Martin; Henin, Stefano; Stelmaszczyk, Kamil; Petrarca, Massimo; Delagrange, Raphaëlle; Hao, Zuoqiang; Lüder, Johannes; Petit, Yannick; Rohwetter, Philipp; Kasparian, Jérôme; Wolf, Jean-Pierre; Wöste, Ludger

    2013-01-01

    Potential impacts of lightning-induced plasma on cloud ice formation and precipitation have been a subject of debate for decades. Here, we report on the interaction of laser-generated plasma channels with water and ice clouds observed in a large cloud simulation chamber. Under the conditions of a typical storm cloud, in which ice and supercooled water coexist, no direct influence of the plasma channels on ice formation or precipitation processes could be detected. Under conditions typical for thin cirrus ice clouds, however, the plasma channels induced a surprisingly strong effect of ice multiplication. Within a few minutes, the laser action led to a strong enhancement of the total ice particle number density in the chamber by up to a factor of 100, even though only a 10−9 fraction of the chamber volume was exposed to the plasma channels. The newly formed ice particles quickly reduced the water vapor pressure to ice saturation, thereby increasing the cloud optical thickness by up to three orders of magnitude. A model relying on the complete vaporization of ice particles in the laser filament and the condensation of the resulting water vapor on plasma ions reproduces our experimental findings. This surprising effect might open new perspectives for remote sensing of water vapor and ice in the upper troposphere. PMID:23733936

  9. Simple Cloud Chambers Using Gel Ice Packs

    ERIC Educational Resources Information Center

    Kamata, Masahiro; Kubota, Miki

    2012-01-01

    Although cloud chambers are highly regarded as teaching aids for radiation education, school teachers have difficulty in using cloud chambers because they have to prepare dry ice or liquid nitrogen before the experiment. We developed a very simple and inexpensive cloud chamber that uses the contents of gel ice packs which can substitute for dry…

  10. Simple Cloud Chambers Using Gel Ice Packs

    ERIC Educational Resources Information Center

    Kamata, Masahiro; Kubota, Miki

    2012-01-01

    Although cloud chambers are highly regarded as teaching aids for radiation education, school teachers have difficulty in using cloud chambers because they have to prepare dry ice or liquid nitrogen before the experiment. We developed a very simple and inexpensive cloud chamber that uses the contents of gel ice packs which can substitute for dry…

  11. Metastable Nitric Acid Trihydrate in Ice Clouds

    NASA Astrophysics Data System (ADS)

    Weiss, Fabian; Kubel, Frank; Gálvez, Oscar; Hölzel, Markus; Parker, Stewart F.; Baloh, Philipp; Iannarelli, Riccardo; Rossi, Michel J.; Grothe, Hinrich

    2016-04-01

    The composition of high altitude ice clouds is still a matter of intense discussion. The constituents in question are ice and nitric acid hydrates. The identification and formation mechanisms, however, are still unknown but are essential to understand atmospheric processing such as the seasonal ozone depletion in the lower polar stratosphere or the radiation balance of planet Earth. We found conclusive evidence for a long-predicted phase, which has been named alpha nitric acid trihydrate (alpha-NAT). This phase has been proven by combination of X-ray and neutron diffraction experiments allowing a convincing structure solution. Additionally, vibrational spectra (infrared and inelastic neutron scattering) were recorded and compared with theoretical calculations. A strong affinity between water ice and alpha-NAT has been found, which explains the experimental spectra and the phase transition kinetics essential for identification in the atmosphere. On the basis of our results, we propose a new three-step mechanism for NAT-formation in high altitude ice clouds. F. Weiss et al. Angew. Chem. Int. Ed. 2016, accepted, DOI:10.1002/anie.201510841

  12. Martian north polar water ice clouds

    NASA Technical Reports Server (NTRS)

    Tamppari, L. K.; Bass, D.

    2000-01-01

    The Viking Orbiter determined that the surface of Mars' northern residual cap consists of water ice. An examination of north polar water-ice clouds could lend insight into the fate of the water vapor during this time period.

  13. Martian north polar water ice clouds

    NASA Technical Reports Server (NTRS)

    Tamppari, L. K.; Bass, D.

    2000-01-01

    The Viking Orbiter determined that the surface of Mars' northern residual cap consists of water ice. An examination of north polar water-ice clouds could lend insight into the fate of the water vapor during this time period.

  14. Ice crystal and ice nucleus measurements in cap clouds

    NASA Technical Reports Server (NTRS)

    Vali, G.; Rogers, D. C.; Deshler, T. L.

    1982-01-01

    Ice nucleation in cap clouds over a mountain in Wyoming was examined with airborne instrumentation. Crosswind and wind parallel passes were made through the clouds, with data being taken on the ice crystal concentrations and sizes. A total of 141 penetrations of 26 separate days in temperatures ranging from -7 to -24 C were performed. Subsequent measurements were also made 100 km away from the mountain. The ice crystal concentrations measured showed good correlation with the ice nucleus content in winter time, midcontinental air masses in Wyoming. Further studies are recommended to determine if the variations in the ice nucleus population are the cause of the variability if ice crystal content.

  15. Ice-Crystal Fallstreaks from Supercooled Liquid Water Parent Clouds

    NASA Technical Reports Server (NTRS)

    Campbell, James R.; O'C. Starr, David; Welton, Ellsworth J.; Spinhirne, James D.; Ferrare, Richard A.

    2003-01-01

    On 31 December 2001, ice-crystal fallstreaks (e.g., cirrus uncinus, or colloquially "Mare's Tails") from supercooled liquid water parent clouds were observed by ground-based lidars pointed vertically from the Atmospheric Radiation Measurement Southern Great Plains (SGP) facility near Lamont, Oklahoma. The incidence of liquid phase cloud with apparent ice-phase precipitation is investigated. Scenarios for mixed-phase particle nucleation, and fallstreak formation and sustenance are discussed. The observations are unique in the context of the historical reverence given to the commonly observed c h s uncinus fallstreak (wholly ice) versus this seemingly contradictory coincidence of liquid water begetting ice-crystal streaks.

  16. SUCCESS Evidence for Cirrus Cloud Ice Nucleation Mechanisms

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

    During the SUCCESS mission, several measurements were made which should improve our understanding of ice nucleation processes in cirrus clouds. Temperature and water vapor concentration were made with a variety of instruments on the NASA DC-8. These observations should provide accurate upper tropospheric humidities. In particular, we will evaluate what humidities are required for ice nucleation. Preliminary results suggest that substantial supersaturations frequently exist in the upper troposphere. The leading-edge region of wave-clouds (where ice nucleation occurs) was sampled extensively at temperatures near -40 and -60C. These observations should give precise information about conditions required for ice nucleation. In addition, we will relate the observed aerosol composition and size distributions to the ice formation observed to evaluate the role of soot or mineral particles on ice nucleation. As an alternative technique for determining what particles act as ice nuclei, numerous samples of aerosols inside ice crystals were taken. In some cases, large numbers of aerosols were detected in each crystal, indicating that efficient scavenging occurred. Analysis of aerosols in ice crystals when only one particle per crystal was detected should help with the ice nucleation issue. Direct measurements of the ice nucleating activity of ambient aerosols drawn into airborne cloud chambers were also made. Finally, measurements of aerosols and ice crystals in contrails should indicate whether aircraft exhaust soot particles are effective ice nuclei.

  17. Microphysical Consequences of the Spatial Distribution of Ice Nucleation in Mixed-Phase Stratiform Clouds

    SciTech Connect

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

    2014-07-28

    Mixed-phase stratiform clouds can persist even with steady ice precipitation fluxes, and the origin and microphysical properties of the ice crystals are of interest. Vapor deposition growth and sedimentation of ice particles along with a uniform volume source of ice nucleation, leads to a power law relation between ice water content wi and ice number concentration ni with exponent 2.5. The result is independent of assumptions about the vertical velocity structure of the cloud and is therefore more general than the related expression of Yang et al. [2013]. The sensitivity of the wi-ni relationship to the spatial distribution of ice nucleation is confirmed by Lagrangian tracking and ice growth with cloud-volume, cloud-top, and cloud-base sources of ice particles through a time-dependent cloud field. Based on observed wi and ni from ISDAC, a lower bound of 0.006 m^3/s is obtained for the ice crystal formation rate.

  18. Ice Nuclei Production in Volcanic Clouds

    NASA Astrophysics Data System (ADS)

    Few, A. A.

    2012-12-01

    The paper [Durant et al., 2008] includes a review of research on ice nucleation in explosive volcanic clouds in addition to reporting their own research on laboratory measurements focused on single-particle ice nucleation. Their research as well as the research they reviewed were concerned with the freezing of supercooled water drops (250 to 260 K) by volcanic ash particles acting as ice freezing nuclei. Among their conclusions are: Fine volcanic ash particles are very efficient ice freezing nuclei. Volcanic clouds likely contain fine ash concentrations 104 to 105 times greater than found in meteorological clouds. This overabundance of ice nuclei will produce a cloud with many small ice crystals that will not grow larger as they do in meteorological clouds because the cloud water content is widely distributed among the numerous small ice crystals. The small ice crystals have a small fall velocity, thus volcanic clouds are very stable. The small ice crystals are easily lofted into the stratosphere transporting water and adsorbed trace gasses. In this paper we examine the mechanism for the production of the small ice nuclei and develop a simple model for calculating the size of the ice nuclei based upon the distribution of magma around imbedded bubbles. We also have acquired a volcanic bomb that exhibits bubble remnants on its entire surface. The naturally occurring fragments from the volcanic bomb reveal a size distribution consistent with that predicted by the simple model. Durant, A. J., R. A. Shaw, W. I. Rose, Y. Mi, and G. G. J. Ernst (2008), Ice nucleation and overseeding of ice in volcanic clouds, J. Geophys. Res., 113, D09206, doi:10.1029/2007JD009064.

  19. Studies of Ice Nucleating Aerosol Particles in Arctic Cloud Systems

    NASA Technical Reports Server (NTRS)

    Rogers, David C.; DeMott, Paul J.; Kreidenweis, Sonia M.

    2001-01-01

    The focus of this research is to improve the understanding of ice nucleating aerosol particles (IN) and the role they play in ice formation in Arctic clouds. IN are important for global climate issues in a variety of ways. The primary effect is their role in determining the phase (liquid or solid) of cloud particles. The microscale impact is on cloud particle size, growth rate, shape, fall speed, concentration, radiative properties, and scavenging of gases and aerosols. On a larger scale, ice formation affects the development of precipitation (rate, amount, type, and distribution), latent heat release (rate and altitude), ambient humidity, the persistence of clouds, and cloud albedo. The overall goals of our FIRE 3 research are to characterize the concentrations and variability of Arctic IN during the winter-spring transition, to compare IN measurements with ice concentrations in Arctic clouds, and to examine selected IN samples for particle morphology and chemical there are distinguishable chemical signatures. The results can be combined with other measurements of aerosols, gaseous species, and cloud characteristics in order to understand the processes that determine the phase and concentration of cloud particles.

  20. Parameterizing Size Distribution in Ice Clouds

    SciTech Connect

    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). 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

  1. Cloud and ice in the planetary scale circulation and in climate

    NASA Technical Reports Server (NTRS)

    Herman, G. F.; Houghton, D. D.; Kutzbach, J. E.; Suomi, V. E.

    1984-01-01

    The roles of the cryosphere, and of cloud-radiative interactions are investigated. The effects clouds and ice have in the climate system are examined. The cloud radiation research attempts explain the modes of interaction (feedback) between raditive transfer, cloud formation, and atmospheric dynamics. The role of sea ice in weather and climate is also discussed. Models are used to describe the ice and atmospheric dynamics under study.

  2. Biological ice nucleation initiates hailstone formation

    NASA Astrophysics Data System (ADS)

    Michaud, Alexander B.; Dore, John E.; Leslie, Deborah; Lyons, W. Berry; Sands, David C.; Priscu, John C.

    2014-11-01

    Cloud condensation and ice nuclei in the troposphere are required precursors to cloud and precipitation formation, both of which influence the radiative balance of Earth. The initial stage of hailstone formation (i.e., the embryo) and the subsequent layered growth allow hail to be used as a model for the study of nucleation processes in precipitation. By virtue of the preserved particle and isotopic record captured by hailstones, they represent a unique form of precipitation that allows direct characterization of the particles present during atmospheric ice nucleation. Despite the ecological and economic consequences of hail storms, the dynamics of hailstone nucleation, and thus their formation, are not well understood. Our experiments show that hailstone embryos from three Rocky Mountain storms contained biological ice nuclei capable of freezing water at warm, subzero (°C) temperatures, indicating that biological particles can act as nucleation sites for hailstone formation. These results are corroborated by analysis of δD and δ18O from melted hailstone embryos, which show that the hailstones formed at similarly warm temperatures in situ. Low densities of ice nucleation active abiotic particles were also present in hailstone embryos, but their low concentration indicates they were not likely to have catalyzed ice formation at the warm temperatures determined from water stable isotope analysis. Our study provides new data on ice nucleation occurring at the bottom of clouds, an atmospheric region whose processes are critical to global climate models but which has challenged instrument-based measurements.

  3. Mars water-ice clouds and precipitation.

    PubMed

    Whiteway, J A; Komguem, L; Dickinson, C; Cook, C; Illnicki, M; Seabrook, J; Popovici, V; Duck, T J; Davy, R; Taylor, P A; Pathak, J; Fisher, D; Carswell, A I; Daly, M; Hipkin, V; Zent, A P; Hecht, M H; Wood, S E; Tamppari, L K; Renno, N; Moores, J E; Lemmon, M T; Daerden, F; Smith, P H

    2009-07-03

    The light detection and ranging instrument on the Phoenix mission observed water-ice clouds in the atmosphere of Mars that were similar to cirrus clouds on Earth. Fall streaks in the cloud structure traced the precipitation of ice crystals toward the ground. Measurements of atmospheric dust indicated that the planetary boundary layer (PBL) on Mars was well mixed, up to heights of around 4 kilometers, by the summer daytime turbulence and convection. The water-ice clouds were detected at the top of the PBL and near the ground each night in late summer after the air temperature started decreasing. The interpretation is that water vapor mixed upward by daytime turbulence and convection forms ice crystal clouds at night that precipitate back toward the surface.

  4. Properties of aerosol processed by ice clouds

    NASA Astrophysics Data System (ADS)

    Rudich, Y.; Adler, G.; Moise, T.; Erlick-Haspel, C.

    2012-12-01

    We suggest that highly porous aerosol (HPA) can form in the upper troposphere/lower stratosphere when ice particles encounter sub-saturation leading to ice sublimation similar to freeze drying. This process can occur at the lower layers of cirrus clouds (few km), at anvils of high convective clouds and thunderstorms, in clouds forming in atmospheric gravitational waves, in contrails and in high convective clouds injecting to the stratosphere. A new experimental system that simulates freeze drying of proxies for atmospheric aerosol at atmospheric pressure was constructed and various proxies for atmospheric soluble aerosol were studied. The properties of resulting HPA were characterized by various methods. It was found that the resulting aerosol have larger sizes (extent depends on substance and mixing), lower density (largevoid fraction), lower optical extinction and higher CCN activity and IN activity. Implication of HPA's unique properties and their atmospheric consequences to aerosol processing in ice clouds and to cloud cycles will be discussed.

  5. Ice Clouds in Color IR

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site]

    Released August 9, 2004 This image shows two representations of the same infra-red image in the Elysium region of Mars. On the left is a grayscale image showing surface temperature, and on the right is a false-color composite made from 3 individual THEMIS bands. The false-color image is colorized using a technique called decorrelation stretch (DCS), which emphasizes the spectral differences between the bands to highlight compositional variations.

    The light blue area in the center of this image is a very nice example of a water ice cloud. Water ice is frequently present in the Martian atmosphere as a thin haze. Clouds such as this one can be difficult to identify in a temperature image, but are easy to spot in the DCS images. In this case, the water ice is relatively confined and concentrated which may be due to the topography of the Elysium volcanic construct.

    Image information: IR instrument. Latitude 23.2, Longitude 150.1 East (209.9 West). 100 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed

  6. Simple cloud chambers using gel ice packs

    NASA Astrophysics Data System (ADS)

    Kamata, Masahiro; Kubota, Miki

    2012-07-01

    Although cloud chambers are highly regarded as teaching aids for radiation education, school teachers have difficulty in using cloud chambers because they have to prepare dry ice or liquid nitrogen before the experiment. We developed a very simple and inexpensive cloud chamber that uses the contents of gel ice packs which can substitute for dry ice or liquid nitrogen. The gel can be frozen in normal domestic freezers, and can be used repeatedly by re-freezing. The tracks of alpha-ray particles can be observed continuously for about 20 min, and the operation is simple and easy.

  7. Dynamics of ice drop explosions in supercooled clouds

    NASA Astrophysics Data System (ADS)

    Lohse, Detlef; Wildeman, Sander; Sterl, Sebastian; Sun, Chao

    2016-11-01

    The rate at which ice particles are produced in the cold top of natural clouds is crucial in predicting whether a cloud will finally develop precipitation. It has been speculated that ice particles could multiply through freezing and subsequent bursting of supercooled cloud droplets. Here we present high-speed footage of cracking and explosive bursting of spherical water droplets that freeze radially inwards under carefully controlled conditions. We model the processes of freezing, the stress build up in the ice shell, and the fast dynamics following the crack formation. This allows us to predict the time it takes for a freezing droplet to explode and the energy released in this event as a function of the size of the droplet and the temperature of the surroundings. Both predictions are in good agreement with our experiments. The models also predict a minimum droplet radius of approximately 50 μm below which ice explosions are unlikely to occur. This finding has direct consequences in the modeling of cloud microphysics, as the droplet sizes in clouds generally fall in this critical range. Furthermore, we identify several mechanisms, besides the final explosion, by which a freezing drop can shed ice particles. This is important for the formation of ice nucleation avalanches.

  8. Recent Ice Ages on Mars: The role of radiatively active clouds and cloud microphysics

    NASA Astrophysics Data System (ADS)

    Madeleine, J.-B.; Head, J. W.; Forget, F.; Navarro, T.; Millour, E.; Spiga, A.; Colaïtis, A.; Määttänen, A.; Montmessin, F.; Dickson, J. L.

    2014-07-01

    Global climate models (GCMs) have been successfully employed to explain the origin of many glacial deposits on Mars. However, the latitude-dependent mantle (LDM), a dust-ice mantling deposit that is thought to represent a recent "Ice Age," remains poorly explained by GCMs. We reexamine this question by considering the effect of radiatively active water-ice clouds (RACs) and cloud microphysics. We find that when obliquity is set to 35°, as often occurred in the past 2 million years, warming of the atmosphere and polar caps by clouds modifies the water cycle and leads to the formation of a several centimeter-thick ice mantle poleward of 30° in each hemisphere during winter. This mantle can be preserved over the summer if increased atmospheric dust content obscures the surface and provides dust nuclei to low-altitude clouds. We outline a scenario for its deposition and preservation that compares favorably with the characteristics of the LDM.

  9. Why does large relative humidity with respect to ice persist in cirrus ice clouds?

    PubMed

    Bogdan, A; Molina, M J

    2009-12-24

    According to observations, a large relative humidity with respect to ice, RH(i) > 100%, often persists outside and inside upper tropospheric cirrus ice clouds. The persistence of the large in-cloud RH(i) means that H(2)O is slowly deposited onto cloud ice crystals. This unusual physical situation is similar to one in which a released body would slowly fall owing to gravitation. Here we present a physical mechanism which can be responsible for the persistence of large in-cloud RH(i). We find that clear-sky RH(i) up to 176% can be built up prior to the formation of ice cirrus by the homogeneous freezing of aqueous droplets containing H(2)SO(4) and HNO(3). As the droplets are cooled, a phase separation, which occurs during freezing, leads to the formation of a residual solution coating around the ice crystals formed. The coating can serve as a shield, slowing the rate of ice growth by approximately 10(3) in comparison with uncoated ice, and this can be a reason for the persistence of the large in-cloud RH(i).

  10. Mars W cloud: Evidence of nighttime ice depositions

    NASA Astrophysics Data System (ADS)

    Moudden, Y.; Forbes, J. M.

    2009-07-01

    Water clouds on Mars, their current and past connections with other forms of water, along with surface features that suggest the early existence of flowing water, continue to be intriguing aspects of the red planet. Discrete afternoon mountain clouds were one of the earliest atmospheric features to be observed on Mars. Their exclusive formation near the high mountains led to the common belief that air lifting associated with local circulation induced by the mountains underlies their formation. We demonstrate that an additional local source of water vapor is needed for the formation of opaque discrete afternoon clouds on the mountains of Mars, including the so-called W-formation. We suggest that the possible deposition of ice from the thick aphelion cloud belt during the night is capable of providing this additional source. This direct cloud water deposition on mountains on Mars bears many similarities with the well-known interception of water by mountains frequently immersed in fogs on Earth.

  11. Heterogeneous ice nucleation of α-pinene SOA particles before and after ice cloud processing

    NASA Astrophysics Data System (ADS)

    Wagner, Robert; Höhler, Kristina; Huang, Wei; Kiselev, Alexei; Möhler, Ottmar; Mohr, Claudia; Pajunoja, Aki; Saathoff, Harald; Schiebel, Thea; Shen, Xiaoli; Virtanen, Annele

    2017-05-01

    The ice nucleation ability of α-pinene secondary organic aerosol (SOA) particles was investigated at temperatures between 253 and 205 K in the Aerosol Interaction and Dynamics in the Atmosphere cloud simulation chamber. Pristine SOA particles were nucleated and grown from pure gas precursors and then subjected to repeated expansion cooling cycles to compare their intrinsic ice nucleation ability during the first nucleation event with that observed after ice cloud processing. The unprocessed α-pinene SOA particles were found to be inefficient ice-nucleating particles at cirrus temperatures, with nucleation onsets (for an activated fraction of 0.1%) as high as for the homogeneous freezing of aqueous solution droplets. Ice cloud processing at temperatures below 235 K only marginally improved the particles' ice nucleation ability and did not significantly alter their morphology. In contrast, the particles' morphology and ice nucleation ability was substantially modified upon ice cloud processing in a simulated convective cloud system, where the α-pinene SOA particles were first activated to supercooled cloud droplets and then froze homogeneously at about 235 K. As evidenced by electron microscopy, the α-pinene SOA particles adopted a highly porous morphology during such a freeze-drying cycle. When probing the freeze-dried particles in succeeding expansion cooling runs in the mixed-phase cloud regime up to 253 K, the increase in relative humidity led to a collapse of the porous structure. Heterogeneous ice formation was observed after the droplet activation of the collapsed, freeze-dried SOA particles, presumably caused by ice remnants in the highly viscous material or the larger surface area of the particles.

  12. Clouds enhance Greenland ice sheet meltwater runoff

    NASA Astrophysics Data System (ADS)

    Van Tricht, Kristof; Lhermitte, Stef; Lenaerts, Jan T. M.; Gorodetskaya, Irina V.; L'Ecuyer, Tristan S.; Noël, Brice; van den Broeke, Michiel R.; Turner, David D.; van Lipzig, Nicole P. M.

    2016-04-01

    The Greenland ice sheet has become one of the main contributors to global sea level rise, predominantly through increased meltwater runoff. The main drivers of Greenland ice sheet runoff, however, remain poorly understood. Here we show that clouds enhance meltwater runoff by about one-third relative to clear skies, using a unique combination of active satellite observations, climate model data and snow model simulations. This impact results from a cloud radiative effect of 29.5 (±5.2) W m-2. Contrary to conventional wisdom, however, the Greenland ice sheet responds to this energy through a new pathway by which clouds reduce meltwater refreezing as opposed to increasing surface melt directly, thereby accelerating bare-ice exposure and enhancing meltwater runoff. The high sensitivity of the Greenland ice sheet to both ice-only and liquid-bearing clouds highlights the need for accurate cloud representations in climate models, to better predict future contributions of the Greenland ice sheet to global sea level rise.

  13. Clouds enhance Greenland ice sheet meltwater runoff

    PubMed Central

    Van Tricht, K.; Lhermitte, S.; Lenaerts, J. T. M.; Gorodetskaya, I. V.; L'Ecuyer, T. S.; Noël, B.; van den Broeke, M. R.; Turner, D. D.; van Lipzig, N. P. M.

    2016-01-01

    The Greenland ice sheet has become one of the main contributors to global sea level rise, predominantly through increased meltwater runoff. The main drivers of Greenland ice sheet runoff, however, remain poorly understood. Here we show that clouds enhance meltwater runoff by about one-third relative to clear skies, using a unique combination of active satellite observations, climate model data and snow model simulations. This impact results from a cloud radiative effect of 29.5 (±5.2) W m−2. Contrary to conventional wisdom, however, the Greenland ice sheet responds to this energy through a new pathway by which clouds reduce meltwater refreezing as opposed to increasing surface melt directly, thereby accelerating bare-ice exposure and enhancing meltwater runoff. The high sensitivity of the Greenland ice sheet to both ice-only and liquid-bearing clouds highlights the need for accurate cloud representations in climate models, to better predict future contributions of the Greenland ice sheet to global sea level rise. PMID:26756470

  14. Clouds enhance Greenland ice sheet meltwater runoff.

    PubMed

    Van Tricht, K; Lhermitte, S; Lenaerts, J T M; Gorodetskaya, I V; L'Ecuyer, T S; Noël, B; van den Broeke, M R; Turner, D D; van Lipzig, N P M

    2016-01-12

    The Greenland ice sheet has become one of the main contributors to global sea level rise, predominantly through increased meltwater runoff. The main drivers of Greenland ice sheet runoff, however, remain poorly understood. Here we show that clouds enhance meltwater runoff by about one-third relative to clear skies, using a unique combination of active satellite observations, climate model data and snow model simulations. This impact results from a cloud radiative effect of 29.5 (±5.2) W m(-2). Contrary to conventional wisdom, however, the Greenland ice sheet responds to this energy through a new pathway by which clouds reduce meltwater refreezing as opposed to increasing surface melt directly, thereby accelerating bare-ice exposure and enhancing meltwater runoff. The high sensitivity of the Greenland ice sheet to both ice-only and liquid-bearing clouds highlights the need for accurate cloud representations in climate models, to better predict future contributions of the Greenland ice sheet to global sea level rise.

  15. Submillimeter-Wave Cloud Ice Radiometry

    NASA Technical Reports Server (NTRS)

    Walter, Steven J.

    1999-01-01

    Submillimeter-wave cloud ice radiometry is a new and innovative technique for characterizing cirrus ice clouds. Cirrus clouds affect Earth's climate and hydrological cycle by reflecting incoming solar energy, trapping outgoing IR radiation, sublimating into vapor, and influencing atmospheric circulation. Since uncertainties in the global distribution of cloud ice restrict the accuracy of both climate and weather models, successful development of this technique could provide a valuable tool for investigating how clouds affect climate and weather. Cloud ice radiometry could fill an important gap in the observational capabilities of existing and planned Earth-observing systems. Using submillimeter-wave radiometry to retrieve properties of ice clouds can be understood with a simple model. There are a number of submillimeter-wavelength spectral regions where the upper troposphere is transparent. At lower tropospheric altitudes water vapor emits a relatively uniform flux of thermal radiation. When cirrus clouds are present, they scatter a portion of the upwelling flux of submillimeter-wavelength radiation back towards the Earth as shown in the diagram, thus reducing the upward flux o f energy. Hence, the power received by a down-looking radiometer decreases when a cirrus cloud passes through the field of view causing the cirrus cloud to appear radiatively cool against the warm lower atmospheric thermal emissions. The reduction in upwelling thermal flux is a function of both the total cloud ice content and mean crystal size. Radiometric measurements made at multiple widely spaced frequencies permit flux variations caused by changes in crystal size to be distinguished from changes in ice content, and polarized measurements can be used to constrain mean crystal shape. The goal of the cloud ice radiometry program is to further develop and validate this technique of characterizing cirrus. A multi-frequency radiometer is being designed to support airborne science and

  16. Submillimeter-Wave Cloud Ice Radiometry

    NASA Technical Reports Server (NTRS)

    Walter, Steven J.

    1999-01-01

    Submillimeter-wave cloud ice radiometry is a new and innovative technique for characterizing cirrus ice clouds. Cirrus clouds affect Earth's climate and hydrological cycle by reflecting incoming solar energy, trapping outgoing IR radiation, sublimating into vapor, and influencing atmospheric circulation. Since uncertainties in the global distribution of cloud ice restrict the accuracy of both climate and weather models, successful development of this technique could provide a valuable tool for investigating how clouds affect climate and weather. Cloud ice radiometry could fill an important gap in the observational capabilities of existing and planned Earth-observing systems. Using submillimeter-wave radiometry to retrieve properties of ice clouds can be understood with a simple model. There are a number of submillimeter-wavelength spectral regions where the upper troposphere is transparent. At lower tropospheric altitudes water vapor emits a relatively uniform flux of thermal radiation. When cirrus clouds are present, they scatter a portion of the upwelling flux of submillimeter-wavelength radiation back towards the Earth as shown in the diagram, thus reducing the upward flux o f energy. Hence, the power received by a down-looking radiometer decreases when a cirrus cloud passes through the field of view causing the cirrus cloud to appear radiatively cool against the warm lower atmospheric thermal emissions. The reduction in upwelling thermal flux is a function of both the total cloud ice content and mean crystal size. Radiometric measurements made at multiple widely spaced frequencies permit flux variations caused by changes in crystal size to be distinguished from changes in ice content, and polarized measurements can be used to constrain mean crystal shape. The goal of the cloud ice radiometry program is to further develop and validate this technique of characterizing cirrus. A multi-frequency radiometer is being designed to support airborne science and

  17. Dust ice nuclei effects on cirrus clouds

    NASA Astrophysics Data System (ADS)

    Kuebbeler, M.; Lohmann, U.; Hendricks, J.; Kärcher, B.

    2013-04-01

    In order to study aerosol-cloud interactions in cirrus clouds we apply a new multiple-mode ice microphysical scheme to the general circulation model ECHAM5-HAM. The multiple-mode ice microphysical scheme allows to analyse the competition between homogeneous freezing of solution droplets, deposition nucleation of pure dust particles, immersion freezing of coated dust particles and pre-existing ice. We base the freezing efficiencies of coated and pure dust particles on most recent laboratory data. The effect of pre-existing ice, which was neglected in previous ice nucleation parameterizations, is to deplete water vapour by depositional growth and thus prevent homogeneous and heterogeneous freezing from occurring. In a first step, we extensively tested the model and validated the results against in-situ measurements from various aircraft campaigns. The results compare well with observations; properties like ice crystal size and number concentration as well as supersaturation are predicted within the observational spread. We find that heterogeneous nucleation on mineral dust particles and the consideration of pre-existing ice in the nucleation process may lead to significant effects: globally, ice crystal number and mass are reduced by 10% and 5%, whereas the ice crystals size is increased by 3%. The reductions in ice crystal number are most pronounced in the tropics and mid-latitudes on the Northern Hemisphere. While changes in the microphysical and radiative properties of cirrus clouds in the tropics are mostly driven by considering pre-existing ice, changes in the northern hemispheric mid-latitudes mainly result from heterogeneous nucleation. The so called negative Twomey-effect in cirrus clouds is represented in ECHAM5-HAM. The net change in the radiation budget is -0.94 W m-2, implying that both, heterogeneous nucleation on dust and pre-existing ice have the potential to modulate cirrus properties in climate simulations and thus should be considered in future

  18. Dust ice nuclei effects on cirrus clouds

    NASA Astrophysics Data System (ADS)

    Kuebbeler, M.; Lohmann, U.; Hendricks, J.; Kärcher, B.

    2014-03-01

    In order to study aerosol-cloud interactions in cirrus clouds, we apply a new multiple-mode ice microphysical scheme to the general circulation model ECHAM5-HAM. The multiple-mode ice microphysical scheme allows for analysis of the competition between homogeneous freezing of solution droplets, deposition nucleation of pure dust particles, and immersion freezing of coated dust particles and pre-existing ice. We base the freezing efficiencies of coated and pure dust particles on the most recent laboratory data. The effect of pre-existing ice, which has been neglected in previous ice nucleation parameterizations, is to deplete water vapour by depositional growth and thus prevent homogeneous and heterogeneous freezing from occurring. As a first step, we extensively tested the model and validated the results against in situ measurements from various aircraft campaigns. The results compare well with observations; properties such as ice crystal size and number concentration as well as supersaturation are predicted within the observational spread. We find that heterogeneous nucleation on mineral dust particles and the consideration of pre-existing ice in the nucleation process may lead to significant effects: globally, ice crystal number and mass are reduced by 10 and 5%, whereas the ice crystals' size is increased by 3%. The reductions in ice crystal number are most pronounced in the tropics and mid-latitudes in the Northern Hemisphere. While changes in the microphysical and radiative properties of cirrus clouds in the tropics are mostly driven by considering pre-existing ice, changes in the northern hemispheric mid-latitudes mainly result from heterogeneous nucleation. The so-called negative Twomey effect in cirrus clouds is represented in ECHAM5-HAM. The net change in the radiation budget is -0.94 W m-2, implying that both heterogeneous nucleation on dust and pre-existing ice have the potential to modulate cirrus properties in climate simulations and thus should be

  19. Ice Nucleating Particles and their Role in California Winter Clouds

    NASA Astrophysics Data System (ADS)

    DeMott, P. J.; Prather, K. A.; Hill, T. C. J.; McCluskey, C. S.; Levin, E. J.; Suski, K. J.; Creamean, J.; Collins, D. B.; Martin, A.; Cornwell, G.; Al-Mashat, H.; Rosenfeld, D.; Leung, L. R.; Comstock, J. M.; Tomlinson, J. M.; Kreidenweis, S. M.; Petters, M. D.

    2014-12-01

    Field studies are providing the opportunity to characterize ice nucleating particle (INP) number concentrations, their varied sources, and to examine their influence on ice formation and precipitation processes in winter clouds in California. Aerosol sources that may influence orographic cloud properties in California include pollution, marine aerosols, and transported dusts. Vertical stratification affects the role of different aerosol types. Boundary layer dust and pollution in Central Valley locations may influence cloud properties at times, but may be decoupled from cloud layers at other times or be restricted in affecting clouds by the Sierra barrier jet phenomenon. Marine layers may sometimes be lifted over topography to influence clouds. Finally, long range transported dust/biological particles may directly enter upper cloud levels to act as the trigger for ice initiation. We present analyses of INP number concentrations, INP chemical composition, and related data collected from flights on the DOE G-1 aircraft during the CalWater 1 field study in winter 2011. Sampling of mostly marine boundary layer INP during the surface-based BBACPAX (Bodega Bay Aerosol-Cloud-Precipitation in Atmospheric rivers eXperiment) study in 2014 included first sampling with an online method for measuring the mass spectral composition of INP, and new immersion freezing INP measurements extending to the warm temperature limit of heterogeneous ice formation. Studies reveal the strong influence of long range transported aerosols on INP populations and typically lower INP concentrations in marine air layers. Plans for new studies including G-1 aircraft flights during the ACAPEX (ARM Cloud Aerosol Precipitation Experiment) study, overlapping with ground-based measurements in the CalWater-2 campaign in winter 2015 will be introduced. Analyses are being applied toward numerical modeling studies of aerosol-cloud-precipitation interactions in California, presented separately in this session.

  20. 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.

  1. Observational Evidence Against Mountain-Wave Generation of Ice Nuclei as a Prerequisite for the Formation of Three Solid Nitric Acid Polar Stratospheric Clouds Observed in the Arctic in Early December 1999

    NASA Technical Reports Server (NTRS)

    Pagan, Kathy L.; Tabazadeh, Azadeh; Drdla, Katja; Hervig, Mark E.; Eckermann, Stephen D.; Browell, Edward V.; Legg, Marion J.; Foschi, Patricia G.

    2004-01-01

    A number of recently published papers suggest that mountain-wave activity in the stratosphere, producing ice particles when temperatures drop below the ice frost point, may be the primary source of large NAT particles. In this paper we use measurements from the Advanced Very High Resolution Radiometer (AVHRR) instruments on board the National Oceanic and Atmospheric Administration (NOAA) polar-orbiting satellites to map out regions of ice clouds produced by stratospheric mountain-wave activity inside the Arctic vortex. Lidar observations from three DC-8 flights in early December 1999 show the presence of solid nitric acid (Type Ia or NAT) polar stratospheric clouds (PSCs). By using back trajectories and superimposing the position maps on the AVHRR cloud imagery products, we show that these observed NAT clouds could not have originated at locations of high-amplitude mountain-wave activity. We also show that mountain-wave PSC climatology data and Mountain Wave Forecast Model 2.0 (MWFM-2) raw hemispheric ray and grid box averaged hemispheric wave temperature amplitude hindcast data from the same time period are in agreement with the AVHRR data. Our results show that ice cloud formation in mountain waves cannot explain how at least three large scale NAT clouds were formed in the stratosphere in early December 1999.

  2. Observational Evidence Against Mountain-Wave Generation of Ice Nuclei as a Prerequisite for the Formation of Three Solid Nitric Acid Polar Stratospheric Clouds Observed in the Arctic in Early December 1999

    NASA Technical Reports Server (NTRS)

    Pagan, Kathy L.; Tabazadeh, Azadeh; Drdla, Katja; Hervig, Mark E.; Eckermann, Stephen D.; Browell, Edward V.; Legg, Marion J.; Foschi, Patricia G.

    2004-01-01

    A number of recently published papers suggest that mountain-wave activity in the stratosphere, producing ice particles when temperatures drop below the ice frost point, may be the primary source of large NAT particles. In this paper we use measurements from the Advanced Very High Resolution Radiometer (AVHRR) instruments on board the National Oceanic and Atmospheric Administration (NOAA) polar-orbiting satellites to map out regions of ice clouds produced by stratospheric mountain-wave activity inside the Arctic vortex. Lidar observations from three DC-8 flights in early December 1999 show the presence of solid nitric acid (Type Ia or NAT) polar stratospheric clouds (PSCs). By using back trajectories and superimposing the position maps on the AVHRR cloud imagery products, we show that these observed NAT clouds could not have originated at locations of high-amplitude mountain-wave activity. We also show that mountain-wave PSC climatology data and Mountain Wave Forecast Model 2.0 (MWFM-2) raw hemispheric ray and grid box averaged hemispheric wave temperature amplitude hindcast data from the same time period are in agreement with the AVHRR data. Our results show that ice cloud formation in mountain waves cannot explain how at least three large scale NAT clouds were formed in the stratosphere in early December 1999.

  3. Comparison of modern icing cloud instruments

    NASA Technical Reports Server (NTRS)

    Takeuchi, D. M.; Jahnsen, L. J.; Callander, S. M.; Humbert, M. C.

    1983-01-01

    Intercomparison tests with Particle Measuring Systems (PMS) were conducted. Cloud liquid water content (LWC) measurements were also taken with a Johnson and Williams (JW) hot-wire device and an icing rate device (Leigh IDS). Tests include varying cloud LWC (0.5 to 5 au gm), cloud median volume diameter (MVD) (15 to 26 microns), temperature (-29 to 20 C), and air speeds (50 to 285 mph). Comparisons were based upon evaluating probe estimates of cloud LWC and median volume diameter for given tunnel settings. Variations of plus or minus 10% and plus or minus 5% in LWC and MVD, respectively, were determined of spray clouds between test made at given tunnel settings (fixed LWC, MVD, and air speed) indicating cloud conditions were highly reproducible. Although LWC measurements from JW and Leigh devices were consistent with tunnel values, individual probe measurements either consistently over or underestimated tunnel values by factors ranging from about 0.2 to 2. Range amounted to a factor of 6 differences between LWC estimates of probes for given cloud conditions. For given cloud conditions, estimates of cloud MVD between probes were within plus or minus 3 microns and 93% of the test cases. Measurements overestimated tunnel values in the range between 10 to 20 microns. The need for improving currently used calibration procedures was indicated. Establishment of test facility (or facilities) such as an icing tunnel where instruments can be calibrated against known cloud standards would be a logical choice.

  4. Ice Clouds in Martian Arctic (Accelerated Movie)

    NASA Technical Reports Server (NTRS)

    2008-01-01

    Clouds scoot across the Martian sky in a movie clip consisting of 10 frames taken by the Surface Stereo Imager on NASA's Phoenix Mars Lander.

    This clip accelerates the motion. The camera took these 10 frames over a 10-minute period from 2:52 p.m. to 3:02 p.m. local solar time at the Phoenix site during Sol 94 (Aug. 29), the 94th Martian day since landing.

    Particles of water-ice make up these clouds, like ice-crystal cirrus clouds on Earth. Ice hazes have been common at the Phoenix site in recent days.

    The camera took these images as part of a campaign by the Phoenix team to see clouds and track winds. The view is toward slightly west of due south, so the clouds are moving westward or west-northwestward.

    The clouds are a dramatic visualization of the Martian water cycle. The water vapor comes off the north pole during the peak of summer. The northern-Mars summer has just passed its peak water-vapor abundance at the Phoenix site. The atmospheric water is available to form into clouds, fog and frost, such as the lander has been observing recently.

    The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

  5. Observing the Cloud Response to Arctic Sea Ice Loss

    NASA Astrophysics Data System (ADS)

    Morrison, Ariel L.; Kay, Jennifer E.; Chepfer, Helene; Guzman, Rodrigo

    2017-04-01

    Observed sea ice loss since 1979 is the most visible signal of anthropogenic Arctic warming. While the influence of clouds on Arctic sea ice is known, the influence of sea ice loss on Arctic clouds is challenging to detect and has never been isolated. Here, we use 8 years (2008 - 2015) of spaceborne lidar observations from the CALIPSO satellite to isolate the cloud response to sea ice loss from cloud changes due to atmospheric circulation. We focus on the liquid cloud response to observed sea ice loss because liquid-containing clouds are the most important cloud type for sea ice melt and growth. There is no observed change in liquid clouds in response to sea ice loss during summer. The absence of a summer cloud response indicates that a summer cloud-sea ice feedback cannot be relied upon to slow the rate of sea ice loss. In contrast, we find more liquid clouds over open water than over sea ice during fall. Thus, human-caused sea ice loss is increasing fall clouds over the Arctic Ocean. Since we robustly isolate the cloud response to sea ice loss, we can for the first time attribute an Arctic cloud change to human activities.

  6. Nowcasting Aircraft Icing Conditions in the Presence of Multilayered Clouds Using Meteorological Satellite Data

    NASA Technical Reports Server (NTRS)

    Spangenberg, Douglas A.; Minnis, Patrick; Smith, William L.; Chang, Fu-Lung

    2011-01-01

    Cloud properties retrieved from satellite data are used to diagnose aircraft icing threat in single layer and multilayered ice-over-liquid clouds. The algorithms are being applied in real time to the Geostationary Operational Environmental Satellite (GOES) data over the CONUS with multilayer data available over the eastern CONUS. METEOSAT data are also used to retrieve icing conditions over western Europe. The icing algorithm s methodology and validation are discussed along with future enhancements and plans. The icing risk product is available in image and digital formats on NASA Langley s Cloud and Radiation Products web site, http://wwwangler. larc.nasa.gov.

  7. Investigating the contribution of secondary ice production to in-cloud ice crystal numbers

    NASA Astrophysics Data System (ADS)

    Sullivan, S. C.; Hoose, C.; Nenes, A.

    2017-09-01

    In-cloud measurements of ice crystal number concentration can be orders of magnitude higher than the precloud ice nucleating particle number concentration. This disparity may be explained with secondary ice production processes. Several such processes have been proposed, but their relative importance and even the exact physics are not well known. In this work, a six-hydrometeor-class parcel model is developed to investigate the ice crystal number enhancement, both its bounds and its value for different cloud states, from rime splintering and breakup upon graupel-graupel collision. The model also includes ice aggregation and droplet coalescence, ice hydrometeor nonsphericity, and a time delay formulation for hydrometeor growth. Conditions to maximize the breakup contribution, as well as the effects of nonsphericity and turbulence, are discussed. We find that the largest enhancement of ice crystal number occurs for "intermediate" conditions, characterized by moderate updrafts and activation and nucleation rates. In this case, vertical motion is strong enough, and new hydrometeor formation limited enough, to sustain supersaturation as hydrometeors grow to larger sizes. After these larger hydrometeors form at sufficient number concentrations, the ice crystal number can be enhanced by a factor of 104 in some cases relative to the number generated by primary ice nucleation alone. Excluding ice hydrometeor nonsphericity limits secondary production significantly, and the parcel updraft can modulate it by about an order of magnitude.

  8. Passive Remote Sensing of Cloud Ice Particles

    NASA Technical Reports Server (NTRS)

    Skofronick-Jackson, Gail; Wang, James R.

    2004-01-01

    Hurricanes, blizzards and other weather events are important to understand not only for disaster preparation, but also to track the global energy balance and to improve weather and climate forecasts. For several decades, passive radiometers and active radars on aircraft and satellites have been employed to remotely sense rain rates and the properties of liquid particles. In the past few years the relationships between frozen particles and millimeter-wave observations have become understood well enough to estimate the properties of ice in clouds. A brief background of passive remote sensing of precipitation will be presented followed by a focused discussion of recent research at NASA Goddard Space Flight Center estimating the properties of frozen particles in clouds. The retrievals are for (1) ice that will eventually melt into rain, (2) for solid precipitation falling in northern climates, and (3) cirrus ice clouds. The electromagnetic absorption and scattering properties and differences of liquid rain versus frozen particles will be summarized for frequencies from 6 to 340+ GHz. Challenges of this work including surface emissivity variability, non-linear and under-constrained relationships, and frozen particle unknowns will be discussed. Retrieved cloud particle contents and size distributions for ice above the melting layer in hurricanes, retrieved snowfall rates for a blizzard, and cirrus ice estimates will be presented. Future directions of this work will also be described.

  9. Salts as Water Ice Cloud Nuclei on Mars

    NASA Astrophysics Data System (ADS)

    Santiago-Materese, D.; Chuang, P. Y.; Iraci, L. T.

    2015-12-01

    In recent years, observations of the Martian surface have indicated the presence of chlorine-bearing minerals, including perchlorates, on the surface of Mars. These salt-bearing minerals would potentially be source material for dust lofted from the surface into the Martian atmosphere, thus providing potential nucleation sites for water ice clouds. Considering that salts play an important role in cloud formation on Earth, it is important to have a better understanding of how salt may affect nucleation processes under Mars-like conditions. We perform laboratory experiments to examine water ice nucleation onto salt substrates. We use a vacuum chamber that simulates the temperatures and pressures observed of the Martian atmosphere. Using infrared spectroscopy we measure the onset of nucleation and calculate the temperature-dependent critical saturation ratio (Scrit) for water ice nucleation onto salts, specifically sodium chloride and sodium perchlorate. Preliminary results of Scrit values for water ice nucleation on sodium chloride show a negative temperature dependence, as did other substrates from previous experiments. Values of Scrit are useful for understanding the realistic conditions under which water ice clouds may form on Mars, and can be used in climate models simulating clouds on Mars.

  10. The Backscattering Linear Depolarization Ratio of Ice Clouds Composed of Small Ice Crystals

    NASA Astrophysics Data System (ADS)

    Schnaiter, M.; Abdelmonem, A.; Benz, S.; Leisner, T.; Möhler, O.; Wagner, R.

    2009-04-01

    The importance of small ice crystals (< 50 µm) for cirrus cloud radiative properties is a matter of controversial debate, mainly because some measurements seemed to clearly overestimate the number concentrations of small ice particles due to particle shattering on the instrument inlets. On the other hand, there is no doubt that small micrometer-sized ice crystals dominate the particle size distributions of contrails and cirrus clouds emerging from contrails. Polarisation LIDAR is frequently used to investigate the microphysics of contrails and contrail cirrus remotely. These investigations reveal unusually high maximum linear depolarization ratios of 0.5 - 0.7. The knowledge of the link between ice crystal depolarization and their size and shape is a prerequisite for the interpretation of these LIDAR data. Since young contrails consist of relatively small ice crystals with sizes typically less than 10 µm, the scattering matrix of these non-spherical particles can be calculated by the T-matrix method. In order to investigate the relation between the linear backscattering depolarization ratio and the microphysical properties of small ice particles that closely resemble those found in contrails and young cirrus, we started to run dedicated ice crystal nucleation and growth experiments at the large cloud simulation chamber AIDA of Forschungszentrum Karlsruhe. Such studies became feasible after the installation of the new in situ laser scattering and depolarization set up SIMONE at the chamber in 2006. The light scattering measurements are analyzed in the context of the microphysical properties of the ice clouds measured by optical cloud particle spectrometers, single particle imaging, and in situ infrared extinction spectroscopy. We compare our experimental results with theoretical results generated by the T-matrix method for finite cylinders. The results give new insight into the scattering depolarisation properties of small ice crystals grown under simulated

  11. Determination of Ice Cloud Models Using MODIS and MISR Data

    NASA Technical Reports Server (NTRS)

    Xie, Yu; Yang, Ping; Kattawar, George W.; Minnis, Patrick; Hu, Yongxiang; Wu, Dong L.

    2012-01-01

    Representation of ice clouds in radiative transfer simulations is subject to uncertainties associated with the shapes and sizes of ice crystals within cirrus clouds. In this study, we examined several ice cloud models consisting of smooth, roughened, homogeneous and inhomogeneous hexagonal ice crystals with various aspect ratios. The sensitivity of the bulk scattering properties and solar reflectances of cirrus clouds to specific ice cloud models is investigated using the improved geometric optics method (IGOM) and the discrete ordinates radiative transfer (DISORT) model. The ice crystal habit fractions in the ice cloud model may significantly affect the simulations of cloud reflectances. A new algorithm was developed to help determine an appropriate ice cloud model for application to the satellite-based retrieval of ice cloud properties. The ice cloud particle size retrieved from Moderate Resolution Imaging Spectroradiometer (MODIS) data, collocated with Multi-angle Imaging Spectroradiometer (MISR) observations, is used to infer the optical thicknesses of ice clouds for nine MISR viewing angles. The relative differences between view-dependent cloud optical thickness and the averaged value over the nine MISR viewing angles can vary from -0.5 to 0.5 and are used to evaluate the ice cloud models. In the case for 2 July 2009, the ice cloud model with mixed ice crystal habits is the best fit to the observations (the root mean square (RMS) error of cloud optical thickness reaches 0.365). This ice cloud model also produces consistent cloud property retrievals for the nine MISR viewing configurations within the measurement uncertainties.

  12. Cloud ice caused by atmospheric mineral dust - Part 1: Parameterization of ice nuclei concentration in the NMME-DREAM model

    NASA Astrophysics Data System (ADS)

    Nickovic, Slobodan; Cvetkovic, Bojan; Madonna, Fabio; Rosoldi, Marco; Pejanovic, Goran; Petkovic, Slavko; Nikolic, Jugoslav

    2016-09-01

    Dust aerosols are very efficient ice nuclei, important for heterogeneous cloud glaciation even in regions distant from desert sources. A new generation of ice nucleation parameterizations, including dust as an ice nucleation agent, opens the way towards a more accurate treatment of cold cloud formation in atmospheric models. Using such parameterizations, we have developed a regional dust-atmospheric modelling system capable of predicting, in real time, dust-induced ice nucleation. We executed the model with the added ice nucleation component over the Mediterranean region, exposed to moderate Saharan dust transport, over two periods lasting 15 and 9 days, respectively. The model results were compared against satellite and ground-based cloud-ice-related measurements, provided by SEVIRI (Spinning Enhanced Visible and InfraRed Imager) and the CNR-IMAA Atmospheric Observatory (CIAO) in Potenza, southern Italy. The predicted ice nuclei concentration showed a reasonable level of agreement when compared against the observed spatial and temporal patterns of cloud ice water. The developed methodology permits the use of ice nuclei as input into the cloud microphysics schemes of atmospheric models, assuming that this approach could improve the predictions of cloud formation and associated precipitation.

  13. Dual-Polarised Doppler X-band Radar Observations of Mixed Phased Clouds from the UK's Ice in Clouds Experiment-Dust (ICE-D)

    NASA Astrophysics Data System (ADS)

    Neely, R. R., III; Bennett, L.; Dufton, D.; Blyth, A. M.; Gallagher, M. W.

    2016-12-01

    Here we present dual-polarised Doppler X-band radar and in situ observations of convective, altocumulus and altostratus clouds relatively close to the Saharan desert to examine the impact of dust on the formation of ice and precipitation. These initial results come the UK's Ice in Clouds Experiment - Dust (UK ICE-D). UK ICE-D was an aircraft and ground-based project based in Cape Verde off the coast of Senegal, Africa during August 2015. The overall goal of this experiment was to determine how desert dust affects primary nucleation of ice particles in convective and layer clouds as well as the subsequent development of precipitation and glaciation of the clouds. This was accomplished by making focused observations when dust was present in high concentrations and when almost no dust was present. Here we focus on examining the differences in hydrometeor types derived from the dual-polarised X-band radar observations observed in the high and low dust loadings with specific emphasis on the role of supercooled rain drops in these two situations.

  14. Dual-Polarised Doppler X-band Radar Observations of Mixed Phased Clouds from the UK's Ice in Clouds Experiment-Dust (ICE-D)

    NASA Astrophysics Data System (ADS)

    Neely, Ryan; Blyth, Alan; Bennett, Lindsay; Dufton, David; Cui, Zhiqiang; McQuaid, Jim; Price, Hannah; Murray, Benjamin; Huang, Yahui

    2016-04-01

    Here we present dual-polarised X-band radar and in situ observations of convective, altocumulus and altostratus clouds relatively close to the Sahara desert in order to examine the impact of dust on the formation of ice and precipitation. These initial results come the UK's Ice in Clouds Experiment - Dust (UK ICE-D). UK ICE-D was an aircraft and ground-based project based in Cape Verde off the coast of Senegal, Africa during August 2015. The overall goal of this experiment was to determine how desert dust affects primary nucleation of ice particles in convective and layer clouds as well as the subsequent development of precipitation and glaciation of the clouds. This was accomplished by making focused observations when dust was present in high concentrations and when almost no dust was present. Here we focus on examining the differences in hydrometeor types derived from the dual-polarised X-band radar observations observed in the high and low dust loadings with specific emphasis on the role of supercooled rain drops in these two situations.

  15. Dual-Polarised Doppler X-band Radar Observations of Mixed Phased Clouds from the UK's Ice in Clouds Experiment-Dust (ICE-D)

    NASA Astrophysics Data System (ADS)

    Neely, R. R., III; Blyth, A. M.; Bennett, L.; Dufton, D.; Cui, Z.; Huang, Y.

    2015-12-01

    Here we present dual-polarised Doppler X-band radar observations of convective, altocumulus and altostratus clouds relatively close to the Sahara desert in order to examine the impact of dust on the formation of ice and precipitation. These initial results come the UK's Ice in Clouds Experiment - Dust (UK ICE-D). UK ICE-D was an aircraft and ground-based project based in Cape Verde off the coast of Senegal, Africa during August 2015. The overall goal of this experiment was to determine how desert dust affects primary nucleation of ice particles in convective and layer clouds as well as the subsequent development of precipitation and glaciation of the clouds. This was accomplished by making focused observations when dust was present in high concentrations and when almost no dust was present. Here we focus on examining the differences in hydrometeor types derived from the dual-polarised X-band radar observations observed in the high and low dust loadings with specific emphasis on the role of supercooled rain drops in these two situations.

  16. Impact of Organic molecules on Ice Nucleation and Cloud Condensation

    NASA Astrophysics Data System (ADS)

    Sun, J.; Ariya, P.

    2004-05-01

    Atmospheric organic aerosols are suggested to be important players in cloud formation, since they serve as ice nuclei (IN) and cloud condensation nuclei (CCN). In this present study, we have attempted to determine the role of bioorganic matter (e.g., bacteria, fungi, and cellulose) in the cloud formation processes using a column version of the model NARCM-CLCM. The local model of the climate (LCM) is a one-dimensional version (column) of NARCM (Northern Aerosol Regional Climate Model). It focuses on one- dimensional (1-D) evolution of aerosol distributions within North America and it simulates deposition, and size distributions of aerosol particles in the region of interest. Bioaerosols are now being incorporated in the column version of NARCM. We mainly consider the dry and humid deposition of bioaerosols, the formation of ice crystals and precipitation. We will present our progress on the development of the new version. Moreover, we will simulate the interactions between the bioaerosols and the clouds and discuss our preliminary results of the impact of bioaerosols on cloud formation.

  17. Water Ice Clouds over the Northern Plains

    NASA Technical Reports Server (NTRS)

    2002-01-01

    (Released 14 May 2002) The Science This image, centered near 48.5 N and 240.5 W, displays splotchy water ice clouds that obscure the northern lowland plains in the region where the Viking 2 spacecraft landed. This image is far enough north to catch the edge of the north polar hood that develops during the northern winter. This is a cap of water and carbon dioxide ice clouds that form over the Martian north pole. As Mars progresses into northern spring, the persistent north polar hood ice clouds will dissipate and the surface viewing conditions will improve greatly. As the season develops, an equatorial belt of water ice clouds will form. This belt of water ice clouds is as characteristic of the Martian climate as the southern hemisphere summer dust storm season. Seasons on Mars have a dramatic effect on the state of the dynamic Martian atmosphere. The Story Muted in an almost air-brushed manner, this image doesn't have the crispness that most THEMIS images have. That's because clouds were rising over the surface of the red planet on the day this picture was taken. Finding clouds on Mars might remind us of conditions here on Earth, but these Martian clouds are made of frozen water and frozen carbon dioxide -- in other words, clouds of ice and 'dry ice.' Strange as that may sound, the clouds seen here form on a pretty regular basis at the north Martian pole during its winter season. As springtime comes to the northern hemisphere of Mars (and fall comes to the southern), these clouds will slowly disappear, and a nice belt of water ice clouds will form around the equator. So, if you were a THEMIS camera aimer, that might tell you when your best viewing conditions for different areas on Mars would be. As interesting as clear pictures of Martian landforms are, however, you wouldn't want to bypass the weather altogether. Pictures showing seasonal shifts are great for scientists to study, because they reveal a lot about the patterns of the Martian climate and the

  18. Water Ice Clouds over the Northern Plains

    NASA Technical Reports Server (NTRS)

    2002-01-01

    (Released 14 May 2002) The Science This image, centered near 48.5 N and 240.5 W, displays splotchy water ice clouds that obscure the northern lowland plains in the region where the Viking 2 spacecraft landed. This image is far enough north to catch the edge of the north polar hood that develops during the northern winter. This is a cap of water and carbon dioxide ice clouds that form over the Martian north pole. As Mars progresses into northern spring, the persistent north polar hood ice clouds will dissipate and the surface viewing conditions will improve greatly. As the season develops, an equatorial belt of water ice clouds will form. This belt of water ice clouds is as characteristic of the Martian climate as the southern hemisphere summer dust storm season. Seasons on Mars have a dramatic effect on the state of the dynamic Martian atmosphere. The Story Muted in an almost air-brushed manner, this image doesn't have the crispness that most THEMIS images have. That's because clouds were rising over the surface of the red planet on the day this picture was taken. Finding clouds on Mars might remind us of conditions here on Earth, but these Martian clouds are made of frozen water and frozen carbon dioxide -- in other words, clouds of ice and 'dry ice.' Strange as that may sound, the clouds seen here form on a pretty regular basis at the north Martian pole during its winter season. As springtime comes to the northern hemisphere of Mars (and fall comes to the southern), these clouds will slowly disappear, and a nice belt of water ice clouds will form around the equator. So, if you were a THEMIS camera aimer, that might tell you when your best viewing conditions for different areas on Mars would be. As interesting as clear pictures of Martian landforms are, however, you wouldn't want to bypass the weather altogether. Pictures showing seasonal shifts are great for scientists to study, because they reveal a lot about the patterns of the Martian climate and the

  19. An observational search for CO2 ice clouds on Mars

    NASA Technical Reports Server (NTRS)

    Bell, James F., III; Calvin, Wendy M.; Pollack, James B.; Crisp, David

    1993-01-01

    CO2 ice clouds were first directly identified on Mars by the Mariner 6 and 7 infrared spectrometer limb scans. These observations provided support for early theoretical modeling efforts of CO2 condensation. Mariner 9 IRIS temperature profiles of north polar hood clouds were interpreted as indicating that these clouds were composed of H2O ice at lower latitudes and CO2 ice at higher latitudes. The role of CO2 condensation on Mars has recently received increased attention because (1) Kasting's model results indicated that CO2 cloud condensation limits the magnitude of the proposed early Mars CO2/H2O greenhouse, and (2) Pollack el al.'s GCM results indicated that the formation of CO2 ice clouds is favorable at all polar latitudes during the fall and winter seasons. These latter authors have shown that CO2 clouds play an important role in the polar energy balance, as the amount of CO2 contained in the polar caps is constrained by a balance between latent heat release, heat advected from lower latitudes, and thermal emission to space. The polar hood clouds reduce the amount of CO2 condensation on the polar caps because they reduce the net emission to space. There have been many extensive laboratory spectroscopic studies of H2O and CO2 ices and frosts. In this study, we use results from these and other sources to search for the occurrence of diagnostic CO2 (and H2O) ice and/or frost absorption features in ground based near-infrared imaging spectroscopic data of Mars. Our primary goals are (1) to try to confirm the previous direct observations of CO2 clouds on Mars; (2) to determine the spatial extent, temporal variability, and composition (H2O/CO2 ratio) of any clouds detected; and (3) through radiative transfer modeling, to try to determine the mean particle size and optical depth of polar hood clouds, thus, assessing their role in the polar heat budget.

  20. Ice Cloud Properties in Ice-Over-Water Cloud Systems Using TRMM VIRS and TMI Data

    NASA Technical Reports Server (NTRS)

    Minnis, Patrick; Huang, Jianping; Lin, Bing; Yi, Yuhong; Arduini, Robert F.; Fan, Tai-Fang; Ayers, J. Kirk; Mace, Gerald G.

    2007-01-01

    A multi-layered cloud retrieval system (MCRS) is updated and used to estimate ice water path in maritime ice-over-water clouds using Visible and Infrared Scanner (VIRS) and TRMM Microwave Imager (TMI) measurements from the Tropical Rainfall Measuring Mission spacecraft between January and August 1998. Lookup tables of top-of-atmosphere 0.65- m reflectance are developed for ice-over-water cloud systems using radiative transfer calculations with various combinations of ice-over-water cloud layers. The liquid and ice water paths, LWP and IWP, respectively, are determined with the MCRS using these lookup tables with a combination of microwave (MW), visible (VIS), and infrared (IR) data. LWP, determined directly from the TMI MW data, is used to define the lower-level cloud properties to select the proper lookup table. The properties of the upper-level ice clouds, such as optical depth and effective size, are then derived using the Visible Infrared Solar-infrared Split-window Technique (VISST), which matches the VIRS IR, 3.9- m, and VIS data to the multilayer-cloud lookup table reflectances and a set of emittance parameterizations. Initial comparisons with surface-based radar retrievals suggest that this enhanced MCRS can significantly improve the accuracy and decrease the IWP in overlapped clouds by 42% and 13% compared to using the single-layer VISST and an earlier simplified MW-VIS-IR (MVI) differencing method, respectively, for ice-over-water cloud systems. The tropical distribution of ice-over-water clouds is the same as derived earlier from combined TMI and VIRS data, but the new values of IWP and optical depth are slightly larger than the older MVI values, and exceed those of single-layered layered clouds by 7% and 11%, respectively. The mean IWP from the MCRS is 8-14% greater than that retrieved from radar retrievals of overlapped clouds over two surface sites and the standard deviations of the differences are similar to those for single-layered clouds. Examples

  1. Slow wave dynamics stalls tropical tropopause ice clouds

    NASA Astrophysics Data System (ADS)

    Spichtinger, Peter; Krämer, Martina; Borrmann, Stephan

    2010-05-01

    Water vapour is the most important natural green house gas. However, in the stratosphere an increase in water vapour would possibly result in a cooling. The major entrance of trace substances into the stratosphere is the tropical tropopause layer (TTL), localized between the main level of convective outflow, 150 hPa, and 70 hPa. The TTL water vapour budget, and thus the exchange with the stratosphere, depends crucially on the occurrence and properties of ice clouds in this cold region (T < 200 K). It is believed that homogeneous freezing of liquid solution particles, which predominate the particle population, is the preferred pathway of ice formation. High water vapour supersaturation with respect to ice is required to initiate homogeneous ice nucleation. The number of emerging ice crystals depends on temperature and the ambient relative humidity over ice (RHi). Strong increase in RHi due to rising vertical velocity will produce large amounts of ice crystals. In the TTL, very slow large-scale updraughts prevail (≤ 0.01 m/s), which would lead to low ice crystal concentrations (≤ 0.1cm-3). However, tropical deep convection initiates intrinsic gravity waves and consequently, we would expect much higher vertical velocities and therefore higher ice crystal number concentrations. Since the many ice crystals rapidly grow by water vapour diffusion it is also expected that the initially high ice supersaturation quickly reduces to saturation after ice formation. Contrarily, during the last years high and persistent ice supersaturations were observed in the cold TTL in several airborne field campaigns inside and outside of ice clouds (Peter et al., 2006), creating a discussion called the 'supersaturation puzzle'. A step forward in that discussion was made recently: Krämer et al. (2009) observed ice crystal concentrations much lower than expected (most often < 0.1cm-3), but consistent with the measured high supersaturations. These observations turned the 'supersaturation

  2. Radar and radiation properties of ice clouds

    SciTech Connect

    Atlas, D.; Heymsfield, A.J.

    1995-11-01

    The authors derive relations of the equivalent radar reflectivity Z{sub e} and extinction coefficient a of ice clouds and confirm the theory by in situ aircraft observations during the First International Satellite Cloud Climatology Project Regional Experiment. Equivalent radar reflectivity Z{sub e} is a function of ice water content Wand a moment of the size distribution such as the median volume diameter D{sub 0}. Stratification of the data by D{sub 0} provides a set of W-Z{sub e} relations from which one may deduce the dependence of particle density on size. This relation is close to that of Brown and Francis and provides confidence in the methodology of estimating particle size and mass. The authors find that there is no universal W-Z{sub e} relation, due both to large scatter and systematic shifts in particle size from day to day and cloud to cloud. These variations manifest the normal changes in ice crystal growth. The result is that, with the exception of temperatures less than -40{degrees}C, temperature cannot be used to reliably parameterize the particle size as has been previously suggested. To do so is to risk large possible systematic errors in retrievals. Even if one could measure monthly averages of ice water content, this is inadequate to estimate the monthly radiative effect because of the nonlinearity between the two. The authors show that a sizable fraction of radiatively significant clouds would be missed at a radar threshold of -30 dBZ, the value proposed for a spaceborne cloud-profiling radar. 29 refs., 13 figs., 3 tabs.

  3. Waves on White: Ice or Clouds?

    NASA Technical Reports Server (NTRS)

    2005-01-01

    As it passed over Antarctica on December 16, 2004, the Multi-angle Imaging SpectroRadiometer (MISR) on NASA's Terra satellite captured this image showing a wavy pattern in a field of white. At most other latitudes, such wavy patterns would likely indicate stratus or stratocumulus clouds. MISR, however, saw something different. By using information from several of its multiple cameras (each of which views the Earth's surface from a different angle), MISR was able to tell that what looked like a wavy cloud pattern was actually a wavy pattern on the ice surface. One of MISR's cloud classification products, the Angular Signature Cloud Mask (ASCM), correctly identified the rippled area as being at the surface.

    In this image pair, the view from MISR's most oblique backward-viewing camera is on the left, and the color-coded image on the right shows the results of the ASCM. The colors represent the level of certainty in the classification. Areas that were classed as cloudy with high confidence are white, and areas where the confidence was lower are yellow; dark blue shows confidently clear areas, while light blue indicates clear with lower confidence. The ASCM works particularly well at detecting clouds over snow and ice, but also works well over ocean and land. The rippled area on the surface which could have been mistaken for clouds are actually sastrugi -- long wavelike ridges of snow formed by the wind and found on the polar plains. Usually sastrugi are only several centimeters high and several meters apart, but large portions of East Antarctica are covered by mega-sastrugi ice fields, with dune-like features as high as four meters separated by two to five kilometers. The mega-sastrugi fields are a result of unusual snow accumulation and redistribution processes influenced by the prevailing winds and climate conditions. MISR imagery indicates that these mega sastrugi were stationary features between 2002 and 2004.

    Being able to distinguish clouds from

  4. Cloud formation in substellar atmospheres

    NASA Astrophysics Data System (ADS)

    Helling, Christiane

    2009-02-01

    Clouds seem like an every-day experience. But-do we know how clouds form on brown dwarfs and extra-solar planets? How do they look like? Can we see them? What are they composed of? Cloud formation is an old-fashioned but still outstanding problem for the Earth atmosphere, and it has turned into a challenge for the modelling of brown dwarf and exo-planetary atmospheres. Cloud formation imposes strong feedbacks on the atmospheric structure, not only due to the clouds own opacity, but also due to the depletion of the gas phase, possibly leaving behind a dynamic and still supersaturated atmosphere. I summarise the different approaches taken to model cloud formation in substellar atmospheres and workout their differences. Focusing on the phase-non-equilibrium approach to cloud formation, I demonstrate the inside we gain from detailed microphysical modelling on for instance the material composition and grain size distribution inside the cloud layer on a Brown Dwarf atmosphere. A comparison study on four different cloud approaches in Brown Dwarf atmosphere simulations demonstrates possible uncertainties in interpretation of observational data.

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

    DOE PAGES

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

    2017-01-31

    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

  6. Cloud Susceptibilities to Ice Nuclei: Microphysical Effects and Dynamical Feedbacks

    NASA Astrophysics Data System (ADS)

    Paukert, Marco; Hoose, Corinna

    2015-04-01

    The impact of aerosols on cloud properties is currently not well established. This is largely attributed to the interdependencies of aerosols and cloud microphysical processes, among which primary ice formation contributes to considerable uncertainties. Although it is known that in a large range of thermodynamic conditions aerosol particles are required to initiate ice formation, identifying and characterizing the effect of specific ice nuclei is among current scientific efforts. Here we attempt to quantify the change of cloud properties with varying aerosol background concentrations. We adapt the concept of susceptibilities for mixed-phase and ice clouds, defining the susceptibility as the derivation of a macrophysical quantity with respect to ice nucleating aerosol concentrations. A focus of our study is the use of different model approaches in order to identify the distinct contributions of both cloud microphysics and cloud-dynamical feedbacks to the overall susceptibility. The classical method is the direct comparison of two independent model runs, where the whole range of microphysical and cloud-dynamical feedbacks contributes to different cloud properties in a perturbed simulation. Our alternative method relies on a single simulation which incorporates multiple executions of the microphysical scheme within the same time step, each "perturbed microphysics" scheme with varying aerosol concentrations and an additional set of cloud particle tracers. Since in the latter case the model dynamics are held constant and only microphysical feedbacks contribute to the properties of perturbed clouds, we can distinguish between the pure microphysical effect and the dynamical enhancement or suppression. For a persistent Arctic mixed-phase stratocumulus cloud layer which is expected to be particularly sensitive to feedback cycles, we show an enhancement of the cloud susceptibility to ice nucleating particles by dynamics of around 50%, but a decay of the enhancement with time

  7. Ice cloud processing of ultra-viscous/glassy aerosol particles leads to enhanced ice nucleation ability

    NASA Astrophysics Data System (ADS)

    Wagner, R.; Möhler, O.; Saathoff, H.; Schnaiter, M.; Skrotzki, J.; Leisner, T.; Wilson, T. W.; Malkin, T. L.; Murray, B. J.

    2012-09-01

    The ice nucleation potential of airborne glassy aqueous aerosol particles has been investigated by controlled expansion cooling cycles in the AIDA aerosol and cloud chamber of the Karlsruhe Institute of Technology at temperatures between 247 and 216 K. Four different solutes were used as proxies for oxygenated organic matter found in the atmosphere: raffinose, 4-hydroxy-3-methoxy-DL-mandelic acid (HMMA), levoglucosan, and a multi-component mixture of raffinose with five dicarboxylic acids and ammonium sulphate. Similar to previous experiments with citric acid aerosols, all particles were found to nucleate ice heterogeneously before reaching the homogeneous freezing threshold provided that the freezing cycles were started well below the respective glass transition temperatures of the compounds; this is discussed in detail in a separate article. In this contribution, we identify a further mechanism by which glassy aerosols can promote ice nucleation below the homogeneous freezing limit. If the glassy aerosol particles are probed in freezing cycles started only a few degrees below their respective glass transition temperatures, they enter the liquid regime of the state diagram upon increasing relative humidity (moisture-induced glass-to-liquid transition) before being able to act as heterogeneous ice nuclei. Ice formation then only occurs by homogeneous freezing at elevated supersaturation levels. When ice forms the remaining solution freeze concentrates and re-vitrifies. If these ice cloud processed glassy aerosol particles are then probed in a second freezing cycle at the same temperature, they catalyse ice formation at a supersaturation threshold between 5 and 30% with respect to ice. By analogy with the enhanced ice nucleation ability of insoluble ice nuclei like mineral dusts after they nucleate ice once, we refer to this phenomenon as pre-activation. We propose a number of possible explanations for why glassy aerosol particles that have re-vitrified in contact

  8. Ice cloud processing of ultra-viscous/glassy aerosol particles leads to enhanced ice nucleation ability

    NASA Astrophysics Data System (ADS)

    Wagner, R.; Möhler, O.; Saathoff, H.; Schnaiter, M.; Skrotzki, J.; Leisner, T.; Wilson, T. W.; Malkin, T. L.; Murray, B. J.

    2012-04-01

    The ice nucleation potential of airborne glassy aqueous aerosol particles has been investigated by controlled expansion cooling cycles in the AIDA aerosol and cloud chamber of the Karlsruhe Institute of Technology at temperatures between 247 and 216 K. Four different solutes were used as proxies for oxygenated organic matter found in the atmosphere: raffinose, 4-hydroxy-3-methoxy-DL-mandelic acid (HMMA), levoglucosan, and a multi-component mixture of raffinose with five dicarboxylic acids and ammonium sulphate. Similar to previous experiments with citric acid aerosols, all particles were found to nucleate ice heterogeneously before reaching the homogeneous freezing threshold provided that the freezing cycles were started well below the respective glass transition temperatures of the compounds; this is discussed in detail in a separate article. In this contribution, we identify a further mechanism by which glassy aerosols can promote ice nucleation below the homogeneous freezing limit. If the glassy aerosol particles are probed in freezing cycles started only a few degrees below their respective glass transition temperatures, they enter the liquid regime of the state diagram upon increasing relative humidity (moisture-induced glass-to-liquid transition) before being able to act as heterogeneous ice nuclei. Ice formation then only occurs by homogeneous freezing at elevated supersaturation levels. When ice forms the remaining solution freeze concentrates and re-vitrifies. If these ice cloud processed glassy aerosol particles are then probed in a second freezing cycle at the same temperature, they catalyse ice formation at a supersaturation threshold between 5 and 30% with respect to ice. By analogy with the enhanced ice nucleation ability of insoluble ice nuclei like mineral dusts after they nucleate ice once, we refer to this phenomenon as pre-activation. We propose a number of possible explanations for why glassy aerosols that have re-vitrified in contact with the

  9. Ice cloud microphysical properties in tropical Pacific regions derived from CloudSat and CALIPSO measurements

    NASA Astrophysics Data System (ADS)

    Takahashi, Naoya; Hayasaka, Tadahiro; Okamoto, Hajime

    2017-02-01

    We revealed the difference in tropical ice cloud microphysical properties between the western Pacific (WP) and the eastern Pacific (EP), based on satellite retrievals. Vertical profile of effective particle radius of ice cloud (re) was estimated from active sensors on board CloudSat and CALIPSO satellites. In this study, we focused only on ice cloud which is defined as clouds with the cloud top temperature lower than 0°C. To investigate the relationship between cloud optical properties and cloud vertical structures, these ice clouds were classified into five types based on cloud optical thickness values. Compared the vertical profile of re in WP with that in the EP, re around the freezing level within convective cloud in EP slightly larger than that in WP. This analysis also shows that re of optically thick cloud is larger than that of optically thin cloud. The difference in re may be caused by differences in moisture convergence, upward motion, aerosols.

  10. Modeling immersion freezing with aerosol-dependent prognostic ice nuclei in Arctic mixed-phase clouds

    NASA Astrophysics Data System (ADS)

    Paukert, M.; Hoose, C.

    2014-07-01

    While recent laboratory experiments have thoroughly quantified the ice nucleation efficiency of different aerosol species, the resulting ice nucleation parameterizations have not yet been extensively evaluated in models on different scales. Here the implementation of an immersion freezing parameterization based on laboratory measurements of the ice nucleation active surface site density of mineral dust and ice nucleation active bacteria, accounting for nucleation scavenging of ice nuclei, into a cloud-resolving model with two-moment cloud microphysics is presented. We simulated an Arctic mixed-phase stratocumulus cloud observed during Flight 31 of the Indirect and Semi-Direct Aerosol Campaign near Barrow, Alaska. Through different feedback cycles, the persistence of the cloud strongly depends on the ice number concentration. It is attempted to bring the observed cloud properties, assumptions on aerosol concentration, and composition and ice formation parameterized as a function of these aerosol properties into agreement. Depending on the aerosol concentration and on the ice crystal properties, the simulated clouds are classified as growing, dissipating, and quasi-stable. In comparison to the default ice nucleation scheme, the new scheme requires higher aerosol concentrations to maintain a quasi-stable cloud. The simulations suggest that in the temperature range of this specific case, mineral dust can only contribute to a minor part of the ice formation. The importance of ice nucleation active bacteria and possibly other ice formation modes than immersion freezing remains poorly constrained in the considered case, since knowledge on local variations in the emissions of ice nucleation active organic aerosols in the Arctic is scarce.

  11. Ultraviolet Mars Reveals Cloud Formation

    NASA Image and Video Library

    Images from MAVEN's Imaging UltraViolet Spectrograph were used to make this movie of rapid cloud formation on Mars on July 9-10, 2016. The ultraviolet colors of the planet have been rendered in fal...

  12. Measuring ice and liquid water content in moderately supercooled clouds with Cloudnet

    NASA Astrophysics Data System (ADS)

    Bühl, Johannes; Seifert, Patric; Myagkov, Alexander; Albert, Ansmann

    2016-04-01

    The interaction between ice nuclei and clouds is an important topic in weather and climate research. Recent laboratory experiments and field in-situ field campaigns present more and more detailed measurements of ice nucleating particles (INP) at temperatures close to 0°C. This brings moderately supercooled mixed-phase clouds into the focus of current cloud research. One current example is the European Union BACCHUS project. A major goal of BACCHUS is the analysis of the anthropogenic impact on ice nucleation. Within this project, we use the Leipzig Aerosol Cloud Remote Observations System (LACROS) and the Cloudnet framework in order to get quantitative insight into the formation of ice in mixed-phase layered clouds with cloud top temperature (CTT) from -40 to 0°C. Depolarization measurements from lidar and radar show a clear dependence between particle shape and the temperature under which the particles have been formed. The special focus of this work is on the CTT range from -10 to 0°C. An algorithm is presented to decide between ice and liquid water precipitation falling from the clouds showing that between 10% and 30% of all layered clouds show ice precipitation with CTT between -5 and 0°C. For these slightly supercooled clouds an average ice-water-content between 10e-7 and 10e-8 [kg per cubic meter] is found.

  13. 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.

  14. Investigating ice nucleation in cirrus clouds with an aerosol-enabled Multiscale Modeling Framework

    DOE PAGES

    Zhang, Chengzhu; Wang, Minghuai; Morrison, H.; ...

    2014-11-06

    In this study, an aerosol-dependent ice nucleation scheme [Liu and Penner, 2005] has been implemented in an aerosol-enabled multi-scale modeling framework (PNNL MMF) to study ice formation in upper troposphere cirrus clouds through both homogeneous and heterogeneous nucleation. The MMF model represents cloud scale processes by embedding a cloud-resolving model (CRM) within each vertical column of a GCM grid. By explicitly linking ice nucleation to aerosol number concentration, CRM-scale temperature, relative humidity and vertical velocity, the new MMF model simulates the persistent high ice supersaturation and low ice number concentration (10 to 100/L) at cirrus temperatures. The low ice numbermore » is attributed to the dominance of heterogeneous nucleation in ice formation. The new model simulates the observed shift of the ice supersaturation PDF towards higher values at low temperatures following homogeneous nucleation threshold. The MMF models predict a higher frequency of midlatitude supersaturation in the Southern hemisphere and winter hemisphere, which is consistent with previous satellite and in-situ observations. It is shown that compared to a conventional GCM, the MMF is a more powerful model to emulate parameters that evolve over short time scales such as supersaturation. Sensitivity tests suggest that the simulated global distribution of ice clouds is sensitive to the ice nucleation schemes and the distribution of sulfate and dust aerosols. Simulations are also performed to test empirical parameters related to auto-conversion of ice crystals to snow. Results show that with a value of 250 μm for the critical diameter, Dcs, that distinguishes ice crystals from snow, the model can produce good agreement to the satellite retrieved products in terms of cloud ice water path and ice water content, while the total ice water is not sensitive to the specification of Dcs value.« less

  15. Investigating ice nucleation in cirrus clouds with an aerosol-enabled Multiscale Modeling Framework

    SciTech Connect

    Zhang, Chengzhu; Wang, Minghuai; Morrison, H.; Somerville, Richard C.; Zhang, Kai; Liu, Xiaohong; Li, J-L F.

    2014-11-06

    In this study, an aerosol-dependent ice nucleation scheme [Liu and Penner, 2005] has been implemented in an aerosol-enabled multi-scale modeling framework (PNNL MMF) to study ice formation in upper troposphere cirrus clouds through both homogeneous and heterogeneous nucleation. The MMF model represents cloud scale processes by embedding a cloud-resolving model (CRM) within each vertical column of a GCM grid. By explicitly linking ice nucleation to aerosol number concentration, CRM-scale temperature, relative humidity and vertical velocity, the new MMF model simulates the persistent high ice supersaturation and low ice number concentration (10 to 100/L) at cirrus temperatures. The low ice number is attributed to the dominance of heterogeneous nucleation in ice formation. The new model simulates the observed shift of the ice supersaturation PDF towards higher values at low temperatures following homogeneous nucleation threshold. The MMF models predict a higher frequency of midlatitude supersaturation in the Southern hemisphere and winter hemisphere, which is consistent with previous satellite and in-situ observations. It is shown that compared to a conventional GCM, the MMF is a more powerful model to emulate parameters that evolve over short time scales such as supersaturation. Sensitivity tests suggest that the simulated global distribution of ice clouds is sensitive to the ice nucleation schemes and the distribution of sulfate and dust aerosols. Simulations are also performed to test empirical parameters related to auto-conversion of ice crystals to snow. Results show that with a value of 250 μm for the critical diameter, Dcs, that distinguishes ice crystals from snow, the model can produce good agreement to the satellite retrieved products in terms of cloud ice water path and ice water content, while the total ice water is not sensitive to the specification of Dcs value.

  16. The DC-8 Submillimeter-Wave Cloud Ice Radiometer

    NASA Technical Reports Server (NTRS)

    Walter, Steven; Batelaan, Paul; Siegel, Peter; Evans, K. Franklin; Evans, Aaron; Balachandra, Balu; Gannon, Jade; Guldalian, John; Raz, Guy; Shea, James; Smith, Christopher; Thomassen, John

    2000-01-01

    Submillimeter-wave cloud ice radiometry is an innovative technique for determining the amount of ice present in cirrus clouds, measuring median crystal size, and constraining crystal shape. The radiometer described in this poster is being developed to acquire data to validate radiometric retrievals of cloud ice at submillimeter wavelengths. The goal of this effort is to develop a technique to enable spaceborne characterization of cirrus, meeting key climate modeling and NASA measurement needs.

  17. A primordial origin for molecular oxygen in comets: a chemical kinetics study of the formation and survival of O2 ice from clouds to discs

    NASA Astrophysics Data System (ADS)

    Taquet, V.; Furuya, K.; Walsh, C.; van Dishoeck, E. F.

    2016-11-01

    Molecular oxygen has been confirmed as the fourth most abundant molecule in cometary material (O2/H2O ˜ 4 per cent) and is thought to have a primordial nature, i.e. coming from the interstellar cloud from which our Solar system was formed. However, interstellar O2 gas is notoriously difficult to detect and has only been observed in one potential precursor of a solar-like system. Here, the chemical and physical origin of O2 in comets is investigated using sophisticated astrochemical models. Three origins are considered: (i) in dark clouds; (ii) during forming protostellar discs; and (iii) during luminosity outbursts in discs. The dark cloud models show that reproduction of the observed abundance of O2 and related species in comet 67P/C-G requires a low H/O ratio facilitated by a high total density (≥105 cm-3), and a moderate cosmic ray ionization rate (≤10-16 s-1) while a temperature of 20 K, slightly higher than the typical temperatures found in dark clouds, also enhances the production of O2. Disc models show that O2 can only be formed in the gas phase in intermediate disc layers, and cannot explain the strong correlation between O2 and H2O in comet 67P/C-G together with the weak correlation between other volatiles and H2O. However, primordial O2 ice can survive transport into the comet-forming regions of discs. Taken together, these models favour a dark cloud (or 'primordial') origin for O2 in comets, albeit for dark clouds which are warmer and denser than those usually considered as Solar system progenitors.

  18. Formation of model polar stratospheric cloud films

    NASA Technical Reports Server (NTRS)

    Middlebrook, Ann M.; Koehler, Birgit G.; Mcneill, Laurie S.; Tolbert, Margaret A.

    1992-01-01

    Fourier transform infrared spectroscopy was used to examine the competitive growth of films representative of polar stratospheric clouds. These experiments show that either crystalline nitric acid trihydrate (beta-NAT) or amorphous films with H2O:HNO3 ratios close to 3:1 formed at temperatures 3-7 K warmer than the ice frost point under stratospheric pressure conditions. In addition, with higher HNO3 pressure, we observed nitric acid dihydrate (NAD) formation at temperatures warmer than ice formation. However, our experiments also show that NAD surfaces converted to beta-NAT upon exposure to stratospheric water pressures. Finally, we determined that the net uptake coefficient for HNO3 on beta-NAT is close to unity, whereas the net uptake coefficient for H2O is much less.

  19. The formation of ice on airplanes

    NASA Technical Reports Server (NTRS)

    Noth, H; Polte, W

    1936-01-01

    The present report examines the problem of ice formation from the point of view of the pilot and the meteorologist. Their experiences prove the ice deposit to be first and foremost a navigational problem and only secondarily a question of de-icing devices. With correct utilization of the meteorological information by the flyer, ice hazard can in many cases be minimized or avoided. Ice formation and the different types of ice deposits are listed and discussed. Weather formation during these ice deposits are also discussed as well as the effect of ice formation on aircraft.

  20. Monitoring the mesospheric CO2 ice clouds by OMEGA/MEx

    NASA Astrophysics Data System (ADS)

    Gondet, B.; Bibring, J. P.; Vincendon, M.

    2012-04-01

    Along four consecutive Martian years, we have discovered and systematically monitored the appearance of CO2 ice clouds, mapping large areas in latitude, longitude and date. These observations have been made from large (at apoapsis) to close (at pericenter) distances, thus with varying resolutions. We have identified the proper locations, altitude and seasons of these clouds. During the past year, we have observed a temporal shift in the occurrence of the clouds, preceded by the evolution of dust clouds, possibly acting as nucleation site for the CO2 clouds. We shall present these new results, and discuss them in the framework of cloud formation processes.

  1. 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

  2. Why does large ice supersaturation persist in cold cirrus clouds?

    NASA Astrophysics Data System (ADS)

    Bogdan, A.; Molina, M. J.; Loerting, T.

    2009-04-01

    )2SO4, NH4NO3, and (NH4)3H(SO4)2 may also consist of the mixed-phase particles. In the absence of any deep convective water vapor sources, the temperature of the onset of the freezing of UT aqueous droplets will determine the highest clear-sky Si. Assuming that the UT droplets have a composition similar to that of the laboratory droplets, we calculated the Si which would exist immediately prior to the formation of cold cirrus. The calculations were performed using the measured freezing temperatures of ice, Ti, and the thermodynamic model of the system 7 H+ - NH4+ - SO42-- NO3-- H2O. The calculations show that Si > 100 % can be formed prior to the formation of cold ice cirrus by homogeneous freezing of aqueous droplets containing H2SO4, HNO3, (NH4)2SO4, (NH4)HSO4, NH4NO3, and (NH4)3H(SO4)2. In the UT, the growth rate of coated ice crystals will differ from that of uncoated ones since the coating can serve as a 'shield' reducing the flux of H2O molecules to the ice surface. The uncoated ice crystals experience rapid growth due to fast deposition of H2O directly on the ice surface. In the case of coated ice, H2O molecules first condense on the coating, dilute it, diffuse to the ice core, and only then become incorporated into the ice lattice. The calculations of the thickness of the coating around ice crystals and the impact of the coating on the rate of ice growth, and consequently on the rate of the consumption of moisture inside cold cirrus, were made for H2SO4/H2O droplets. The H2SO4/H2O system has been well studied and its thermodynamic data are well documented. We find that the coating can slow down the rate of ice growth by ~103 in comparison with uncoated ice and this can be a reason for the persistent in-cloud Si >> 0 %. 1. Jensen, E. J. et al. (2005), Atmos. Chem. Phys. 5, 851-862. 2. Koop, T., Ng, H.P., Molina, L.T. and Molina, M.J. (1998), J. Phys. Chem. A, 102, 8924-8931. 3. Koop, T., Bertram, A.K., Molina, L.T. and Molina, M.J. (1999), J. Phys. Chem. A, 103

  3. In-situ aircraft observations of ice concentrations within clouds over the Antarctic Peninsula and Larsen Ice Shelf

    NASA Astrophysics Data System (ADS)

    Grosvenor, D. P.; Choularton, T. W.; Lachlan-Cope, T.; Gallagher, M. W.; Crosier, J.; Bower, K. N.; Ladkin, R. S.; Dorsey, J. R.

    2012-07-01

    In-situ aircraft observations of ice crystal concentrations in Antarctic clouds are presented for the first time. Orographic, layer and wave clouds around the Antarctic Peninsula and Larsen Ice shelf regions were penetrated by the British Antarctic Survey's Twin Otter Aircraft, which was equipped with modern cloud physics probes. The clouds studied were mostly in the free troposphere and hence ice crystals blown from the surface are unlikely to have been a major source for the ice phase. The temperature range covered by the experiments was 0 to -21°C. The clouds were found to contain supercooled liquid water in most regions and at heterogeneous ice formation temperatures ice crystal concentrations (60 s averages) were often less than 0.07 l-1, although values up to 0.22 l-1 were observed. Estimates of observed aerosol concentrations were used as input into the DeMott et al., 2010 ice nuclei (IN) parameterisation. The observed ice crystal number concentrations were generally in broad agreement with the IN predictions, although on the whole the predicted values were higher. Possible reasons for this are discussed and include the lack of IN observations in this region with which to characterise the parameterisation, and/or problems in relating ice concentration measurements to IN concentrations. Other IN parameterisations significantly overestimated the number of ice particles. Generally ice particle concentrations were much lower than found in clouds in middle latitudes for a given temperature. Higher ice crystal concentrations were sometimes observed at temperatures warmer than -9 °C, with values of several per litre reached. These were attributable to secondary ice particle production by the Hallett Mossop process. Even in this temperature range it was observed that there were regions with little or no ice that were dominated by supercooled liquid water. It is likely that in some cases this was due to a lack of seeding ice crystals to act as rimers to initiate

  4. In-situ aircraft observations of ice concentrations within clouds over the Antarctic Peninsula and Larsen Ice Shelf

    NASA Astrophysics Data System (ADS)

    Grosvenor, D. P.; Choularton, T. W.; Lachlan-Cope, T.; Gallagher, M. W.; Crosier, J.; Bower, K. N.; Ladkin, R. S.; Dorsey, J. R.

    2012-12-01

    In-situ aircraft observations of ice crystal concentrations in Antarctic clouds are presented for the first time. Orographic, layer and wave clouds around the Antarctic Peninsula and Larsen Ice shelf regions were penetrated by the British Antarctic Survey's Twin Otter aircraft, which was equipped with modern cloud physics probes. The clouds studied were mostly in the free troposphere and hence ice crystals blown from the surface are unlikely to have been a major source for the ice phase. The temperature range covered by the experiments was 0 to -21 °C. The clouds were found to contain supercooled liquid water in most regions and at heterogeneous ice formation temperatures ice crystal concentrations (60 s averages) were often less than 0.07 l-1, although values up to 0.22 l-1 were observed. Estimates of observed aerosol concentrations were used as input into the DeMott et al. (2010) ice nuclei (IN) parameterisation. The observed ice crystal number concentrations were generally in broad agreement with the IN predictions, although on the whole the predicted values were higher. Possible reasons for this are discussed and include the lack of IN observations in this region with which to characterise the parameterisation, and/or problems in relating ice concentration measurements to IN concentrations. Other IN parameterisations significantly overestimated the number of ice particles. Generally ice particle concentrations were much lower than found in clouds in middle latitudes for a given temperature. Higher ice crystal concentrations were sometimes observed at temperatures warmer than -9 °C, with values of several per litre reached. These were attributable to secondary ice particle production by the Hallett Mossop process. Even in this temperature range it was observed that there were regions with little or no ice that were dominated by supercooled liquid water. It is likely that in some cases this was due to a lack of seeding ice crystals to act as rimers to initiate

  5. Visible and near infrared reflectances measured from laboratory ice clouds.

    PubMed

    Barkey, Brian; Liou, K N

    2008-05-01

    We present laboratory results of the 0.68 microm visible (VIS) and 1.617 microm near infrared (NIR) reflectances typically used for inferring optical depth and ice crystal size from satellite radiometers, from ice clouds generated in a temperature controlled column cloud chamber. Two types of ice crystals were produced in this experiment: small columns and dendrites with mean maximum dimensions of about 17 and 35 microm. Within experimental uncertainty, the measured reflectances from ice clouds at both wavelengths agree reasonably well with the theoretical results computed from the plane-parallel adding-doubling method for radiative transfer using the measured ice particle morphology. We demonstrate that laboratory scattering and reflectance data for thin ice clouds with optical depths less than 0.4 can be used for validation of the thin cirrus optical depth and ice crystal size that have been routinely retrieved from the satellite VIS-NIR two channel pair.

  6. 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.

  7. Cloud Ice: A Climate Model Challenge With Signs and Expectations of Progress

    NASA Astrophysics Data System (ADS)

    Li, F.; Waliser, D.; Bacmeister, J.; Chern, J.; Del Genio, T.; Jiang, J.; Kharitondov, M.; Liou, K.; Meng, H.; Minnis, P.; Rossow, B.; Stephens, G.; Sun-Mack, S.; Tao, W.; Vane, D.; Woods, C.; Tompkins, A.; Wu, D.

    2007-12-01

    Global climate models (GCMs), including those assessed in the IPCC AR4, exhibit considerable disagreement in the amount of cloud ice - both in terms of the annual global mean as well as their spatial variability. Global measurements of cloud ice have been difficult due to the challenges involved in remotely sensing ice water content (IWC) and its vertical profile - including complications associated with multi-level clouds, mixed-phases and multiple hydrometer types, the uncertainty in classifying ice particle size and shape for remote retrievals, and the relatively small time and space scales associated with deep convection. Together, these measurement difficulties make it a challenge to characterize and understand the mechanisms of ice cloud formation and dissipation. Fortunately, there are new observational resources recently established that can be expected to lead to considerable reduction in the observational uncertainties of cloud ice, and in turn improve the fidelity of model representations. Specifically, these include the Microwave Limb Sounder (MLS) on the Earth Observing System (EOS) Aura satellite, and the CloudSat and Calipso satellite missions, all of which fly in formation in what is referred to as the A-Train. Based on radar and limb-sounding techniques, these new satellite measurements provide a considerable leap forward in terms of the information gathered regarding upper-tropospheric cloud IWC as well as other macrophysical and microphysical properties. In this presentation, we describe the current state of GCM representations of cloud ice and their associated uncertainties, the nature of the new observational resources for constraining cloud ice values in GCMs, the challenges in making model-data comparisons with these data resources, and prospects for near-term improvements in model representations.

  8. 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.

  9. CLaMS-Ice: Large-scale cirrus cloud simulations in comparison with observations

    NASA Astrophysics Data System (ADS)

    Costa, Anja; Rolf, Christian; Grooß, Jens-Uwe; Spichtinger, Peter; Afchine, Armin; Spelten, Nicole; Dreiling, Volker; Zöger, Martin; Krämer, Martina

    2016-04-01

    Cirrus clouds are an element of uncertainty in the climate system and have received increasing attention since the last IPCC reports. The interactions of different freezing mechanisms, sedimentation rates, updraft velocity fluctuations and other factors that determine the formation and evolution of those clouds is still not fully understood. Thus, a reliable representation of cirrus clouds in models representing real atmospheric conditions is still a challenging task. At last year's EGU, Rolf et al. (2015) introduced the new large-scale microphysical cirrus cloud model CLaMS-Ice: based on trajectories calculated with CLaMS (McKenna et al., 2002 and Konopka et al. 2007), it simulates the development of cirrus clouds relying on the cirrus bulk model by Spichtinger and Gierens (2009). The qualitative agreement between CLaMS-Ice simulations and observations could be demonstrated at that time. Now we present a detailed quantitative comparison between standard ECMWF products, CLaMS-Ice simulations, and in-situ measurements obtained during the ML-Cirrus campaign 2014. We discuss the agreement of the parameters temperature (observational data: BAHAMAS), relative humidity (SHARC), cloud occurrence, cloud particle concentration, ice water content and cloud particle radii (all NIXE-CAPS). Due to the precise trajectories based on ECMWF wind and temperature fields, CLaMS-Ice represents the cirrus cloud vertical and horizontal coverage more accurately than the ECMWF ice water content (IWC) fields. We demonstrate how CLaMS-Ice can be used to evaluate different input settings (e.g. amount of ice nuclei, freezing thresholds, sedimentation settings) that lead to cirrus clouds with the microphysical properties observed during ML-Cirrus (2014).

  10. Diagnosing Aircraft Icing Potential from Satellite Cloud Retrievals

    NASA Technical Reports Server (NTRS)

    Smith, William L., Jr.; Minnis, Patrick; Fleeger, Cecilia; Spangenberg, Douglas

    2013-01-01

    The threat for aircraft icing in clouds is a significant hazard that routinely impacts aviation operations. Accurate diagnoses and forecasts of aircraft icing conditions requires identifying the location and vertical distribution of clouds with super-cooled liquid water (SLW) droplets, as well as the characteristics of the droplet size distribution. Traditional forecasting methods rely on guidance from numerical models and conventional observations, neither of which currently resolve cloud properties adequately on the optimal scales needed for aviation. Satellite imagers provide measurements over large areas with high spatial resolution that can be interpreted to identify the locations and characteristics of clouds, including features associated with adverse weather and storms. This paper describes new techniques for interpreting cloud products derived from satellite data to infer the flight icing threat to aircraft. For unobscured low clouds, the icing threat is determined using empirical relationships developed from correlations between satellite imager retrievals of liquid water path and droplet size with icing conditions reported by pilots (PIREPS). For deep ice over water cloud systems, ice and liquid water content (IWC and LWC) profiles are derived by using the imager cloud properties to constrain climatological information on cloud vertical structure and water phase obtained apriori from radar and lidar observations, and from cloud model analyses. Retrievals of the SLW content embedded within overlapping clouds are mapped to the icing threat using guidance from an airfoil modeling study. Compared to PIREPS and ground-based icing remote sensing datasets, the satellite icing detection and intensity accuracies are approximately 90% and 70%, respectively, and found to be similar for both low level and deep ice over water cloud systems. The satellite-derived icing boundaries capture the reported altitudes over 90% of the time. Satellite analyses corresponding to

  11. Discrimination of water, ice and aerosols by light polarisation in the CLOUD experiment

    NASA Astrophysics Data System (ADS)

    Nichman, L.; Fuchs, C.; Järvinen, E.; Ignatius, K.; Höppel, N. F.; Dias, A.; Heinritzi, M.; Simon, M.; Tröstl, J.; Wagner, A. C.; Wagner, R.; Williamson, C.; Yan, C.; Bianchi, F.; Connolly, P. J.; Dorsey, J. R.; Duplissy, J.; Ehrhart, S.; Frege, C.; Gordon, H.; Hoyle, C. R.; Kristensen, T. B.; Steiner, G.; Donahue, N. M.; Flagan, R.; Gallagher, M. W.; Kirkby, J.; Möhler, O.; Saathoff, H.; Schnaiter, M.; Stratmann, F.; Tomé, A.

    2015-11-01

    Cloud microphysical processes involving the ice phase in tropospheric clouds are among the major uncertainties in cloud formation, weather and General Circulation Models (GCMs). The simultaneous detection of aerosol particles, liquid droplets, and ice crystals, especially in the small cloud-particle size range below 50 μm, remains challenging in mixed phase, often unstable ice-water phase environments. The Cloud Aerosol Spectrometer with Polarisation (CASPOL) is an airborne instrument that has the ability to detect such small cloud particles and measure their effects on the backscatter polarisation state. Here we operate the versatile Cosmics-Leaving-OUtdoor-Droplets (CLOUD) chamber facility at the European Organisation for Nuclear Research (CERN) to produce controlled mixed phase and other clouds by adiabatic expansions in an ultraclean environment, and use the CASPOL to discriminate between different aerosols, water and ice particles. In this paper, optical property measurements of mixed phase clouds and viscous Secondary Organic Aerosol (SOA) are presented. We report observations of significant liquid - viscous SOA particle polarisation transitions under dry conditions using CASPOL. Cluster analysis techniques were subsequently used to classify different types of particles according to their polarisation ratios during phase transition. A classification map is presented for water droplets, organic aerosol (e.g., SOA and oxalic acid), crystalline substances such as ammonium sulphate, and volcanic ash. Finally, we discuss the benefits and limitations of this classification approach for atmospherically relevant concentration and mixtures with respect to the CLOUD 8-9 campaigns and its potential contribution to Tropical Troposphere Layer (TTL) analysis.

  12. How Temperature and Water levels affect Polar Mesospheric Cloud Formation

    NASA Astrophysics Data System (ADS)

    Smith, L. L.; Randall, C. E.; Harvey, V.

    2012-12-01

    Using the Cloud Imaging and Particle Size (CIPS) instrument data, which is part of the Aeronomy in the Mesosphere (AIM) mission, we compare the albedo and ice water content measurements of CIPS with the Navy Operation Global Atmospheric Prediction System - Advanced Level Phyiscs and High Altitude (NOGAPS-ALPHA) temperature and water vapor data in order to derive a greater understanding of cloud formation and physics. We particularly focus on data from June 2007 and July 2007 in this case study because of particular cloud structures and formations during this time period for future studies.

  13. Meteorological conditions during the formation of ice on aircraft

    NASA Technical Reports Server (NTRS)

    Samuels, L T

    1932-01-01

    These are the results of a number of records recently secured from autographic meteorological instruments mounted on airplanes at times when ice formed. Ice is found to collect on an airplane only when the airplane is in some form of visible moisture, such as cloud, fog, mist, rain. etc., and the air temperature is within certain critical limits. Described here are the characteristics of clear ice and rime ice and the specific types of hazards they present to airplanes and lighter than air vehicles. The weather records are classified according to the two general types of formation (clear ice and rime) together with the respective temperatures, relative humidities, clouds, and elevations above ground at which formations occurred. This classification includes 108 cases where rime formed, 43 cases in which clear ice formed, and 4 cases when both rime and clear ice formed during the same flight. It is evident from the above figures that there was a preponderance of rime by the ratio of 2.5 to 1, while in only a few cases both types of ice formation occurred during the same flight.

  14. Ice nucleation by combustion ash particles at conditions relevant to mixed-phase clouds

    NASA Astrophysics Data System (ADS)

    Umo, N. S.; Murray, B. J.; Baeza-Romero, M. T.; Jones, J. M.; Lea-Langton, A. R.; Malkin, T. L.; O'Sullivan, D.; Neve, L.; Plane, J. M. C.; Williams, A.

    2015-05-01

    Ice-nucleating particles can modify cloud properties with implications for climate and the hydrological cycle; hence, it is important to understand which aerosol particle types nucleate ice and how efficiently they do so. It has been shown that aerosol particles such as natural dusts, volcanic ash, bacteria and pollen can act as ice-nucleating particles, but the ice-nucleating ability of combustion ashes has not been studied. Combustion ashes are major by-products released during the combustion of solid fuels and a significant amount of these ashes are emitted into the atmosphere either during combustion or via aerosolization of bottom ashes. Here, we show that combustion ashes (coal fly ash, wood bottom ash, domestic bottom ash, and coal bottom ash) nucleate ice in the immersion mode at conditions relevant to mixed-phase clouds. Hence, combustion ashes could play an important role in primary ice formation in mixed-phase clouds, especially in clouds that are formed near the emission source of these aerosol particles. In order to quantitatively assess the impact of combustion ashes on mixed-phase clouds, we propose that the atmospheric abundance of combustion ashes should be quantified since up to now they have mostly been classified together with mineral dust particles. Also, in reporting ice residue compositions, a distinction should be made between natural mineral dusts and combustion ashes in order to quantify the contribution of combustion ashes to atmospheric ice nucleation.

  15. Investigating ice nucleation in cirrus clouds with an aerosol-enabled Multiscale Modeling Framework

    NASA Astrophysics Data System (ADS)

    Zhang, Chengzhu; Wang, Minghuai; Morrison, Hugh; Somerville, Richard C. J.; Zhang, Kai; Liu, Xiaohong; Li, Jui-Lin F.

    2014-12-01

    In this study, an aerosol-dependent ice nucleation scheme has been implemented in an aerosol-enabled Multiscale Modeling Framework (PNNL MMF) to study ice formation in upper troposphere cirrus clouds through both homogeneous and heterogeneous nucleation. The MMF model represents cloud scale processes by embedding a cloud-resolving model (CRM) within each vertical column of a GCM grid. By explicitly linking ice nucleation to aerosol number concentration, CRM-scale temperature, relative humidity and vertical velocity, the new MMF model simulates the persistent high ice supersaturation and low ice number concentration (10-100/L) at cirrus temperatures. The new model simulates the observed shift of the ice supersaturation PDF toward higher values at low temperatures following the homogeneous nucleation threshold. The MMF model predicts a higher frequency of midlatitude supersaturation in the Southern Hemisphere and winter hemisphere, which is consistent with previous satellite and in situ observations. It is shown that compared to a conventional GCM, the MMF is a more powerful model to simulate parameters that evolve over short time scales such as supersaturation. Sensitivity tests suggest that the simulated global distribution of ice clouds is sensitive to the ice nucleation scheme and the distribution of sulfate and dust aerosols. Simulations are also performed to test empirical parameters related to auto-conversion of ice crystals to snow. Results show that with a value of 250 μm for the critical diameter, Dcs, that distinguishes ice crystals from snow, the model can produce good agreement with the satellite-retrieved products in terms of cloud ice water path and ice water content, while the total ice water is not sensitive to the specification of Dcs value.

  16. Interplanetary dust particles, not wind blown dust, control high altitude ice clouds on Mars

    NASA Astrophysics Data System (ADS)

    Hartwick, Victoria; Toon, Owen B.

    2016-10-01

    Water ice clouds on Mars are commonly observed at high altitudes. However, current generation Mars three-dimensional general circulation models (GCM) struggle to reproduce clouds above approximately 20-30 km. On Mars, as on Earth, ice cloud formation likely initiates by heterogeneous nucleation, which requires a population of suspended ice nuclei contiguous with supersaturated atmospheric water vapor. Although supersaturation is observed at high altitudes and has been reproduced in models, models predict very few ice nuclei. The small number of ice nuclei in the upper atmosphere is due to the assumption in Mars GCMs that the only source of ice nuclei is dust from the Martian surface. However, terrestrial mesospheric noctilucent clouds have been shown to form by ice nucleation on particles originating from ablated micrometeroids. Therefore, it is reasonable to assume that a population of micrometeoric ablation biproducts on Mars exists and can act as a site for cloud nucleation at high altitudes. We present simulations using the Community Atmosphere Model for Mars (MarsCAM) based on the National Center for Atmospheric Research (NCAR) Community Atmosphere Model for Earth,coupled with a physically based, state-of-the-art cloud and dust physics model, the Community Aerosol and Radiation Model for Atmospheres (CARMA) to show that ablating micrometeoroids can yield abundant ice nuclei throughout the upper atmosphere of Mars. We find that simulations including a constant annual micrometeoroid flux allows us to reproduce the observed properties of high altitude water ice clouds including vertical distribution and particle size. In general, effective radius decreases with increasing altitude. We have additionally explored the impact of variable ablation rates. Preliminary results suggest that relatively high ablation rates, near or greater than 50%, are required to reproduce observed cloud features.

  17. Ice nucleation active particles are efficiently removed by precipitating clouds

    PubMed Central

    Stopelli, Emiliano; Conen, Franz; Morris, Cindy E.; Herrmann, Erik; Bukowiecki, Nicolas; Alewell, Christine

    2015-01-01

    Ice nucleation in cold clouds is a decisive step in the formation of rain and snow. Observations and modelling suggest that variations in the concentrations of ice nucleating particles (INPs) affect timing, location and amount of precipitation. A quantitative description of the abundance and variability of INPs is crucial to assess and predict their influence on precipitation. Here we used the hydrological indicator δ18O to derive the fraction of water vapour lost from precipitating clouds and correlated it with the abundance of INPs in freshly fallen snow. Results show that the number of INPs active at temperatures ≥ −10 °C (INPs−10) halves for every 10% of vapour lost through precipitation. Particles of similar size (>0.5 μm) halve in number for only every 20% of vapour lost, suggesting effective microphysical processing of INPs during precipitation. We show that INPs active at moderate supercooling are rapidly depleted by precipitating clouds, limiting their impact on subsequent rainfall development in time and space. PMID:26553559

  18. Ice nucleation active particles are efficiently removed by precipitating clouds.

    PubMed

    Stopelli, Emiliano; Conen, Franz; Morris, Cindy E; Herrmann, Erik; Bukowiecki, Nicolas; Alewell, Christine

    2015-11-10

    Ice nucleation in cold clouds is a decisive step in the formation of rain and snow. Observations and modelling suggest that variations in the concentrations of ice nucleating particles (INPs) affect timing, location and amount of precipitation. A quantitative description of the abundance and variability of INPs is crucial to assess and predict their influence on precipitation. Here we used the hydrological indicator δ(18)O to derive the fraction of water vapour lost from precipitating clouds and correlated it with the abundance of INPs in freshly fallen snow. Results show that the number of INPs active at temperatures ≥ -10 °C (INPs-10) halves for every 10% of vapour lost through precipitation. Particles of similar size (>0.5 μm) halve in number for only every 20% of vapour lost, suggesting effective microphysical processing of INPs during precipitation. We show that INPs active at moderate supercooling are rapidly depleted by precipitating clouds, limiting their impact on subsequent rainfall development in time and space.

  19. Water Ice Cloud Opacities and Temperatures Derived from the Viking IRTM Data Set

    NASA Technical Reports Server (NTRS)

    TamppariL. K.; Zurek, R. W.; Paige, D. A.

    1999-01-01

    The degree to which water ice clouds play a role in the Mars climate is unknown. Latent heating of water ice clouds is small and since most hazes appeared to be thin (tau less than or = 1) their radiative effects have been neglected. Condensation likely limits the vertical extent of water vapor in the water column and a lowering of the condensation altitude, as seen in the northern spring and summer, could increase the seasonal exchange of water between the atmosphere and the surface. It has been suggested that water ice cloud formation is more frequent and widespread in the aphelic hemisphere (currently the northern). This may limit water to the northern hemisphere through greater exchange with the regolith and through restricted southward transport of water vapor by the Mars Hadley circulation. In addition, it has been suggested that water ice cloud formation also controls the vertical distribution of atmospheric dust in some seasons. This scavenging of dust may Continuing from the IRTM cloud maps, derived cloud opacities and cloud temperatures for several locations and seasons will be presented. Sensitivities to cloud particle sizes, surface temperature, and dust opacity will be discussed.

  20. Cubic ice and large humidity with respect to ice in cold cirrus clouds

    NASA Astrophysics Data System (ADS)

    Bogdan, A.; Loerting, T.

    2009-04-01

    Recently several studies have reported about the possible formation of cubic ice in upper-tropospheric cirrus ice clouds and its role in the observed elevated relative humidity with respect to hexagonal ice, RHi, within the clouds. Since cubic ice is metastable with respect to stable hexagonal ice, its vapour pressure is higher. A key issue in determining the ratio of vapour pressures of cubic ice Pc and hexagonal ice Ph is the enthalpy of transformation from cubic to hexagonal ice Hc→h. By dividing the two integrated forms of the Clausius-Clapeyron equation for cubic ice and hexagonal ice, one obtains the relationship (1): ln Pc-- ln P*c-=--(Hc→h--) Ph P*h R 1T-- 1T* (1) from which the importance of Hc→h is evident. In many literature studies the approximation (2) is used: ln Pc-= Hc-→h. Ph RT (2) Using this approximated form one can predict the ratio of vapour pressures by measuring Hc→h. Unfortunately, the measurement of Hc→h is difficult. First, the enthalpy difference is very small, and the transition takes place over a broad temperature range, e.g., between 230 K and 260 K in some of our calorimetry experiments. Second, cubic ice (by contrast to hexagonal ice) can not be produced as a pure crystal. It always contains hexagonal stacking faults, which are evidenced by the (111)-hexagonal Bragg peak in the powder diffractogram. If the number of hexagonal stacking faults in cubic ice is high, then one could even consider this material as hexagonal ice with cubic stacking faults. Using the largest literature value of the change of enthalpy of transformation from cubic to hexagonal ice, Hc→h ? 160 J/mol, Murphy and Koop (2005) calculated that Pc would be ~10% higher than that of hexagonal ice Phat 180 K - 190 K, which agrees with the measurements obtained later by Shilling et al. (2006). Based on this result Shilling et al. concluded that "the formation of cubic ice at T < 202 K may significantly contribute to the persistent in-cloud

  1. Ice Formation Potential of Field-Collected Marine Biogenic Particles

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    Marine biogenic particles composed mainly of sea salt and organic material aerosolized from a mesocosm in laboratory experiments have recently been found to act as ice nuclei. How these particles relate to those collected from sea spray under ambient conditions in the field is unknown. This study reports on the heterogeneous ice nucleation potential of particles collected during the marine aerosol characterization experiment (MACE) on the south shore of Long Island, New York. Ambient aerosol size distributions were measured and particles were collected on hydrophobically coated substrates and subsequently used for ice nucleation experiments using an ice nucleation cell coupled to an optical microscope. This technique allows detection of ice formation for temperatures between 200 and 273 K and for relative humidity with respect to ice (RHice) from 100% up to water saturation. Individual ice nucleating particles were identified for subsequent chemical and physical characterization using both X-ray and electron micro-spectroscopic techniques. Concentrations of bacteria, viruses, and transparent exopolymer particles (TEP) in the bulk seawater, sea-surface microlayer (SML), and in sea spray were determined using established methods and related to airborne sea spray particles and their ice nucleation potential. Onshore aerosol size distribution measurements taken at 5 m height and 10 m away from the breaking waves, revealed a peak maximum at 100 nm and Ntot = 6.8 x 10^2 cm^-3. Bacterial, viral, and TEP were found to be enriched in the SML. Ambient particles collected during MACE were found to nucleate ice efficiently, e. g. at 215 K, ice nucleation occurred on average at 125% RHice. Results of aerosol size distributions and ice nucleation efficiencies are compared to laboratory bubble bursting experiments in which natural seawater was used. The goal of this study is to understand the connection between sea spray aerosolization and atmospheric ice cloud formation and to

  2. Effects of ice particle size vertical inhomogeneity on the passive remote sensing of ice clouds

    NASA Astrophysics Data System (ADS)

    Zhang, Zhibo; Platnick, Steven; Yang, Ping; Heidinger, Andrew K.; Comstock, Jennifer M.

    2010-09-01

    The solar reflectance bi-spectral (SRBS) and infrared split-window (IRSpW) methods are two of the most popular techniques for passive ice cloud property retrievals from multispectral imagers. Ice clouds are usually assumed to be vertically homogeneous in global operational algorithms based on these methods, although significant vertical variations of ice particle size are typically observed in ice clouds. In this study we investigate uncertainties in retrieved optical thickness, effective particle size, and ice water path introduced by a homogeneous cloud assumption in both the SRBS and IRSpW methods, and focus on whether the assumption can lead to significant discrepancies between the two methods. The study simulates the upwelling spectral radiance associated with vertically structured clouds and passes the results through representative SRBS and IRSpW retrieval algorithms. Cloud optical thickness is limited to values for which IRSpW retrievals are possible (optical thickness less than about 7). When the ice cloud is optically thin and yet has a significant ice particle size vertical variation, it is found that both methods tend to underestimate the effective radius and ice water path. The reason for the underestimation is the nonlinear dependence of ice particle scattering properties (extinction and single scattering albedo) on the effective radius. Because the nonlinearity effect is stronger in the IRSpW than the SRBS method, the IRSpW-based IWP tends to be smaller than the SRBS counterpart. When the ice cloud is moderately optically thick, the IRSpW method is relatively insensitive to cloud vertical structure and effective radius retrieval is weighted toward smaller ice particle size, while the weighting function makes the SRBS method more sensitive to the ice particle size in the upper portion of the cloud. As a result, when ice particle size increases monotonically toward cloud base, the two methods are in qualitative agreement; in the event that ice particle

  3. Effects of Ice Particle Size Vertical Inhomogeneity on the Passive Remote Sensing of Ice Clouds

    NASA Technical Reports Server (NTRS)

    Zhang, Zhibo; Platnick, Steven; Yang, Ping; Heidinger, Andrew K.; Comstock, Jennifer M.

    2010-01-01

    The solar reflectance bi-spectral (SRBS) and infrared split-window (IRSpW) methods are two of the most popular techniques for passive ice cloud property retrievals from multispectral imagers. Ice clouds are usually assumed to be vertically homogeneous in global operational algorithms based on these methods, although significant vertical variations of ice particle size are typically observed in ice clouds. In this Study we investigate uncertainties in retrieved optical thickness, effective particle size, and ice water path introduced by a homogeneous cloud assumption in both the SRBS and IRSpW methods, and focus on whether the assumption can lead to significant discrepancies between the two methods. The study simulates the upwelling spectral radiance associated with vertically structured clouds and passes the results through representative SRBS and IRSpW retrieval algorithms. Cloud optical thickness is limited to values for which IRSpW retrievals are possible (optical thickness less than about 7). When the ice cloud is optically thin and yet has a significant ice particle size vertical variation, it is found that both methods tend to underestimate the effective radius and ice water path. The reason for the underestimation is the nonlinear dependence of ice particle scattering properties (extinction and single scattering albedo) on the effective radius. Because the nonlinearity effect is stronger in the IRSpW than the SRBS method, the IRSpW-based IWP tends to be smaller than the SRBS counterpart. When the ice cloud is moderately optically thick, the IRSpW method is relatively insensitive to cloud vertical structure and effective radius retrieval is weighted toward smaller ice particle size, while the weighting function makes the SRBS method more sensitive to the ice particle size in the upper portion of the cloud. As a result, when ice particle size increases monotonically toward cloud base, the two methods are in qualitative agreement; in the event that ice particle

  4. Characteristics of Interstitial Aerosol in Cold and Warm Clouds during the Ice-T Campaign

    NASA Astrophysics Data System (ADS)

    Dhaniyala, S.; He, M.; Moharreri, A.; Craig, L.

    2012-12-01

    Accurate calculation of the contribution of aerosols to the radiative forcing budget requires an understanding of the aerosol role in cloud formation. From a global climate perspective, aerosol-cloud processes must be represented by simple parametric models that can relate aerosol properties to the characteristics of the clouds formed. The development and testing of such simple models requires aerosol-cloud data from a large number of clouds systems. While reasonably accurate cloud data is currently available from a large number of well-established cloud probes, information about aerosol particles in clouds is largely unavailable because of the problem of artifacts in aerosol measurements from the shatter of cloud droplets. During the recent ICE-T campaign (Summer 2011), several different interstitial aerosol inlets were deployed and aerosol measurements were made in a variety of tropical convective clouds, focused particularly on conditions that permit the formation of ice within these systems. The flight operations were based in St. Croix, U.S. Virgin Islands and sampling was largely conducted within ~ 600 miles of this location. The use of new samplers that permit shatter-free sampling of aerosol particles in cold and clouds has allowed for the collection of significant data on interstitial aerosol in tropical convective clouds. Of particular interest are measurements of aerosol size distributions inside and outside clouds made with a fast mobility spectrometer. Size distributions were obtained at 20-30 second resolution, permitting direct measurements of the scavenged aerosol population in clouds and the differences in the scavenged fraction as a function of cloud properties. As part of this presentation, the characteristics of interstitial aerosol in various cloud conditions will be presented and the transformation of aerosol population during cloud processing will be discussed.

  5. Studies of ice nuclei at the Leipzig Aerosol Cloud Interaction Simulator and their implications

    NASA Astrophysics Data System (ADS)

    Wex, Heike

    2013-04-01

    Ice containing clouds permanently cover 40% of the earth's surface. Ice formation processes have a large impact on the formation of precipitation, cloud radiative properties, cloud electrification and hence influence both, weather and climate. Our understanding of the physical and chemical processes underlying ice formation is limited. However what we know is that the two main pathways of atmospheric ice formation are homogeneous and heterogeneous ice nucleation. The latter involves aerosol particles that act as ice nuclei inducing cloud droplet freezing at temperatures significantly above the homogeneous freezing threshold temperature. Particles acting as IN are e.g. dust particles, but also biological particles like bacteria, pollen and fungal spores. Different heterogeneous freezing mechanisms do exit, with their relative importance for atmospheric clouds still being debated. However, there are strong indications that immersion freezing is the most important mechanism when considering mixed phase clouds. What we are still lacking is a) the fundamental process understanding on how aerosol particles induce ice nucleation and b) means to quantify ice nucleation in atmospheric models. Concerning a) there most likely is not only one answer, considering the variety of IN found in the atmosphere. With respect to b) different approaches based on either the stochastic or singular hypotheses have been suggested. However it is still being debated which would be a suitable way to parameterize laboratory data for use in atmospheric modeling. In this presentation, both topics will be addressed. Using the Leipzig Aerosol Cloud Interaction Simulator (LACIS) (Hartmann et al., 2011), we examined different types of dust particles with and without coating, and biological particles such as bacteria and pollen, with respect to their immersion freezing behaviour. We will summarize our findings concerning the properties controlling the ice nucleation behaviour of these particles and

  6. Automated detection of Martian water ice clouds: the Valles Marineris

    NASA Astrophysics Data System (ADS)

    Ogohara, Kazunori; Munetomo, Takafumi; Hatanaka, Yuji; Okumura, Susumu

    2016-10-01

    We need to extract water ice clouds from the large number of Mars images in order to reveal spatial and temporal variations of water ice cloud occurrence and to meteorologically understand climatology of water ice clouds. However, visible images observed by Mars orbiters for several years are too many to visually inspect each of them even though the inspection was limited to one region. Therefore, an automated detection algorithm of Martian water ice clouds is necessary for collecting ice cloud images efficiently. In addition, it may visualize new aspects of spatial and temporal variations of water ice clouds that we have never been aware. We present a method for automatically evaluating the presence of Martian water ice clouds using difference images and cross-correlation distributions calculated from blue band images of the Valles Marineris obtained by the Mars Orbiter Camera onboard the Mars Global Surveyor (MGS/MOC). We derived one subtracted image and one cross-correlation distribution from two reflectance images. The difference between the maximum and the average, variance, kurtosis, and skewness of the subtracted image were calculated. Those of the cross-correlation distribution were also calculated. These eight statistics were used as feature vectors for training Support Vector Machine, and its generalization ability was tested using 10-fold cross-validation. F-measure and accuracy tended to be approximately 0.8 if the maximum in the normalized reflectance and the difference of the maximum and the average in the cross-correlation were chosen as features. In the process of the development of the detection algorithm, we found many cases where the Valles Marineris became clearly brighter than adjacent areas in the blue band. It is at present unclear whether the bright Valles Marineris means the occurrence of water ice clouds inside the Valles Marineris or not. Therefore, subtracted images showing the bright Valles Marineris were excluded from the detection of

  7. The influence of small aerosol particles on the properties of water and ice clouds.

    PubMed

    Choularton, T W; Bower, K N; Weingartner, E; Crawford, I; Coe, H; Gallagher, M W; Flynn, M; Crosier, J; Connolly, P; Targino, A; Alfarra, M R; Baltensperger, U; Sjogren, S; Verheggen, B; Cozic, J; Gysel, M

    2008-01-01

    In this paper, results are presented of the influence of small organic- and soot-containing particles on the formation of water and ice clouds. There is strong evidence that these particles have grown from nano particle seeds produced by the combustion of oil products. Two series of field experiments are selected to represent the observations made. The first is the CLoud-Aerosol Characterisation Experiment (CLACE) series of experiments performed at a high Alpine site (Jungfraujoch), where cloud was in contact with the ground and the measuring station. Both water and ice clouds were examined at different times of the year. The second series of experiments is the CLOud Processing of regional Air Pollution advecting over land and sea (CLOPAP) series, where ageing pollution aerosol from UK cities was observed, from an airborne platform, to interact with warm stratocumulus cloud in a cloud-capped atmospheric boundary layer. Combining the results it is shown that aged pollution aerosol consists of an internal mixture of organics, sulfate, nitrate and ammonium, the organic component is dominated by highly oxidized secondary material. The relative contributions and absolute loadings of the components vary with location and season. However, these aerosols act as Cloud Condensation Nuclei (CCN) and much of the organic material, along with the other species, is incorporated into cloud droplets. In ice and mixed phase cloud, it is observed that very sharp transitions (extending over just a few metres) are present between highly glaciated regions and regions consisting of supercooled water. This is a unique finding; however, aircraft observations in cumulus suggest that this kind of structure may be found in these cloud types too. It is suggested that this sharp transition is caused by ice nucleation initiated by oxidised organic aerosol coated with sulfate in more polluted regions of cloud, sometimes enhanced by secondary ice particle production in these regions.

  8. STORMVEX. Ice Nuclei and Cloud Condensation Nuclei Characterization Field Campaign Report

    SciTech Connect

    Cziczo, D.

    2016-03-01

    The relationship between aerosol particles and the formation of clouds is among the most uncertain aspects in our current understanding of climate change. Warm clouds have been the most extensively studied, in large part because they are normally close to the Earth’s surface and only contain large concentrations of liquid droplets. Ice and mixed-phase clouds have been less studied even though they have extensive global coverage and dominate precipitation formation. Because they require low temperatures to form, both cloud types are infrequently found at ground level, resulting in more difficult field studies. Complex mixtures of liquid and ice elements, normally at much lower concentrations than found in warm clouds, require precise separation techniques and accurate identification of phase. Because they have proved so difficult to study, the climatic impact of ice-containing clouds remains unresolved. In this study, cloud condensation nuclei (CCN) concentrations and associated single particles’ composition and size were measured at a high-elevation research site—Storm Peak Lab, east of Steamboat Springs, Colorado, operated by the Desert Research Institute. Detailed composition analyses were presented to compare CCN activation with single-particle composition. In collaboration with the scientists of the Storm Peak Lab Cloud Property Validation Experiment (STORMVEX), our goal was to relate these findings to the cloud characteristics and the effect of anthropogenic activities.

  9. Global Ice Cloud Properties Based on CALIPSO and CloudSat Measurements and Their Radiative Effect

    NASA Astrophysics Data System (ADS)

    Hong, Y.; Liu, G.

    2013-12-01

    The radiative influence of atmospheric ice clouds varies widely from shortwave to longwave. This frequency-dependent response is convenient, and various techniques have been developed to better understand ice cloud properties. In recent years, the joint observations of the CloudSat Radar and Infrared Pathfinder Satellite Observations (CALIPSO) lidar have frequently been used to examine clouds of varying optical depth (OD). The former excels in probing thick clouds, usually associated with cooling, while the latter performs better with thin clouds, which are generally associated with localized warming. This study aims at investigating global ice cloud properties based on DarDar (raDar/liDar) data that combines both lidar and radar observations, while at the same modeling ice cloud radiative effects. Using DarDar data, this study firstly examines global Ice Water Path (IWP), and shows a global mean IWP value of 113.55 g/m2 for all measurements and 196.34 g/m2 for cloudy situations. The global frequency of ice cloud occurrence reveals that ice clouds predominate in deep convectional regions and storm tracks. Conversely, the subtropics contain fewer ice clouds. Due to Intertropical Convergence Zone (ITCZ) seasonal shifting and storm seasonal changes, a global map of ice cloud occurrence likewise varies seasonally. Global ice cloud occurrence also depends on the day-night cycle. Occurrence at night is 4.8% higher than during the day. IWP, on the contrary, is 1.75 g/m2 lower at night. There is considerable variation among sampled clouds, in which the visible OD ranges from near zero to over 100. Within this range, thin cirrus with OD < 3.0 are most common (75.87%). To better ascertain ice cloud properties, we group ice clouds into five bins according to visible OD: 0 < OD < 0.03, 0.03 < OD < 0.3, 0.3 < OD < 3.0, 3.0 < OD < 20 and OD > 20. The ice clouds with lowest OD are common at midlatitudes, while those with largest OD occur mostly in tropical convective zones and

  10. Mixed-phased particles in polar stratospheric ice clouds

    NASA Astrophysics Data System (ADS)

    Bogdan, Anatoli; Molina, Mario J.; Loerting, Thomas

    2010-05-01

    Keywords: polar stratospheric clouds (PSCs), ozone depletion, differential scanning calorimeter. The rate of chlorine activation reactions, which lead to ozone depletion in the winter/spring polar stratosphere (Molina, 1994), depends on the phase state of the surface of polar stratospheric cloud (PSC) ice crystals (McNeil et al., 2006). PSCs are thought to consist of solid ice and NAT (nitric acid trihydrate, HNO3× 3H2O) particles and supercooled HNO3/H2SO4/H2O droplets. The corresponding PSCs are called Type II, Ia, and Ib PSCs, respectively (Zondlo et al., 1998). Type II PSCs are formed in the Antarctic region below the ice frost point of 189 K by homogeneous freezing of HNO3/H2SO4/H2O droplets (Chang et al., 1999) with the excess of HNO3. The PSC ice crystals are thought to be solid. However, the fate of H+, NO3-, SO42- ions during freezing was not investigated. Our differential scanning calorimetry (DSC) studies of freezing emulsified HNO3/H2SO4/H2O droplets of sizes and compositions representative of the polar stratosphere demonstrate that during the freezing of the droplets, H+, NO3-, SO42- are expelled from the ice lattice. The expelled ions form a residual solution around the formed ice crystals. The residual solution does not freeze but transforms to glassy state at ~150 K (Bogdan et al., 2010). By contrast to glass-formation in these nitric-acid rich ternary mixtures the residual solution freezes in the case of sulphuric-acid rich ternary mixtures (Bogdan and Molina, 2009). For example, we can consider the phase separation into ice and a residual solution during the freezing of 23/3 wt% HNO3/H2SO4/H2O droplets. On cooling, ice is formed at ~189 K. This is inferred from the fact that the corresponding melting peak at ~248 K exactly matches the melting point of ice in the phase diagram of HNO3/H2SO4/H2O containing 3 wt % H2SO4. After the ice has formed, the glass transition occurs at Tg ≈ 150 K. The appearance of the glass transition indicates that the

  11. CloudSat and Aura MLS Constrain upon Ice Cloud Particle Size Distribution

    NASA Astrophysics Data System (ADS)

    Millan Valle, L. F.; Livesey, N. J.; Read, W. G.

    2014-12-01

    Despite years of measurements, ice clouds remain one of the largest uncertainties in climate models. In part, because individual cloud ice remote sensing techniques or instruments observe only portions of the complete ice particle size distribution (PSD) and therefore, to deduce cloud ice water, the retrievals need to assume a given PSD. Uncertainty in such knowledge currently accounts for most of the factor of two or greater uncertainties in satellite based cloud ice water content measurements. The Aura-Microwave Limb Sounder (MLS) observes limb microwave emissions from the Earth's atmosphere at 118, 191, 240, 640 and 2500 GHz enabling cloud ice measurements across a large range of particle sizes. This study explores the synergy of collocated A-train radar backscatter CloudSat measurements and MLS radiances in search of a better understanding of cloud ice PSDs. For each "scene" jointly observed by CloudSat and MLS, we quantify the ability of each of several candidate PSDs to account for the observed signals. First, a CloudSat retrieval is used to determine the cloud altitude and location along the MLS line of sight as well as the cloud ice water content that, for a given PSD, would give rise to the observed CloudSat signal. Then, for each PSD, estimated MLS measurements are reconstructed, compared to those actually observed and a chi-squared metric is used to determined which PSD gives the best fit. We will discuss potential applications of this technique to studies of convection and the impacts of aerosol pollution on ice PSD.

  12. Metastable Ice and Glass Formation in Atmospherically Relevant Aqueous Droplets

    NASA Astrophysics Data System (ADS)

    Murray, B. J.; Moehler, O.

    2008-12-01

    In this presentation an X ray diffraction study of homogeneous nucleation and the subsequent crystallisation of ice in aqueous organic acid solution droplets will be presented. Aqueous citric acid solutions have been chosen as a model system and are thought to be representative of organic material found in many upper tropospheric aerosols. It will be shown that the metastable cubic form of ice can nucleate, crystallise and is stabilised in citric acid solution droplets which freeze homogeneously below about 219 K. Cubic ice is only produced when ammonium bisulphate solution droplets freeze below about 183 K. This solute dependence is related to the viscosity and glass forming ability of the respective aqueous solutions. Experiments were also performed with more concentrated citric acid solution droplets, in which ice should nucleate at lower temperatures. It is found that ice crystallisation is inhibited below ~198 K in citric acid solution droplets. These droplets most likely formed ultra-viscous liquids or glassy material rather than crystallise. In order to test the impact of glassy particles on cloud formation, glassy citric acid particles were recently produced within the AIDA cloud simulation chamber in Karlsruhe Germany. Preliminary results suggest glassy citric acid aerosol do not produce an ice cloud via a homogeneous freezing route. In fact, ice particle production is markedly suppressed.

  13. Formation and spread of aircraft-induced holes in clouds.

    PubMed

    Heymsfield, Andrew J; Thompson, Gregory; Morrison, Hugh; Bansemer, Aaron; Rasmussen, Roy M; Minnis, Patrick; Wang, Zhien; Zhang, Damao

    2011-07-01

    Hole-punch and canal clouds have been observed for more than 50 years, but the mechanisms of formation, development, duration, and thus the extent of their effect have largely been ignored. The holes have been associated with inadvertent seeding of clouds with ice particles generated by aircraft, produced through spontaneous freezing of cloud droplets in air cooled as it flows around aircraft propeller tips or over jet aircraft wings. Model simulations indicate that the growth of the ice particles can induce vertical motions with a duration of 1 hour or more, a process that expands the holes and canals in clouds. Global effects are minimal, but regionally near major airports, additional precipitation can be induced.

  14. Interactions Between Arctic Sea Ice, Clouds, and the Circulation

    NASA Astrophysics Data System (ADS)

    Taylor, P. C.; Kato, S.; Xu, K. M.; Baker, N. C.

    2014-12-01

    The Arctic is one of the most climatically sensitive regions of the Earth. Climate models robustly project the Arctic to warm 2-3 times faster than the global mean surface temperature—termed polar warming amplification (PWA)—but also display the widest range of surface temperature projections in this region. The response of the Arctic to increased CO2 modulates the response in tropical and extra-tropical regions through teleconnections in the atmospheric circulation. An increased frequency of extreme precipitation events in the northern mid-latitudes, for example, has been linked to the change in the background equator-to-pole temperature gradient implied by PWA. Understanding the Arctic climate system is therefore important for predicting global climate change. The ice albedo feedback is the primary mechanism driving PWA, however cloud and dynamical feedbacks significantly contribute. These feedback mechanisms, however, do not operate independently. How do clouds respond to variations in sea ice? This critical question is addressed by combining sea ice, cloud, and radiation observations from satellites—including CERES, CloudSAT, CALIPSO, MODIS, and microwave radiometers—to investigate sea ice-cloud interactions at the interannual timescale in the Arctic. Cloud characteristics are strongly tied to the atmospheric dynamic and thermodynamic state. Therefore, the sensitivity of Arctic cloud characteristics—vertical distribution and optical properties—to sea ice anomalies is computed within atmospheric dynamic and thermodynamic regimes. Results indicate that the cloud response to changes in sea ice concentration differs significantly between atmospheric state regimes. This suggests that (1) the atmospheric dynamic and thermodynamic characteristics and (2) the characteristics of the marginal ice zone are important for determining the seasonal forcing by cloud on sea ice variability.

  15. 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.

  16. Quantifying the Amount of Ice in Cold Tropical Cirrus Clouds

    NASA Technical Reports Server (NTRS)

    Avery, Melody A.; Winker, David M.; Garnier, Anne; Lawson, R. Paul; Heymsfield, Andrew J.; Mo, Qixu; Schoeberl, Mark R.; Woods, Sarah; Lance, Sara; Young, Stuart A.; Vaughan, Mark A.; Trepte, Charles R.

    2014-01-01

    How much ice is there in the Tropical Tropopause layer, globally? How does one begin to answer that question? Clouds are currently the largest source of uncertainty in climate models, and the ice water content (IWC) of cold cirrus clouds is needed to understand the total water and radiation budgets of the upper troposphere and lower stratosphere (UT/LS). The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite, originally a "pathfinder" mission only expected to last for three years, has now been operational for more than eight years. Lidar data from CALIPSO can provide information about how IWC is vertically distributed in the UT/LS, and about inter-annual variability and seasonal changes in cloud ice. However, cloud IWC is difficult to measure accurately with either remote or in situ instruments because IWC from cold cirrus clouds is derived from the particle cross-sectional area or visible extinction coefficient. Assumptions must be made about the relationship between the area, volume and density of ice particles with various crystal habits. Recently there have been numerous aircraft field campaigns providing detailed information about cirrus ice water content from cloud probes. This presentation evaluates the assumptions made when creating the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) global IWC data set, using recently reanalyzed aircraft particle probe measurements of very cold, thin TTL cirrus from the 2006 CR-AVE.

  17. Formation of planetesimals in collapsing pebble clouds

    NASA Astrophysics Data System (ADS)

    Wahlberg Jansson, K.; Johansen, A.

    2014-07-01

    Asteroids and Kuiper belt objects are remnant planetesimals from the epoch of planet formation. Their physical properties hold important clues to understanding how minor bodies formed in the Solar Nebula. The first stage of the planet formation process is the accumulation of dust and ice grains into mm-cm-sized pebbles. Due to the interaction with the gas in the protoplanetary disk, these pebbles can clump together through the streaming instability and form gravitationally bound particle pebble 'clouds'. Pebbles in the cloud collide with each other, dissipating energy into heat. As the cloud loses energy, it contracts, and one would expect the particles to move faster and faster due to the negative heat capacity nature of self-gravitating systems. However, for high-mass clouds, the collapse is limited by free-fall and the cloud does not have time to virialize. This in turn leads to lower collision speeds but thanks to increased density also to increased collision rates and a runaway collapse. We investigate three important properties of the collapse: (i) the time-scale to collapse to solid density, (ii) the temporal evolution of the size spectrum of the pebbles, and (iii) the multiplicity of the resulting planetesimals. We find that planetesimals larger than 100 km in radius collapse on the free-fall time-scale of about 25 years. Lower-mass clouds have longer pebble collision time-scales and hence collapse much more slowly, with collapse times of a few hundred years for 10-km-scale planetesimals and a few thousand years for 1-km-scale planetesimals. The mass of the pebble cloud also determines the structure of the resulting planetesimal. The collision speed among the pebbles in low- mass clouds is below the threshold for fragmentation, forming pebble- pile planetesimals consisting of the primordial pebbles from the nebula. Planetesimals above 100 km in radius, on the other hand, consist of mixtures of dust (pebble fragments) and pebbles which have undergone

  18. Water ice clouds on Mars: Exploring processes through modeling and laboratory work

    NASA Astrophysics Data System (ADS)

    Santiago-Materese, Delia Liza

    Water ice clouds on Mars are an important component of the hydrologic cycle as well as the overall climate system of the planet. The goal of this research is to better understand water ice cloud formation and behavior on Mars. We use modeling and laboratory experiments to explore different processes related to water ice cloud formation and evolution. The first goal of this work is to examine how well the Martian water cycle is simulated by the NASA Ames Mars General Circulation Model. The simulation predicts atmospheric water vapor amounts approximately half of those observed, globally. We identify water ice clouds as being a major contributor to this discrepancy. The model closely reproduces the convective aphelion cloud belt at the equator, but deviates substantially from observations over the North Polar Cap region. Modifying the nucleation scheme within the cloud microphysical model brings model results closer to observations and affects the surface radiative balance, which affects the annual cycle of sublimation and deposition of water ice at the residual North Polar Cap. The most realistic global water vapor and cloud patterns come from limiting the nucleation rate of particles at the poles. Our simulations show that the North Polar Cap region exhibits atmospheric dynamics where stratiform clouds form. We hypothesize that the modified nucleation scheme compensates for biases in the radiative properties of the stratiform clouds expected over the North Polar Cap. More broadly, this study illustrates the strong sensitivity of the Martian global water cycle to clouds over the North Polar Cap region. The second goal of this work is to assess the ability of various salts to serve as water ice cloud condensation nuclei under Martian conditions. We use a vacuum chamber to simulate the cold, lower pressure atmospheric conditions on Mars and find the critical saturation ratios at which the substrates nucleate water ice. We find no significant difference between sodium

  19. Lobster Tail Ice Formation on Aerosurface

    NASA Technical Reports Server (NTRS)

    1999-01-01

    Glace Ice formation commonly refered to as 'Lobster Tail' by scientists and engineers, is caused to form on the leading edge of a aircraft tail section in the icing research tunnel at the NASA Glenn Research Center, Cleveland, Ohio.

  20. Modulation of Cloud Phase, Precipitation and Radiation by Ice Nuclei Perturbations in High Resolution Model Simulations

    NASA Astrophysics Data System (ADS)

    Paukert, M.; Hoose, C.

    2015-12-01

    The distribution of cloud phase determines a multitude of cloud properties, such as albedo, precipitation and temporal evolution. The crucial role of primary ice formation has been recognized decades ago, yet only in the last years our knowledge has reached a level that allows for approximate estimations of the aerosol-dependent effect of ice nucleation in high resolution cloud simulations. However, besides primary formation of cloud particles, also their thermodynamic trajectories as well as particle-particle interactions are determinants of the cloud phase. Although the conversion of liquid to ice in the mixed-phase regime is unidirectional, a perturbation in the primary ice formation (with increased aerosol concentrations as a trigger) does not necessarily yield higher ice fractions. This can be attributed to the modified efficiencies of depositional particle growth, liquid-ice-collisions and particle sedimentation. Consequently a modified mixed-phase regime impacts both warm (T>0°C) and cold (T<-40°C) parts of the atmosphere by sedimentation and vertical advection, respectively. Our study is motivated by the question how the liquid-ice partitioning is modulated by perturbed ice nuclei concentrations. By suppressing the feedback of microphysical perturbations on the model dynamics we are able to extract the microphysical effects. We define different microphysical regimes based on liquid and ice mass changes in order to analyze the processes which have led to those regimes. We find that conversion via the vapor phase is dominant only in distinct temperature regimes, while liquid mass changes are often linked to riming-dominated regimes, and sedimentation efficiencies make an important contribution to ice mass changes which finally determine the surface precipitation via melting. For our case of deep convection, cloud albedo is highly sensitive to the amount of small droplets reaching the homogeneous freezing level. We investigated simulations of three

  1. Clarifying the dominant sources and mechanisms of cirrus cloud formation.

    PubMed

    Cziczo, Daniel J; Froyd, Karl D; Hoose, Corinna; Jensen, Eric J; Diao, Minghui; Zondlo, Mark A; Smith, Jessica B; Twohy, Cynthia H; Murphy, Daniel M

    2013-06-14

    Formation of cirrus clouds depends on the availability of ice nuclei to begin condensation of atmospheric water vapor. Although it is known that only a small fraction of atmospheric aerosols are efficient ice nuclei, the critical ingredients that make those aerosols so effective have not been established. We have determined in situ the composition of the residual particles within cirrus crystals after the ice was sublimated. Our results demonstrate that mineral dust and metallic particles are the dominant source of residual particles, whereas sulfate and organic particles are underrepresented, and elemental carbon and biological materials are essentially absent. Further, composition analysis combined with relative humidity measurements suggests that heterogeneous freezing was the dominant formation mechanism of these clouds.

  2. Understanding Ice Supersaturation, Particle Growth, and Number Concentration in Cirrus Clouds

    SciTech Connect

    Comstock, Jennifer M.; Lin, Ruei-Fong; Starr, David O.; Yang, P.

    2008-12-10

    Many factors control the ice supersaturation and microphysical properties in cirrus clouds. We explore the effects of dynamic forcing, ice nucleation mechanisms, and ice crystal growth rate on the evolution and distribution of water vapor and cloud properties in cirrus clouds using a detailed microphysical model and remote sensing measurements obtained at the Department of Energy’s Atmospheric Radiation Measurement (ARM) Climate Research Facility located near Lamont, OK. To help understand dynamic scales important in cirrus formation, we force the model using both large-scale forcing derived using ARM variational analysis, and mean mesoscale velocity derived from radar Doppler velocity measurements. Both heterogeneous and homogeneous nucleation processes are explored, where we have implemented a rigorous classical theory heterogeneous nucleation scheme to compare with empirical representations. We evaluate model simulations by examining both bulk cloud properties and distributions of measured radar reflectivity, lidar extinction, and water vapor profiles, as well as retrieved cloud microphysical properties. This approach allows for independent verification of both the large and small particle modes of the particle size distribution. Our results suggest that mesoscale variability is the primary mechanism needed to reproduce observed quantities, while nucleation mechanism is secondary. Slow ice crystal growth tends to overestimate the number of small ice crystals, but does not seem to influence bulk properties such as ice water path and cloud thickness. The most realistic simulations as compared with observations are forced using mesoscale waves, include fast ice crystal growth, and initiate ice by either homogeneous or heterogeneous nucleation. Ice crystal number concentrations on the order of 10-100 L-1 produce results consistent with both lidar and radar observations during a cirrus event observed on 7 December 1999, which has an optical depth range typical of

  3. Effects of ice particle size vertical inhomogeneity on the passive remote sensing of ice clouds

    SciTech Connect

    Zhang, Zhibo; Platnick, Steven; Yang, Ping; Heidinger, Andrew K.; Comstock, Jennifer M.

    2010-09-03

    The solar reflectance bi-spectral (SRBS) and infrared split-window (IRSpW) methods are two of the most popular techniques for passive ice cloud property retrievals from multispectral imagers. Ice clouds are usually assumed to be vertically homogeneous in global operational algorithms based on these methods, although significant vertical variations of ice particle size are typically observed in ice clouds. In this study we investigate uncertainties in retrieved optical thickness, effective particle size, and ice water path introduced by a homogeneous cloud assumption in both the SRBS and IRSpW methods, and focus on whether the assumption can lead to significant discrepancies between the two methods. The study simulates the upwelling spectral radiance associated with vertically structured clouds and passes the results through representative SRBS and IRSpW retrieval algorithms. Cloud optical thickness is limited to values for which IRSpW retrievals are possible (optical thickness less than about 7). When the ice cloud is optically thin and yet has a significant ice particle size vertical variation, it is found that both methods tend to underestimate the effective radius and ice water path. The reason for the underestimation is the nonlinear dependence of ice particle scattering properties (extinction and single scattering albedo) on the effective radius. Because the nonlinearity effect is stronger in the IRSpW than the SRBS method, the IRSpW-based IWP tends to be smaller than the SRBS counterpart. When the ice cloud is moderately optically thick and ice particle size increases monotonically towards cloud base, the two methods are in qualitative agreement; in the event that ice particle size decreases towards cloud base, the effective radius and ice water path retrievals based on the SRBS method are substantially larger than those from the IRSpW. The main findings of this study suggest that the homogenous cloud assumption can affect the SRBS and IRSpW methods to

  4. The formation of ice sails

    NASA Astrophysics Data System (ADS)

    Fowler, Andrew; Mayer, Christoph

    2017-04-01

    Ice sails are prominent pyramid-like ice forms which are found on certain debris-covered glaciers in the Karakoram, for example on Baltoro Glacier. Two questions immediately arise concerning their existence: what causes their formation (and their subsequent eventual disappearance), and why are they not found more widely? The answer to both of these questions can be provided by a mathematical model of glacier surface melting which takes account of the effect of debris cover on the melt rate. In particular, the effect noted by Östrem that very thin debris cover causes an increase in melt rate allows for instability in a uniform debris cover, and numerical solutions of the model show that sails of the correct dimensions and shape grow and subsequently decay as the debris cover thickens downglacier. The apparent distinguishing feature which promotes sail growth is a low relative humidity, which allows the bare ice melt rate to be significantly lower than the peak debris-covered value.

  5. Monstrous Ice Cloud System in Titan's Present South Polar Stratosphere

    NASA Astrophysics Data System (ADS)

    Anderson, Carrie; Samuelson, Robert; McLain, Jason; Achterberg, Richard; Flasar, F. Michael; Milam, Stefanie

    2015-11-01

    During southern autumn when sunlight was still available, Cassini's Imaging Science Subsystem discovered a cloud around 300 km near Titan's south pole (West, R. A. et al., AAS/DPS Abstracts, 45, #305.03, 2013); the cloud was later determined by Cassini's Visible and InfraRed Mapping Spectrometer to contain HCN ice (de Kok et al., Nature, 514, pp 65-67, 2014). This cloud has proven to be only the tip of an extensive ice cloud system contained in Titan's south polar stratosphere, as seen through the night-vision goggles of Cassini's Composite InfraRed Spectrometer (CIRS). As the sun sets and the gloom of southern winter approaches, evidence is beginning to accumulate from CIRS far-IR spectra that a massive system of nitrile ice clouds is developing in Titan's south polar stratosphere. Even during the depths of northern winter, nothing like the strength of this southern system was evident in corresponding north polar regions.From the long slant paths that are available from limb-viewing CIRS far-IR spectra, we have the first definitive detection of the ν6 band of cyanoacetylene (HC3N) ice in Titan’s south polar stratosphere. In addition, we also see a strong blend of nitrile ice lattice vibration features around 160 cm-1. From these data we are able to derive ice abundances. The most prominent (and still chemically unidentified) ice emission feature, the Haystack, (at 220 cm-1) is also observed. We establish the vertical distributions of the ice cloud systems associated with both the 160 cm-1 feature and the Haystack. The ultimate aim is to refine the physical and possibly the chemical relationships between the two. Transmittance thin film spectra of nitrile ice mixtures obtained in our Spectroscopy for Planetary ICes Environments (SPICE) laboratory are used to support these analyses.

  6. Cloud chamber experiments on the origin of ice crystal complexity in cirrus clouds

    NASA Astrophysics Data System (ADS)

    Schnaiter, M.; Järvinen, E.; Vochezer, P.; Abdelmonem, A.; Wagner, R.; Jourdan, O.; Mioche, G.; Shcherbakov, V. N.; Schmitt, C. G.; Tricoli, U.; Ulanowski, Z.; Heymsfield, A. J.

    2015-11-01

    This study reports on the origin of ice crystal complexity and its influence on the angular light scattering properties of cirrus clouds. Cloud simulation experiments were conducted at the AIDA (Aerosol Interactions and Dynamics in the Atmosphere) cloud chamber of the Karlsruhe Institute of Technology (KIT). A new experimental procedure was applied to grow and sublimate ice particles at defined super- and subsaturated ice conditions and for temperatures in the -40 to -60 °C range. The experiments were performed for ice clouds generated via homogeneous and heterogeneous initial nucleation. Ice crystal complexity was deduced from measurements of spatially resolved single particle light scattering patterns by the latest version of the Small Ice Detector (SID-3). It was found that a high ice crystal complexity is dominating the microphysics of the simulated clouds and the degree of this complexity is dependent on the available water vapour during the crystal growth. Indications were found that the crystal complexity is influenced by unfrozen H2SO4/H2O residuals in the case of homogeneous initial ice nucleation. Angular light scattering functions of the simulated ice clouds were measured by the two currently available airborne polar nephelometers; the Polar Nephelometer (PN) probe of LaMP and the Particle Habit Imaging and Polar Scattering (PHIPS-HALO) probe of KIT. The measured scattering functions are featureless and flat in the side- and backward scattering directions resulting in low asymmetry parameters g around 0.78. It was found that these functions have a rather low sensitivity to the crystal complexity for ice clouds that were grown under typical atmospheric conditions. These results have implications for the microphysical properties of cirrus clouds and for the radiative transfer through these clouds.

  7. 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.

    2017-01-31

    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

  8. Molecular cloud evolution and star formation

    NASA Technical Reports Server (NTRS)

    Silk, J.

    1985-01-01

    The present state of knowledge of the relationship between molecular clouds and young stars is reviewed. The determination of physical parameters from molecular line observations is summarized, and evidence for fragmentation of molecular clouds is discussed. Hierarchical fragmentation is reviewed, minimum fragment scales are derived, and the stability against fragmentation of both spherically and anisotropically collapsing clouds is discussed. Observational evidence for high-velocity flows in clouds is summarized, and the effects of winds from pre-main sequence stars on molecular gas are discussed. The triggering of cloud collapse by enhanced pressure is addressed, as is the formation of dense shells by spherical outflows and their subsequent breakup. A model for low-mass star formation is presented, and constraints on star formation from the initial mass function are examined. The properties of giant molecular clouds and massive star formation are described. The implications of magnetic fields for cloud evolution and star formation are addressed.

  9. Molecular cloud evolution and star formation

    NASA Technical Reports Server (NTRS)

    Silk, J.

    1985-01-01

    The present state of knowledge of the relationship between molecular clouds and young stars is reviewed. The determination of physical parameters from molecular line observations is summarized, and evidence for fragmentation of molecular clouds is discussed. Hierarchical fragmentation is reviewed, minimum fragment scales are derived, and the stability against fragmentation of both spherically and anisotropically collapsing clouds is discussed. Observational evidence for high-velocity flows in clouds is summarized, and the effects of winds from pre-main sequence stars on molecular gas are discussed. The triggering of cloud collapse by enhanced pressure is addressed, as is the formation of dense shells by spherical outflows and their subsequent breakup. A model for low-mass star formation is presented, and constraints on star formation from the initial mass function are examined. The properties of giant molecular clouds and massive star formation are described. The implications of magnetic fields for cloud evolution and star formation are addressed.

  10. Water-ice clouds on Mars: Location and seasonal variation

    NASA Astrophysics Data System (ADS)

    Christensen, P. R.; Jaramillo, L.; Greeley, R.

    1985-04-01

    Water-ice clouds were located on Mars using Viking infrared thermal mapper (IRTM) broadband spectral observations. The IRTM instrument had 5 thermal bands centered at 7, 9, 11, 15, and 20 microns. Clouds and hazes were consistently observed in four northern hemisphere regions centered over Tharsis, Arabia, Elysium, and along the boundary between the crater uplands and the northern plains. During the northern spring and summer when the atmosphere is relatively free of dust, there is a distinct difference between the cloud abundance in the Northern and Southern Hemispheres, with clouds and hazes being rare in the south. A second important class of water-ice clouds are those observed along the boundary of the retreating north polar cap. These clouds occur at all longitudes around the cap and are generally confined to within +/- 5 deg of the cap boundary. The cloud opacities can be estimated using a delta-Eddington radiative transfer model which incorporates Mie scattering and the electrical properties of water-ice. Assuming realistic, but non-unique, values for the ice particle size and cloud temperature, the derived opacities range from near-zero to 1.

  11. Water-ice Clouds on Mars: Location and Seasonal Variation

    NASA Technical Reports Server (NTRS)

    Christensen, P. R.; Jaramillo, L.; Greeley, R.

    1985-01-01

    Water-ice clouds were located on Mars using Viking infrared thermal mapper (IRTM) broadband spectral observations. The IRTM instrument had 5 thermal bands centered at 7, 9, 11, 15, and 20 microns. Clouds and hazes were consistently observed in four northern hemisphere regions centered over Tharsis, Arabia, Elysium, and along the boundary between the crater uplands and the northern plains. During the northern spring and summer when the atmosphere is relatively free of dust, there is a distinct difference between the cloud abundance in the Northern and Southern Hemispheres, with clouds and hazes being rare in the south. A second important class of water-ice clouds are those observed along the boundary of the retreating north polar cap. These clouds occur at all longitudes around the cap and are generally confined to within +/- 5 deg of the cap boundary. The cloud opacities can be estimated using a delta-Eddington radiative transfer model which incorporates Mie scattering and the electrical properties of water-ice. Assuming realistic, but non-unique, values for the ice particle size and cloud temperature, the derived opacities range from near-zero to 1.

  12. Cloud chamber experiments on the origin of ice crystal complexity in cirrus clouds

    NASA Astrophysics Data System (ADS)

    Schnaiter, Martin; Järvinen, Emma; Vochezer, Paul; Abdelmonem, Ahmed; Wagner, Robert; Jourdan, Olivier; Mioche, Guillaume; Shcherbakov, Valery N.; Schmitt, Carl G.; Tricoli, Ugo; Ulanowski, Zbigniew; Heymsfield, Andrew J.

    2016-04-01

    This study reports on the origin of small-scale ice crystal complexity and its influence on the angular light scattering properties of cirrus clouds. Cloud simulation experiments were conducted at the AIDA (Aerosol Interactions and Dynamics in the Atmosphere) cloud chamber of the Karlsruhe Institute of Technology (KIT). A new experimental procedure was applied to grow and sublimate ice particles at defined super- and subsaturated ice conditions and for temperatures in the -40 to -60 °C range. The experiments were performed for ice clouds generated via homogeneous and heterogeneous initial nucleation. Small-scale ice crystal complexity was deduced from measurements of spatially resolved single particle light scattering patterns by the latest version of the Small Ice Detector (SID-3). It was found that a high crystal complexity dominates the microphysics of the simulated clouds and the degree of this complexity is dependent on the available water vapor during the crystal growth. Indications were found that the small-scale crystal complexity is influenced by unfrozen H2SO4 / H2O residuals in the case of homogeneous initial ice nucleation. Angular light scattering functions of the simulated ice clouds were measured by the two currently available airborne polar nephelometers: the polar nephelometer (PN) probe of Laboratoire de Métérologie et Physique (LaMP) and the Particle Habit Imaging and Polar Scattering (PHIPS-HALO) probe of KIT. The measured scattering functions are featureless and flat in the side and backward scattering directions. It was found that these functions have a rather low sensitivity to the small-scale crystal complexity for ice clouds that were grown under typical atmospheric conditions. These results have implications for the microphysical properties of cirrus clouds and for the radiative transfer through these clouds.

  13. Laboratory studies of heterogeneous reactions on ice and nitric acid-doped ice surfaces representative of polar stratospheric clouds and cirrus clouds

    NASA Astrophysics Data System (ADS)

    Zondlo, Mark Andrew

    1999-10-01

    Heterogeneous reactions on ice particles play an important role in the formation of the Antarctic ozone hole and in the chemistry of cirrus clouds and airplane condensation trails. Nonetheless, the phase, composition, and state of adsorption of surface products are largely unknown. To this end, atmospherically relevant molecules were studied on thin ice and HNO3 /H2O films. FTIR reflection absorption infrared spectroscopy was used to probe the condensed phases, and a Knudsen cell reactor was used to measure heterogeneous reaction rates. N2O5 and ClONO2 reacted rapidly on ice at 185 K to form a supercooled ~3:1 H2O:HNO3 liquid layer over the ice surface. Reaction efficiencies over the supercooled liquid layer were γ = 0.0007 +/- 0.0003 for N2O5 and γ = 0.0003 +/- 0.002 for ClONO2. Although nitric acid trihydrate (NAT) was most thermodynamically stable, the supercooled H 2O/HNO3 liquid never crystallized to NAT when at the ice frost point. These results suggest that polar stratospheric cloud (PSC) ice particles may be coated with a supercooled H2O/HNO3 liquid layer over the surface. Therefore, water-ice PSCs may be most accurately modeled with reaction rates over supercooled H2O/HNO3 liquids. The reaction of ClONO2 on crystalline H2O/HNO 3 films was studied at 185 K. As the relative humidity increased from 5 to 130%, reaction efficiencies increased from 0.0004 to 0.007 and progressively water-rich surface layers formed. The availability of surface water largely controls the observed kinetics of this reaction. The interaction of HNO3 and HCl with ice showed a monolayer and a multilayer uptake regime from 180-205 K delineated by the ice/liquid coexistence curve for each species. HBr and HI showed continuous uptake on ice with the formation of amorphous H2O/HX layers. All species are expected to show monolayer uptake under cirrus cloud conditions. Finally, the uptake of methanol on ice was examined from 120-200 K. Methanol surface coverages at a partial pressure of 2

  14. Convective Formation of Pileus Cloud Near the Tropopause

    NASA Technical Reports Server (NTRS)

    Garrett, Timothy J.; Dean-Day, Jonathan; Liu, Chuntao; Barnett, Brian K.; Mace, Gerald G.; Baumgardner, Darrel G.; Webster, Christopher R.; Bui, T. Paul; Read, William G.; Minnis, Patrick

    2005-01-01

    Pileus clouds form where humid, stably stratified air is mechanically displaced vertically ahead of rising convection. This paper describes convective formation of pileus cloud in the tropopause transition layer (TTL), and explores a possible link to the formation of long-lasting cirrus at cold temperatures. In-situ measurements from off the coast of Honduras during the July 2002 CRYSTALFACE experiment show an example of TTL cirrus associated with, and penetrated by, deep convection. The cirrus was enriched with total water compared to its surroundings, but composed of extremely small ice crystals with effective radii between 2 and 4 m. Through gravity wave analysis, and intercomparison of measured and simulated cloud microphysics, it is argued that the TTL cirrus in this case originated neither from convectively-forced gravity wave motions nor environmental mixing alone. Rather, it is hypothesized that some combination was involved in which, first, convection forced pileus cloud to form from TTL air; second, it punctured the pileus layer, contributing larger ice crystals through interfacial mixing; third, the addition of condensate inhibited evaporation of the original pileus ice crystals in the warm phase of the ensuing gravity wave; fourth, through successive pulses, deep convection formed the observed layer of TTL cirrus. While the general incidence and longevity of pileus cloud remains unknown, in-situ measurements, and satellite-based Microwave Limb Sounder retrievals, suggest that much of the tropical TTL is sufficiently humid to be susceptible to its formation. Where these clouds form and persist, there is potential for an irreversible repartition from water vapor to ice at cold temperatures.

  15. 2006 Icing Cloud Calibration of the NASA Glenn Icing Research Tunnel

    NASA Technical Reports Server (NTRS)

    Ide, Robert F.; Sheldon, David W.

    2008-01-01

    In order to improve icing cloud uniformity, changes were made to the tunnel at the NASA Glenn Research Center in the vicinity of the spray bars. These changes necessitated a complete recalibration of the icing clouds. This report describes the methods used in the recalibration, including the procedure used to optimize the uniformity of the icing cloud and the use of a standard icing blade technique for measurement of liquid water content. The instruments and methods used to perform the droplet size calibration are also described. The liquid water content/droplet size operating envelopes of the icing tunnel are shown for a range of airspeeds and compared to the FAA icing certification criteria.

  16. The occurrence of ice production in slightly supercooled Arctic stratiform clouds as observed by ground-based remote sensors at the ARM NSA site

    NASA Astrophysics Data System (ADS)

    Zhang, Damao; Wang, Zhien; Luo, Tao; Yin, Yan; Flynn, Connor

    2017-03-01

    Ice particle formation in slightly supercooled stratiform clouds is not well documented or understood. In this study, 4 years of combined lidar depolarization and radar reflectivity (Ze) measurements are analyzed to distinguish between cold drizzle and ice crystal formations in slightly supercooled Arctic stratiform clouds over the Atmospheric Radiation Measurement Program Climate Research Facility North Slope of Alaska Utqiaġvik ("Barrow") site. Ice particles are detected and statistically shown to be responsible for the strong precipitation in slightly supercooled Arctic stratiform clouds at cloud top temperatures as high as -4°C. For ice precipitating Arctic stratiform clouds, the lidar particulate linear depolarization ratio (δpar_lin) correlates well with radar Ze at each temperature range, but the δpar_lin-Ze relationship varies with temperature ranges. In addition, lidar depolarization and radar Ze observations of ice generation characteristics in Arctic stratiform clouds are consistent with laboratory-measured temperature-dependent ice growth habits.

  17. Biological ice nuclei are rapidly lost from precipitating clouds

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    Ice nucleation is a key step for the formation of precipitation in cold clouds. Particularly interesting is the nucleating behaviour of aerosols of biological origin, showing activity at temperatures up to -2° C. Yet, the effective impact of biological ice nuclei (IN) on the development of precipitation on global and local scales compared to more abundant IN active at colder temperatures is still ambiguous. The results coming from a year of observations at the High Altitude Research Station of Jungfraujoch, in the Swiss Alps, 3580 m a.s.l. will be presented. Freshly fallen snow was collected (91 samples in total) from precipitating tropospheric clouds and analysed immediately on site for the concentration of IN active at temperatures warmer than -12° C by immersion freezing. The stable oxygen ratio (δ18O) of each sample was measured as well; this value was used to estimate the fraction of water vapour lost from a precipitating cloud (1-fv) prior to its arrival at Jungfraujoch. IN and the fraction of water vapour lost showed a very similar pattern of variation both on a time scale of hours and over the whole year. Our analysis of the data suggests that the abundance of IN in snowfall is rapidly halved, with every 10% of water vapour lost through precipitation and that IN tend to be preferentially activated and lost compared to other particles of similar size. This provides a substantial constraint for the role of such IN in conditioning precipitation in time and space. Up to 75% of the observed variability in IN concentrations at Jungfraujoch was explained by the factors 1-fv and wind speed, suggesting that wind may play a role in keeping activated IN suspended in the air. Unresolved issues like the role of other parameters (seasonality, source region) in describing IN abundances and a deeper characterisation of biological IN active material collected at Jungfraujoch will be discussed.

  18. Field and Laboratory Studies of Ice Nucleation in Winter Orographic Clouds.

    NASA Astrophysics Data System (ADS)

    Rogers, David Clark

    The present research was divided into two separate but related areas: (1) Cloud microphysical data from instrumented aircraft flights through winter clouds over Elk Mountain were analyzed to assess the formation of ice crystals under natural conditions. The results indicated that for these supercooled clouds, most crystals form near the upwind edge of the cloud, where water vapor condenses on available cloud condensation nuclei (CCN). Two possible explanations were offered: the active nuclei are either very small contact ice nuclei, or they are a subset of the CCN known as "condensation -freezing ice nuclei ". Furthermore, this formation was indicated as likely to be a primary nucleation process since there was a strong temperature dependence of crystal concentration: the ensemble of data showed typical concentrations of one per liter at -15(DEGREES)C and changed by a factor 10(DEGREES) for a 9(DEGREES)C temperature change. (2) In order to assess the contribution made by condensation-freezing nuclei, natural concentrations of both deposition and condensation -freezing nuclei were measured with a continuous flow thermal gradient diffusion chamber (CFC). Significant characteristics of the chamber design included: concentric cylinder geometry, vertical axis alignment and flow, ice covered walls of ebonized copper, and optical detection of ice crystals which form and grow on active ice nuclei. As an aid to instrument design and data interpretation, a mathematical model of the temperature and vapor fields in the chamber and of the growth and fallout of water and ice particles was constructed. Its predictions compared favorably with those of another numerical model. Laboratory experiments were performed with artificial aerosols and confirmed both the ability of the chamber to detect known ice nuclei and of the optical-electronic system to distinguish crystals from droplets. Ice nucleus measurements were obtained for natural aerosols over the range of temperatures -7

  19. Factors That Influence Polar Stratospheric Cloud Formation Over Antarctica

    NASA Astrophysics Data System (ADS)

    Steele, H.; Lumpe, J.; Bevilacqua, R.; Hoppel, K.; Turco, R.

    2001-05-01

    Polar stratospheric clouds (PSCs), the precursors of springtime ozone loss in the polar stratosphere, are formed under the conditions of extreme cold found in the winter polar stratosphere. Analysis of the first satellite observations of these clouds concluded that unrealistically high concentrations of water vapor would be required to account for their formation by dissolution of sulfate aerosols alone, and that freezing to ice, which would require a lower water vapor mixing ratio, was therefore more likely. Freezing to water ice is now thought to be only one of the plausible mechanisms for cloud formation, and the resultant clouds have been labelled type II PSCs. More recent observations of PSCs by in-situ and satellite instruments have revealed their nature to be more heterogeneous. Lidar measurements have recorded a wide range of depolarisations which suggest the presence of both liquid and frozen particles. It is now thought that possible compositions include nitric acid trihydrate (NAT) (type Ia PSCs), nitric acid dihydrate (NAD) and supercooled ternary solutions (STS) of sulfuric acid, nitric acid and water (type Ib clouds). Although there are plausible and well-accepted mechanisms for cloud formation, there remain many unanswered questions, and modellers have been unable to explain all the observations within the scope of a single theory. Many observations are best be explained by a model in which PSCs are ternary solution droplets, but with a small fraction forming NAT primarily in conjunction with water ice after exposure to temperatures below the ice frost point. It has therefore been suggested that perhaps temperature history, as well as ambient temperature, plays a role in determining which clouds form. It is also thought that rapid cooling caused by orographically induced lee-waves might trigger the crystallisation of NAT from STS droplets. Some investigators have hypothesized that exposure time to temperatures below the NAT frost point are a

  20. A kinetic isotope effect during ice formation by water freezing

    NASA Astrophysics Data System (ADS)

    Souchez, R.; Jouzel, J.; Lorrain, R.; Sleewaegen, S.; Stiévenard, M.; Verbeke, V.

    2000-07-01

    A kinetic isotope effect is known to occur during ice formation from water vapour in a cloud ; it is due to the difference in molecular diffusivities in air of HDO and H218O molecules. A similar effect is likely during water freezing since diffusion coefficients of HDO and H218O are also different in liquid water. Their values are however less different from each other than those in air. Therefore, such a kinetic isotope effect during water freezing is less frequently observed in Nature. This paper describes a situation in Antarctica where this effect is conspicuous in icings (aufeis). In this type of ice indeed there is no relationship between δD (or δ18O) and deuterium excess whereas a clear inverse relationship between these parameters exists in ice formed by water freezing when equilibrium isotopic fractionation applies. This kinetic effect is potentially present in hail within clouds, in infiltration ice (formed during sea ice growth) and in some kinds of ground ice.

  1. Comet Formation in Collapsing Pebble Clouds: Pebble Formation

    NASA Astrophysics Data System (ADS)

    Lorek, Sebastian; Lacerda, Pedro; Blum, Jürgen

    2016-10-01

    The formation of comets by gradual growth from (sub-)micron sized ice and dust monomers to km-sized bodies suffers from growth barriers (bouncing, fragmentation, drift). Growth stalls at sizes between mm and m, rendering it considerably difficult to form km-sized objects. However, the streaming instability and subsequent gravitational collapse of clouds of pebbles (particle agglomerates) provide an alternative. The pebbles require Stokes numbers between 0.01 and 3, which corresponds to sizes between mm and dm, unless the pebbles are very porous. Furthermore, the local solid/gas density ratio must be near unity and the local total mass in solids must be >2-3x higher than the minimum mass solar nebula value (1% of gas mass). The gravitational collapse of the pebble clouds then bypasses the growth barriers, forming km-sized bodies directly. The observed bulk properties of comets, e.g. porosity near 80%, are consistent with this scenario. Okuzumi et al. (2012) showed that including porosity comets can form directly via coagulation from sub-micron monomers. However, this relies on using 0.1 micron monomers and pure sticking collisions. Krijt et al. (2015) included erosion and found that highly porous pebbles around 109 g in mass can form and might trigger the streaming instability. Drazkowska & Dullemond (2014) showed that compact coagulation can lead to triggering the streaming instability. All those studies include only ice and a simplified collision model. However, a large fraction of a comet's mass is dust. Here, we develop a pebble formation model that includes sticking, bouncing, mass transfer/erosion, and fragmentation, as well as porosity. To take dust and ice into account, we extended the collision model for the treatment of mixed pebbles by linearly interpolating the threshold velocities and compression curves between the cases of pure dust and pure ice based on the fractional abundance of dust monomers. Our simulations show that pebble formation with the full

  2. NASA Glenn Icing Research Tunnel: 2014 Cloud Calibration

    NASA Technical Reports Server (NTRS)

    VanZante, Judith Foss; Ide, Robert F.; Steen, Laura; Acosta, Waldo J.

    2014-01-01

    The results of the December 2013 to February 2014 Icing Research Tunnel full icing cloud calibration are being presented to the SAE AC-9C committee, as represented in the 2014 cloud calibration report. The calibration steps included establishing a uniform cloud and conducting drop size and liquid water content calibrations. The goal of the calibration was to develop a uniform cloud, and to generate a transfer function from the inputs of air speed, spray bar atomizing air pressure and water pressure to the outputs of median volumetric drop diameter and liquid water content. This was done for both 14 CFR Parts 25 and 29, Appendix C (typical icing) and soon-to-be released Appendix O (supercooled large drop) conditions.

  3. ICES IN THE QUIESCENT IC 5146 DENSE CLOUD

    SciTech Connect

    Chiar, J. E.; Pendleton, Y. J.; Allamandola, L. J.; Ennico, K.; Greene, T. P.; Roellig, T. L.; Sandford, S. A.; Boogert, A. C. A.; Geballe, T. R.; Mason, R. E.; Keane, J. V.; Lada, C. J.; Tielens, A. G. G. M.; Werner, M. W.; Whittet, D. C. B.; Decin, L.; Eriksson, K.

    2011-04-10

    This paper presents spectra in the 2 to 20 {mu}m range of quiescent cloud material located in the IC 5146 cloud complex. The spectra were obtained with NASA's Infrared Telescope Facility SpeX instrument and the Spitzer Space Telescope's Infrared Spectrometer. We use these spectra to investigate dust and ice absorption features in pristine regions of the cloud that are unaltered by embedded stars. We find that the H{sub 2}O-ice threshold extinction is 4.03 {+-} 0.05 mag. Once foreground extinction is taken into account, however, the threshold drops to 3.2 mag, equivalent to that found for the Taurus dark cloud, generally assumed to be the touchstone quiescent cloud against which all other dense cloud and embedded young stellar object observations are compared. Substructure in the trough of the silicate band for two sources is attributed to CH{sub 3}OH and NH{sub 3} in the ices, present at the {approx}2% and {approx}5% levels, respectively, relative to H{sub 2}O-ice. The correlation of the silicate feature with the E(J - K) color excess is found to follow a much shallower slope relative to lines of sight that probe diffuse clouds, supporting the previous results by Chiar et al.

  4. Instrument for Aircraft-Icing and Cloud-Physics Measurements

    NASA Technical Reports Server (NTRS)

    Lilie, Lyle; Bouley, Dan; Sivo, Chris

    2006-01-01

    The figure shows a compact, rugged, simple sensor head that is part of an instrumentation system for making measurements to characterize the severity of aircraft-icing conditions and/or to perform research on cloud physics. The quantities that are calculated from measurement data acquired by this system and that are used to quantify the severity of icing conditions include sizes of cloud water drops, cloud liquid water content (LWC), cloud ice water content (IWC), and cloud total water content (TWC). The sensor head is mounted on the outside of an aircraft, positioned and oriented to intercept the ambient airflow. The sensor head consists of an open housing that is heated in a controlled manner to keep it free of ice and that contains four hot-wire elements. The hot-wire sensing elements have different shapes and sizes and, therefore, exhibit different measurement efficiencies with respect to droplet size and water phase (liquid, frozen, or mixed). Three of the hot-wire sensing elements are oriented across the airflow so as to intercept incoming cloud water. For each of these elements, the LWC or TWC affects the power required to maintain a constant temperature in the presence of cloud water.

  5. Characterization of Arctic ice cloud properties observed during ISDAC

    NASA Astrophysics Data System (ADS)

    Jouan, Caroline; Girard, Eric; Pelon, Jacques; Gultepe, Ismail; Delanoë, Julien; Blanchet, Jean-Pierre

    2012-12-01

    Extensive measurements from ground-based sites and satellite remote sensing (CloudSat and CALIPSO) reveal the existence of two types of ice clouds (TICs) in the Arctic during the polar night and early spring. The first type (TIC-2A), being topped by a cover of nonprecipitating very small (radar unseen) ice crystals (TIC-1), is found more frequently in pristine environment, whereas the second type (TIC-2B), detected by both sensors, is associated preferentially with a high concentration of aerosols. To further investigate the microphysical properties of TIC-1/2A and TIC-2B, airborne in situ and satellite measurements of specific cases observed during Indirect and Semi-Direct Aerosol Campaign (ISDAC) have been analyzed. For the first time, Arctic TIC-1/2A and TIC-2B microstructures are compared using in situ cloud observations. Results show that the differences between them are confined in the upper part of the clouds where ice nucleation occurs. TIC-2B clouds are characterized by fewer (by more than 1 order of magnitude) and larger (by a factor of 2 to 3) ice crystals and a larger ice supersaturation (of 15-20%) compared to TIC-1/2A. Ice crystal growth in TIC-2B clouds seems explosive, whereas it seems more gradual in TIC-1/2A. It is hypothesized that these differences are linked to the number concentration and the chemical composition of aerosols. The ice crystal growth rate in very cold conditions impinges on the precipitation efficiency, dehydration and radiation balance. These results represent an essential and important first step to relate previous modeling, remote sensing and laboratory studies with TICs cloud in situ observations.

  6. IceCube: CubeSat 883-GHz Radiometry for Future Ice Cloud Remote Sensing

    NASA Technical Reports Server (NTRS)

    Wu, Dongliang; Esper, Jaime; Ehsan, Negar; Johnson, Thomas; Mast, William; Piepmeier, Jeffery R.; Racette, Paul E.

    2015-01-01

    Ice clouds play a key role in the Earth's radiation budget, mostly through their strong regulation of infrared radiation exchange. Accurate observations of global cloud ice and its distribution have been a challenge from space, and require good instrument sensitivities to both cloud mass and microphysical properties. Despite great advances from recent spaceborne radar and passive sensors, uncertainty of current ice water path (IWP) measurements is still not better than a factor of 2. Submillimeter (submm) wave remote sensing offers great potential for improving cloud ice measurements, with simultaneous retrievals of cloud ice and its microphysical properties. The IceCube project is to enable this cloud ice remote sensing capability in future missions, by raising 874-GHz receiver technology TRL from 5 to 7 in a spaceflight demonstration on 3-U CubeSat in a low Earth orbit (LEO) environment. The NASAs Goddard Space Flight Center (GSFC) is partnering with Virginia Diodes Inc (VDI) on the 874-GHz receiver through its Vector Network Analyzer (VNA) extender module product line, to develop an instrument with precision of 0.2 K over 1-second integration and accuracy of 2.0 K or better. IceCube is scheduled to launch to and subsequent release from the International Space Station (ISS) in mid-2016 for nominal operation of 28 plus days. We will present the updated design of the payload and spacecraft systems, as well as the operation concept. We will also show the simulated 874-GHz radiances from the ISS orbits and cloud scattering signals as expected for the IceCube cloud radiometer.

  7. Remote Sensing of Crystal Shapes in Ice Clouds

    NASA Technical Reports Server (NTRS)

    van Diedenhoven, Bastiaan

    2017-01-01

    Ice crystals in clouds exist in a virtually limitless variation of geometries. The most basic shapes of ice crystals are columnar or plate-like hexagonal prisms with aspect ratios determined by relative humidity and temperature. However, crystals in ice clouds generally display more complex structures owing to aggregation, riming and growth histories through varying temperature and humidity regimes. Crystal shape is relevant for cloud evolution as it affects microphysical properties such as fall speeds and aggregation efficiency. Furthermore, the scattering properties of ice crystals are affected by their general shape, as well as by microscopic features such as surface roughness, impurities and internal structure. To improve the representation of ice clouds in climate models, increased understanding of the global variation of crystal shape and how it relates to, e.g., location, cloud temperature and atmospheric state is crucial. Here, the remote sensing of ice crystal macroscale and microscale structure from airborne and space-based lidar depolarization observations and multi-directional measurements of total and polarized reflectances is reviewed. In addition, a brief overview is given of in situ and laboratory observations of ice crystal shape as well as the optical properties of ice crystals that serve as foundations for the remote sensing approaches. Lidar depolarization is generally found to increase with increasing cloud height and to vary with latitude. Although this variation is generally linked to the variation of ice crystal shape, the interpretation of the depolarization remains largely qualitative and more research is needed before quantitative conclusions about ice shape can be deduced. The angular variation of total and polarized reflectances of ice clouds has been analyzed by numerous studies in order to infer information about ice crystal shapes from them. From these studies it is apparent that pristine crystals with smooth surfaces are generally

  8. Soot Aerosol Particles as Cloud Condensation Nuclei: from Ice Nucleation Activity to Ice Crystal Morphology

    NASA Astrophysics Data System (ADS)

    Pirim, Claire; Ikhenazene, Raouf; Ortega, Isamel Kenneth; Carpentier, Yvain; Focsa, Cristian; Chazallon, Bertrand; Ouf, François-Xavier

    2016-04-01

    Emissions of solid-state particles (soot) from engine exhausts due to incomplete fuel combustion is considered to influence ice and liquid water cloud droplet activation [1]. The activity of these aerosols would originate from their ability to be important centers of ice-particle nucleation, as they would promote ice formation above water homogeneous freezing point. Soot particles are reported to be generally worse ice nuclei than mineral dust because they activate nucleation at higher ice-supersaturations for deposition nucleation and at lower temperatures for immersion freezing than ratios usually expected for homogeneous nucleation [2]. In fact, there are still numerous opened questions as to whether and how soot's physico-chemical properties (structure, morphology and chemical composition) can influence their nucleation ability. Therefore, systematic investigations of soot aerosol nucleation activity via one specific nucleation mode, here deposition nucleation, combined with thorough structural and compositional analyzes are needed in order to establish any association between the particles' activity and their physico-chemical properties. In addition, since the morphology of the ice crystals can influence their radiative properties [3], we investigated their morphology as they grow over both soot and pristine substrates at different temperatures and humidity ratios. In the present work, Combustion Aerosol STandart soot samples were produced from propane using various experimental conditions. Their nucleation activity was studied in deposition mode (from water vapor), and monitored using a temperature-controlled reactor in which the sample's relative humidity is precisely measured with a cryo-hygrometer. Formation of water/ice onto the particles is followed both optically and spectroscopically, using a microscope coupled to a Raman spectrometer. Vibrational signatures of hydroxyls (O-H) emerge when the particle becomes hydrated and are used to characterize ice

  9. New Icing Cloud Simulation System at the NASA Glenn Research Center Icing Research Tunnel

    NASA Technical Reports Server (NTRS)

    Irvine, Thomas B.; Oldenburg, John R.; Sheldon, David W.

    1999-01-01

    A new spray bar system was designed, fabricated, and installed in the NASA Glenn Research Center's Icing Research Tunnel (IRT). This system is key to the IRT's ability to do aircraft in-flight icing cloud simulation. The performance goals and requirements levied on the design of the new spray bar system included increased size of the uniform icing cloud in the IRT test section, faster system response time, and increased coverage of icing conditions as defined in Appendix C of the Federal Aviation Regulation (FAR), Part 25 and Part 29. Through significant changes to the mechanical and electrical designs of the previous-generation spray bar system, the performance goals and requirements were realized. Postinstallation aerodynamic and icing cloud calibrations were performed to quantify the changes and improvements made to the IRT test section flow quality and icing cloud characteristics. The new and improved capability to simulate aircraft encounters with in-flight icing clouds ensures that the 1RT will continue to provide a satisfactory icing ground-test simulation method to the aeronautics community.

  10. Arctic sea ice melt leads to atmospheric new particle formation.

    PubMed

    Dall Osto, M; Beddows, D C S; Tunved, P; Krejci, R; Ström, J; Hansson, H-C; Yoon, Y J; Park, Ki-Tae; Becagli, S; Udisti, R; Onasch, T; O Dowd, C D; Simó, R; Harrison, Roy M

    2017-06-12

    Atmospheric new particle formation (NPF) and growth significantly influences climate by supplying new seeds for cloud condensation and brightness. Currently, there is a lack of understanding of whether and how marine biota emissions affect aerosol-cloud-climate interactions in the Arctic. Here, the aerosol population was categorised via cluster analysis of aerosol size distributions taken at Mt Zeppelin (Svalbard) during a 11 year record. The daily temporal occurrence of NPF events likely caused by nucleation in the polar marine boundary layer was quantified annually as 18%, with a peak of 51% during summer months. Air mass trajectory analysis and atmospheric nitrogen and sulphur tracers link these frequent nucleation events to biogenic precursors released by open water and melting sea ice regions. The occurrence of such events across a full decade was anti-correlated with sea ice extent. New particles originating from open water and open pack ice increased the cloud condensation nuclei concentration background by at least ca. 20%, supporting a marine biosphere-climate link through sea ice melt and low altitude clouds that may have contributed to accelerate Arctic warming. Our results prompt a better representation of biogenic aerosol sources in Arctic climate models.

  11. Observation of Sea Ice Surface Thermal States Under Cloud Cover

    NASA Technical Reports Server (NTRS)

    Nghiem, S. V.; Perovich, D. K.; Gow, A. J.; Kwok, R.; Barber, D. G.; Comiso, J. C.; Zukor, Dorothy J. (Technical Monitor)

    2001-01-01

    Clouds interfere with the distribution of short-wave and long-wave radiations over sea ice, and thereby strongly affect the surface energy balance in polar regions. To evaluate the overall effects of clouds on climatic feedback processes in the atmosphere-ice-ocean system, the challenge is to observe sea ice surface thermal states under both clear sky and cloudy conditions. From laboratory experiments, we show that C-band radar (transparent to clouds) backscatter is very sensitive to the surface temperature of first-year sea ice. The effect of sea ice surface temperature on the magnitude of backscatter change depends on the thermal regimes of sea ice thermodynamic states. For the temperature range above the mirabilite (Na2SO4.10H20) crystallization point (-8.2 C), C-band data show sea ice backscatter changes by 8-10 dB for incident angles from 20 to 35 deg at both horizontal and vertical polarizations. For temperatures below the mirabilite point but above the crystallization point of MgCl2.8H2O (-18.0 C), relatively strong backwater changes between 4-6 dB are observed. These backscatter changes correspond to approximately 8 C change in temperature for both cases. The backscattering mechanism is related to the temperature which determines the thermodynamic distribution of brine volume in the sea ice surface layer. The backscatter is positively correlated to temperature and the process is reversible with thermodynamic variations such as diurnal insolation effects. From two different dates in May 1993 with clear and overcast conditions determined by the Advanced Very High Resolution Radiometer (AVHRR), concurrent Earth Resources Satellite 1 (ERS-1) C-band ice observed with increases in backscatter over first-year sea ice, and verified by increases in in-situ sea ice surface temperatures measured at the Collaborative-Interdisciplinary Cryosphere Experiment (C-ICE) site.

  12. Disk and circumsolar radiances in the presence of ice clouds

    NASA Astrophysics Data System (ADS)

    Haapanala, Päivi; Räisänen, Petri; McFarquhar, Greg M.; Tiira, Jussi; Macke, Andreas; Kahnert, Michael; DeVore, John; Nousiainen, Timo

    2017-06-01

    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 the 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. 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.

  13. 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

  14. ICESat: Ice, Cloud and Land Elevation Satellite

    NASA Technical Reports Server (NTRS)

    Zwally, Jay; Shuman, Christopher

    2002-01-01

    Ice exists in the natural environment in many forms. The Earth dynamic ice features shows that at high elevations and/or high latitudes,snow that falls to the ground can gradually build up tu form thick consolidated ice masses called glaciers. Glaciers flow downhill under the force of gravity and can extend into areas that are too warm to support year-round snow cover. The snow line, called the equilibrium line on a glacier or ice sheet, separates the ice areas that melt on the surface and become show free in summer (net ablation zone) from the ice area that remain snow covered during the entire year (net accumulation zone). Snow near the surface of a glacier that is gradually being compressed into solid ice is called firm.

  15. Occurrence of Ice Supersaturations, Ice Clouds, and Ternary Aerosols in the Arctic Lowermost Stratosphere

    NASA Technical Reports Server (NTRS)

    Jensen, Eric; Selkirk, Henry; Pfister, Leonhard; Sachee, Glen; Podolske, James; Anderson, Bruce; Gore, Warren J. (Technical Monitor)

    2000-01-01

    Relative humidity, aerosol concentration, and ice crystals all have important impacts on chemistry and radiative transfer in the lowermost stratosphere. In this study, we have combined SOLVE measurements with meteorological analyses to investigate the statistics of humidity, aerosols, and clouds in the arctic lower stratosphere. First, we will present a statistical analysis of relative humidity with respect to ice in the lowermost stratosphere, used on the DC-8 in situ measurements. We will show examples of ice supersaturation well within the stratosphere. Generally, these cases were associated with extremely low temperatures near the tropopause. Next, we will discuss the climatological occurrence frequency of tropopause temperatures low enough for ice saturation even with typically low stratospheric water vapor mixing ratios. Really, we will examine case studies of ice clouds observed in the lowermost stratosphere during SOLVE. We will discuss the possible origin of these clouds (i.e., precipitation from higher type II PSCs, injection of tropospheric air into the lower stratosphere, etc.).

  16. Relationship between Ice Cloud Microphysics and Supersaturation from Spaceborne Cloud Radar, Lidar and Infrared Sounder

    NASA Astrophysics Data System (ADS)

    Tanaka, K.; Okamoto, H.; Sato, K.; Ishimoto, H.

    2014-12-01

    We examined the relationship between ice cloud microphysics retrieved from cloud radar on CloudSat and CALIOP on CALIPSO and super saturation inferred from AIRS on AQUA. Ice microphysics such as ice water content (IWC) and effective radius was estimated by CloudSat and CALIPSO data. Unique features of the algorithm is that it has been designed to use depolarization ratio from CALIOP addition to radar reflectivity factor from CloudSat and attenuated backscattering coefficient from CALIOP in order to take into account the variation of ice particle shapes and their orientations [Okamoto et al., 2010]. Water vapor density and temperature were retrieved with much finer resolution by the application of Ishimoto's algorithm [2009] compared with standard AIRS products where horizontal resolution is 45km. The algorithm allows retrievals of water vapor density and temperature every 13.5km in horizontal direction with 1km in vertical. The retrievals are carried out when there is no cloud with its cloud top pressure <200hPa. That is, it is possible to report water vapor information above low-level clouds. Then we sampled the amount of water vapor and temperature estimated from AIRS data to match the CloudSat and CALIPSO foot-print and the data were interpolated to have the same space and time resolution of the merged data sets of CloudSat and CALIPSO, i.e., 1.1km and 240m for horizontal and vertical resolutions. In the new AIRS products, ice super saturation often reached 150% while standard AIRS products showed less frequent super saturation. The ECMWF results generally showed smaller fraction of ice super saturation compared with the new AIRS products. In order to quantitatively compare the water vapor amount and retrieved IWC, we estimated the excess of water amount respect to ice saturation by using ice super saturation. The occurrences of ice clouds inferred from CloudSat and CALIOP agreed with the occurrences of ice-supersaturation reported in the new AIRS products. The

  17. Simulating Arctic clouds during Arctic Radiation- IceBridge Sea and Ice Experiment (ARISE)

    NASA Astrophysics Data System (ADS)

    Bromwich, D. H.; Hines, K. M.; Wang, S. H.

    2015-12-01

    The representation within global and regional models of the extensive low-level cloud cover over polar oceans remains a critical challenge for quantitative studies and forecasts of polar climate. In response, the polar-optimized version of the Weather Research and Forecasting model (Polar WRF) is used to simulate the meteorology, boundary layer, and Arctic clouds during the September-October 2014 Arctic Radiation- IceBridge Sea and Ice Experiment (ARISE) project. Polar WRF was developed with several adjustments to the sea ice thermodynamics in WRF. ARISE was based out of Eielson Air Force Base near Fairbanks, Alaska and included multiple instrumented C-130 aircraft flights over open water and sea ice of the Beaufort Sea. Arctic boundary layer clouds were frequently observed within cold northeasterly flow over the open ocean and ice. Preliminary results indicate these clouds were primarily liquid water, with characteristics differing between open water and sea ice surfaces. Simulated clouds are compared to ARISE observations. Furthermore, Polar WRF simulations are run for the August-September 2008 Arctic Summer Cloud Ocean Study (ASCOS) for comparison to the ARISE. Preliminary analysis shows that simulated low-level water clouds over the sea ice are too extensive during the the second half of the ASCOS field program. Alternatives and improvements to the Polar WRF cloud schemes are considered. The goal is to use the ARISE and ASCOS observations to achieve an improved polar supplement to the WRF code for open water and sea ice that can be provided to the Polar WRF community.

  18. The origin of midlatitude ice clouds and the resulting influence on their microphysical properties

    NASA Astrophysics Data System (ADS)

    Luebke, Anna E.; Afchine, Armin; Costa, Anja; Grooß, Jens-Uwe; Meyer, Jessica; Rolf, Christian; Spelten, Nicole; Avallone, Linnea M.; Baumgardner, Darrel; Krämer, Martina

    2016-05-01

    The radiative role of ice clouds in the atmosphere is known to be important, but uncertainties remain concerning the magnitude and net effects. However, through measurements of the microphysical properties of cirrus clouds, we can better characterize them, which can ultimately allow for their radiative properties to be more accurately ascertained. Recently, two types of cirrus clouds differing by formation mechanism and microphysical properties have been classified - in situ and liquid origin cirrus. In this study, we present observational evidence to show that two distinct types of cirrus do exist. Airborne, in situ measurements of cloud ice water content (IWC), ice crystal concentration (Nice), and ice crystal size from the 2014 ML-CIRRUS campaign provide cloud samples that have been divided according to their origin type. The key features that set liquid origin cirrus apart from the in situ origin cirrus are higher frequencies of high IWC ( > 100 ppmv), higher Nice values, and larger ice crystals. A vertical distribution of Nice shows that the in situ origin cirrus clouds exhibit a median value of around 0.1 cm-3, while the liquid origin concentrations are slightly, but notably higher. The median sizes of the crystals contributing the most mass are less than 200 µm for in situ origin cirrus, with some of the largest crystals reaching 550 µm in size. The liquid origin cirrus, on the other hand, were observed to have median diameters greater than 200 µm, and crystals that were up to 750 µm. An examination of these characteristics in relation to each other and their relationship to temperature provides strong evidence that these differences arise from the dynamics and conditions in which the ice crystals formed. Additionally, the existence of these two groups in cirrus cloud populations may explain why a bimodal distribution in the IWC-temperature relationship has been observed. We hypothesize that the low IWC mode is the result of in situ origin cirrus and the

  19. Numerical Experiments on the Formation and Maintenance of Cirriform Clouds.

    NASA Astrophysics Data System (ADS)

    Starr, David O'connell

    The role and relative importance of the dynamic and diabatic processes influencing the formation and maintenance of ice phase stratiform clouds are investigated at the cloud scale. The primary focus is on fair weather cirrus. A two-dimensional, time dependent, Eulerian numerical model is developed. The grid interval is 100 m and the domain is a vertical plane of (TURN) 3 km depth and (TURN) 6 km horizontal extent. The influence of larger scale processes are incorporated via a specified basic state vertical velocity and the initially specified thermodynamic structure. In addition to energy transformations between potential and kinetic forms and advection by the resolved wind field, other important physical processes, which are incorporated into the model in a parametric fashion, are transports due to subgrid scale processes, phase changes of water, infrared and short-wave radiative processes and the relative fall velocity of cloud particles. The parameterizations are based upon observations and theoretical consideration. This model is unique in its applicability to ice phase stratiform clouds. Comparable parameterizations for liquid phase stratiform clouds are given. The model is described in detail in all aspects. The approach is one of examining the sensitivity of simulations to the specification of various computational and parametric model constants and functions. The characteristics of the model are fully examined and the model is calibrated by means of comparison to observations and theory such that realistic simulations are obtained. The influence of the ice water relative fall speed on the physical properties of the cloud layer and the consequent modulation of the other cloud processes is found to be quite dramatic. Radiative processes are also found to have a significant impact. In particular, significant differences in the organization of convective elements between daytime and nighttime cases are found. Differences between ice phase and liquid phase

  20. The Ice Selective Inlet: a novel technique for exclusive extraction of pristine ice crystals in mixed-phase clouds

    NASA Astrophysics Data System (ADS)

    Kupiszewski, P.; Weingartner, E.; Vochezer, P.; Schnaiter, M.; Bigi, A.; Gysel, M.; Rosati, B.; Toprak, E.; Mertes, S.; Baltensperger, U.

    2015-08-01

    Climate predictions are affected by high uncertainties partially due to an insufficient knowledge of aerosol-cloud interactions. One of the poorly understood processes is formation of mixed-phase clouds (MPCs) via heterogeneous ice nucleation. Field measurements of the atmospheric ice phase in MPCs are challenging due to the presence of much more numerous liquid droplets. The Ice Selective Inlet (ISI), presented in this paper, is a novel inlet designed to selectively sample pristine ice crystals in mixed-phase clouds and extract the ice residual particles contained within the crystals for physical and chemical characterization. Using a modular setup composed of a cyclone impactor, droplet evaporation unit and pumped counterflow virtual impactor (PCVI), the ISI segregates particles based on their inertia and phase, exclusively extracting small ice particles between 5 and 20 μm in diameter. The setup also includes optical particle spectrometers for analysis of the number size distribution and shape of the sampled hydrometeors. The novelty of the ISI is a droplet evaporation unit, which separates liquid droplets and ice crystals in the airborne state, thus avoiding physical impaction of the hydrometeors and limiting potential artefacts. The design and validation of the droplet evaporation unit is based on modelling studies of droplet evaporation rates and computational fluid dynamics simulations of gas and particle flows through the unit. Prior to deployment in the field, an inter-comparison of the optical particle size spectrometers and a characterization of the transmission efficiency of the PCVI was conducted in the laboratory. The ISI was subsequently deployed during the Cloud and Aerosol Characterization Experiment (CLACE) 2013 and 2014 - two extensive international field campaigns encompassing comprehensive measurements of cloud microphysics, as well as bulk aerosol, ice residual and ice nuclei properties. The campaigns provided an important opportunity for a

  1. Ice particles in stratiform clouds in the Arctic and possible mechanisms for the production of high ice concentrations

    NASA Astrophysics Data System (ADS)

    Rangno, Arthur L.; Hobbs, Peter V.

    2001-07-01

    The presence of ice particles in clouds affects precipitation processes, the radiative properties of the clouds, and the derivation of cloud properties from remote sensing measurements. High ice particle concentrations occur often in slightly to moderately supercooled clouds in the Arctic. This paper combines data collected in a common type of ice-producing arctic cloud (stratocumulus) with calculations based on laboratory experiments to elucidate mechanisms that might be responsible for the ice. Ice splinters produced during riming could account for the relatively high concentrations of ice particles in clouds that encompass temperatures between -2.5°C and -8°C. However, it has generally been assumed that ice splinters grow into pristine ice crystal habits, whereas detailed measurements in an arctic stratocumulus cloud showed that only 32% of the ice particles were pristine crystals (needles, sheaths, short columns, and plates) and 10% were broken pieces of needles or sheaths. Thirty-seven percent of the ice particles were not identifiable crystal types, 20% were frozen drops, and 1% were aggregates and graupel. The large numbers of unidentifiable ice particles could have originated from the fragmentation of delicate ice crystals and the shattering of some drops during freezing in free fall. These two mechanisms may also play a role in the production of relatively high ice particle concentrations in moderately supercooled arctic clouds that lie outside of the temperature zone where ice splinter production by riming occurs.

  2. Advances in Understanding the Role of Aerosols on Ice Clouds from the Fifth International Ice Nucleation (FIN) Workshops

    NASA Astrophysics Data System (ADS)

    Cziczo, D. J.; Moehler, O.; DeMott, P. J.

    2015-12-01

    The relationship of ambient aerosol particles to the formation of ice-containing clouds is one of the largest uncertainties in understanding climate. This is due to several poorly understood processes including the microphysics of how particles nucleate ice, the number of effective heterogeneous ice nuclei and their atmospheric distribution, the role of anthropogenic activities in producing or changing the behavior of ice forming particles and the interplay between effective heterogeneous ice nuclei and homogeneous ice formation. Our team recently completed a three-part international workshop to improve our understanding of atmospheric ice formation. Termed the Fifth International Ice Nucleation (FIN) Workshops, our motivation was the limited number of measurements and a lack of understanding of how to compare data acquired by different groups. The first activity, termed FIN1, addressed the characterization of ice nucleating particle size, number and chemical composition. FIN2 addressed the determination of ice nucleating particle number density. Groups modeling ice nucleation joined FIN2 to provide insight on measurements critically needed to model atmospheric ice nucleation and to understand the performance of ice chambers. FIN1 and FIN2 took place at the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) chamber at the Karlsruhe Institute of Technology. A particular emphasis of FIN1 and FIN2 was the use of 'blind' intercomparisons using a highly characterized, but unknown to the instrument operators, aerosol sample. The third activity, FIN3, took place at the Desert Research Institute's Storm Peak Laboratory (SPL). A high elevation site not subject to local emissions, SPL allowed for a comparison of ice chambers and subsequent analysis of the ice residuals under the challenging conditions of low particle loading, temperature and pressure found in the atmosphere. The presentation focuses on the improvement in understanding how mass spectra from different

  3. Progress on low altitude cloud icing research

    NASA Technical Reports Server (NTRS)

    Jeck, R. K.

    1981-01-01

    The icing environment at altitudes below 10,000 feet were studied. The following questions are asked, are: (1) existing aircraft certification criteria applicable; (2) too stringent on icing for helos; (3) based on accurate data; (4) appropriate for low (10,000 ft) altitudes? The research plan is outlined: review historical icing data, obtain new measurements, collect modern icing data from other groups, and recommend LWC, OAT, and MVD criteria for helicopters. Estimated accuracies and known sources of error are included. It is concluded that the net effect of possible sources of error of both signs is uncertain.

  4. Progress on low altitude cloud icing research

    NASA Technical Reports Server (NTRS)

    Jeck, R. K.

    1981-01-01

    The icing environment at altitudes below 10,000 feet were studied. The following questions are asked, are: (1) existing aircraft certification criteria applicable; (2) too stringent on icing for helos; (3) based on accurate data; (4) appropriate for low (10,000 ft) altitudes? The research plan is outlined: review historical icing data, obtain new measurements, collect modern icing data from other groups, and recommend LWC, OAT, and MVD criteria for helicopters. Estimated accuracies and known sources of error are included. It is concluded that the net effect of possible sources of error of both signs is uncertain.

  5. 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

  6. Star formation in Lynds dark clouds

    NASA Astrophysics Data System (ADS)

    Spuck, Tim; Rebull, Luisa

    2008-03-01

    Recent research on star formation in large molecular cloud complexes, such as the Cepheus Flare (Kun 1995), Orion, Perseus (Rebull et al. 2007), and Taurus molecular clouds, have included studies of a number of Lynds dark nebulae (LDN). Less attention has been given to isolated Lynds clouds. Both LDN 981 and LDN 425 are smaller, more isolated, dark molecular clouds that could contain regions of active star formation within them -- they both are associated with IRAS sources, and based on prior shallow surveys, they both have a YSO candidate in the neigborhood. Spitzer observations with IRAC and MIPS will allow us to see deep inside the cloud, deeper than any prior observations could see, and reveal any hidden star formation that is ongoing in these clouds. This project is part of the Spitzer Teachers Program.

  7. The Ice Selective Inlet: a novel technique for exclusive extraction of pristine ice crystals in mixed-phase clouds

    NASA Astrophysics Data System (ADS)

    Kupiszewski, P.; Weingartner, E.; Vochezer, P.; Bigi, A.; Rosati, B.; Gysel, M.; Schnaiter, M.; Baltensperger, U.

    2014-12-01

    Climate predictions are affected by high uncertainties partially due to an insufficient knowledge of aerosol-cloud interactions. One of the poorly understood processes is formation of mixed-phase clouds (MPCs) via heterogeneous ice nucleation. Field measurements of the atmospheric ice phase in MPCs are challenging due to the presence of supercooled liquid droplets. The Ice Selective Inlet (ISI), presented in this paper, is a novel inlet designed to selectively sample pristine ice crystals in mixed-phase clouds and extract the ice residual particles contained within the crystals for physical and chemical characterisation. Using a modular setup composed of a cyclone impactor, droplet evaporation unit and pumped counterflow virtual impactor (PCVI), the ISI segregates particles based on their inertia and phase, exclusively extracting small ice particles between 5 and 20 μm in diameter. The setup also includes optical particle spectrometers for analysis of the number size distribution and shape of the sampled hydrometeors. The novelty of the ISI is a droplet evaporation unit, which separates liquid droplets and ice crystals in the airborne state, thus avoiding physical impaction of the hydrometeors and limiting potential artifacts. The design and validation of the droplet evaporation unit is based on modelling studies of droplet evaporation rates and computational fluid dynamics simulations of gas and particle flows through the unit. Prior to deployment in the field, an inter-comparison of the WELAS optical particle size spectrometers and a characterisation of the transmission efficiency of the PCVI was conducted in the laboratory. The ISI was subsequently deployed during the Cloud and Aerosol Characterisation Experiment (CLACE) 2013 - an extensive international field campaign encompassing comprehensive measurements of cloud microphysics, as well as bulk aerosol, ice residual and ice nuclei properties. The campaign provided an important opportunity for a proof of

  8. Frost flower formation on sea ice and lake ice

    NASA Astrophysics Data System (ADS)

    Style, Robert W.; Worster, M. Grae

    2009-06-01

    Frost flowers are clusters of ice crystals found on freshly formed sea ice and occasionally on frozen lakes. They belong to a class of vapour-related phenomena that includes freezing fog, hoar frost and dew. It has hitherto been supposed that they form by condensation from a supersaturated atmosphere or from water wicked up through porous sea ice. Here we show that they can form on solid, pure ice sublimating into an unsaturated atmosphere. We derive a general regime diagram showing the atmospheric conditions under which the different vapour-related phenomena occur and confirm our predictions of frost-flower formation with a series of laboratory experiments. Our results can be used in climate models to predict occurrence of frost flowers, which significantly enhance albedo and provide the substrate for chemical production of ozone-depleting bromine monoxide, and in paleo-climate reconstructions by relating observations of sea-salt aerosols in ice cores to atmospheric conditions.

  9. How Does a Raindrop Grow?: Precipitation in natural clouds may develop from ice crystals or from large hygroscopic aerosols.

    PubMed

    Braham, R R

    1959-01-16

    On the basis of presently available data, combined with present-day knowledge of the physics and chemistry of cloud particle development, it is possible to make the following generalizations about the mode of precipitation in natural clouds. 1) The all-water mechanism begins to operate as soon as a parcel of cloud air is formed and continues to operate throughout the life of the cloud. The ice-crystal mechanism, on the other hand, can begin to operate only after the top of the cloud has reached levels where ice nuclei can be effective (about -15 degrees C). Some clouds never reach this height; any precipitation from them must be through the all-water mechanism. In cold climates and at high levels in the atmosphere, the cloud bases may be very close to this critical temperature. In the tropics, approximately 25,000 feet separate the bases of low clouds from the natural ice level. 2) The number of large hygroscopic nuclei in maritime air over tropical oceans is entirely adequate to rain-out any cloud with a base below about 10,000 feet, provided the cloud duration and cloud depth is sufficient for the precipitation process to operate. Extensive trajectories over land will decrease the number of sea-salt particles, both because of sedimentation and removal in rain. Measurements show an order-of-magnitude decrease in the number of large particles as maritime air moves from the Gulf of Mexico to the vicinity of St. Louis, during the summer months. Measurements in Arizona and New Mexico show even smaller chloride concentrations, presumably because of the long overland trajectories required in reaching these areas. The maritime particles lost in overland trajectories apparently are more than replaced by particles of land origin. The latter are usually of mixed composition and are less favorable for the formation of outsized solution droplets. 3) Ice nuclei, required for the formation of ice crystals and for droplet freezing, are rather rare at temperatures higher than

  10. Distinguishing Clouds from Ice over the East Siberian Sea, Russia

    NASA Technical Reports Server (NTRS)

    2002-01-01

    As a consequence of its capability to retrieve cloud-top elevations, stereoscopic observations from the Multi-angle Imaging SpectroRadiometer (MISR) can discriminate clouds from snow and ice. The central portion of Russia's East Siberian Sea, including one of the New Siberian Islands, Novaya Sibir, are portrayed in these views from data acquired on May 28, 2002.

    The left-hand image is a natural color view from MISR's nadir camera. On the right is a height field retrieved using automated computer processing of data from multiple MISR cameras. Although both clouds and ice appear white in the natural color view, the stereoscopic retrievals are able to identify elevated clouds based on the geometric parallax which results when they are observed from different angles. Owing to their elevation above sea level, clouds are mapped as green and yellow areas, whereas land, sea ice, and very low clouds appear blue and purple. Purple, in particular, denotes elevations very close to sea level. The island of Novaya Sibir is located in the lower left of the images. It can be identified in the natural color view as the dark area surrounded by an expanse of fast ice. In the stereo map the island appears as a blue region indicating its elevation of less than 100 meters above sea level. Areas where the automated stereo processing failed due to lack of sufficient spatial contrast are shown in dark gray. The northern edge of the Siberian mainland can be found at the very bottom of the panels, and is located a little over 250 kilometers south of Novaya Sibir. Pack ice containing numerous fragmented ice floes surrounds the fast ice, and narrow areas of open ocean are visible.

    The East Siberian Sea is part of the Arctic Ocean and is ice-covered most of the year. The New Siberian Islands are almost always covered by snow and ice, and tundra vegetation is very scant. Despite continuous sunlight from the end of April until the middle of August, the ice between the island and the

  11. Distinguishing Clouds from Ice over the East Siberian Sea, Russia

    NASA Technical Reports Server (NTRS)

    2002-01-01

    As a consequence of its capability to retrieve cloud-top elevations, stereoscopic observations from the Multi-angle Imaging SpectroRadiometer (MISR) can discriminate clouds from snow and ice. The central portion of Russia's East Siberian Sea, including one of the New Siberian Islands, Novaya Sibir, are portrayed in these views from data acquired on May 28, 2002.

    The left-hand image is a natural color view from MISR's nadir camera. On the right is a height field retrieved using automated computer processing of data from multiple MISR cameras. Although both clouds and ice appear white in the natural color view, the stereoscopic retrievals are able to identify elevated clouds based on the geometric parallax which results when they are observed from different angles. Owing to their elevation above sea level, clouds are mapped as green and yellow areas, whereas land, sea ice, and very low clouds appear blue and purple. Purple, in particular, denotes elevations very close to sea level. The island of Novaya Sibir is located in the lower left of the images. It can be identified in the natural color view as the dark area surrounded by an expanse of fast ice. In the stereo map the island appears as a blue region indicating its elevation of less than 100 meters above sea level. Areas where the automated stereo processing failed due to lack of sufficient spatial contrast are shown in dark gray. The northern edge of the Siberian mainland can be found at the very bottom of the panels, and is located a little over 250 kilometers south of Novaya Sibir. Pack ice containing numerous fragmented ice floes surrounds the fast ice, and narrow areas of open ocean are visible.

    The East Siberian Sea is part of the Arctic Ocean and is ice-covered most of the year. The New Siberian Islands are almost always covered by snow and ice, and tundra vegetation is very scant. Despite continuous sunlight from the end of April until the middle of August, the ice between the island and the

  12. Minimalist Model of Ice Microphysics in Mixed-phase Stratiform Clouds

    SciTech Connect

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

    2013-07-28

    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 law 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.

  13. Modeling the microphysics of CO2 ice clouds within wave-induced cold pockets in the martian mesosphere

    NASA Astrophysics Data System (ADS)

    Listowski, C.; Määttänen, A.; Montmessin, F.; Spiga, A.; Lefèvre, F.

    2014-07-01

    Mesospheric CO2 ice clouds on Mars are simulated with a 1D microphysical model, which includes a crystal growth rate adapted to high supersaturations encountered in the martian mesosphere. Observational constraints (crystal radius and opacity) exist for these clouds observed during the day around the equator at ∼60-80 km altitude. Nighttime mesospheric clouds interpreted as CO2 ice clouds have also been characterized at low southern latitudes, at ∼90-100 km altitude. From modeling and observational evidence, it is believed that mesospheric clouds are formed within temperature minima created by thermal tides, where gravity wave propagation allows for the creation of supersaturated layers (cold pockets). Thus, temperature profiles perturbed by gravity waves are used in the model to initiate nucleation and maintain growth of CO2 ice crystals. We show that it is possible to reproduce the observed effective radii for daytime and nighttime clouds. Crystal sizes are mainly governed by the altitude where the cloud forms, and by the amplitude of supersaturation. The temporal and spatial behavior of the cloud is controlled by the extent and lifetime of the cold pocket. The cloud evaporates fast after the cold pocket has vanished, implying a strong correlation between gravity wave activity and CO2 cloud formation. Simulated opacities remain far below the observed ones as long as typical dust conditions are used. In the case of the lower daytime clouds, the enhanced mesospheric dust loading typically reached during dust storm conditions, allows for greater cloud opacities, close to observed values, by supplying the atmosphere with condensation nuclei. However, CO2 ice clouds are not detected during the dust storm season, and, because of fast sedimentation of dust particles, an exogenous supply (meteoritic flux) appears necessary to explain opacities of both daytime and nighttime mesospheric CO2 ice clouds along their whole period of observation.

  14. ICE AND DUST IN THE PRESTELLAR DARK CLOUD LYNDS 183: PREPLANETARY MATTER AT THE LOWEST TEMPERATURES

    SciTech Connect

    Whittet, D. C. B.; Poteet, C. A.; Bajaj, V. M.; Horne, D.; Chiar, J. E.; Pagani, L.; Shenoy, S. S.; Adamson, A. J.

    2013-09-10

    Dust grains are nucleation centers and catalysts for the growth of icy mantles in quiescent interstellar clouds, the products of which may accumulate into preplanetary matter when new stars and solar systems form within the clouds. In this paper, we present the first spectroscopic detections of silicate dust and the molecular ices H{sub 2}O, CO, and CO{sub 2} in the vicinity of the prestellar core L183 (L134N). An infrared photometric survey of the cloud was used to identify reddened background stars, and we present spectra covering solid-state absorption features in the wavelength range 2-20 {mu}m for nine of them. The mean composition of the ices in the best-studied line of sight (toward J15542044-0254073) is H{sub 2}O:CO:CO{sub 2} Almost-Equal-To 100:40:24. The ices are amorphous in structure, indicating that they have been maintained at low temperature ({approx}< 15 K) since formation. The ice column density N(H{sub 2}O) correlates with reddening by dust, exhibiting a threshold effect that corresponds to the transition from unmantled grains in the outer layers of the cloud to ice-mantled grains within, analogous to that observed in other dark clouds. A comparison of results for L183 and the Taurus and IC 5146 dark clouds suggests common behavior, with mantles first appearing in each case at a dust column corresponding to a peak optical depth {tau}{sub 9.7} = 0.15 {+-} 0.03 in the silicate feature. Our results support a previous conclusion that the color excess E{sub J-K} does not obey a simple linear correlation with the total dust column in lines of sight that intercept dense clouds. The most likely explanation is a systematic change in the optical properties of the dust as the density increases.

  15. Ice and Dust in the Prestellar Dark Cloud Lynds 183: Preplanetary Matter at the Lowest Temperatures

    NASA Astrophysics Data System (ADS)

    Whittet, D. C. B.; Poteet, C. A.; Chiar, J. E.; Pagani, L.; Bajaj, V. M.; Horne, D.; Shenoy, S. S.; Adamson, A. J.

    2013-09-01

    Dust grains are nucleation centers and catalysts for the growth of icy mantles in quiescent interstellar clouds, the products of which may accumulate into preplanetary matter when new stars and solar systems form within the clouds. In this paper, we present the first spectroscopic detections of silicate dust and the molecular ices H2O, CO, and CO2 in the vicinity of the prestellar core L183 (L134N). An infrared photometric survey of the cloud was used to identify reddened background stars, and we present spectra covering solid-state absorption features in the wavelength range 2-20 μm for nine of them. The mean composition of the ices in the best-studied line of sight (toward J15542044-0254073) is H2O:CO:CO2 ≈ 100:40:24. The ices are amorphous in structure, indicating that they have been maintained at low temperature (lsim 15 K) since formation. The ice column density N(H2O) correlates with reddening by dust, exhibiting a threshold effect that corresponds to the transition from unmantled grains in the outer layers of the cloud to ice-mantled grains within, analogous to that observed in other dark clouds. A comparison of results for L183 and the Taurus and IC 5146 dark clouds suggests common behavior, with mantles first appearing in each case at a dust column corresponding to a peak optical depth τ9.7 = 0.15 ± 0.03 in the silicate feature. Our results support a previous conclusion that the color excess E J - K does not obey a simple linear correlation with the total dust column in lines of sight that intercept dense clouds. The most likely explanation is a systematic change in the optical properties of the dust as the density increases.

  16. Onset of atmospheric ice formation in natural conditions

    NASA Astrophysics Data System (ADS)

    Conen, Franz; Zimmermann, Lukas

    2015-04-01

    Bacteria growing on plants are the particles with the warmest freezing temperature known for natural particles (-2 oC). Their onset of freezing is known to be conditioned by themperature, growth and nutrient status, and probably other factors that can not be assessed in situ, but are also not likely to be conserved when taking airborne bacteria to the laboratory. Whether such bacteria play a role in initiating the ice phase in clouds is therefore best studied directly in a cooling air mass in the natural environment. Investigations directly at cloud tops would be desirable. A more amenable place is the bottom of a valley where a cold air pool forms during clear nights and when radiation fog is likely to form. When shallow, such fog may resemble an inverted cloud with its top on the land surface and warmer air above it. The temperature of bacteria and other particles suspended in air under a clear sky around the onset of fog formation is probably several degrees below that of the surrounding air because of radiative cooling, which will affect the particle's activation as a cloud condensation nucleus and as an ice nucleus. Hence, ice particles probably form earlier than expected at a particular air temperature, grow rapidly and parachute to the surface, where their descent can be recorded by traps charged with supercooled water. We present, and would like to discuss, this kind of observation in principle and show some first results (subject to suitable weather conditions before the presentation).

  17. Formation of Massive Molecular Cloud Cores by Cloud-Cloud Collision

    NASA Astrophysics Data System (ADS)

    Inoue, Tsuyoshi; Fukui, Yasuo

    2013-09-01

    Recent observations of molecular clouds around rich massive star clusters including NGC 3603, Westerlund 2, and M20 revealed that the formation of massive stars could be triggered by a cloud-cloud collision. By using three-dimensional, isothermal, magnetohydrodynamics simulations with the effect of self-gravity, we demonstrate that massive, gravitationally unstable, molecular cloud cores are formed behind the strong shock waves induced by cloud-cloud collision. We find that the massive molecular cloud cores have large effective Jeans mass owing to the enhancement of the magnetic field strength by shock compression and turbulence in the compressed layer. Our results predict that massive molecular cloud cores formed by the cloud-cloud collision are filamentary and threaded by magnetic fields perpendicular to the filament.

  18. FORMATION OF MASSIVE MOLECULAR CLOUD CORES BY CLOUD-CLOUD COLLISION

    SciTech Connect

    Inoue, Tsuyoshi; Fukui, Yasuo

    2013-09-10

    Recent observations of molecular clouds around rich massive star clusters including NGC 3603, Westerlund 2, and M20 revealed that the formation of massive stars could be triggered by a cloud-cloud collision. By using three-dimensional, isothermal, magnetohydrodynamics simulations with the effect of self-gravity, we demonstrate that massive, gravitationally unstable, molecular cloud cores are formed behind the strong shock waves induced by cloud-cloud collision. We find that the massive molecular cloud cores have large effective Jeans mass owing to the enhancement of the magnetic field strength by shock compression and turbulence in the compressed layer. Our results predict that massive molecular cloud cores formed by the cloud-cloud collision are filamentary and threaded by magnetic fields perpendicular to the filament.

  19. NASA Glenn Icing Research Tunnel: Upgrade and Cloud Calibration

    NASA Technical Reports Server (NTRS)

    VanZante, Judith Foss; Ide, Robert F.; Steen, Laura E.

    2012-01-01

    In 2011, NASA Glenn s Icing Research Tunnel underwent a major modification to it s refrigeration plant and heat exchanger. This paper presents the results of the subsequent full cloud calibration. Details of the calibration procedure and results are presented herein. The steps include developing a nozzle transfer map, establishing a uniform cloud, conducting a drop sizing calibration and finally a liquid water content calibration. The goal of the calibration is to develop a uniform cloud, and to build a transfer map from the inputs of air speed, spray bar atomizing air pressure and water pressure to the output of median volumetric droplet diameter and liquid water content.

  20. Simple Cloud Chambers Using a Freezing Mixture of Ice and Cooking Salt

    ERIC Educational Resources Information Center

    Yoshinaga, Kyohei; Kubota, Miki; Kamata, Masahiro

    2015-01-01

    We have developed much simpler cloud chambers that use only ice and cooking salt instead of the dry ice or ice gel pack needed for the cloud chambers produced in our previous work. The observed alpha-ray particle tracks are as clear as those observed using our previous cloud chambers. The tracks can be observed continuously for about 20?min, and…

  1. Simple Cloud Chambers Using a Freezing Mixture of Ice and Cooking Salt

    ERIC Educational Resources Information Center

    Yoshinaga, Kyohei; Kubota, Miki; Kamata, Masahiro

    2015-01-01

    We have developed much simpler cloud chambers that use only ice and cooking salt instead of the dry ice or ice gel pack needed for the cloud chambers produced in our previous work. The observed alpha-ray particle tracks are as clear as those observed using our previous cloud chambers. The tracks can be observed continuously for about 20?min, and…

  2. Estimating the Influence of Biological Ice Nuclei on Clouds with Regional Scale Simulations

    NASA Astrophysics Data System (ADS)

    Hummel, Matthias; Hoose, Corinna; Schaupp, Caroline; Möhler, Ottmar

    2014-05-01

    Cloud properties are largely influenced by the atmospheric formation of ice particles. Some primary biological aerosol particles (PBAP), e.g. certain bacteria, fungal spores or pollen, have been identified as effective ice nuclei (IN). The work presented here quantifies the IN concentrations originating from PBAP in order to estimate their influences on clouds with the regional scale atmospheric model COSMO-ART in a six day case study for Western Europe. The atmospheric particle distribution is calculated for three different PBAP (bacteria, fungal spores and birch pollen). The parameterizations for heterogeneous ice nucleation of PBAP are derived from AIDA cloud chamber experiments with Pseudomonas syringae bacteria and birch pollen (Schaupp, 2013) and from published data on Cladosporium spores (Iannone et al., 2011). A constant fraction of ice-active bacteria and fungal spores relative to the total bacteria and spore concentration had to be assumed. At cloud altitude, average simulated PBAP number concentrations are ~17 L-1 for bacteria and fungal spores and ~0.03 L-1 for birch pollen, including large temporal and spatial variations of more than one order of magnitude. Thus, the average, 'diagnostic' in-cloud PBAP IN concentrations, which only depend on the PBAP concentrations and temperature, without applying dynamics and cloud microphysics, lie at the lower end of the range of typically observed atmospheric IN concentrations . Average PBAP IN concentrations are between 10-6 L-1 and 10-4 L-1. Locally but not very frequently, PBAP IN concentrations can be as high as 0.2 L-1 at -10° C. Two simulations are compared to estimate the cloud impact of PBAP IN, both including mineral dust as an additional background IN with a constant concentration of 100 L-1. One of the simulations includes additional PBAP IN which can alter the cloud properties compared to the reference simulation without PBAP IN. The difference in ice particle and cloud droplet concentration between

  3. The origin of midlatitude ice clouds and the resulting influence on their microphysical properties

    NASA Astrophysics Data System (ADS)

    Luebke, Anna; Rolf, Christian; Costa, Anja; Afchine, Armin; Avallone, Linnea; Borrmann, Stephan; Baumgardner, Darrel; Klingebiel, Marcus; Kraemer, Martina

    2015-04-01

    Ice clouds are known to play an important role in the radiative balance of the atmosphere. The nature of this role is determined by the macrophysical and microphysical properties of a cloud. Thus, it is crucial that we have an accurate understanding of properties such as the ice water content (IWC), ice crystal concentration (Ni), and ice crystal size (Ri). However, these properties are difficult to parameterize due to their large variability and the fact that they are influenced by a number of other factors such as temperature, vertical velocity, relative humidity with respect to ice (RHice), and the available ice nuclei. The combination of those factors ultimately establishes whether heterogeneous or homogeneous nucleation will lead to ice crystal formation. The aforementioned factors are largely determined by the dynamics of the environment in which the ice cloud forms, collectively contained in a meteorological situation. Ice clouds have been observed in a variety of situations such as frontal systems, jet streams, gravity waves, and convective systems. Most recently, the concept of the influence of large-scale dynamics on midlatitude cirrus properties has been demonstrated in the work of Muehlbauer et al. (2014). In the work presented here, we explore this concept further by examining how differences in dynamics are translated into the differences in IWC, Ni, and Ri that are found within and between datasets. Data from two American-based campaigns, the 2004 Midlatitude Cirrus Experiment (MidCiX) and the 2011 Midlatitude Airborne Cirrus Properties Experiment (MACPEX), as well as some European-based campaigns, the 2004 and 2006 CIRRUS campaigns, the 2013 AIRTOSS-ICE campaign, and the 2014 ML-CIRRUS campaign are combined to form a large, and more latitudinally comprehensive database of Northern Hemisphere in-situ, midlatitude ice cloud observations. We have divided the data by meteorological situation and explored the differences and similarities between

  4. Fragmentation of interstellar clouds and star formation

    NASA Technical Reports Server (NTRS)

    Silk, J.

    1982-01-01

    The principal issues are addressed: the fragmentation of molecular clouds into units of stellar mass and the impact of star formation on molecular clouds. The observational evidence for fragmentation is summarized, and the gravitational instability described of a uniform spherical cloud collapsing from rest. The implications are considered of a finite pressure for the minimum fragment mass that is attainable in opacity-limited fragmentation. The role of magnetic fields is discussed in resolving the angular momentum problem and in making the collapse anisotropic, with notable consequences for fragmentation theory. Interactions between fragments are described, with emphasis on the effect of protostellar winds on the ambient cloud matter and on inhibiting further star formation. Such interactions are likely to have profound consequences for regulating the rate of star formation and on the energetics and dynamics of molecular clouds.

  5. Remote Sensing of Water and Ice Clouds Frommsg/seviri

    NASA Astrophysics Data System (ADS)

    Mayer, B.; Bugliaro, L.; Mannstein, H.; Zinner, T.; Krebs, W.; Wendling, P.

    2006-08-01

    Clouds and their interaction with radiation are still one of the main uncertainties in our understanding of present and the prediction of future climate. Within the frame- work of the MSG RAO-project we have developed a new water and ice cloud detection and microphysical prop- erties remote sensing algorithm, APICS (Algorithm for the Physical Interpretation of Clouds with SEVIRI). An MSG cirrus detection algorithm (MeCiDA) was devel- oped with special emphasis on optically thin ice clouds. Finally, a fast method to derive top-of-atmosphere ra- diation fluxes from MSG was developed. With these tools we studied the impact of air traffic on cirrus cloud cover and on the Earth’s radiation budget. Our current work concentrates on the generation of artificial satel- lite images, combining our experience with remote sens- ing of inhomogeneous clouds and radiative transfer. This manuscript is an update of the paper produced for the 2nd RAO workshop and summarizes the final results. Key words: radiative transfer, cloud, cirrus.

  6. Liquid and Ice Cloud Microphysics in the CSU General Circulation Model. Part III: Sensitivity to Modeling Assumptions.

    NASA Astrophysics Data System (ADS)

    Fowler, Laura D.; Randall, David A.

    1996-03-01

    The inclusion of cloud microphysical processes in general circulation models makes it possible to study the multiple interactions among clouds, the hydrological cycle, and radiation. The gaps between the temporal and spatial scales at which such cloud microphysical processes work and those at which general circulation models presently function force climate modelers to crudely parameterize and simplify the various interactions among the different water species (namely, water vapor, cloud water, cloud ice, rain, and snow) and to use adjustable parameters to which large-scale models can be highly sensitive. Accordingly, the authors have investigated the sensitivity of the climate, simulated with the Colorado State University general circulation model, to various aspects of the parameterization of cloud microphysical processes and its interactions with the cumulus convection and radiative transfer parameterizations.The results of 120-day sensitivity experiments corresponding to perpetual January conditions have been compared with those of a control simulation in order to 1 ) determine the importance of advecting cloud water, cloud ice, rain, and snow at the temporal and spatial scale resolutions presently used in the model; 2) study the importance of the formation of extended stratiform anvils at the tops of cumulus towers, 3) analyze the role of mixed-phase clouds in determining the partitioning among cloud water, cloud ice, rain, and snow and, hence, their impacts on the simulated cloud optical properties; 4) evaluate the sensitivity of the atmospheric moisture budget and precipitation rates to a change in the fall velocities of rain and snow; 5) determine the model's sensitivity to the prescribed thresholds of autoconversion of cloud water to rain and cloud ice to snow; and 6) study the impact of the collection of supercooled cloud water by snow, as well as accounting for the cloud optical properties of snow.Results are presented in terms of 30-day mean differences

  7. Far infrared microbolometers for radiometric measurements of ice cloud

    NASA Astrophysics Data System (ADS)

    Ngo Phong, Linh; Proulx, Christian; Oulachgar, Hassane; Châteauneuf, François

    2015-02-01

    Focal planes of 80x60 VOx microbolometers with pixel pitch of 104 μm were developed in support of the remote sensing of ice clouds in the spectral range from 7.9 to 50 μm. A new design that relies on the use of central posts to support the microbolometer platform was shown effective in minimizing the structural deformation usually occurred in platforms of large area. A process for goldblack coating and patterning of the focal plane arrays was established. It was found that the goldblack absorbs more than 98 % and 92 % of incident light respectively at wavelengths shorter and longer than 20 μm. Moreover, a spectral uniformity of better than 96 % was achieved in all spectral channels required for the measurements. The noise figures derived from the data acquired over short periods of acquisition time showed the evidence of a correlation with the format of the addressed sub-arrays. This correlation was not observed in the data acquired over long periods of time, suggesting the presence of low frequency effects. Regardless of the length of acquisition time, an improvement of noise level could be confirmed when the operating temperature was increased. The dependence of responsivity on sub-array format and operating temperature was investigated. The noise equivalent power derived from this study was found to be in the range from 45 to 80 pW, showing that the far infrared focal plane arrays are suited for use in the intended application.

  8. Using A-Train Observations to Evaluate Ice Water Path and Ice Cloud Radiative Effects in the Community Atmosphere Model

    NASA Astrophysics Data System (ADS)

    Berry, B. J.

    2015-12-01

    In this study we first use A-Train satellite data to investigate the distribution of clouds, along with their radiative and microphysical properties, in Southeast Asia during the summer monsoon. The distribution of ice water path (IWP) in this region is highly skewed, such that the mean value is not representative of the typical ice cloud. In examining how cirrus cloud radiative effects at the TOA vary as a function of IWP, we find that cirrus with an IWP less than 200 g m-2 produce a net warming. And weighting the radiative effect by the frequency of occurrence of IWP, reveals that cirrus with an IWP around 20 g m-2contribute most to the heating at the TOA. Next, we use the A-Train results to address the issues of IWP occurrence and high cloud forcing in the Community Atmosphere Model version 5. Our goal is to determine if the clouds that heat the upper troposphere in the model are the same genre of clouds that heat the upper troposphere in the real atmosphere. First, we assess the distribution of ice cloud fraction in the model. Then we define a cloud radiative kernel that's a function of cloud top pressure and IWP, to determine whether the modeled ice clouds produce similar shortwave and longwave radiative effects at the TOA. Lastly, we use the cloud radiative kernel and cloud fraction histogram to evaluate how the ice cloud forcing in the model compares to the ice cloud forcing derived from A-Train.

  9. Ice-nucleation negative fluorescent pseudomonads isolated from Hebridean cloud and rain water produce biosurfactants

    NASA Astrophysics Data System (ADS)

    Ahern, H. E.; Walsh, K. A.; Hill, T. C. J.; Moffett, B. F.

    2006-10-01

    Microorganisms were discovered in clouds over 100 years ago but information on bacterial community structure and function is limited. Clouds may not only be a niche within which bacteria could thrive but they might also influence dynamic processes using ice nucleating and cloud condensing abilities. Cloud and rain samples were collected from two mountains in the Outer Hebrides, NW Scotland, UK. Community composition was determined using a combination of amplified 16S ribosomal DNA restriction analysis and sequencing. 256 clones yielded 100 operational taxonomic units (OTUs) of which half were related to bacteria from terrestrial psychrophilic environments. Cloud samples were dominated by a mixture of fluorescent Pseudomonas spp., some of which have been reported to be ice nucleators. It was therefore possible that these bacteria were using the ice nucleation (IN) gene to trigger the Bergeron-Findeisen process of raindrop formation as a mechanism for dispersal. In this study the IN gene was not detected in any of the isolates using both polymerase chain reaction (PCR) and differential scanning calorimetry (DSC). Instead 55% of the total isolates from both cloud and rain samples displayed significant biosurfactant activity when analyzed using the drop-collapse technique. All were characterised as fluorescent pseudomonads. Surfactants have been found to be very important in lowering atmospheric critical supersaturations required for the activation of aerosols into cloud condensation nuclei (CCN). It is also known that surfactants influence cloud droplet size and increase cloud lifetime and albedo. Some bacteria are known to act as CCN and so it is conceivable that these fluorescent pseudomonads are using surfactants to facilitate their activation from aerosols into CCN. This would allow water scavenging, countering desiccation, and assist in their widespread dispersal.

  10. Global Simulations of Ice nucleation and Ice Supersaturation with an Improved Cloud Scheme in the Community Atmosphere Model

    SciTech Connect

    Gettelman, A.; Liu, Xiaohong; Ghan, Steven J.; Morrison, H.; Park, Sungsu; Conley, Andrew; Klein, Stephen A.; Boyle, James; Mitchell, David; Li, J-L F.

    2010-09-28

    A process-based treatment of ice supersaturation and ice-nucleation is implemented in the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM). The new scheme is designed to allow (1) supersaturation with respect to ice, (2) ice nucleation by aerosol particles and (3) ice cloud cover consistent with ice microphysics. The scheme is implemented with a 4-class 2 moment microphysics code and is used to evaluate ice cloud nucleation mechanisms and supersaturation in CAM. The new model is able to reproduce field observations of ice mass and mixed phase cloud occurrence better than previous versions of the model. Simulations indicate heterogeneous freezing and contact nucleation on dust are both potentially important over remote areas of the Arctic. Cloud forcing and hence climate is sensitive to different formulations of the ice microphysics. Arctic radiative fluxes are sensitive to the parameterization of ice clouds. These results indicate that ice clouds are potentially an important part of understanding cloud forcing and potential cloud feedbacks, particularly in the Arctic.

  11. In Situ Airborne Instrumentation: Addressing and Solving Measurement Problems in Ice Clouds

    DOE PAGES

    Baumgardner, Darrel; Kok, Greg; Avallone, L.; ...

    2012-02-01

    A meeting of 31 international experts on in situ measurements from aircraft was held to identify unresolved questions concerning ice formation and evolution in ice clouds, assess the current state of instrumentation that can address these problems, introduce emerging technology that may overcome current measurement issues and recommend future courses of action that can improve our understanding of ice cloud microphysical processes and their impact on the environment. The meeting proceedings and outcome has been described in detail in a manuscript submitted to the Bulletin of the American Meteorological Society (BAMS) on March 24, 2011. This paper is currently undermore » review. The remainder of this summary, in the following pages, is the text of the BAMS article. A technical note that will be published by the National Center for Atmospheric Research is currently underway and is expected to be published before the end of the year.« less

  12. In Situ Airborne Instrumentation: Addressing and Solving Measurement Problems in Ice Clouds

    SciTech Connect

    Baumgardner, Darrel; Kok, Greg; Avallone, L.; Bansemer, A.; Borrmann, S.; Brown, P.; Bundke, U.; Chuang, P. Y.; Cziczo, D.; Field, P.; Gallagher, M.; Gayet, J. -F.; Korolev, A.; Kraemer, M.; McFarquhar, G.; Mertes, S.; Moehler, O.; Lance, S.; Lawson, P.; Petters, M. D.; Pratt, K.; Roberts, G.; Rogers, D.; Stetzer, O.; Stith, J.; Strapp, W.; Twohy, C.; Wendisch, M.

    2012-02-01

    A meeting of 31 international experts on in situ measurements from aircraft was held to identify unresolved questions concerning ice formation and evolution in ice clouds, assess the current state of instrumentation that can address these problems, introduce emerging technology that may overcome current measurement issues and recommend future courses of action that can improve our understanding of ice cloud microphysical processes and their impact on the environment. The meeting proceedings and outcome has been described in detail in a manuscript submitted to the Bulletin of the American Meteorological Society (BAMS) on March 24, 2011. This paper is currently under review. The remainder of this summary, in the following pages, is the text of the BAMS article. A technical note that will be published by the National Center for Atmospheric Research is currently underway and is expected to be published before the end of the year.

  13. Revisiting the Scattering Greenhouse Effect of CO2 Ice Clouds

    NASA Astrophysics Data System (ADS)

    Kitzmann, D.

    2016-02-01

    Carbon dioxide ice clouds are thought to play an important role for cold terrestrial planets with thick CO2 dominated atmospheres. Various previous studies showed that a scattering greenhouse effect by carbon dioxide ice clouds could result in a massive warming of the planetary surface. However, all of these studies only employed simplified two-stream radiative transfer schemes to describe the anisotropic scattering. Using accurate radiative transfer models with a general discrete ordinate method, this study revisits this important effect and shows that the positive climatic impact of carbon dioxide clouds was strongly overestimated in the past. The revised scattering greenhouse effect can have important implications for the early Mars, but also for planets like the early Earth or the position of the outer boundary of the habitable zone.

  14. The role of ice nuclei recycling in the maintenance of cloud ice in Arctic mixed-phase stratocumulus

    DOE PAGES

    Solomon, A.; Feingold, G.; Shupe, M. D.

    2015-09-25

    This study investigates the maintenance of cloud ice production in Arctic mixed-phase stratocumulus in large eddy simulations that include a prognostic ice nuclei (IN) formulation and a diurnal cycle. Balances derived from a mixed-layer model and phase analyses are used to provide insight into buffering mechanisms that maintain ice in these cloud systems. We find that, for the case under investigation, IN recycling through subcloud sublimation considerably prolongs ice production over a multi-day integration. This effective source of IN to the cloud dominates over mixing sources from above or below the cloud-driven mixed layer. Competing feedbacks between dynamical mixing andmore » recycling are found to slow the rate of ice lost from the mixed layer when a diurnal cycle is simulated. The results of this study have important implications for maintaining phase partitioning of cloud ice and liquid that determine the radiative forcing of Arctic mixed-phase clouds.« less

  15. Star formation in the Magellanic clouds

    NASA Technical Reports Server (NTRS)

    Frogel, Jay A.

    1987-01-01

    Because of their proximity, the Magellanic Clouds provide the opportunity to conduct a detailed study of the history and current state of star formation in dwarf irregular galaxies. There is considerable evidence that star formation in the Clouds was and is proceeding in a manner different from that found in a typical well-ordered spiral galaxy. Star formation in both Clouds appears to have undergone a number of relatively intense bursts. There exist a number of similarities and differences in the current state of star formation in the Magellanic Clouds and the Milky Way. Examination of Infrared Astronomy Satellite (IRAS) sources with ground based telescopes allows identification of highly evolved massive stars with circumstellar shells as well as several types of compact emission line objects.

  16. Ice Concentration Retrieval in Stratiform Mixed-phase Clouds Using Cloud Radar Reflectivity Measurements and 1D Ice Growth Model Simulations

    SciTech Connect

    Zhang, Damao; Wang, Zhien; Heymsfield, Andrew J.; Fan, Jiwen; Luo, Tao

    2014-10-01

    Measurement of ice number concentration in clouds is important but still challenging. Stratiform mixed-phase clouds (SMCs) provide a simple scenario for retrieving ice number concentration from remote sensing measurements. The simple ice generation and growth pattern in SMCs offers opportunities to use cloud radar reflectivity (Ze) measurements and other cloud properties to infer ice number concentration quantitatively. To understand the strong temperature dependency of ice habit and growth rate quantitatively, we develop a 1-D ice growth model to calculate the ice diffusional growth along its falling trajectory in SMCs. The radar reflectivity and fall velocity profiles of ice crystals calculated from the 1-D ice growth model are evaluated with the Atmospheric Radiation Measurements (ARM) Climate Research Facility (ACRF) ground-based high vertical resolution radar measurements. Combining Ze measurements and 1-D ice growth model simulations, we develop a method to retrieve the ice number concentrations in SMCs at given cloud top temperature (CTT) and liquid water path (LWP). The retrieved ice concentrations in SMCs are evaluated with in situ measurements and with a three-dimensional cloud-resolving model simulation with a bin microphysical scheme. These comparisons show that the retrieved ice number concentrations are within an uncertainty of a factor of 2, statistically.

  17. Biological Ice Nucleation Activity in Cloud Water (Invited)

    NASA Astrophysics Data System (ADS)

    Delort, A.

    2013-12-01

    Ice nucleation active (INA) biological particles, in particular microorganisms, were studied in cloud water. Twelve cloud samples were collected over a period of 16 months from the puy de Dôme summit (1465 m, France) using sterile cloud droplet impactors. The samples were characterized through biological (cultures, cell counts) and physico-chemical measurements (pH, ion concentrations, carbon content...), and biological ice nuclei were investigated by droplet-freezing assays from -3°C to -13°C. The concentration of total INA particles within this temperature range typically varied from ~1 to ~100 per mL of cloud water; the concentrations of biological IN were several orders of magnitude higher than the values previously reported for precipitations. At -12°C, at least 76% of the IN were biological in origin, i.e. they were inactivated by heating at 95°C, and at temperatures above -8°C only biological material could induce ice. By culture, 44 Pseudomonas-like strains of bacteria were isolated from cloud water samples; 16% of them were found INA at the temperature of -8°C and they were identified as Pseudomonas syringae, Xanthomonas sp. and Pseudoxanthomonas sp.. Two strains induced freezing at as warm as -2°C, positioning them among the most active ice nucleators described so far. We estimated that, in average, 0.18% and more than 1%.of the bacterial cells present in clouds (~104 mL-1) are INA at the temperatures of -8°C and -12°C, respectively.

  18. A scheme for parameterizing cirrus cloud ice water content in general circulation models

    NASA Technical Reports Server (NTRS)

    Heymsfield, Andrew J.; Donner, Leo J.

    1990-01-01

    Clouds strongly influence th earth's energy budget. They control th amount of solar radiative energy absorbed by the climate system, partitioning the energy between the atmosphere and the earth's surface. They also control the loss of energy to space by their effect on thermal emission. Cirrus and altostratus are the most frequent cloud types, having an annual average global coverage of 35 and 40 percent, respectively. Cirrus is composed almost entirely of ice crystals and the same is frequently true of the upper portions of altostratus since they are often formed by the thickening of cirrostratus and by the spreading of the middle or upper portions of thunderstorms. Thus, since ice clouds cover such a large portion of the earth's surface, they almost certainly have an important effect on climate. With this recognition, researchers developing climate models are seeking largely unavailable methods for specifying the conditions for ice cloud formation, and quantifying the spatial distribution of ice water content, IWC, a necessary step in deriving their radiative characteristics since radiative properties are apparently related to IWC. A method is developed for specifying IWC in climate models, based on theory and measurements in cirrus during FIRE and other experiments.

  19. Ice-gas interactions during planet formation

    NASA Astrophysics Data System (ADS)

    Oberg, Karin I.

    2015-08-01

    The interplay between ice and gas in protoplanetary disks is believed to have played a critical role in the formation of the Solar System, and should be affecting the ongoing formation of exoplanets in the disks (Solar Nebula analogs) observed around young stars. “Snowlines”, i.e. the midplane condensation fronts of major volatiles such as water and CO in protoplanetary disks, should enhance particle growth and thus planet formation efficiencies. More importantly for this session, snowline locations affect the relative ice and gas molecular and elemental composition throughout the disk, which in its turn affects elemental composition of planetesimals as well as their water and organic content.Snowline locations are set by a combination of chemistry, ice sublimation energy barriers, and protoplanetary disk temperature and density structures. Together these properties regulate the abundances of the most common volatiles, in which temperature regimes these volatiles are predominantly present as ice, and where in the disk such temperatures are realized. Ice chemistry also regulates the organic trace composition of icy bodies, i.e. the abundances of cyanides and other prebiotically interesting molecules. The past couple of years have given us the first observations of snowlines in protoplanetary disks. There is also evidence of an active ice chemistry in disks and feedback of this chemistry into the gas-phase through thermal and non-thermal desorption. I will review the protoplanetary disk, protostellar and Solar System observations and models that can help us constrain what the most common volatiles are during planet formation, how the volatiles are distributed between ice and gas in the disk at different distances from the star (Sun), and how ice-gas interactions may enable us to trace the underlying ice reservoir during planet formation using gas-phase observations of protoplanetary disks.

  20. Star formation relations in nearby molecular clouds

    SciTech Connect

    Evans, Neal J. II; Heiderman, Amanda; Vutisalchavakul, Nalin

    2014-02-20

    We test some ideas for star formation relations against data on local molecular clouds. On a cloud by cloud basis, the relation between the surface density of star formation rate and surface density of gas divided by a free-fall time, calculated from the mean cloud density, shows no significant correlation. If a crossing time is substituted for the free-fall time, there is even less correlation. Within a cloud, the star formation rate volume and surface densities increase rapidly with the corresponding gas densities, faster than predicted by models using the free-fall time defined from the local density. A model in which the star formation rate depends linearly on the mass of gas above a visual extinction of 8 mag describes the data on these clouds, with very low dispersion. The data on regions of very massive star formation, with improved star formation rates based on free-free emission from ionized gas, also agree with this linear relation.

  1. Formation of brine channels in sea ice.

    PubMed

    Morawetz, Klaus; Thoms, Silke; Kutschan, Bernd

    2017-03-01

    Liquid salty micro-channels (brine) between growing ice platelets in sea ice are an important habitat for CO2-binding microalgaea with great impact on polar ecosystems. The structure formation of ice platelets is microscopically described and a phase field model is developed. The pattern formation during solidification of the two-dimensional interstitial liquid is considered by two coupled order parameters, the tetrahedricity as structure of ice and the salinity. The coupling and time evolution of these order parameters are described by a consistent set of three model parameters. They determine the velocity of the freezing process and the structure formation, the phase diagram, the super-cooling and super-heating region, and the specific heat. The model is used to calculate the short-time frozen micro-structures. The obtained morphological structure is compared with the vertical brine pore space obtained from X-ray computed tomography.

  2. Vertical Variation of Ice Particle Size in Convective Cloud Tops

    NASA Technical Reports Server (NTRS)

    Van Diedenhoven, Bastiaan; Fridlind, Ann M.; Cairns, Brian; Ackerman, Andrew S.; Yorks, John E.

    2016-01-01

    A novel technique is used to estimate derivatives of ice effective radius with respect to height near convective cloud tops (dr(sub e)/dz) from airborne shortwave reflectance measurements and lidar. Values of dr(sub e)/dz are about -6 micrometer/km for cloud tops below the homogeneous freezing level, increasing to near 0 micrometer/km above the estimated level of neutral buoyancy. Retrieved dr(sub e)/dz compares well with previously documented remote sensing and in situ estimates. Effective radii decrease with increasing cloud top height, while cloud top extinction increases. This is consistent with weaker size sorting in high, dense cloud tops above the level of neutral buoyancy where fewer large particles are present and with stronger size sorting in lower cloud tops that are less dense. The results also confirm that cloud top trends of effective radius can generally be used as surrogates for trends with height within convective cloud tops. These results provide valuable observational targets for model evaluation.

  3. Vertical Variation of Ice Particle Size in Convective Cloud Tops

    NASA Technical Reports Server (NTRS)

    Van Diedenhoven, Bastiaan; Fridlind, Ann M.; Cairns, Brian; Ackerman, Andrew S.; Yorks, John E.

    2016-01-01

    A novel technique is used to estimate derivatives of ice effective radius with respect to height near convective cloud tops (dr(sub e)/dz) from airborne shortwave reflectance measurements and lidar. Values of dr(sub e)/dz are about -6 micrometer/km for cloud tops below the homogeneous freezing level, increasing to near 0 micrometer/km above the estimated level of neutral buoyancy. Retrieved dr(sub e)/dz compares well with previously documented remote sensing and in situ estimates. Effective radii decrease with increasing cloud top height, while cloud top extinction increases. This is consistent with weaker size sorting in high, dense cloud tops above the level of neutral buoyancy where fewer large particles are present and with stronger size sorting in lower cloud tops that are less dense. The results also confirm that cloud top trends of effective radius can generally be used as surrogates for trends with height within convective cloud tops. These results provide valuable observational targets for model evaluation.

  4. Determination of Ice Water Path in Ice-over-Water Cloud Systems Using Combined MODIS and AMSR-E Measurements

    NASA Technical Reports Server (NTRS)

    Huang, Jianping; Minnis, Patrick; Lin, Bing; Yi, Yuhong; Fan, T.-F.; Sun-Mack, Sunny; Ayers, J. K.

    2006-01-01

    To provide more accurate ice cloud properties for evaluating climate models, the updated version of multi-layered cloud retrieval system (MCRS) is used to retrieve ice water path (IWP) in ice-over-water cloud systems over global ocean using combined instrument data from the Aqua satellite. The liquid water path (LWP) of lower layer water clouds is estimated from the Advanced Microwave Scanning Radiometer for EOS (AMSR-E) measurements. With the lower layer LWP known, the properties of the upper-level ice clouds are then derived from Moderate Resolution Imaging Spectroradiometer measurements by matching simulated radiances from a two-cloud layer radiative transfer model. Comparisons with single-layer cirrus systems and surface-based radar retrievals show that the MCRS can significantly improve the accuracy and reduce the over-estimation of optical depth and ice water path retrievals for ice over-water cloud systems. During the period from December 2004 through February 2005, the mean daytime ice cloud optical depth and IWP for overlapped ice-over-water clouds over ocean from Aqua are 7.6 and 146.4 gm(sup -2), respectively, significantly less than the initial single layer retrievals of 17.3 and 322.3 gm(sup -2). The mean IWP for actual single-layer clouds was 128.2 gm(sup -2).

  5. Terahertz Remote Sensing of Ice Clouds - Sensitivity on Ice Dielectric Properties

    NASA Astrophysics Data System (ADS)

    Mendrok, J.; Baron, P.; Kasai, Y.

    2007-12-01

    Initiated by current developments in terahertz sensor technology the application of instruments operating in the spectral region between 0.1 - 30 THz is considered for a number of remote sensing issues. Accounting for more than 50 percent of the outgoing longwave radiation and with the major component of cirrus radiative forcing in the far-infrared, satellite measurements in this spectral region will significantly support the determination of the radiation budget of the Earth. Furthermore, spanning the whole range of particle sizes found in tropospheric ice clouds, the Terahertz region bears the potential to complement existing methods and improve our knowlegde and understanding of those clouds. Both, determination of the Earth's radiation budget as well as retrieving ice cloud properties require appropriately accurate calculations of radiative transfer. Hence, a good knowledge of the input parameters to the radiative transfer models is needed. In particular, this includes spectrally dependent properties of the molecular as well as particulate atmospheric matter, i.e., spectroscopic parameters of the molecular absorption lines and continua as well as the dielectric properties of aerosol and cloud particle material. Due to the lack of Terahertz light source and receiver technology in the past, measurements of these parameters have been sparse and the knowledge about them is rather poor. In preparation to evaluate the feasibility of monitoring tropospheric ice clouds using passive Terahertz observations, we study the modeling uncertainties due to the unconfident knowledge of the complex refractive index of ice. We give an overview of the consistency and discrepancies, respectively, of the existing measurements and models for ice refractive index in the Terahertz region. Using calculations of particle optical properties according to Mie theory as well as the radiative transfer models Moliere and SARTre, we estimate the deviations in particle optical properties and

  6. Evidence of Meteor Smoke Particles as precursors for formation of mesospheric clouds on Mars

    NASA Astrophysics Data System (ADS)

    Määttänen, Anni; Listowski, Constantino

    2017-04-01

    Mesospheric clouds have been systematically observed in the Martian mesosphere for about a decade. Not all of the observations allow for the cloud composition to be defined. However, several observations have revealed clouds formed of CO2 ice crystals, although in some cases a water ice composition has been detected as well. The condensation of the main component of the atmosphere is a fairly unique phenomenon. Although the lower atmosphere of Mars is very dusty and rich in ice nuclei, the mesosphere should be fairly devoid of dust lifted from lower layers (due to weak probability of lifting to high altitudes and low atmospheric densities favouring sedimentation). A very interesting candidate as a source of ice nuclei in the mesosphere comes from a terrestrial analogue. Meteor Smoke Particles have been shown to play a role in the formation of the mesospheric clouds on the Earth, and in a recent modelling study we have been able to show that an exogenous source of ice nuclei is required in the Martian mesosphere to be able to model clouds with observed properties. We will present a short review of observations and a summary of the cloud properties, and then discuss the model results pointing towards Meteor Smoke Particles as a necessary ingredient for the formation of mesospheric clouds on Mars.

  7. Star formation in evolving molecular clouds

    NASA Astrophysics Data System (ADS)

    Völschow, M.; Banerjee, R.; Körtgen, B.

    2017-09-01

    Molecular clouds are the principle stellar nurseries of our universe; they thus remain a focus of both observational and theoretical studies. From observations, some of the key properties of molecular clouds are well known but many questions regarding their evolution and star formation activity remain open. While numerical simulations feature a large number and complexity of involved physical processes, this plethora of effects may hide the fundamentals that determine the evolution of molecular clouds and enable the formation of stars. Purely analytical models, on the other hand, tend to suffer from rough approximations or a lack of completeness, limiting their predictive power. In this paper, we present a model that incorporates central concepts of astrophysics as well as reliable results from recent simulations of molecular clouds and their evolutionary paths. Based on that, we construct a self-consistent semi-analytical framework that describes the formation, evolution, and star formation activity of molecular clouds, including a number of feedback effects to account for the complex processes inside those objects. The final equation system is solved numerically but at much lower computational expense than, for example, hydrodynamical descriptions of comparable systems. The model presented in this paper agrees well with a broad range of observational results, showing that molecular cloud evolution can be understood as an interplay between accretion, global collapse, star formation, and stellar feedback.

  8. Quasi-Liquid Layer Formation on Ice under Stratospheric Conditions

    NASA Technical Reports Server (NTRS)

    McNeill, V. Faye; Loerting, Thomas; Trout, Bernhardt L.; Molina, Luisa T.; Molina, Mario J.

    2004-01-01

    Characterization of the interaction of hydrogen chloride (HCl) with ice is essential to understanding at a molecular level the processes responsible for ozone depletion involving polar stratospheric cloud (PSC) particles. To explain the catalytic role PSC particle surfaces play during chlorine activation, we proposed previously that HCl induces the formation of a disordered region on the ice surface, a quasi-liquid layer (QLL), at stratospheric conditions. The QLL is known to exist in pure ice crystals at temperatures near the melting point, but its existence at stratospheric temperatures (-85 C to -70 C) had not been reported yet. We studied the interaction of HCl with ice under stratospheric conditions using the complementary approach of a) ellipsometry to directly monitor the ice surface, using chemical ionization mass spectrometry (CIMS) to monitor the gas phase species present in the ellipsometry experiments, and b) flow-tube experiments with CIMS detection. Here we show that trace amounts of HCl induce QLL formation at stratospheric temperatures, and that the QLL enhances the chlorine-activation reaction of HCl with chlorine nitrate (ClONO2), and also enhances acetic acid (CH3COOH) adsorption.

  9. Effect of cloud-scale vertical velocity on the contribution of homogeneous nucleation to cirrus formation and radiative forcing

    NASA Astrophysics Data System (ADS)

    Shi, X.; Liu, X.

    2016-06-01

    Ice nucleation is a critical process for the ice crystal formation in cirrus clouds. The relative contribution of homogeneous nucleation versus heterogeneous nucleation to cirrus formation differs between measurements and predictions from general circulation models. Here we perform large-ensemble simulations of the ice nucleation process using a cloud parcel model driven by observed vertical motions and find that homogeneous nucleation occurs rather infrequently, in agreement with recent measurement findings. When the effect of observed vertical velocity fluctuations on ice nucleation is considered in the Community Atmosphere Model version 5, the relative contribution of homogeneous nucleation to cirrus cloud occurrences decreases to only a few percent. However, homogeneous nucleation still has strong impacts on the cloud radiative forcing. Hence, the importance of homogeneous nucleation for cirrus cloud formation should not be dismissed on the global scale.

  10. LWC and Temperature Effects on Ice Accretion Formation on Swept Wings at Glaze Ice Conditions

    NASA Technical Reports Server (NTRS)

    Vargas, Mario; Reshotko, Eli

    2000-01-01

    An experiment was conducted to study the effect of liquid water content and temperature on the critical distance in ice accretion formation on swept wings at glaze ice conditions. The critical distance is defined as the distance from the attachment line to tile beginning of the zone where roughness elements develop into glaze ice feathers. A baseline case of 150 mph, 25 F, 0.75 g/cu m. Cloud Liquid Water Content (LWC) and 20 micrometers in Water Droplet Median Volume Diameter (MVD) was chosen. Icing runs were performed on a NACA 0012 swept wing tip at 150 mph and MVD of 20 micrometers for liquid water contents of 0.5 g/cu m, 0.75 g/cu m, and 1.0 g/cu m, and for total temperatures of 20 F, 25 F and 30 F. At each tunnel condition, the sweep angle was changed from 0 deg to 45 deg in 5 deg increments. Casting data, ice shape tracings, and close-up photographic data were obtained. The results showed that decreasing the LWC to 0.5 g/cu m decreases the value of the critical distance at a given sweep angle compared to the baseline case, and starts the formation of complete scallops at 30 sweep angle. Increasing the LWC to 1.0 g/cu m increases the value of the critical distance compared to the baseline case, the critical distance remains always above 0 millimeters and complete scallops are not formed. Decreasing the total temperature to 20 F decreases the critical distance with respect to the baseline case and formation of complete scallops begins at 25 deg sweep angle. When the total temperature is increased to 30 F, bumps covered with roughness elements appear on the ice accretion at 25 deg and 30 deg sweep angles, large ice structures appear at 35 deg and 40 deg sweep angles, and complete scallops are formed at 45 deg sweep angle.

  11. Laboratory studies of cirrus clouds: the ins and outs of ice nucleation

    NASA Astrophysics Data System (ADS)

    Tolbert, M. A.; Schill, G. P.; Baustian, K. J.

    2012-12-01

    Although cirrus clouds are ever-present in the upper troposphere, the precise mechanisms governing their formation are still uncertain. Recent field observations suggest that ice nucleation in the atmosphere is often more consistent with a heterogeneous nucleation mechanism than a homogeneous one. In the present work, we use optical microscopy coupled with Raman spectroscopy to examine ice nucleation on individual micron-sized particles. Because upper tropospheric particles as well as sub-visible cirrus residues are enhanced in both sulfates and organics, our focus is on complex particles containing these two species. Particles with well-defined structures were generated by nebulization of solutions containing ammonium sulfate and an organic. As the relative humidity was decreased, the aqueous particles underwent liquid-liquid phase separation forming an organic coating over ammonium sulfate. Lowering the relative humidity further resulted in ammonium sulfate efflorescence to a crystalline solid. Ice nucleation was then studied on the layered particles as a function of temperature and relative humidity. During particle formation and ice nucleation, Raman mapping was used to determine the particle structures. Depending on the organic composition and temperature, ice was sometimes observed to nucleate on the ammonium sulfate core within the particle and sometimes nucleated on the organic outer layer. The combination of Raman and optical microscopy allows visualization of the ice nucleation process for complex particles. These studies reveal that the mechanism of heterogeneous ice nucleation depends not just on particle size, but also on particle composition, phase and mixing state.

  12. Polar Mesospheric Cloud Mass and the Ice Budget: 2. Application to Satellite Data Sets

    DTIC Science & Technology

    2007-04-20

    now indicate that the environment over Antarctica is less conducive to PMC formation than over the Arctic [Thomas et al., 1991; Bailey et al., 2005...satellites operating at vari- ous times since November 1978 [DeLand et al., 2006]. SBUV PMC albedos are reported at 252.0 nm and the ice mass from one northern...2007]. Such high frequencies can lead to a negative bias in SBUV cloud frequencies and albedos because there are not enough clear air data to reliably

  13. Ice Formation in Gas-Diffusion Layers

    SciTech Connect

    Dursch, Thomas; Radke, Clayton J.; Weber, Adam Z.

    2010-07-10

    Under sub-freezing conditions, ice forms in the gas-diffusion layer (GDL) of a proton exchange membrane fuel cell (PEMFC) drastically reducing cell performance. Although a number of strategies exist to prevent ice formation, there is little fundamental understanding of the mechanisms of freezing within PEMFC components. Differential scanning calorimetry (DSC) is used to elucidate the effects of hydrophobicity (Teflon® loading) and water saturation on the rate of ice formation within three commercial GDLs. We find that as the Teflon® loading increases, the crystallization temperature decreases due to a change in internal ice/substrate contact angle, as well as the attainable level of water saturation. Classical nucleation theory predicts the correct trend in freezing temperature with Teflon® loading.

  14. Near-Real-Time Satellite Cloud Products for Icing Detection and Aviation Weather over the USA

    NASA Technical Reports Server (NTRS)

    Minnis, Patrick; Smith, William L., Jr.; Nguyen, Louis; Murray, J. J.; Heck, Patrick W.; Khaiyer, Mandana M.

    2003-01-01

    A set of physically based retrieval algorithms has been developed to derive from multispectral satellite imagery a variety of cloud properties that can be used to diagnose icing conditions when upper-level clouds are absent. The algorithms are being applied in near-real time to the Geostationary Operational Environmental Satellite (GOES) data over Florida, the Southern Great Plains, and the midwestern USA. The products are available in image and digital formats on the world-wide web. The analysis system is being upgraded to analyze GOES data over the CONUS. Validation, 24-hour processing, and operational issues are discussed.

  15. SGP and TWP (Manus) Ice Cloud Vertical Velocities

    SciTech Connect

    Kalesse, Heike

    2013-06-27

    Daily netcdf-files of ice-cloud dynamics observed at the ARM sites at SGP (Jan1997-Dec2010) and Manus (Jul1999-Dec2010). The files include variables at different time resolution (10s, 20min, 1hr). Profiles of radar reflectivity factor (dbz), Doppler velocity (vel) as well as retrieved vertical air motion (V_air) and reflectivity-weighted particle terminal fall velocity (V_ter) are given at 10s, 20min and 1hr resolution. Retrieved V_air and V_ter follow radar notation, so positive values indicate downward motion. Lower level clouds are removed, however a multi-layer flag is included.

  16. Mechanisms of intracellular ice formation.

    PubMed Central

    Muldrew, K; McGann, L E

    1990-01-01

    The phenomenon of intracellular freezing in cells was investigated by designing experiments with cultured mouse fibroblasts on a cryomicroscope to critically assess the current hypotheses describing the genesis of intracellular ice: (a) intracellular freezing is a result of critical undercooling; (b) the cytoplasm is nucleated through aqueous pores in the plasma membrane; and (c) intracellular freezing is a result of membrane damage caused by electrical transients at the ice interface. The experimental data did not support any of these theories, but was consistent with the hypothesis that the plasma membrane is damaged at a critical gradient in osmotic pressure across the membrane, and intracellular freezing occurs as a result of this damage. An implication of this hypothesis is that mathematical models can be used to design protocols to avoid damaging gradients in osmotic pressure, allowing new approaches to the preservation of cells, tissues, and organs by rapid cooling. PMID:2306499

  17. The Nature of Carbon Dioxide Bearing Ices in Quiescent Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Whittet, D. C. B.; Cook, A. M.; Chiar, J. E.; Pendleton, Y. J.; Shenoy, S. S.; Gerakines, P. A.

    2009-04-01

    The properties of the ices that form in dense molecular clouds represent an important set of initial conditions in the evolution of interstellar and preplanetary matter in regions of active star formation. Of the various spectral features available for study, the bending mode of solid CO2 near 15 μm has proven to be a particularly sensitive probe of physical conditions, especially temperature. We present new observations of this absorption feature in the spectrum of Q21-1, a background field star located behind a dark filament in the Cocoon Nebula (IC 5146). We show the profile of the feature to be consistent with a two-component (polar + nonpolar) model for the ices, based on spectra of laboratory analogs with temperatures in the range 10-20 K. The polar component accounts for ~85% of the CO2 in the line of sight. We compare for the first time 15 μm profiles in three widely separated dark clouds (Taurus, Serpens, and IC 5146), and show that they are indistinguishable to within observational scatter. Systematic differences in the observed CO2/H2O ratio in the three clouds have little or no effect on the 15 μm profile. The abundance of elemental oxygen in the ices appears to be a unifying factor, displaying consistent behavior in the three clouds. We conclude that the ice formation process is robust and uniformly efficient, notwithstanding compositional variations arising from differences in how the O is distributed between the primary species (H2O, CO2, and CO) in the ices.

  18. THE NATURE OF CARBON DIOXIDE BEARING ICES IN QUIESCENT MOLECULAR CLOUDS

    SciTech Connect

    Whittet, D. C. B.; Cook, A. M.; Chiar, J. E.; Pendleton, Y. J.; Shenoy, S. S.; Gerakines, P. A.

    2009-04-10

    The properties of the ices that form in dense molecular clouds represent an important set of initial conditions in the evolution of interstellar and preplanetary matter in regions of active star formation. Of the various spectral features available for study, the bending mode of solid CO{sub 2} near 15 {mu}m has proven to be a particularly sensitive probe of physical conditions, especially temperature. We present new observations of this absorption feature in the spectrum of Q21-1, a background field star located behind a dark filament in the Cocoon Nebula (IC 5146). We show the profile of the feature to be consistent with a two-component (polar + nonpolar) model for the ices, based on spectra of laboratory analogs with temperatures in the range 10-20 K. The polar component accounts for {approx}85% of the CO{sub 2} in the line of sight. We compare for the first time 15 {mu}m profiles in three widely separated dark clouds (Taurus, Serpens, and IC 5146), and show that they are indistinguishable to within observational scatter. Systematic differences in the observed CO{sub 2}/H{sub 2}O ratio in the three clouds have little or no effect on the 15 {mu}m profile. The abundance of elemental oxygen in the ices appears to be a unifying factor, displaying consistent behavior in the three clouds. We conclude that the ice formation process is robust and uniformly efficient, notwithstanding compositional variations arising from differences in how the O is distributed between the primary species (H{sub 2}O, CO{sub 2}, and CO) in the ices.

  19. Fast Molecular Cloud Destruction Requires Fast Cloud Formation

    NASA Astrophysics Data System (ADS)

    Mac Low, Mordecai-Mark; Burkert, Andreas; Ibáñez-Mejía, Juan C.

    2017-09-01

    A large fraction of the gas in the Galaxy is cold, dense, and molecular. If all this gas collapsed under the influence of gravity and formed stars in a local free-fall time, the star formation rate in the Galaxy would exceed that observed by more than an order of magnitude. Other star-forming galaxies behave similarly. Yet, observations and simulations both suggest that the molecular gas is indeed gravitationally collapsing, albeit hierarchically. Prompt stellar feedback offers a potential solution to the low observed star formation rate if it quickly disrupts star-forming clouds during gravitational collapse. However, this requires that molecular clouds must be short-lived objects, raising the question of how so much gas can be observed in the molecular phase. This can occur only if molecular clouds form as quickly as they are destroyed, maintaining a global equilibrium fraction of dense gas. We therefore examine cloud formation timescales. We first demonstrate that supernova and superbubble sweeping cannot produce dense gas at the rate required to match the cloud destruction rate. On the other hand, Toomre gravitational instability can reach the required production rate. We thus argue that, although dense, star-forming gas may last only around a single global free-fall time; the dense gas in star-forming galaxies can globally exist in a state of dynamic equilibrium between formation by gravitational instability and disruption by stellar feedback. At redshift z ≳ 2, the Toomre instability timescale decreases, resulting in a prediction of higher molecular gas fractions at early times, in agreement with the observations.

  20. Linking atmospheric synoptic transport, cloud phase, surface energy fluxes, and sea-ice growth: observations of midwinter SHEBA conditions

    NASA Astrophysics Data System (ADS)

    Persson, P. Ola G.; Shupe, Matthew D.; Perovich, Don; Solomon, Amy

    2016-10-01

    Observations from the Surface Heat Budget of the Arctic Ocean (SHEBA) project are used to describe a sequence of events linking midwinter long-range advection of atmospheric heat and moisture into the Arctic Basin, formation of supercooled liquid water clouds, enhancement of net surface energy fluxes through increased downwelling longwave radiation, and reduction in near-surface conductive heat flux loss due to a warming of the surface, thereby leading to a reduction in sea-ice bottom growth. The analyses provide details of two events during Jan. 1-12, 1998, one entering the Arctic through Fram Strait and the other from northeast Siberia; winter statistics extend the results. Both deep, precipitating frontal clouds and post-frontal stratocumulus clouds impact the surface radiation and energy budget. Cloud liquid water, occurring preferentially in stratocumulus clouds extending into the base of the inversion, provides the strongest impact on surface radiation and hence modulates the surface forcing, as found previously. The observations suggest a minimum water vapor threshold, likely case dependent, for producing liquid water clouds. Through responses to the radiative forcing and surface warming, this cloud liquid water also modulates the turbulent and conductive heat fluxes, and produces a thermal wave penetrating into the sea ice. About 20-33 % of the observed variations of bottom ice growth can be directly linked to variations in surface conductive heat flux, with retarded ice growth occurring several days after these moisture plumes reduce the surface conductive heat flux. This sequence of events modulate pack-ice wintertime environmental conditions and total ice growth, and has implications for the annual sea-ice evolution, especially for the current conditions of extensive thinner ice.

  1. Linking atmospheric synoptic transport, cloud phase, surface energy fluxes, and sea-ice growth: observations of midwinter SHEBA conditions

    NASA Astrophysics Data System (ADS)

    Persson, P. Ola G.; Shupe, Matthew D.; Perovich, Don; Solomon, Amy

    2017-08-01

    Observations from the Surface Heat Budget of the Arctic Ocean (SHEBA) project are used to describe a sequence of events linking midwinter long-range advection of atmospheric heat and moisture into the Arctic Basin, formation of supercooled liquid water clouds, enhancement of net surface energy fluxes through increased downwelling longwave radiation, and reduction in near-surface conductive heat flux loss due to a warming of the surface, thereby leading to a reduction in sea-ice bottom growth. The analyses provide details of two events during Jan. 1-12, 1998, one entering the Arctic through Fram Strait and the other from northeast Siberia; winter statistics extend the results. Both deep, precipitating frontal clouds and post-frontal stratocumulus clouds impact the surface radiation and energy budget. Cloud liquid water, occurring preferentially in stratocumulus clouds extending into the base of the inversion, provides the strongest impact on surface radiation and hence modulates the surface forcing, as found previously. The observations suggest a minimum water vapor threshold, likely case dependent, for producing liquid water clouds. Through responses to the radiative forcing and surface warming, this cloud liquid water also modulates the turbulent and conductive heat fluxes, and produces a thermal wave penetrating into the sea ice. About 20-33 % of the observed variations of bottom ice growth can be directly linked to variations in surface conductive heat flux, with retarded ice growth occurring several days after these moisture plumes reduce the surface conductive heat flux. This sequence of events modulate pack-ice wintertime environmental conditions and total ice growth, and has implications for the annual sea-ice evolution, especially for the current conditions of extensive thinner ice.

  2. Cloud Optimized Image Format and Compression

    NASA Astrophysics Data System (ADS)

    Becker, P.; Plesea, L.; Maurer, T.

    2015-04-01

    Cloud based image storage and processing requires revaluation of formats and processing methods. For the true value of the massive volumes of earth observation data to be realized, the image data needs to be accessible from the cloud. Traditional file formats such as TIF and NITF were developed in the hay day of the desktop and assumed fast low latency file access. Other formats such as JPEG2000 provide for streaming protocols for pixel data, but still require a server to have file access. These concepts no longer truly hold in cloud based elastic storage and computation environments. This paper will provide details of a newly evolving image storage format (MRF) and compression that is optimized for cloud environments. Although the cost of storage continues to fall for large data volumes, there is still significant value in compression. For imagery data to be used in analysis and exploit the extended dynamic range of the new sensors, lossless or controlled lossy compression is of high value. Compression decreases the data volumes stored and reduces the data transferred, but the reduced data size must be balanced with the CPU required to decompress. The paper also outlines a new compression algorithm (LERC) for imagery and elevation data that optimizes this balance. Advantages of the compression include its simple to implement algorithm that enables it to be efficiently accessed using JavaScript. Combing this new cloud based image storage format and compression will help resolve some of the challenges of big image data on the internet.

  3. ESA's Ice Cloud Imager on Metop Second Generation

    NASA Astrophysics Data System (ADS)

    Klein, Ulf; Loiselet, Marc; Mason, Graeme; Gonzalez, Raquel; Brandt, Michael

    2016-04-01

    Since 2006, the European contribution to operational meteorological observations from polar orbit has been provided by the Meteorological Operational (MetOp) satellites, which is the space segment of the EUMETSAT Polar System (EPS). The first MetOp satellite was launched in 2006, 2nd 2012 and 3rd satellite is planned for launch in 2018. As part of the next generation EUMETSAT Polar System (EPS-SG), the MetOp Second Generation (MetOp-SG) satellites will provide continuity and enhancement of these observations in the 2021 - 2042 timeframe. The noel Ice Cloud Imager (ICI) is one of the instruments selected to be on-board the MetOp-SG satellite "B". The main objective of the ICI is to enable cloud ice retrieval, with emphasis on cirrus clouds. ICI will provide information on cloud ice mean altitude, cloud ice water path and cloud ice effective radius. In addition, it will provide water vapour profile measurement capability. ICI is a 13-channel microwave/sub-millimetre wave radiometer, covering the frequency range from 183 GHz up to 664 GHz. The instrument is composed of a rotating part and a fixed part. The rotating part includes the main antenna, the feed assembly and the receiver electronics. The fixed part contains the hot calibration target, the reflector for viewing the cold sky and the electronics for the instrument control and interface with the platform. Between the fixed and the rotating part is the scan mechanism. Scan mechanism is not only responsible of rotating the instrument and providing its angular position, but it will also have pass through the power and data lines. The Scan mechanism is controlled by the fully redundant Control and Drive Electronics ICI is calibrated using an internal hot target and a cold sky mirror, which are viewed once per rotation. The internal hot target is a traditional pyramidal target. The hot target is covered by an annular shield during rotation with only a small opening for the feed horns to guarantee a stable environment

  4. Modeling CO 2 ice clouds with a Mars Global Climate Model

    NASA Astrophysics Data System (ADS)

    Audouard, Joachim; Määttänen, Anni; Listowski, Constantino; Millour, Ehouarn; Forget, Francois; Spiga, Aymeric

    2016-10-01

    Since the first claimed detection of CO2 ice clouds by the Mariner campaign (Herr and Pimentel, 1970), more recent observations and modelling works have put new constraints concerning their altitude, region, time and mechanisms of formation (Clancy and Sandor, 1998; Montmessin et al., 2007; Colaprete et al., 2008; Määttänen et al., 2010; Vincendon et al., 2011; Spiga et al. 2012; Listowski et al. 2014). CO2 clouds are observed at the poles at low altitudes (< 20 km) during the winter and at high altitudes (60-110 km) in the equatorial regions during the first half of the year. However, Martian CO2 clouds's variability and dynamics remain somehow elusive.Towards an understanding of Martian CO2 clouds and especially of their precise radiative impact on the climate throughout the history of the planet, including their formation and evolution in a Global Climate Model (GCM) is necessary.Adapting the CO2 clouds microphysics modeling work of Listowski et al. (2013; 2014), we aim at implementing a complete CO2 clouds scheme in the GCM of the Laboratoire de Météorologie Dynamique (LMD, Forget et al., 1999). It covers CO2 microphysics, growth, evolution and dynamics with a methodology inspired from the water ice clouds scheme recently included in the LMD GCM (Navarro et al., 2014).Two main factors control the formation and evolution of CO2 clouds in the Martian atmosphere: sufficient supersaturation of CO2 is needed and condensation nuclei must be available. Topography-induced gravity-waves (GW) are expected to propagate to the upper atmosphere where they produce cold pockets of supersaturated CO2 (Spiga et al., 2012), thus allowing the formation of clouds provided enough condensation nuclei are present. Such supersaturations have been observed by various instruments, in situ (Schofield et al., 1997) and from orbit (Montmessin et al., 2006, 2011; Forget et al., 2009).Using a GW-induced temperature profile and the 1-D version of the GCM, we simulate the formation of CO2

  5. ICE CHEMISTRY IN EMBEDDED YOUNG STELLAR OBJECTS IN THE LARGE MAGELLANIC CLOUD

    SciTech Connect

    Oliveira, J. M.; Van Loon, J. Th.; Chen, C.-H. R.; Indebetouw, R.; Tielens, A. G. G. M.; Sloan, G. C.; Woods, P. M.; Kemper, F.; Gordon, K. D.; Boyer, M. L.; Shiao, B.; Meixner, M.; Madden, S.; Speck, A. K.; Marengo, M.

    2009-12-20

    We present spectroscopic observations of a sample of 15 embedded young stellar objects (YSOs) in the Large Magellanic Cloud (LMC). These observations were obtained with the Spitzer Infrared Spectrograph (IRS) as part of the SAGE-Spec Legacy program. We analyze the two prominent ice bands in the IRS spectral range: the bending mode of CO{sub 2} ice at 15.2 mum and the ice band between 5 and 7 mum that includes contributions from the bending mode of water ice at 6 mum among other ice species. The 5-7 mum band is difficult to identify in our LMC sample due to the conspicuous presence of polycyclic aromatic hydrocarbon emission superimposed onto the ice spectra. We identify water ice in the spectra of two sources; the spectrum of one of those sources also exhibits the 6.8 mum ice feature attributed in the literature to ammonium and methanol. We model the CO{sub 2} band in detail, using the combination of laboratory ice profiles available in the literature. We find that a significant fraction (approx>50%) of CO{sub 2} ice is locked in a water-rich component, consistent with what is observed for Galactic sources. The majority of the sources in the LMC also require a pure-CO{sub 2} contribution to the ice profile, evidence of thermal processing. There is a suggestion that CO{sub 2} production might be enhanced in the LMC, but the size of the available sample precludes firmer conclusions. We place our results in the context of the star formation environment in the LMC.

  6. The application of time-dependent ice crystal trajectory and growth model for the evaluation of cloud seeding experiment using liquid carbon dioxide

    NASA Astrophysics Data System (ADS)

    Nishiyama, K.; Wakimizu, K.; Maki, T.; Suzuki, Y.; Morita, O.; Tomine, K.

    2012-12-01

    This study evaluated the results of cloud seeding experiment conducted on 17th January, 2008, in western Kyushu, Japan, using simplified time-dependent ice crystal growth and trajectory cloud model, which is characterized by 1) depositional diffusion growth process only of an ice crystal, and 2) the pursuit of the growing ice crystal based on wind field and ice crystal terminal velocity. For the estimation of the ice crystal growth and trajectory, the model specifies ice supersaturation ratio that expresses the degree of competition growth among ice crystals formed by LC seeding for existing water vapor, assuming no effect of natural ice crystals. The model is based on ice crystal growth along a- and c-axes depending on air temperature and ice supersatuation, according to Chen and Lamb (1994). The cloud seeding experiment was conducted by applying homogeneous nucleation (rapid cooling of air mass and subsequent formation of many ice crystals~1013/g LC) of Liquid Carbon (LC) dioxide seeding under typical winter-type snowfall-inducing weather situation characterized by the outbreak of cold air masses from the Siberia. The result of aircraft horizontally-penetrating seeding of LC into lower layer (-2 degree C) of supercooled convective cloud with 1km thickness above the freezing level led to the formation of an artificially-induced 'isolated' radar echo (the left figures of Fig. 1) in dominant 'no-natural radar echo region'. In other words, natural biases were eliminated by the formation of the isolated radar echo. This fact provides the shortcut for evaluating the result of cloud seeding experiment. In the next, the observed cloud seeding results were evaluated by estimating the trajectory of artificially-induced growing ice crystal. The results show that the trajectory of artificial ice crystals depends on the degree of completion growth mode. Free growth brings rapid growth of an ice crystal and, therefore, the ice crystal falls into lower layers for a short time

  7. Sensitivity of Cirrus and Mixed-phase Clouds to the Ice Nuclei Spectra in McRAS-AC: Single Column Model Simulations

    NASA Technical Reports Server (NTRS)

    Betancourt, R. Morales; Lee, D.; Oreopoulos, L.; Sud, Y. C.; Barahona, D.; Nenes, A.

    2012-01-01

    The salient features of mixed-phase and ice clouds in a GCM cloud scheme are examined using the ice formation parameterizations of Liu and Penner (LP) and Barahona and Nenes (BN). The performance of LP and BN ice nucleation parameterizations were assessed in the GEOS-5 AGCM using the McRAS-AC cloud microphysics framework in single column mode. Four dimensional assimilated data from the intensive observation period of ARM TWP-ICE campaign was used to drive the fluxes and lateral forcing. Simulation experiments where established to test the impact of each parameterization in the resulting cloud fields. Three commonly used IN spectra were utilized in the BN parameterization to described the availability of IN for heterogeneous ice nucleation. The results show large similarities in the cirrus cloud regime between all the schemes tested, in which ice crystal concentrations were within a factor of 10 regardless of the parameterization used. In mixed-phase clouds there are some persistent differences in cloud particle number concentration and size, as well as in cloud fraction, ice water mixing ratio, and ice water path. Contact freezing in the simulated mixed-phase clouds contributed to transfer liquid to ice efficiently, so that on average, the clouds were fully glaciated at T approximately 260K, irrespective of the ice nucleation parameterization used. Comparison of simulated ice water path to available satellite derived observations were also performed, finding that all the schemes tested with the BN parameterization predicted 20 average values of IWP within plus or minus 15% of the observations.

  8. Ice nucleation by plant structural materials and its potential contribution to glaciation in clouds

    NASA Astrophysics Data System (ADS)

    Hiranuma, N.; Hoose, C.; Järvinen, E.; Kiselev, A. A.; Moehler, O.; Schnaiter, M.; Ullrich, R.; Cziczo, D. J.; Felgitsch, L.; Gourihar, K.; Grothe, H.; Reicher, N.; Rudich, Y.; Tobo, Y.; Zawadowicz, M. A.

    2015-12-01

    Glaciation of supercooled clouds through immersion freezing is an important atmospheric process affecting the formation of precipitation and the Earth's energy budget. Currently, the climatic impact of ice-nucleating particles (INPs) is being reassessed due to increasing evidence of their diversity and abundance in the atmosphere as well as their ability to influence cloud properties. Recently, it has been found that microcrystalline cellulose (MCC; extracted from natural wood pulp) can act as an efficient INP and may add crucial importance to quantify the role of primary biological INP (BINP) in the troposphere. However, it is still unclear if the laboratory results of MCC can be representatively scaled up to the total cellulose content in the atmosphere to assess the overall role of BINPs in clouds and the climate system. Here, we use the AIDA (Aerosol Interaction and Dynamics in the Atmosphere) cloud simulation chamber in Karlsruhe, Germany to demonstrate that several important plant constituents as well as natural plant debris can act as BINPs in simulated super-cooled clouds of the lower and middle troposphere. More specifically, we measured the surface-scaled ice nucleation activity of a total 16 plant structural materials (i.e., celluloses, lignins, lipids and carbohydrates), which were dispersed and immersed in cloud droplets in the chamber, and compared to that of dried leaf powder as a model proxy for atmospheric BINPs. Using these surface-based activities, we developed parameters describing the ice nucleation ability of these particles. Subsequently, we applied them to observed airborne plant debris concentrations and compared to the background INP simulated in a global aerosol model. Our results suggest that cellulose is the most active BINPs amongst the 16 materials and the concentration of ice nucleating cellulose and plant debris to become significant (>0.1 L-1) below about -20 ˚C. Overall, our findings support the view that MCC may be a good proxy

  9. Decreasing clouds drive mass loss on the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Hofer, Stefan; Bamber, Jonathan; Tedstone, Andrew; Fettweis, Xavier

    2017-04-01

    The Greenland ice sheet (GrIS) has been losing mass at an accelerating rate since the mid-1990s. This has been due to both increased ice discharge into the ocean and melting at the surface, with the latter being the dominant contribution. This change in state has been attributed to rising temperatures and a decrease in surface albedo. Here we show, using satellite data and climate model output, that the abrupt reduction in surface mass balance since about 1995 can be largely attributed to a coincident trend of decreasing summer cloud cover. Satellite observations show that, from 1995 to 2009, summer cloud cover decreased by 0.9% ± 0.28%.yr. Model output indicates that the GrIS surface mass balance has a sensitivity of -5.4 ± 2 Gt per percent reduction in summer cloud cover, due principally to the impact of increased shortwave radiation over the low albedo ablation zone. The observed reduction in cloud cover is strongly correlated with a state shift of the North Atlantic Oscillation, suggesting that the enhanced surface mass loss from the GrIS is driven by synoptic-scale changes in Arctic-wide atmospheric circulation.

  10. Infrared Spectroscopy of Ammonia - Hydrocarbon Ices Relevant to Jupiter's Clouds

    NASA Astrophysics Data System (ADS)

    Engel, P. A.; Kalogerakis, K. S.

    2005-12-01

    Observational evidence and thermochemical models indicate an abundance of ammonia ice clouds in Jupiter's atmosphere. However, spectrally identifiable ammonia ice clouds are found covering less than 1% of Jupiter's atmosphere, notably in turbulent areas.1,2 This discrepancy highlights an important gap in our understanding of ammonia and its spectral signatures in Jupiter's atmosphere. Current literature suggests two possible explanations: coating by a hydrocarbon haze and/or photochemical processing ("tanning").2,3 We are performing laboratory experiments that investigate the above hypotheses. Thin films of ammonia ices are deposited in a cryogenic apparatus, coated with hydrocarbons, and characterized by infrared spectroscopy. The ice films can be irradiated by ultraviolet light. These spectroscopic measurements aim to identify the photophysical and chemical processes that control the optical properties of the ice mixtures and quantify their dependence on the identity of the coating, the temperature, and the ice composition. Our current results indicate a consistent suppression of the ammonia absorption feature at 3 μm with coverage by thin layers of hexane, cyclohexane, and benzene. Furthermore, strongest suppression is observed in the case of benzene, followed in magnitude by hexane and cyclohexane. Funding from the NSF Planetary Astronomy Program under grant AST-0206270 is gratefully acknowledged. The participation of Patricia A. Engel was made possible by the NSF Research Experiences for Undergraduates Program under grant PHY-0353745. 1. S. K. Atreya, A.-S. Wong, K. H. Baines, M. H. Wong, T. C. Owen, Planet. Space Science 53, 498 (2005). 2. K. H. Baines, R. W. Carlson, and L. W. Kamp, Icarus 159, 74 (2002). 3. A.-S. Wong, Y. L. Yung, and A. J. Friedson, Geophys. Res. Lett. 30, 1447 (2003).

  11. Implications of the ISOCLOUD campaigns at the AIDA Cloud Chamber for ice growth in cold cirrus

    NASA Astrophysics Data System (ADS)

    Lamb, Kara; Clouser, Benjamin; Sarkozy, Laszlo; Wagner, Steven; Ebert, Volker; Kerstel, Erik; Saathoff, Harald; Möhler, Ottmar; Moyer, Elisabeth

    2015-04-01

    In-situ water vapor measurements in the upper troposphere and lower stratosphere (UTLS) have routinely observed anomalous supersaturations on the order of 10-20particles when temperatures were below 200 K, raising questions about the physics of how ice forms at cold temperatures in the atmosphere1,2,3,4. The ISOCLOUD campaigns in 2012-2013 at the AIDA Aerosol and Cloud Chamber sought to investigate ice growth at cold temperatures by simulating cirrus clouds at temperatures and pressures characteristic of the upper troposphere. Experiments tested both homogeneous nucleation of sulfate aerosols and heterogeneous nucleation with various ice nuclei, including mineral dust and organic aerosols with and without nitric acid coatings. Optical instruments, both in-situ (TDLAS) and extractive (TDLAS and OFCEAS), measured ice particle number density, water vapor, total water, and water vapor isotopic concentrations, with multiple instruments measuring water. In a series of cirrus formation experiments, we observed no evidence of anomalous saturation vapor pressure and no evidence of ice growth inhibition at low temperatures for the parameter space tested during the ISOCLOUD campaigns. That is, we see no evidence for temperature dependence in the deposition coefficient. In these experiments we determined the deposition coefficient from bulk parameters of the gas (vapor concentration and ice number density). The ISOCLOUD experiments were particularly suited to deposition coefficient measurements since they involved lower pressures and often lower temperatures than previous similar campaigns, producing lower error bars.5 These results can aid in the interpretation of data from aircraft campaigns in the UTLS by solidifying our understanding of the microphysics of ice formation at cold temperatures. [1] Gao, R. et al., Science, 303, no. 6567, 516-520, (2004). [2] Jensen, E. et al., Atmos. Chem. Phys., 5, 851-862, (2005). [3] Peter, T. et al., Science, 314, no. 5804, 1399

  12. Wintertime Cloud Cover as a Contributor towards Inter-Annual Sea Ice Variability.

    NASA Astrophysics Data System (ADS)

    Letterly, A.; Key, J. R.

    2014-12-01

    The role of cloud forcing on Arctic sea ice is fundamental but also complex, serving as an accelerant or antagonist to ice growth on a hemispheric scale. Though sea ice decline in recent decades is largely attributed to arctic amplification, plunges in ice extent and restorative winter refreezes occurring on a year-to-year basis cannot be adequately explained by this general trend. For improved understanding and prediction of these inter-annual fluctuations in ice area, cloud forcing effects on surface energy budgets must be seen as an important factor for ice growth and melt. For example, the significant rebound of arctic sea ice from the record minimum of September 2012 was aided by the surface cooling effects of negative winter cloud cover anomalies (fewer clouds), according to a recent study using satellite and reanalysis data. For this study, the ERA-Interim reanalysis is used to diagnose and quantify the contribution of surface radiative forcing by wintertime cloud cover on sea ice during years with anomalous total ice areas. Comparisons between reanalysis of cloud forcing from September through March and passive microwave-derived ice concentrations in September demonstrate a significant inverse correlation between cloud cover during winter and the ice extent at the end of a melt season. Cloud re-emission of longwave radiation in winter months acts to curb the process by which polar seas radiatively cool to space and freeze, so that less winter cloud generally results in thicker sea ice. Here we investigate the role of winter cloud cover as a predictor and contributor to anomalous ice extent over the past 32 years. Our results stand to improve climate model projections of sea ice melt and assign some cause to large year-to-year ice area variability in a warming arctic regime.

  13. Physical processes controlling the evolution of ice concentration in cirrus clouds

    NASA Astrophysics Data System (ADS)

    Jensen, E. J.; Pfister, L.

    2011-12-01

    Several past studies have compared measured cirrus ice concentrations with calculations based on nucleation theory. However, such calculations only indicate the peak ice concentrations occurring just after nucleation events. Various cloud processes (e.g., differential sedimentation, entrainment, dispersion, and aggregation) conspire to reduce mean ice concentrations as the cloud evolves. Here, we use both a one-dimensional cloud model and a three-dimensional cloud-resolving model to evaluate the impact of these processes on the evolution of ice concentration through the lifecycle of cirrus clouds. Results are compared statistically with recent airborne measurements of ice concentration in the midlatitude and tropical uppermost troposphere. We will show that mean ice concentrations are reduced substantially by processes occurring after nucleation events, and this issue should be taken into consideration when comparing with observations that necessarily represent a range of cloud ages.

  14. Detecting Dust Storms and Water Ice Clouds Onboard THEMIS

    NASA Astrophysics Data System (ADS)

    Wagstaff, K. L.; Bandfield, J. L.; Castano, R.; Chien, S.; Smith, M. D.; Stough, T. M.

    2006-05-01

    We are developing and testing the first data analysis algorithms to be used onboard a spacecraft in Mars orbit. In particular, these algorithms will be uploaded to the Mars Odyssey spacecraft, where they will analyze data collected by the Thermal Emission Imaging System (THEMIS) instrument. In order of increasing sophistication, they can detect thermal anomalies (which could be indicators of geothermal activity), track the movements of the seasonal polar caps, detect dust storms, and detect water ice clouds in the atmosphere. The benefit of estimating atmospheric constituents in an onboard setting is that we can then detect features or events of interest and use them to prioritize data for transmission back to Earth. Rather than collecting only a pre-specified list of target images, THEMIS can use a more continuous operating mode and only return images that successfully capture events of interest, such as the onset of a dust storm or particularly dense water ice clouds. We will present recent results obtained by our dust and water ice cloud detection algorithms when applied to raw data that was collected by THEMIS. To estimate the dust and water ice content of the atmosphere, we trained a support vector machine (SVM) to perform regression based on previous analyses of a combination of fully calibrated TES and THEMIS data by Smith et al. (JGR 108, 2003). We find that both algorithms are, on average, able to estimate optical depth to within the same level of the uncertainty associated with the values computed by Smith et al. We conclude that these algorithms are performing at a level suitable for use onboard THEMIS. We will also report on the status of onboard infusion of these methods.

  15. Trends and solar cycle effects in mesospheric ice clouds

    NASA Astrophysics Data System (ADS)

    Lübken, Franz-Josef; Berger, Uwe; Fiedler, Jens; Baumgarten, Gerd; Gerding, Michael

    Lidar observations of mesospheric ice layers (noctilucent clouds, NLC) are now available since 12 years which allows to study solar cycle effects on NLC parameters such as altitudes, bright-ness, and occurrence rates. We present observations from our lidar stations in Kuehlungsborn (54N) and ALOMAR (69N). Different from general expectations the mean layer characteris-tics at ALOMAR do not show a persistent anti-correlation with solar cycle. Although a nice anti-correlation of Ly-alpha and occurrence rates is detected in the first half of the solar cycle, occurrence rates decreased with decreasing solar activity thereafter. Interestingly, in summer 2009 record high NLC parameters were detected as expected in solar minimum conditions. The morphology of NLC suggests that other processes except solar radiation may affect NLC. We have recently applied our LIMA model to study in detail the solar cycle effects on tempera-tures and water vapor concentration the middle atmosphere and its subsequent influence on mesospheric ice clouds. Furthermore, lower atmosphere effects are implicitly included because LIMA nudges to the conditions in the troposphere and lower stratosphere. We compare LIMA results regarding solar cycle effects on temperatures and ice layers with observations at ALO-MAR as well as satellite borne measurements. We will also present LIMA results regarding the latitude variation of solar cycle and trends, including a comparison of northern and southern hemisphere. We have adapted the observation conditions from SBUV (wavelength and scatter-ing angle) in LIMA for a detailed comparison with long term observations of ice clouds from satellites.

  16. MLS and CALIOP Cloud Ice Measurements in the Upper Troposphere: A Constraint from Microwave on Cloud Microphysics

    NASA Technical Reports Server (NTRS)

    Wu, Dong L.; Lambert, Alyn; Read, William G.; Eriksson, Patrick; Gong, Jie

    2014-01-01

    This study examines the consistency and microphysics assumptions among satellite ice water content (IWC) retrievals in the upper troposphere with collocated A-Train radiances from Microwave Limb Sounder (MLS) and lidar backscatters from Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP). For the cases in which IWC values are small (less than 10mg m(exp-23)), the cloud ice retrievals are constrained by both MLS 240- and 640- GHz radiances and CALIOP 532-nm backscatter beta(532). From the observed relationships between MLS cloud-induced radiance T(sub cir) and the CALIOP backscatter integrated gamma532 along the MLS line of sight, an empirical linear relation between cloud ice and the lidar backscatter is found: IWC/beta532=0.58+/-0.11. This lidar cloud ice relation is required to satisfy the cloud ice emission signals simultaneously observed at microwave frequencies, in which ice permittivity is relatively well known. This empirical relationship also produces IWC values that agree well with the CALIOP, version 3.0, retrieval at values, less than 10mg m(exp-3). Because the microphysics assumption is critical in satellite cloud ice retrievals, the agreement found in the IWC-beta532 relationships increase fidelity of the assumptions used by the lidar and microwave techniques for upper-tropospheric clouds.

  17. Ice Formation Delay on Penguin Feathers

    NASA Astrophysics Data System (ADS)

    Alizadehbirjandi, Elaheh; Tavakoli-Dastjerdi, Faryar; St. Leger, Judy; Davis, Stephen H.; Rothstein, Jonathan P.; Kavehpour, H. Pirouz

    2015-11-01

    Antarctic penguins reside in a harsh environment where air temperature may reach -40 °C with wind speed of 40 m/s and water temperature remains around -2.2 °C. Penguins are constantly in and out of the water and splashed by waves, yet even in sub-freezing conditions, the formation of macroscopic ice is not observed on their feathers. Bird feathers are naturally hydrophobic; however, penguins have an additional hydrophobic coating on their feathers to reinforce their non-wetting properties. This coating consists of preen oil which is applied to the feathers from the gland near the base of the tail. The combination of the feather's hydrophobicity and surface texture is known to increase the contact angle of water drops on penguin feathers to over 140 ° and classify them as superhydrophobic. We here develop an in-depth analysis of ice formation mechanism on superhydrophobic surfaces through careful experimentations and development of a theory to address how ice formation is delayed on these surfaces. Furthermore, we investigate the anti-icing properties of warm and cold weather penguins with and without preen oil to further design a surface minimizing the frost formation which is of practical interest especially in aircraft industry.

  18. Update on the NASA Glenn PSL Ice Crystal Cloud Characterization (2016)

    NASA Technical Reports Server (NTRS)

    Van Zante, J.; Bencic, T.; Ratvasky, Thomas P.; Struk, Peter M.

    2016-01-01

    NASA Glenn's Propulsion Systems Laboratory (PSL) is an altitude engine research test facility capable of producing ice-crystal and supercooled liquid clouds. The cloud characterization parameter space is fairly large and complex, but the phase of the cloud seems primarily governed by wet bulb temperature. The presentation will discuss some of the issues uncovered through four cloud characterization efforts to date, as well as some of instrumentation that has been used to characterize cloud parameters including cloud uniformity, bulk total water content, median volumetric diameter and max-diameter, percent freeze-out, relative humidity, and an update on the NASA Glenn PSL Ice Crystal Cloud Characterization (2016).

  19. Simple cloud chambers using a freezing mixture of ice and cooking salt

    NASA Astrophysics Data System (ADS)

    Yoshinaga, Kyohei; Kubota, Miki; Kamata, Masahiro

    2015-01-01

    We have developed much simpler cloud chambers that use only ice and cooking salt instead of the dry ice or ice gel pack needed for the cloud chambers produced in our previous work. The observed alpha-ray particle tracks are as clear as those observed using our previous cloud chambers. The tracks can be observed continuously for about 20 min, and the preparation and operation are simple.

  20. An overview of the Ice Nuclei Research Unit Jungfraujoch/Cloud and Aerosol Characterization Experiment 2013 (INUIT-JFJ/CLACE-2013)

    NASA Astrophysics Data System (ADS)

    Schneider, Johannes

    2014-05-01

    Ice formation in mixed phase tropospheric clouds is an essential prerequisite for the formation of precipitation at mid-latitudes. Ice formation at temperatures warmer than -35°C is only possible via heterogeneous ice nucleation, but up to now the exact pathways of heterogeneous ice formation are not sufficiently well understood. The research unit INUIT (Ice NUcleation research unIT), funded by the Deutsche Forschungsgemeinschaft (DFG FOR 1525) has been established in 2012 with the objective to investigate heterogeneous ice nucleation by combination of laboratory studies, model calculation and field experiments. The main field campaign of the INUIT project (INUIT-JFJ) was conducted at the High Alpine Research Station Jungfraujoch (Swiss Alps, 3580 m asl) during January and February 2013, in collaboration with several international partners in the framework of CLACE2013. The instrumentation included a large set of aerosol chemical and physical analysis instruments (particle counters, particle sizers, particle mass spectrometers, cloud condensation nuclei counters, ice nucleus counters etc.), that were operated inside the Sphinx laboratory and sampled in mixed phase clouds through two ice selective inlets (Ice-CVI, ISI) as well as through a total aerosol inlet that was used for out-of-cloud aerosol measurements. Besides the on-line measurements, also samples for off-line analysis (ESEM, STXM) have been taken in and out of clouds. Furthermore, several cloud microphysics instruments were operated outside the Sphinx laboratory. First results indicate that a large fraction of ice residues sampled from mixed phase clouds contain organic material, but also mineral dust. Soot and lead were not found to be enriched in ice residues. The concentration of heterogeneous ice nuclei was found to be variable (ranging between < 1 and > 100 per liter) and to be strongly dependent on the operating conditions of the respective IN counter. The number size distribution of ice residues

  1. A study of Type I polar stratospheric cloud formation

    NASA Technical Reports Server (NTRS)

    Tabazadeh, A.; Turco, R. P.; Drdla, K.; Jacobson, M. Z.; Toon, O. B.

    1994-01-01

    Mechanisms for the formation of Type I (nitric acid-based) polar stratospheric clouds (PSCs) are discussed. If the pre-existing sulfate aerosols are liquid prior to PSC formation, then nitric acid particles (Type Ib) form by HNO3 dissolution in aqueous H2SO4 solution droplets. This process does not require a nucleation step for the formation of HNO3 aerosols, so most pre-existing aerosols grow to become relatively small HNO3-containing particles. At significantly lower temperatures, the resulting supercooled solutions (Type Ib) may freeze to form HNO3 ice particles (Type Ia). If the pre-existing sulfate aerosols are initially solid before PSC formation, then HNO3 vapor can be deposited directly on the frozen sulfate particles. However, because an energy barrier to the condensation exists a nucleation mechanism is involved. Here, we suggest a unique nucleation mechanism that involves formation of HNO3/H20 solutions on the sulfate ice particles. These nucleation processes may be highly selective, resulting in the formation of relatively small number of large particles.

  2. Evidence of High Ice Supersaturation in Cirrus Clouds Using ARM Raman Lidar Measurements

    SciTech Connect

    Comstock, Jennifer M.; Ackerman, Thomas P.; Turner, David D.

    2004-06-05

    Water vapor amounts in the upper troposphere are crucial to understanding the radiative feedback of cirrus clouds on the Earth’s climate. We use a unique, year-long dataset of water vapor mixing ratio inferred from ground-based Raman lidar measurements to study the role of ice supersaturation in ice nucleation processes. We find that ice supersaturation occurs 31% of the time in over 300,000 data points. We also examine the distribution of ice supersaturation with height and find that in the uppermost portion of a cloud layer, the air is ice supersaturated 43% of the time. These measurements show that large ice supersaturation is common in cirrus clouds, which supports the theory of ice forming homogeneously. Given the continuous nature of these Raman lidar measurements, our results have important implications for studying ice nucleation processes using cloud microphysical models.

  3. ARM Raman Lidar Measurements of High Ice Supersaturation in Cirrus Clouds

    SciTech Connect

    Comstock, Jennifer M.; Ackerman, Thomas P.; Turner, David D.

    2004-09-01

    Water vapor amounts in the upper troposphere are crucial to understanding the radiative feedback of cirrus clouds on the Earth's climate. We use a unique, year-long dataset of water vapor mixing ratio inferred from ground-based Raman lidar measurements to study the role of ice supersaturation in ice nucleation processes. We find that ice supersaturation occurs 31% of the time in over 300,000 data points. We also examine the distribution of ice supersaturation with height and find that in the uppermost portion of a cloud layer, the air is ice supersaturated 43% of the time. These measurements show that large ice supersaturation is common in cirrus clouds, which supports the theory of ice forming homogeneously. Given the continuous nature of these Raman lidar measurements, our results have important implications for studying ice nucleation processes using cloud microphysical models.

  4. Vertical Structure of Ice Cloud Layers From CloudSat and CALIPSO Measurements and Comparison to NICAM Simulations

    NASA Technical Reports Server (NTRS)

    Ham, Seung-Hee; Sohn, Byung-Ju; Kato, Seiji; Satoh, Masaki

    2013-01-01

    The shape of the vertical profile of ice cloud layers is examined using 4 months of CloudSat and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) global measurements taken on January, April, July, and October 2007. Ice clouds are selected using temperature profiles when the cloud base is located above the 253K temperature level. The obtained ice water content (IWC), effective radius, or extinction coefficient profiles are normalized by their layer mean values and are expressed in the normalized vertical coordinate, which is defined as 0 and 1 at the cloud base and top heights, respectively. Both CloudSat and CALIPSO observations show that the maximum in the IWC and extinction profiles shifts toward the cloud bottom, as the cloud depth increases. In addition, clouds with a base reaching the surface in a high-latitude region show that the maximum peak of the IWC and extinction profiles occurs near the surface, which is presumably due to snow precipitation. CloudSat measurements show that the seasonal difference in normalized cloud vertical profiles is not significant, whereas the normalized cloud vertical profile significantly varies depending on the cloud type and the presence of precipitation. It is further examined if the 7 day Nonhydrostatic Icosahedral Atmospheric Model (NICAM) simulation results from 25 December 2006 to 1 January 2007 generate similar cloud profile shapes. NICAM IWC profiles also show maximum peaks near the cloud bottom for thick cloud layers and maximum peaks at the cloud bottom for low-level clouds near the surface. It is inferred that oversized snow particles in the NICAM cloud scheme produce a more vertically inhomogeneous IWC profile than observations due to quick sedimentation.

  5. Vertical Structure of Ice Cloud Layers From CloudSat and CALIPSO Measurements and Comparison to NICAM Simulations

    NASA Technical Reports Server (NTRS)

    Ham, Seung-Hee; Sohn, Byung-Ju; Kato, Seiji; Satoh, Masaki

    2013-01-01

    The shape of the vertical profile of ice cloud layers is examined using 4 months of CloudSat and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) global measurements taken on January, April, July, and October 2007. Ice clouds are selected using temperature profiles when the cloud base is located above the 253K temperature level. The obtained ice water content (IWC), effective radius, or extinction coefficient profiles are normalized by their layer mean values and are expressed in the normalized vertical coordinate, which is defined as 0 and 1 at the cloud base and top heights, respectively. Both CloudSat and CALIPSO observations show that the maximum in the IWC and extinction profiles shifts toward the cloud bottom, as the cloud depth increases. In addition, clouds with a base reaching the surface in a high-latitude region show that the maximum peak of the IWC and extinction profiles occurs near the surface, which is presumably due to snow precipitation. CloudSat measurements show that the seasonal difference in normalized cloud vertical profiles is not significant, whereas the normalized cloud vertical profile significantly varies depending on the cloud type and the presence of precipitation. It is further examined if the 7 day Nonhydrostatic Icosahedral Atmospheric Model (NICAM) simulation results from 25 December 2006 to 1 January 2007 generate similar cloud profile shapes. NICAM IWC profiles also show maximum peaks near the cloud bottom for thick cloud layers and maximum peaks at the cloud bottom for low-level clouds near the surface. It is inferred that oversized snow particles in the NICAM cloud scheme produce a more vertically inhomogeneous IWC profile than observations due to quick sedimentation.

  6. Modelling the impact of fungal spore ice nuclei on clouds and precipitation

    NASA Astrophysics Data System (ADS)

    Sesartic, Ana; Lohmann, Ulrike; Storelvmo, Trude

    2013-04-01

    Fungal spores are part of the atmospheric bioaerosols such as pollen or bacteria. Interest in bioaerosols is mainly related to their health effects, impacts on agriculture, ice nucleation and cloud droplet activation, as well as atmospheric chemistry (Morris et al. 2011). Spores of some fungal species have been found to be very efficient ice nuclei, e.g. in laboratory studies by Pouleur et al. (1992). Recent field studies by Poehlker et al. (2012) found that fungal spores are important contributors to the development of mist and clouds in rainforest ecosystems. In our study we investigated the impact of fungal spores acting as ice nuclei on clouds and precipitation on a global scale. Fungal spores as a new aerosol species were introduced into the global climate model ECHAM5-HAM (Sesartic et al. 2012) using observational fungal spore data compiled by Sesartic & Dallafior (2011). The addition of fungal spores lead to only minor changes in cloud formation and precipitation on a global level, however, changes in the liquid water path and ice water path as well as stratiform precipitation in the model were observed in the boreal regions where tundra and forests act as sources of fungal spores. This goes hand in hand with a decreased ice crystal number concentration and increased effective radius of ice crystals. An increase in stratiform precipitation and snowfall can be observed in those regions as well. Although fungal spores contribute to heterogeneous freezing, their impact in the model was reduced by their low numbers compared to other heterogeneous ice nuclei. These results for fungal spores are comparable to the ones achieved with bacteria (Sesartic et al. 2012). REFERENCES Morris, C. E. et al. 2011: Microbiology and atmospheric processes: research challenges concerning the impact of airborne micro-organisms on the atmosphere and climate, Biogeosciences, 8, 17-25. Poehlker, C. et al. 2012: Biogenic Potassium Salt Particles as Seeds for Secondary Organic Aerosol

  7. Homogeneous ice nucleation and supercooled liquid water in orographic wave clouds

    NASA Technical Reports Server (NTRS)

    Heymsfield, Andrew J.; Miloshevich, Larry M.

    1993-01-01

    This study investigates ice nucleation mechanisms in cold lenticular wave clouds, a cloud type characterized by quasi-steady-state air motions and microphysical properties. It is concluded that homogeneous ice nucleation is responsible for the ice production in these clouds at temperatures below about -33 C. The lack of ice nucleation observed above -33 C indicates a dearth of ice-forming nuclei, and hence heterogeneous ice nucleation, in these clouds. Aircraft measurements in the temperature range -31 to -41 C show the following complement of simultaneous and abrupt changes in cloud properties that indicate a transition from the liquid phase to ice: disappearance of liquid water; decrease in relative humidity from near water saturation to ice saturation; increase in mean particle size; change in particle concentration; and change in temperature due to the release of latent heat. A numerical model of cloud particle growth and homogeneous ice nucleation is used to aid in interpretation of our in situ measurements. The abrupt changes in observed cloud properties compare favorably, both qualitatively and quantitatively, with results from the homogeneous ice nucleation model. It is shown that the homogeneous ice nucleation rates from the measurements are consistent with the temperature-dependent rates employed by the model (within a factor of 100, corresponding to about 1 C in temperature) in the temperature range -35 deg to -38 C. Given the theoretical basis of the modeled rates, it may be reasonable to apply them throughout the -30 to -50 C temperature range considered by the theory.

  8. The Formation of Molecular Clouds: Insights from Numerical Models

    NASA Astrophysics Data System (ADS)

    Heitsch, Fabian

    2010-10-01

    Galactic star formation occurs at a surprisingly low rate. Yet, recent large-scale surveys of dark clouds in the Galaxy show that one rarely finds molecular clouds without young stellar objects, suggesting that star formation should occur rapidly upon molecular cloud formation. This rapid onset challenges the traditional concept of ``slow'' star formation in long-lived molecular clouds. It also imposes strong constraints on the physical properties of the parental clouds, mandating that a cloud's structure and dynamics controlling stellar birth must arise during its formation. This requires a new approach to study initial conditions of star formation, namely addressing the formation of molecular clouds. Taking into account the observational constraints, I will outline the physics of flow-driven molecular cloud formation. I will discuss the relevance and the limitations of this scenario for setting the star formation efficiency in our Galaxy and beyond.

  9. Studies of ice clouds using 95 GHz airborne radar

    NASA Astrophysics Data System (ADS)

    Wolde, Mengistu Yirdaw

    2000-12-01

    This study presents results from analyses of 95 GHz airborne polarimetric radar measurements and other in situ data in a variety of ice clouds. Measurements were made in winter clouds over Wyoming and Colorado. Radar parameters analyzed were the differential reflectivity factor (ZDR) and the linear depolarization ratio (LDR). Examination of the specific signatures for different crystal forms, and the dependence of the signatures on beam angle, led to a diagnostic matrix in terms ZDR and LDR values. Planar crystals, columnar crystals, and melting particles can be differentiated based on combined ZDR and LDR measurements at various radar elevation angles. Unique LDR signatures were also observed in Cu con. clouds containing large graupel particles and high concentrations of small particles. It is also shown that among planar crystals P1a and P1d types can be differentiated from P1e types. Overall, the frequencies of occurrence of significant polarimetric signatures were only few percent in the cloud volumes examined, but can approach near 100% in certain clouds. Polarimetric signatures were found to be most frequent in the temperature interval -10 to -18°C due to plate-like crystals growing there. The presence of significant polarimetric signatures is associated with the absence of riming and provides a means of identifying cloud regions where diffusional crystal growth dominates. In the second part of the dissertation, cloud structure and crystal growth in Ns clouds sampled in Wyoming and Oregon are presented. In spite of differences in location and time, the two Ns data sets have shown similar features. In both cases, generating cells were present near cloud top and the melting layer was well defined in the radar images. Thin dry layers just above the melting layer were also observed in both cases. In accordance with earlier studies, particle spectra in these clouds are adequately described by exponential relationships. The slope and intercept parameters of the

  10. Formation of giant molecular clouds in global spiral structures: The role of orbital dynamics and cloud-cloud collisions

    NASA Technical Reports Server (NTRS)

    Roberts, W. W., Jr.; Stewart, G. R.

    1987-01-01

    The different roles played by orbital dynamics and dissipative cloud-cloud collisions in the formation of giant molecular clouds (GMCs) in a global spiral structure are investigated. The interstellar medium (ISM) is simulated by a system of particles, representing clouds, which orbit in a spiral-perturbed, galactic gravitational field. The overall magnitude and width of the global cloud density distribution in spiral arms is very similar in the collisional and collisionless simulations. The results suggest that the assumed number density and size distribution of clouds and the details of individual cloud-cloud collisions have relatively little effect on these features. Dissipative cloud-cloud collisions play an important steadying role for the cloud system's global spiral structure. Dissipative cloud-cloud collisions also damp the relative velocity dispersion of clouds in massive associations and thereby aid in the effective assembling of GMC-like complexes.

  11. Simulating the effects of semivolatile aerosol species on cloud formation and lifecycle

    NASA Astrophysics Data System (ADS)

    Kokkola, Harri; Kudzotsa, Innocent; Tonttila, Juha; Raatikainen, Tomi; Romakkaniemi, Sami

    2017-04-01

    The effect of aerosol has been acknowledged to cause a significant uncertainty in estimating the anthropogenic aerosol effect on climate. Research efforts on the formation and growth of atmospheric particles to sizes where they become cloud condensation nuclei have been extensive. In comparison, much less attention is given on cloud processing of particles and aerosol removal through wet deposition. However, aerosol removal processes largely dictate how well aerosol is transported from source regions. This means that in order to model the global distribution aerosol, both in vertical and horizontal, wet deposition processes have to be properly modelled. However, in large scale models, the description of wet removal and the vertical redistribution of aerosol by cloud processes is very limited. Here we present a novel aerosol-cloud model SALSA, where the aerosol properties are tracked though cloud processes including: cloud droplet activation, precipitation formation, ice nucleation, melting, and evaporation. It is a sectional model that includes separate size sections for non-activated aerosol, cloud droplets, precipitation droplets, and ice crystals. The aerosol-cloud model was coupled to a large eddy model UCLALES which simulates the boundary-layer dynamics. In this study, the model has been applied in studying the wet removal as well as interactions between clouds and semi-volatile compounds, ammonia and nitric acid. These compounds are special in the sense that they co-condense together with water during cloud activation and have been suggested to form droplets that can be considered cloud-droplet-like already in subsaturated conditions. In our model, we calculate the kinetic partitioning of ammonia and sulfate thus explicitly taking into account the effect of ammonia and nitric acid in the cloud formation. Our simulations indicate that especially in polluted conditions, these compounds significantly affect the properties of cloud droplets thus significantly

  12. Martian Boundary Layer Water Ice Clouds At The Proposed NASA Phoenix Lander Site

    NASA Astrophysics Data System (ADS)

    Michelangeli, Diane; Pathak, J.

    2006-12-01

    Results from the one-dimensional University of Helsinki atmospheric boundary layer (ABL) model are applied to a one-dimensional Mars microphysics model (MMM) to study the diurnal variation of ground fogs and ice cloud formation at the proposed NASA Phoenix landing site. Phoenix is scheduled to reach Mars in 2008 and land in the northern plains (65°-72°N). A Meteorology station (MET), consisting of a pressure sensor, 3 mast-mounted temperature sensors and an upward-looking LIDAR, will enable weather and boundary layer observations. The LIDAR (Light Detection and Ranging) instrument will be capable of monitoring dust and ice clouds, including fog and dust plumes, in the Martian boundary layer. Understanding these future LIDAR observations is the motivation for the modeling studies conducted for this paper. Observations from the MGS TES for the proposed landing site and season Ls 76 125 have been used for the model initialization, both in the ABL and MMM. The diurnal variations of temperature and eddy diffusion coefficients produced by the ABL are then applied to the MMM. Sensitivity to water ice cloud simulation is studied by varying the vertical resolution of the MMM and by inclusion of surface fluxes of dust and water vapor. The results from these studies will be presented at the conference. Acknowledgements: This work is supported by the Canadian Space Agency and Natural Sciences and Engineering Research Council of Canada.

  13. Methanol Formation via Oxygen Insertion Chemistry in Ices

    NASA Astrophysics Data System (ADS)

    Bergner, Jennifer B.; Öberg, Karin I.; Rajappan, Mahesh

    2017-08-01

    We present experimental constraints on the insertion of oxygen atoms into methane to form methanol in astrophysical ice analogs. In gas-phase and theoretical studies this process has previously been demonstrated to have a very low or nonexistent energy barrier, but the energetics and mechanisms have not yet been characterized in the solid state. We use a deuterium UV lamp filtered by a sapphire window to selectively dissociate O2 within a mixture of O2:CH4 and observe efficient production of CH3OH via O(1D) insertion. CH3OH growth curves are fit with a kinetic model, and we observe no temperature dependence of the reaction rate constant at temperatures below the oxygen desorption temperature of 25 K. Through an analysis of side products we determine the branching ratio of ice-phase oxygen insertion into CH4: ∼65% of insertions lead to CH3OH, with the remainder leading instead to H2CO formation. There is no evidence for CH3 or OH radical formation, indicating that the fragmentation is not an important channel and that insertions typically lead to increased chemical complexity. CH3OH formation from O2 and CH4 diluted in a CO-dominated ice similarly shows no temperature dependence, consistent with expectations that insertion proceeds with a small or nonexistent barrier. Oxygen insertion chemistry in ices should therefore be efficient under low-temperature ISM-like conditions and could provide an important channel to complex organic molecule formation on grain surfaces in cold interstellar regions such as cloud cores and protoplanetary disk midplanes.

  14. Retrieval of ice cloud microphysical parameters using the CloudSat millimeter-wave radar and temperature

    NASA Astrophysics Data System (ADS)

    Austin, Richard T.; Heymsfield, Andrew J.; Stephens, Graeme L.

    2009-04-01

    A new remote sensing retrieval of ice cloud microphysics has been developed for use with millimeter-wave radar from ground-, air-, or space-based sensors. Developed from an earlier retrieval that used measurements of radar reflectivity factor together with a priori information about the likely cloud targets, the new retrieval includes temperature information as well to assist in determining the correct region of state space, particularly for those size distribution parameters that are less constrained by the radar measurements. These algorithms have served as the ice cloud retrieval algorithms in Releases 3 and 4 of the CloudSat 2B-CWC-RO Standard Data Product. Several comparison studies have been performed on the previous and current retrieval algorithms: some involving tests of the algorithms on simulated radar data (based on actual cloud probe data or cloud resolving models) and others featuring statistical comparisons of the R04 2B-CWC-RO product (current algorithm) to ice cloud mass retrievals by other spaceborne, airborne, and ground-based instruments or alternative algorithms using the same CloudSat radar data. Comparisons involving simulated radar data based on a database of cloud probe data showed generally good performance, with ice water content (IWC) bias errors estimated to be less than 40%. Comparisons to ice water content and ice water path estimates by other instruments are mixed. When the comparison is restricted to different retrieval approaches using the same CloudSat radar measurements, CloudSat R04 results generally agree with alternative IWC retrievals for IWC < 1000 mg m-3 at altitudes below 12 km but differ at higher ice contents and altitudes, either exceeding other retrievals or falling within a spread of retrieval values. Validation and reconciliation of all these approaches will continue to be a topic for further research.

  15. Interference phenomena at backscattering by ice crystals of cirrus clouds.

    PubMed

    Borovoi, Anatoli; Kustova, Natalia; Konoshonkin, Alexander

    2015-09-21

    It is shown that light backscattering by hexagonal ice crystals of cirrus clouds is formed within the physical-optics approximation by both diffraction and interference phenomena. Diffraction determines the angular width of the backscattering peak and interference produces the interference rings inside the peak. By use of a simple model for distortion of the pristine hexagonal shape, we show that the shape distortion leads to both oscillations of the scattering (Mueller) matrix within the backscattering peak and to a strong increase of the depolarization, color, and lidar ratios needed for interpretation of lidar signals.

  16. Backscattering by hexagonal ice crystals of cirrus clouds.

    PubMed

    Borovoi, Anatoli; Konoshonkin, Alexander; Kustova, Natalia

    2013-08-01

    Light backscattering by randomly oriented hexagonal ice crystals of cirrus clouds is considered within the framework of the physical-optics approximation. The fine angular structure of all elements of the Mueller matrix in the vicinity of the exact backward direction is first calculated and discussed. In particular, an approximate equation for the differential scattering cross section is obtained. Its simple spectral dependence is discussed. Also, a hollow of the linear depolarization ratio around the exact backward direction inherent to the long hexagonal columns is revealed.

  17. The DC-8 Submillimeter-Wave Cloud Ice Radiometer

    NASA Technical Reports Server (NTRS)

    Walter, Steven J.; Batelaan, Paul; Siegel, Peter; Evans, K. Franklin; Evans, Aaron; Balachandra, Balu; Gannon, Jade; Guldalian, John; Raz, Guy; Shea, James

    2000-01-01

    An airborne radiometer is being developed to demonstrate the capability of radiometry at submillimeter-wavelengths to characterize cirrus clouds. At these wavelengths, cirrus clouds scatter upwelling radiation from water vapor in the lower troposphere. Radiometric measurements made at multiple widely spaced frequencies permit flux variations caused by changes in scattering due to crystal size to be distinguished from changes in cloud ice content. Measurements at dual polarizations can also be used to constrain the mean crystal shape. An airborne radiometer measuring the upwelling submillimeter-wave flux should then able to retrieve both bulk and microphysical cloud properties. The radiometer is being designed to make measurements at four frequencies (183 GHz, 325 GHz, 448 GHz, and 643 GHz) with dual-polarization capability at 643 GHz. The instrument is being developed for flight on NASA's DC-8 and will scan cross-track through an aircraft window. Measurements with this radiometer in combination with independent ground-based and airborne measurements will validate the submillimeter-wave radiometer retrieval techniques. The goal of this effort is to develop a technique to enable spaceborne characterization of cirrus, which will meet a key climate measurement need. The development of an airborne radiometer to validate cirrus retrieval techniques is a critical step toward development of spaced-based radiometers to investigate and monitor cirrus on a global scale. The radiometer development is a cooperative effort of the University of Colorado, Colorado State University, Swales Aerospace, and Jet Propulsion Laboratory and is funded by the NASA Instrument Incubator Program.

  18. The DC-8 Submillimeter-Wave Cloud Ice Radiometer

    NASA Technical Reports Server (NTRS)

    Walter, Steven J.; Batelaan, Paul; Siegel, Peter; Evans, K. Franklin; Evans, Aaron; Balachandra, Balu; Gannon, Jade; Guldalian, John; Raz, Guy; Shea, James

    2000-01-01

    An airborne radiometer is being developed to demonstrate the capability of radiometry at submillimeter-wavelengths to characterize cirrus clouds. At these wavelengths, cirrus clouds scatter upwelling radiation from water vapor in the lower troposphere. Radiometric measurements made at multiple widely spaced frequencies permit flux variations caused by changes in scattering due to crystal size to be distinguished from changes in cloud ice content. Measurements at dual polarizations can also be used to constrain the mean crystal shape. An airborne radiometer measuring the upwelling submillimeter-wave flux should then able to retrieve both bulk and microphysical cloud properties. The radiometer is being designed to make measurements at four frequencies (183 GHz, 325 GHz, 448 GHz, and 643 GHz) with dual-polarization capability at 643 GHz. The instrument is being developed for flight on NASA's DC-8 and will scan cross-track through an aircraft window. Measurements with this radiometer in combination with independent ground-based and airborne measurements will validate the submillimeter-wave radiometer retrieval techniques. The goal of this effort is to develop a technique to enable spaceborne characterization of cirrus, which will meet a key climate measurement need. The development of an airborne radiometer to validate cirrus retrieval techniques is a critical step toward development of spaced-based radiometers to investigate and monitor cirrus on a global scale. The radiometer development is a cooperative effort of the University of Colorado, Colorado State University, Swales Aerospace, and Jet Propulsion Laboratory and is funded by the NASA Instrument Incubator Program.

  19. Biofilm formation in an ice cream plant.

    PubMed

    Gunduz, Gulten Tiryaki; Tuncel, Gunnur

    2006-01-01

    The sites of biofilm formation in an ice cream plant were investigated by sampling both the production line and the environment. Experiments were carried out twice within a 20-day period. First, stainless steel coupons were fixed to surfaces adjacent to food contact surfaces, the floor drains and the doormat. They were taken for the analysis of biofilm at three different production stages. Then, biofilm forming bacteria were enumerated and also presence of Listeria monocytogenes was monitored. Biofilm forming isolates were selected on the basis of colony morphology and Gram's reaction; Gram negative cocci and rod, Gram positive cocci and spore forming isolates were identified. Most of the biofilm formations were seen on the conveyor belt of a packaging machine 8 h after the beginning of the production, 6.5 x 10(3) cfu cm(-2). Most of the Gram negative bacteria identified belong to Enterobacteriaceae family such as Proteus, Enterobacter, Citrobacter, Shigella, Escherichia, Edwardsiella. The other Gram negative microflora included Aeromonas, Plesiomonas, Moraxella, Pseudomonas or Alcaligenes spp. were also isolated. Gram positive microflora of the ice cream plant included Staphyloccus, Bacillus, Listeria and lactic acid bacteria such as Streptococcus, Leuconostoc or Pediococcus spp. The results from this study highlighted the problems of spread of pathogens like Listeria and Shigella and spoilage bacteria. In the development of cleaning and disinfection procedures in ice cream plants, an awareness of these biofilm-forming bacteria is essential for the ice cream plants.

  20. Dense cloud formation and star formation in a barred galaxy

    NASA Astrophysics Data System (ADS)

    Nimori, M.; Habe, A.; Sorai, K.; Watanabe, Y.; Hirota, A.; Namekata, D.

    2013-03-01

    We investigate the properties of massive, dense clouds formed in a barred galaxy and their possible relation to star formation, performing a two-dimensional hydrodynamical simulation with the gravitational potential obtained from the 2MASS data from the barred spiral galaxy, M83. Since the environment for cloud formation and evolution in the bar region is expected to be different from that in the spiral arm region, barred galaxies are a good target to study the environmental effects on cloud formation and the subsequent star formation. Our simulation uses for an initial 80 Myr isothermal flow of non-self gravitating gas in the barred potential, then including radiative cooling, heating and self-gravitation of the gas for the next 40 Myr, during which dense clumps are formed. We identify many cold, dense gas clumps for which the mass is more than 104 M⊙ (a value corresponding to the molecular clouds) and study the physical properties of these clumps. The relation of the velocity dispersion of the identified clump's internal motion with the clump size is similar to that observed in the molecular clouds of our Galaxy. We find that the virial parameters for clumps in the bar region are larger than that in the spiral arm region. From our numerical results, we estimate star formation in the bar and spiral arm regions by applying the simple model of Krumholz & McKee (2005). The mean relation between star formation rate and gas surface density agrees well with the observed Kennicutt-Schmidt relation. The star formation efficiency in the bar region is ˜60 per cent of the spiral arm region. This trend is consistent with observations of barred galaxies.

  1. Laboratory studies with cloud-derived Bacterial Cells acting as Ice Nuclei in the Immersion and Deposition Mode

    NASA Astrophysics Data System (ADS)

    Oehm, C.; Chou, C.; Amato, P.; Attard, E.; Delort, A.-M.; Morris, C.; Kiselev, A.; Stetzer, O.; Möhler, O.; Leisner, T.

    2012-04-01

    Atmospheric aerosol particles play an important role in cloud microphysics. Aerosols of biological origin are a subgroup, and some of them are able to act as heterogeneous ice nuclei and thus influence cloud life cycles and the climate. Some bacteria species have been found to act as ice nuclei at relatively high temperatures up to -2 degree Celsius and are therefore of particular importance as "high temperature" ice nuclei. Recently, ice nucleation experiments with bacterial cells from different sources were performed at the aerosol and cloud simulation chamber AIDA at the Karlsruhe Institute of Technology. At the AIDA facility, microphysical cloud processes can be simulated and investigated in laboratory at realistic atmospheric cloud conditions. Different ice nucleation active (INA) bacteria strains were isolated from cloud water, glacier melt water and phyllosphere and examined in AIDA experiments. The living cells were suspended in nanopure or artificial cloud water and injected into the cloud chamber through a dispersion nozzle. The injected droplets evaporated in the chamber and the bacterial cells were transformed into the aerosol phase. After the spraying, the cloud formation was started by expansion cooling. Experiments were performed in the temperature range from -2 down to -20 degree Celsius. Detailed measurements of the number concentration and size distribution of the aerosol particles as well as of the droplets and ice particles were carried out during the AIDA experiments. A minor fraction of the bacteria cells was observed to act as ice nuclei in the immersion nucleation mode at higher temperatures as well as in the deposition nucleation mode at lower temperatures. The ice activity started at -6 degree Celsius. The most efficient INA bacteria species were Pseudomonas syringae 32b74 and Pseudomonas fluorescens Antarctica1. The ice active number fraction with respect to the cells varied from 0,01 to 0,1, and it does not change at different

  2. Improvements on the ice cloud modeling capabilities of the Community Radiative Transfer Model

    NASA Astrophysics Data System (ADS)

    Yi, Bingqi; Yang, Ping; Liu, Quanhua; Delst, Paul; Boukabara, Sid-Ahmed; Weng, Fuzhong

    2016-11-01

    Noticeable improvements on the ice cloud modeling capabilities of the Community Radiative Transfer Model (CRTM) are reported, which are based on the most recent advances in understanding ice cloud microphysical (particularly, ice particle habit/shape characteristics) and optical properties. The new CRTM ice cloud model is derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) collection 6 ice cloud habit model, which represents ice particles as severely roughened hexagonal ice column aggregates with a gamma size distribution. The single-scattering properties of the new ice particle model are derived from a state-of-the-art ice optical property library and are constructed as look-up tables for rapid CRTM computations. Various sensitivity studies concerning instrument-specific applications and simulations are performed to validate CRTM against satellite observations. In particular, radiances in a spectral region covering the infrared wavelengths are simulated. Comparisons of brightness temperatures between CRTM simulations and observations (from MODIS, the Atmospheric Infrared Sounder, and the Advanced Microwave Sounding Unit) show that the new ice cloud optical property look-up table substantially enhances the performance of the CRTM under ice cloud conditions.

  3. Influence of Aerosol Chemical Composition on Heterogeneous Ice Formation under Mid-Upper Troposphere Conditions

    NASA Astrophysics Data System (ADS)

    Kanji, Z. A.; Niemand, M.; Saathoff, H.; Möhler, O.; Chou, C.; Abbatt, J.; Stetzer, O.

    2011-12-01

    Aerosols are involved in cooling/warming the atmosphere directly via interaction with incoming solar radiation (aerosol direct effect), or via their ability to act as cloud condensation or ice nuclei (IN) and thus play a role in cloud formation (indirect effect). In particular, the physical properties of aerosols such as size and solubility and chemical composition can influence their behavior and fate in the atmosphere. Ice nucleation taking place via IN is termed as heterogeneous ice nucleation and can take place with via deposition (ice forming on IN directly from the vapor phase), condensation/immersion (freezing via formation of the liquid phase on IN) or condensation (IN colliding with supercooled liquid drops). This presentation shows how the chemical composition and surface area of various tropospherically relevant aerosols influence conditions of temperature (T) and relative humidity (RH) required for heterogeneous ice formation conditions in the mid-upper troposphere regime (253 - 220K)? Motivation for this comes first from, the importance of being able to predict ice formation accurately so as to understand the hydrological cycle since the ice is the primary initiator of precipitation forming clouds. Second, the tropospheric budget of water vapour, an especially active greenhouse gas is strongly influenced by ice nucleation and growth. Third, ice surfaces in the atmosphere act as heterogeneous surfaces for chemical reactions of trace gases (e.g., SO2, O3, NOx and therefore being able to accurately estimate ice formation rates and quantify ice surface concentrations will allow a more accurate calculation of trace gas budgets in the troposphere. Ice nucleation measurements were conducted using a self-developed continuous flow diffusion chamber and static chamber. A number of tropospherically relevant particulates with naturally-varying and laboratory-modified surface chemistry/structure were investigated for their ice formation efficiency based on highest

  4. Validation of quasi-invariant ice cloud radiative quantities with MODIS satellite-based cloud property retrievals

    NASA Astrophysics Data System (ADS)

    Ding, Jiachen; Yang, Ping; Kattawar, George W.; King, Michael D.; Platnick, Steven; Meyer, Kerry G.

    2017-06-01

    Similarity relations applied to ice cloud radiance calculations are theoretically analyzed and numerically validated. If τ(1-ϖ) and τ(1-ϖg) are conserved where τ is optical thickness, ϖ the single-scattering albedo, and g the asymmetry factor, it is possible that substantially different phase functions may give rise to similar radiances in both conservative and non-conservative scattering cases, particularly in the case of large optical thicknesses. In addition to theoretical analysis, this study uses operational ice cloud optical thickness retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS) Level 2 Collection 5 (C5) and Collection 6 (C6) cloud property products to verify radiative similarity relations. It is found that, if the MODIS C5 and C6 ice cloud optical thickness values are multiplied by their respective (1-ϖg) factors, the resultant products referred to as the effective optical thicknesses become similar with their ratio values around unity. Furthermore, the ratios of the C5 and C6 ice cloud effective optical thicknesses display an angular variation pattern similar to that of the corresponding ice cloud phase function ratios. The MODIS C5 and C6 values of ice cloud similarity parameter, defined as [(1-ϖ)/(1-ϖg)]1/2, also tend to be similar.

  5. Meteorological conditions influencing the formation of level ice within the Baltic Sea

    NASA Astrophysics Data System (ADS)

    Mazur, A. K.; Krezel, A.

    2012-12-01

    The Baltic Sea is covered by ice every winter and on average, the ice-covered area is 45% of the total area of the Baltic Sea. The beginning of ice season usually starts in the end of November, ice extent is the largest between mid-February and mid-March and sea ice disappears completely in May. The ice covered areas during a typical winter are the Gulf of Bothnia, the Gulf of Finland and the Gulf of Riga. The studies of sea ice in the Baltic Sea are related to two aspects: climate and marine transport. Depending on the local weather conditions during the winter different types of sea ice can be formed. From the point of winter shipping it is important to locate level and deformed ice areas (rafted ice, ridged ice, and hummocked ice). Because of cloud and daylight independency as well as good spatial resolution, SAR data seems to be the most suitable source of data for sea ice observation in the comparatively small area of the Baltic Sea. We used ASAR Wide Swath Mode data with spatial resolution 150 m. We analyzed data from the three winter seasons which were examples of severe, typical and mild winters. To remove the speckle effect the data were resampled to 250 m pixel size and filtred using Frost filter 5x5. To detect edges we used Sobel filter. The data were also converted into grayscale. Sea ice classification was based on Object-Based Image Analysis (OBIA). Object-based methods are not a common tool in sea ice studies but they seem to accurately separate level ice within the ice pack. The data were segmented and classified using eCognition Developer software. Level ice were classified based on texture features defined by Haralick (Grey Level Co-Occurrence Matrix homogeneity, GLCM contrast, GLCM entropy and GLCM correlation). The long-term changes of the Baltic Sea ice conditions have been already studied. They include date of freezing, date of break-up, sea ice extent and some of work also ice thickness. There is a little knowledge about the relationship of

  6. A New Parameterisation of Frazil and Grease Ice Formation in a Climate Sea Ice Model

    NASA Astrophysics Data System (ADS)

    Feltham, D. L.; Heorton, H. D.; Wilchinsky, A. V.

    2014-12-01

    An idealised model describing frazil ice formation in the ocean mixed layer beneath a lead in the sea ice cover is developed and incorporated into the sea ice climate model CICE. The frazil ice model assumes a steady state formation of single size frazil ice crystals. The crystals are uniformly distributed under the lead over the mixed layer depth and the lead width. The basic processes affecting the frazil ice mass balance is the rate of frazil ice formation due to the heat loss from the open water to the atmosphere, advection of heat and frazil ice volume into the lead from the water under sea ice, and precipitation of frazil ice crystals to the ocean surface and formation of grease ice. The grease ice is pushed against one of the lead edges by wind and water drag keeping the lead open. The frazil ice model is incorporated into CICE and used to simulate the sea ice state in the Arctic Basin and Southern Ocean.In contrast to the original frazil ice treatment in CICE which produces sea ice with only around 10% frazil ice fraction, the new model produces of order of 50% of frazil-derived sea ice, which corresponds better to observations. While the original model can be re-tuned in order to produce a similar average fraction of frazil ice by having a frazil collection thickness of 30 cm in the Antarctic and 5 cm in the Arctic, the new model's collection thickness is dynamically calculated, allowing for a larger collection thickness in large leads whereas the old model assumes it to be equal for wide and narrow leads. The new model keeps leads open for a longer period thus increasing the period of frazil ice formation. This is particularly important in the central Arctic where the new model's increased frazil ice production results in sea ice 0.5 m thicker than in the old model.

  7. Sensitivity of CAM5-Simulated Arctic Clouds and Radiation to Ice Nucleation Parameterization

    SciTech Connect

    Xie, Shaocheng; Liu, Xiaohong; Zhao, Chuanfeng; Zhang, Yuying

    2013-08-01

    Sensitivity of Arctic clouds and radiation in the Community Atmospheric Model version 5 to the ice nucleation process is examined by testing a new physically based ice nucleation scheme that links the variation of ice nuclei (IN) number concentration to aerosol properties. The default scheme parameterizes the IN concentration simply as a function of ice supersaturation. The new scheme leads to a significant reduction in simulated IN number concentrations at all latitudes while changes in cloud amount and cloud properties are mainly seen in high latitudes and middle latitude storm tracks. In the Arctic, there is a considerable increase in mid-level clouds and a decrease in low clouds, which result from the complex interaction among the cloud macrophysics, microphysics, and the large-scale environment. The smaller IN concentrations result in an increase in liquid water path and a decrease in ice water path due to the slow-down of the Bergeron-Findeisen process in mixed-phase clouds. Overall, there is an increase in the optical depth of Arctic clouds, which leads to a stronger cloud radiative forcing (net cooling) at the top of the atmosphere. The comparison with satellite data shows that the new scheme slightly improves low cloud simulations over most of the Arctic, but produces too many mid-level clouds. Considerable improvements are seen in the simulated low clouds and their properties when compared to Arctic ground-based measurements. Issues with the observations and the model-observation comparison in the Arctic region are discussed.

  8. The Retrieval of Ice-Cloud Properties from Cloud Radar and Lidar Synergy.

    NASA Astrophysics Data System (ADS)

    Tinel, Claire; Testud, Jacques; Pelon, Jacques; Hogan, Robin J.; Protat, Alain; Delanoë, Julien; Bouniol, Dominique

    2005-06-01

    Clouds are an important component of the earth's climate system. A better description of their microphysical properties is needed to improve radiative transfer calculations. In the framework of the Earth, Clouds, Aerosols, and Radiation Explorer (EarthCARE) mission preparation, the radar-lidar (RALI) airborne system, developed at L'Institut Pierre Simon Laplace (France), can be used as an airborne demonstrator. This paper presents an original method that combines cloud radar (94-95 GHz) and lidar data to derive the radiative and microphysical properties of clouds. It combines the apparent backscatter reflectivity from the radar and the apparent backscatter coefficient from the lidar. The principle of this algorithm relies on the use of a relationship between the extinction coefficient and the radar specific attenuation, derived from airborne microphysical data and Mie scattering calculations. To solve radar and lidar equations in the cloud region where signals can be obtained from both instruments, the extinction coefficients at some reference range z0 must be known. Because the algorithms are stable for inversion performed from range z0 toward the emitter, z0 is chosen at the farther cloud boundary as observed by the lidar. Then, making an assumption of a relationship between extinction coefficient and backscattering coefficient, the whole extinction coefficient, the apparent reflectivity, cloud physical parameters, the effective radius, and ice water content profiles are derived. This algorithm is applied to a blind test for downward-looking instruments where the original profiles are derived from in situ measurements. It is also applied to real lidar and radar data, obtained during the 1998 Cloud Lidar and Radar Experiment (CLARE'98) field project when a prototype airborne RALI system was flown pointing at nadir. The results from the synergetic algorithm agree reasonably well with the in situ measurements.

  9. How important is biological ice nucleation in clouds on a global scale? (Invited)

    NASA Astrophysics Data System (ADS)

    Hoose, C.; Kristjansson, J. E.; Burrows, S. M.; Chen, J.; Hazra, A.

    2010-12-01

    The high ice nucleating ability of some biological particles has led to speculations about living and dead organisms being involved in cloud ice and precipitation formation, exerting a possibly significant influence on weather and climate. In the present study, the role of primary biological aerosol particles (PBAPs) in competition with mineral dust and soot as heterogeneous ice nuclei is investigated with the global climate model CAM-Oslo. Emission parameterizations for bacteria, fungal spores and pollen based on recent literature are introduced, as well as heterogeneous ice nucleation parameterizations based on classical nucleation theory and laboratory measurements. The simulated PBAP number concentrations are compared to data from various locations. The agreement between measurements and observations is overall satisfactory for bacteria and fungal spore concentrations, but the model tends to underestimate total PBAP number. This likely indicates that either pollen or other (possibly submicron) PBAP that are not considered here contribute significantly to the total PBAP number at the measurement locations. The simulated contribution of PBAPs to the global average ice nucleation rate is only 10-5 %, with an uppermost estimate of 0.6% when the emission strengths and ice nucleation efficiencies are varied within the uncertainty ranges. At the same time, observed PBAP concentrations in air and biological ice nucleus concentrations in snow are reasonably well captured by the model. This implies that ‘bioprecipitation’ processes (snow and rain initiated by PBAPs) are of minor importance on the global scale. However, our results do not rule out local, regional or seasonal importance of biological ice nuclei. We will discuss the uncertainties in the underlying model assumptions, compare to results of previous modeling studies and suggest directions for future work.

  10. Ice crystal concentration in cumulus clouds: influence of the drop spectrum.

    PubMed

    Mossop, S C; Hallett, J

    1974-11-15

    Secondary ice crystals are thrown off when supercooled cloud drops are captured and freeze on a moving target in a cloud at -5 degrees C. The rate of production of these ice crystals is proportional to the rate of accretion of drops of the diameter >/=24 micrometers.

  11. 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.

  12. 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 (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 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

  13. Convective Cloud Ice Water Content Distribution in the Upper Tropical Troposphere

    NASA Astrophysics Data System (ADS)

    Avery, M. A.; Davis, S. M.; Vaughan, M. A.; Young, S. A.; Schoeberl, M. R.; Rosenlof, K. H.; Trepte, C. R.; Winker, D. M.

    2015-12-01

    The Cloud and Aerosol LIdar with Orthogonal Polarization (CALIOP) has been making backscatter measurements of cirrus clouds in the upper tropical troposphere and lowermost stratosphere for more than nine years. Using empirical relationships between backscatter and extinction coefficients, as well as cloud ice water content measured by aircraft, the lidar backscatter can be converted into cloud ice water content. A nine-year climatology of ice water content from CALIOP shows that the distribution of ice mass in the tropical UT/LS is dominated by convection over land, with a large longitudinal variation. There are four centers of activity for high altitude tropical convection, over South America, Africa, the Asian Monsoon region and in the tropical Western Pacific over the maritime continent. The distribution of cloud ice water content is very different from that of cloud fraction, which includes many thin cloud layers in the TTL that do not contain much ice, and that are locally and not convectively generated. These results suggest that approaches based on zonal means, or on cloud fraction do not give an accurate accounting of the total water budget of the UT/LS, and that a regional approach is needed. It is found that "overshooting" convection likely dominates the stratospheric moistening process in specific regions and at specific times of the year. Finally, upper tropical tropospheric cloud ice mass loading is correlated with the Asian monsoon and with climate cycles such as ENSO and the QBO.

  14. A FIRE-ACE/SHEBA Case Study of Mixed-Phase Arctic Boundary Layer Clouds: Entrainment Rate Limitations on Rapid Primary Ice Nucleation Processes

    NASA Technical Reports Server (NTRS)

    Fridlin, Ann; vanDiedenhoven, Bastiaan; Ackerman, Andrew S.; Avramov, Alexander; Mrowiec, Agnieszka; Morrison, Hugh; Zuidema, Paquita; Shupe, Matthew D.

    2012-01-01

    Observations of long-lived mixed-phase Arctic boundary layer clouds on 7 May 1998 during the First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE)Arctic Cloud Experiment (ACE)Surface Heat Budget of the Arctic Ocean (SHEBA) campaign provide a unique opportunity to test understanding of cloud ice formation. Under the microphysically simple conditions observed (apparently negligible ice aggregation, sublimation, and multiplication), the only expected source of new ice crystals is activation of heterogeneous ice nuclei (IN) and the only sink is sedimentation. Large-eddy simulations with size-resolved microphysics are initialized with IN number concentration N(sub IN) measured above cloud top, but details of IN activation behavior are unknown. If activated rapidly (in deposition, condensation, or immersion modes), as commonly assumed, IN are depleted from the well-mixed boundary layer within minutes. Quasi-equilibrium ice number concentration N(sub i) is then limited to a small fraction of overlying N(sub IN) that is determined by the cloud-top entrainment rate w(sub e) divided by the number-weighted ice fall speed at the surface v(sub f). Because w(sub c)< 1 cm/s and v(sub f)> 10 cm/s, N(sub i)/N(sub IN)<< 1. Such conditions may be common for this cloud type, which has implications for modeling IN diagnostically, interpreting measurements, and quantifying sensitivity to increasing N(sub IN) (when w(sub e)/v(sub f)< 1, entrainment rate limitations serve to buffer cloud system response). To reproduce observed ice crystal size distributions and cloud radar reflectivities with rapidly consumed IN in this case, the measured above-cloud N(sub IN) must be multiplied by approximately 30. However, results are sensitive to assumed ice crystal properties not constrained by measurements. In addition, simulations do not reproduce the pronounced mesoscale heterogeneity in radar reflectivity that is observed.

  15. The formation, destruction and chemical influence of water ice: a review of recent laboratory results

    NASA Astrophysics Data System (ADS)

    Oberg, Karin I.

    2015-08-01

    Water ice is ubiquitous in dense molecular clouds, the stellar nurseries of the Galaxy. Recent theoretical investigations (Cleeves et al. 2014) suggest that much of this pre-stellar ice survives disk formation and thus takes part in forming of planets and planetesimals. Interstellar and circumstellar ice abundances thus affect the compositions of planets. The presence of water ice is also important for the formation of other molecules on grains. Water is the most abundant ice constituent and therefore sets the ice diffusion environment, which regulates for example the organic photochemistry proposed to drive the complex chemical evolution during star formation.The processes that regulate the formation, destruction and chemical influence of water have all been explored in laboratory experiments. One of the most significant advances in recent years is the arrival of laboratory experiments on hydrogen additions to condensed O, O2 and O3 — the proposed main formation pathways of water ice. These experiments have revealed how the interplay between diffusion and reaction barriers together regulate the water formation chemistry as well as the chemistry of closely related carbon-bearing species such as CO2. A very different set of laboratory experiments have in the same time period constrained the efficiency of non-thermal water desorption, especially UV-induced ice photodesorption. Laboratory work on other non-thermal desorption pathways, e.g. chemical desorption, has also advanced, though more experiments are needed to quantify the importance of these desorption pathways relative to photodesorption. There are also an increasing number of experiments aimed at constraining the diffusion environment of water-dominated ices and its effects on the formation of organics when ice mixtures are exposed to UV photons or other kinds of energetic radiation.I will review the many significant laboratory water ice experiments that has been relaized in the past few years and how they

  16. Ice cloud properties in ice-over-water cloud systems using Tropical Rainfall Measuring Mission (TRMM) visible and infrared scanner and TRMM Microwave Imager data

    NASA Astrophysics Data System (ADS)

    Minnis, Patrick; Huang, Jianping; Lin, Bing; Yi, Yuhong; Arduini, Robert F.; Fan, Tai-Fang; Ayers, J. Kirk; Mace, Gerald G.

    2007-03-01

    A multilayered cloud retrieval system (MCRS) is updated and used to estimate ice water path in maritime ice-over-water clouds using Visible and Infrared Scanner (VIRS) and Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) measurements acquired over the Tropics between January and August 1998. Lookup tables of top-of-atmosphere 0.65-μm reflectance are developed for ice-over-water cloud systems using radiative transfer calculations for various combinations of ice-over-water cloud layers. The liquid and ice water paths, LWP and IWP, respectively, are determined with the MCRS using these lookup tables with a combination of microwave (MW), visible (VIS), and infrared (IR) data. LWP, determined directly from the TMI MW data, is used to define the lower-level cloud properties to select the proper lookup table. The properties of the upper-level ice clouds, such as optical depth and effective size, are then derived using the Visible-Infrared Solar-infrared Split-Window technique (VISST), which matches the VIRS IR, 3.9 μm, and VIS data to the multilayer cloud lookup table reflectances and a set of emittance parameterizations. Initial comparisons with surface-based radar retrievals suggest that this enhanced MCRS can significantly improve the accuracy and decrease the IWP in overlapped clouds by 42 and 13% compared to using the single-layer VISST and an earlier simplified MW-VIS-IR (MVI) differencing method, respectively, for ice-over-water cloud systems. The tropical distribution of ice-over-water clouds is the same as derived earlier from combined TMI and VIRS data, but the new values of IWP and optical depth are slightly larger than the older MVI values and exceed those of single-layered clouds by 7 and 11%, respectively. The mean IWP from the MCRS is 8-14% greater than that retrieved from radar retrievals of overlapped clouds over two surface sites, and the standard deviations of the differences are similar to those for single-layered clouds. Examples of

  17. Update on the NASA Glenn Propulsion Systems Lab Ice Crystal Cloud Characterization (2015, 2016)

    NASA Technical Reports Server (NTRS)

    Van Zante, Judith; Bencic, Timothy; Ratvasky, Thomas

    2016-01-01

    NASA Glenn's Propulsion Systems Lab, an altitude engine test facility, was outfitted with a spray system to generate ice crystals in 2011. Turbine engines and driven rigs can experience ice crystal icing at flight altitudes, temperatures and Mach numbers. To support these tests, four ice crystal characterizations have been conducted in two different facility configurations. In addition, super-cooled liquid and mixed phase clouds have also been generated. This paper represents a work in progress. It will describe some of the 11-parameter calibration space, and how those parameters interact with each other, the instrumentation used to characterize the cloud and present a sample of the cloud characterization results.

  18. Retrieving cloud ice water content and geometrical thickness from microwave and infrared radiometric observations

    NASA Technical Reports Server (NTRS)

    Wu, M.-L. C.

    1986-01-01

    Techniques are presented and their application illustrated for analysis of remotely sensed data collected with an aircraft carrying a multispectral cloud radiometer and an advanced microwave moisture sounder. The instruments were used on NASA high altitude flights to perform cloud field experiments. Sample IR and microwave brightness temperature data are provided as functions of the ice water path and of the ice water content. Quantitative models are described for deriving the cloud ice (or liquid) water content and the cloud geometric thickness from the radiometric data.

  19. Single particle analysis of ice crystal residuals observed in orographic wave clouds over Scandinavia during INTACC experiment

    NASA Astrophysics Data System (ADS)

    Targino, A. C.; Krejci, R.; Noone, K. J.; Glantz, P.

    2006-06-01

    represent significant part of the analyzed cloud residual particles. This indicates that organic material may be poor ice nuclei, in contrast to polluted cases when ice crystal formation was observed at the same environmental conditions and when the cloud residual composition was dominated by mineral dust. The presented results suggest that the chemical composition of cloud nuclei and airmass origin have a strong impact on the ice formation through heterogeneous nucleation in supercooled clouds.

  20. Sensitivity of CAM5-simulated Arctic clouds and radiation to ice nucleation parameterization

    SciTech Connect

    Xie, Shaocheng; Liu, Xiaohong; Zhao, Chuanfeng; Zhang, Yuying

    2013-08-06

    Sensitivity of Arctic clouds and radiation in the Community Atmospheric Model, version 5, to the ice nucleation process is examined by testing a new physically based ice nucleation scheme that links the variation of ice nuclei (IN) number concentration to aerosol properties. The default scheme parameterizes the IN concentration simply as a function of ice supersaturation. The new scheme leads to a significant reduction in simulated IN concentration at all latitudes while changes in cloud amounts and properties are mainly seen at high- and midlatitude storm tracks. In the Arctic, there is a considerable increase in midlevel clouds and a decrease in low-level clouds, which result from the complex interaction among the cloud macrophysics, microphysics, and large-scale environment. The smaller IN concentrations result in an increase in liquid water path and a decrease in ice water path caused by the slowdown of the Bergeron–Findeisen process in mixed-phase clouds. Overall, there is an increase in the optical depth of Arctic clouds, which leads to a stronger cloud radiative forcing (net cooling) at the top of the atmosphere. The comparison with satellite data shows that the new scheme slightly improves low-level cloud simulations over most of the Arctic but produces too many midlevel clouds. Considerable improvements are seen in the simulated low-level clouds and their properties when compared with Arctic ground-based measurements. As a result, issues with the observations and the model–observation comparison in the Arctic region are discussed.

  1. Correlations of oriented ice and precipitation in marine midlatitude low clouds using collocated CloudSat, CALIOP, and MODIS observations

    NASA Astrophysics Data System (ADS)

    Ross, Alexa; Holz, Robert E.; Ackerman, Steven A.

    2017-08-01

    In April 2006, the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) launched aboard the CALIPSO satellite and into the A-Train constellation of satellites with its transmitter pointed near nadir. This proved problematic due to specular reflection from horizontally oriented ice crystals occurring more frequently than expected. Because the specular backscatter from oriented ice crystals has large attenuated backscatter and almost no depolarization, the standard lidar inversions cannot be applied. To mitigate this issue, the CALIOP transmitter was moved to 3° off nadir in November 2007. Though problematic for global CALIOP retrievals, the sensitivity to oriented ice during the first year of observations provides a unique data set to investigate scenes of this ice crystal signature. This study focuses on the CALIOP-oriented signature that occurs in midlatitude ocean regions whose cloud tops are relatively warm and low, existing below 6 km. A significant seasonal dependence is found in the Northern Hemisphere with up to 19% of clouds below 6 km yielding specular reflection by CALIOP during the colder months. In contrast, the Southern Hemisphere lacks such seasonal dependence and sees fewer oriented ice crystals. Using collocated CloudSat observations with both CALIOP and Moderate Resolution Imaging Spectroradiometer (MODIS), we investigate the correlations of the oriented signature with MODIS cloud properties. Comparing with CloudSat precipitation retrievals, we find that the oriented signature is strongly correlated with surface precipitation with 64% of CALIOP-oriented ice crystal cases precipitating compared to 40% for nonoriented cases.

  2. Four Mars Years of Mapping Water Ice Clouds with MRO/MARCI

    NASA Astrophysics Data System (ADS)

    Wolff, M. J.; Clancy, R. T.; Cantor, B. A.

    2013-12-01

    The ultraviolet bands of the Mars Color Imager (MARCI) instrument (aboard the Mars Reconnaissance Orbiter, MRO) have provided for the retrieval of column-integrated water ice cloud optical depths. We have developed a mapping retrieval scheme using a multiple-scattering, radiative transfer approach (based upon the DISORT package developed by K. Stamnes and collaborators), with preliminary results having been reported at the 2010 Fall AGU meeting. Since then, we have updated the algorithm to include the spatial variation of the Band 7 (320 nm) reflectance function and adopted improved dust and water ice aerosol scattering properties. In our presentation, we will briefly outline the retrieval procedure, including the provenance of the various input parameters. However, the bulk of our results will show and discuss the annual and interannual behavior of zonal water ice cloud optical depths (excluding the region over the residual polar caps). We will include the temporal evolution of specific regions of interest (longitudinally resolved), such as high latitudes (i.e., polar hood), Tharsis, and Hellas. The analysis will include data from from November 7, 2006 (LS=132deg, Mars year 28) through November 15, 2013 (LS=50deg, Mars year 32). Finally, we will review the retrieval products from Mars Years 28-30 that are to be released by December 1, 2013 through the Twiki portal: https://gemelli.spacescience.org/twiki/bin/view/MarsObservations/MarciObservations/WaterIceClouds. Formats will include IDL saveset and NetCDF files. This work was supported by NASA through the MRO Project and a contract to Malin Space Science Systems (JPL Contract 1275776).

  3. Low-latitude variability of ice cloud properties and cloud thermodynamic phase observed by the Atmospheric Infrared Sounder (AIRS)

    NASA Astrophysics Data System (ADS)

    Kahn, B. H.; Yue, Q.; Davis, S. M.; Fetzer, E. J.; Schreier, M. M.; Tian, B.; Wong, S.

    2016-12-01

    We will quantify the time and space dependence of ice cloud effective radius (CER), optical thickness (COT), cloud top temperature (CTT), effective cloud fraction (ECF), and cloud thermodynamic phase (ice, liquid, or unknown) with the Version 6 Atmospheric Infrared Sounder (AIRS) satellite observational data set from September 2002 until present. We show that cloud frequency, CTT, COT, and ECF have substantially different responses to ENSO variations. Large-scale changes in ice CER are also observed with a several micron tropics-wide increase during the 2015-2016 El Niño and similar decreases during the La Niña phase. We show that the ice CER variations reflect fundamental changes in the spatial distributions and relative frequencies of different ice cloud types. Lastly, the high spatial and temporal resolution variability of the cloud fields are explored and we show that these data capture a multitude of convectively coupled tropical waves such as Kelvin, westward and eastward intertio-gravity, equatorial Rossby, and mixed Rossby-gravity waves.

  4. Observations of snow-ice formation in a thinner Arctic sea ice regime during the N-ICE2015 campaign: influence of basal ice melt and storms

    NASA Astrophysics Data System (ADS)

    Provost, C.; Sennechael, N.; Itkin, P.; Rösel, A.; Koenig, Z.; Villacieros-Robineau, N.; Granskog, M. A.

    2016-12-01

    Seven ice mass balance instruments deployed on different first-year and second-year ice floes, within a distance of 50 km near 83°N representing variable snow and ice conditions, documented the evolution of snow and ice conditions in the Arctic Ocean north of Svalbard in Jan-Mar 2015. Frequent profiles of temperature and thermal resistivity proxy were recorded to distinguish changes in snow depth and ice thickness with 2 cm vertical resolution. Four instruments documented snow-ice formation which was clearly detectable in the simultaneous changes in thermal resistivity proxy, increased temperature and heat propagation through the underlying ice. Snow-ice formation restored a positive freeboard after storm-induced break-up of snow-loaded floes and/or after loss of buoyancy due to basal ice melt. In the case of break-up, when the ice was cold and not permeable, the rapid snow-ice formation, probably due to lateral intrusion of seawater, led to snow-ice layers at the ocean freezing temperature (-1.88°C). After the storm the instruments registered basal sea-ice melt over warm Atlantic waters. Basal ablation reached 71 cm and ocean heat fluxes peaked at 400 Wm-2. The warm ice was permeable and the gradual snow-ice formation probably involved vertical intrusion of brines and led to colder snow-ice (-3°C). In both cases, the exothermal reaction warmed the underlying sea-ice. N-ICE2015 campaign provided the first documentation of significant snow-ice formation in the Arctic ice pack with a fraction of snow-ice to total ice thickness 28%. Snow-ice formation may become a more important process in a thinner-ice Arctic.

  5. Effect of retreating sea ice on Arctic cloud cover in simulated recent global warming

    NASA Astrophysics Data System (ADS)

    Abe, Manabu; Nozawa, Toru; Ogura, Tomoo; Takata, Kumiko

    2016-11-01

    This study investigates the effect of sea ice reduction on Arctic cloud cover in historical simulations with the coupled atmosphere-ocean general circulation model MIROC5. Arctic sea ice has been substantially retreating since the 1980s, particularly in September, under simulated global warming conditions. The simulated sea ice reduction is consistent with satellite observations. On the other hand, Arctic cloud cover has been increasing in October, with about a 1-month lag behind the sea ice reduction. The delayed response leads to extensive sea ice reductions because the heat and moisture fluxes from the underlying open ocean into the atmosphere are enhanced. Sensitivity experiments with the atmospheric part of MIROC5 clearly show that sea ice reduction causes increases in cloud cover. Arctic cloud cover increases primarily in the lower troposphere, but it decreases in the near-surface layers just above the ocean; predominant temperature rises in these near-surface layers cause drying (i.e., decreases in relative humidity), despite increasing moisture flux. Cloud radiative forcing due to increases in cloud cover in autumn brings an increase in the surface downward longwave radiation (DLR) by approximately 40-60 % compared to changes in clear-sky surface DLR in fall. These results suggest that an increase in Arctic cloud cover as a result of reduced sea ice coverage may bring further sea ice retreat and enhance the feedback processes of Arctic warming.

  6. Microbial production of ice crystals in clouds as a novel atmospheric biosignature

    NASA Astrophysics Data System (ADS)

    Santl-Temkiv, T.; Sahyoun, M.; Kjeldsen, H.; Ling, M.; Boesen, T.; Karlson, U. G.; Finster, K.

    2014-03-01

    A diverse assembly of exoplanets has been discovered during recent decades (Howard 2013), their atmospheres providing some of the most accessible evidence for the presence of biological activity on these planets. Metabolic gases have been commonly proposed as atmospheric biosignatures (Seager et al 2012). However, airborne microbes are also involved in cloud- and precipitation formation on Earth. Thus, meteorological phenomena may serve as alternative atmospheric biosignatures, for which appropriate observational techniques have yet to be developed. The atmospheric part of the Earth's water cycle heavily relies on the presence of nucleating particles, which promote the condensation and freezing of atmospheric water, both potentially leading to precipitation. While cloud condensation nuclei are diverse and relatively common, ice nuclei are poorly understood and comparably rare airborne particles. According to current knowledge, most ice nucleation below ñ15∞C is driven by the presence of inorganic dust particles, which are considered inactive at higher temperatures. Biogenic IN are the only reported particles that promote ice formation above ñ10∞C. Some bacteria, e.g. Pseudomonas syringae, produce Ice Nucleation Active (INA) proteins that are most efficient ice nuclei currently known. These INA bacteria are common in the atmosphere, and may thus be involved in precipitation processes of mixed phase clouds (Möhler et al 2007). We investigate the relevance of bacterial INA proteins for atmospheric processes using three approaches: (i) study of the presence of INA bacteria and their INA proteins in the atmosphere, (ii) a detailed molecular and physical study of isolated INA proteins, and finally (iii) a modeling study of the importance of INA proteins for ice-path in clouds as well as their importance for precipitation. During 14 precipitation events, we observed that 12% of isolated bacteria carried INA genes. INA bacteria had likely been emitted to the

  7. Qualitative analysis of the e-cloud formation

    SciTech Connect

    Heifets, Samuel A

    2002-01-17

    The qualitative analysis of the electron cloud formation is presented. Two mechanisms of the cloud formation, generation of jets of primary photo-electrons and thermalization of electrons in the electron cloud, are analyzed and compared with simulations for the NLC damping ring.

  8. Covariance Between Arctic Sea Ice and Clouds Within Atmospheric State Regimes at the Satellite Footprint Level

    NASA Technical Reports Server (NTRS)

    Taylor, Patrick C.; Kato, Seiji; Xu, Kuan-Man; Cai, Ming

    2015-01-01

    Understanding the cloud response to sea ice change is necessary for modeling Arctic climate. Previous work has primarily addressed this problem from the interannual variability perspective. This paper provides a refined perspective of sea ice-cloud relationship in the Arctic using a satellite footprint-level quantification of the covariance between sea ice and Arctic low cloud properties from NASA A-Train active remote sensing data. The covariances between Arctic low cloud properties and sea ice concentration are quantified by first partitioning each footprint into four atmospheric regimes defined using thresholds of lower tropospheric stability and mid-tropospheric vertical velocity. Significant regional variability in the cloud properties is found within the atmospheric regimes indicating that the regimes do not completely account for the influence of meteorology. Regional anomalies are used to account for the remaining meteorological influence on clouds. After accounting for meteorological regime and regional influences, a statistically significant but weak covariance between cloud properties and sea ice is found in each season for at least one atmospheric regime. Smaller average cloud fraction and liquid water are found within footprints with more sea ice. The largest-magnitude cloud-sea ice covariance occurs between 500m and 1.2 km when the lower tropospheric stability is between 16 and 24 K. The covariance between low cloud properties and sea ice is found to be largest in fall and is accompanied by significant changes in boundary layer temperature structure where larger average near-surface static stability is found at larger sea ice concentrations.

  9. Covariance Between Arctic Sea Ice and Clouds Within Atmospheric State Regimes at the Satellite Footprint Level

    NASA Technical Reports Server (NTRS)

    Taylor, Patrick C.; Kato, Seiji; Xu, Kuan-Man; Cai, Ming

    2015-01-01

    Understanding the cloud response to sea ice change is necessary for modeling Arctic climate. Previous work has primarily addressed this problem from the interannual variability perspective. This paper provides a refined perspective of sea ice-cloud relationship in the Arctic using a satellite footprint-level quantification of the covariance between sea ice and Arctic low cloud properties from NASA A-Train active remote sensing data. The covariances between Arctic low cloud properties and sea ice concentration are quantified by first partitioning each footprint into four atmospheric regimes defined using thresholds of lower tropospheric stability and mid-tropospheric vertical velocity. Significant regional variability in the cloud properties is found within the atmospheric regimes indicating that the regimes do not completely account for the influence of meteorology. Regional anomalies are used to account for the remaining meteorological influence on clouds. After accounting for meteorological regime and regional influences, a statistically significant but weak covariance between cloud properties and sea ice is found in each season for at least one atmospheric regime. Smaller average cloud fraction and liquid water are found within footprints with more sea ice. The largest-magnitude cloud-sea ice covariance occurs between 500m and 1.2 km when the lower tropospheric stability is between 16 and 24 K. The covariance between low cloud properties and sea ice is found to be largest in fall and is accompanied by significant changes in boundary layer temperature structure where larger average near-surface static stability is found at larger sea ice concentrations.

  10. Covariance between Arctic sea ice and clouds within atmospheric state regimes at the satellite footprint level.

    PubMed

    Taylor, Patrick C; Kato, Seiji; Xu, Kuan-Man; Cai, Ming

    2015-12-27

    Understanding the cloud response to sea ice change is necessary for modeling Arctic climate. Previous work has primarily addressed this problem from the interannual variability perspective. This paper provides a refined perspective of sea ice-cloud relationship in the Arctic using a satellite footprint-level quantification of the covariance between sea ice and Arctic low cloud properties from NASA A-Train active remote sensing data. The covariances between Arctic low cloud properties and sea ice concentration are quantified by first partitioning each footprint into four atmospheric regimes defined using thresholds of lower tropospheric stability and midtropospheric vertical velocity. Significant regional variability in the cloud properties is found within the atmospheric regimes indicating that the regimes do not completely account for the influence of meteorology. Regional anomalies are used to account for the remaining meteorological influence on clouds. After accounting for meteorological regime and regional influences, a statistically significant but weak covariance between cloud properties and sea ice is found in each season for at least one atmospheric regime. Smaller average cloud fraction and liquid water are found within footprints with more sea ice. The largest-magnitude cloud-sea ice covariance occurs between 500 m and 1.2 km when the lower tropospheric stability is between 16 and 24 K. The covariance between low cloud properties and sea ice is found to be largest in fall and is accompanied by significant changes in boundary layer temperature structure where larger average near-surface static stability is found at larger sea ice concentrations.

  11. Fluorescent pseudomonads isolated from Hebridean cloud and rain water produce biosurfactants but do not cause ice nucleation

    NASA Astrophysics Data System (ADS)

    Ahern, H. E.; Walsh, K. A.; Hill, T. C. J.; Moffett, B. F.

    2007-02-01

    Microorganisms were discovered in clouds over 100 years ago but information on bacterial community structure and function is limited. Clouds may not only be a niche within which bacteria could thrive but they might also influence dynamic processes using ice nucleating and cloud condensing abilities. Cloud and rain samples were collected from two mountains in the Outer Hebrides, NW Scotland, UK. Community composition was determined using a combination of amplified 16S ribosomal DNA restriction analysis and sequencing. 256 clones yielded 100 operational taxonomic units (OTUs) of which half were related to bacteria from terrestrial psychrophilic environments. Cloud samples were dominated by a mixture of fluorescent Pseudomonas spp., some of which have been reported to be ice nucleators. It was therefore possible that these bacteria were using the ice nucleation (IN) gene to trigger the Bergeron-Findeisen process of raindrop formation as a mechanism for dispersal. In this study the IN gene was not detected in any of the isolates using both polymerase chain reaction (PCR) and differential scanning calorimetry (DSC). Instead 55% of the total isolates from both cloud and rain samples displayed significant biosurfactant activity when analyzed using the drop-collapse technique. All isolates were characterised as fluorescent pseudomonads. Surfactants have been found to be very important in lowering atmospheric critical supersaturations required for the activation of aerosols into cloud condensation nuclei (CCN). It is also known that surfactants influence cloud droplet size and increase cloud lifetime and albedo. Some bacteria are known to act as CCN and so it is conceivable that these fluorescent pseudomonads are using surfactants to facilitate their activation from aerosols into CCN. This would allow water scavenging,~countering desiccation, and assist in their widespread dispersal.

  12. Collisions of solid ice in planetesimal formation

    NASA Astrophysics Data System (ADS)

    Deckers, J.; Teiser, J.

    2016-03-01

    We present collision experiments of centimetre projectiles on to decimetre targets, both made up of solid ice, at velocities of 15-45 m s-1 at an average temperature of {T_{avg}}=255.8 ± 0.7 K. In these collisions, the centimetre body gets disrupted and part of it sticks to the target. This behaviour can be observed up to an upper threshold, that depends on the projectile size, beyond which there is no mass transfer. In collisions of small particles, as produced by the disruption of the centimetre projectiles, we also find mass transfer to the target. In this way, the larger body can gain mass, although the efficiency of the initial mass transfer is rather low. These collision results can be applied to planetesimal formation near the snowline, where evaporation and condensation is expected to produce solid ice. In free fall collisions at velocities up to about 7 m s-1, we investigated the threshold to fragmentation and coefficient of restitution of centimetre ice spheres.

  13. Aerosol Inflluence on Ice Nucleation via the Immersion Mode in Mixed-Phase Arctic Stratiform Clouds

    NASA Astrophysics Data System (ADS)

    de Boer, G.; Hashino, T.; Tripoli, G. J.; Eloranta, E. W.

    2009-12-01

    Mixed-phase stratiform clouds are commonly observed at high latitudes (e.g. Shupe et al., 2006; de Boer et al., 2009a). Herman and Goody (1976), as well as Curry et al. (1996) present summaries of Arctic cloud climatologies that show low altitude stratus frequencies of up to 70% during transitional seasons. In addition to their frequent occurrence, these clouds have significant impacts on the near-surface atmospheric radiative budget, with estimates of wintertime reductions in net surface cooling of 40-50 Wm-2 (Curry et al., 1996) due predominantly to liquid in the mixed-phase layer. Both observational and modeling studies (e.g. Harrington et al., 1999; Jiang et al., 2000; Shupe et al., 2008; Klein et al., 2008) show a strong connection between the amount of ice present and the lifetime of the liquid portion of the cloud layer. This is thought to occur via the Bergeron-Findeissen mechanism (Pruppacher and Klett, 1997) in which ice grows at the expense of liquid due to its lower saturation vapor pressure. Unfortunately, the mechanisms by which ice is nucleated within these mixed-phase layers are not yet fully understood, and therefore an accurate depiction of this process for mixed-phase stratiform clouds has not yet been characterized. The nucleation mechanisms that are active in a given environment are sensitive to aerosol properties. Insoluble particles are typically good nuclei for ice particle formation, while soluble particles are typically better at nucleating water droplets. Aerosol observations from the Arctic often show mixed aerosol particles that feature both soluble and insoluble mass (Leaitch et al., 1984). Soluble mass fractions for these particles have been shown to be high, with estimates of 60-80% and are often made up of sulfates (Zhou et al., 2001; Bigg and Leck, 2001). It is believed that a significant portion of this sulfate mass comes from dimethyl sulfide (DMS) production in the Arctic Ocean and subsequent atmospheric oxidation. Since these

  14. Single particle analysis of ice crystal residuals observed in orographic wave clouds over Scandinavia during INTACC experiment

    NASA Astrophysics Data System (ADS)

    Targino, A. C.; Krejci, R.; Noone, K. J.; Glantz, P.

    2005-09-01

    represent significant part of the analyzed cloud residual particles. This indicates that organic material inhibits freezing, in contrast to polluted cases when ice crystal formation was observed at the same conditions and when the cloud residual composition was dominated by mineral dust. The presented results suggest that the chemical composition of cloud nuclei and airmass origin have a strong impact on the ice formation through heterogeneous freezing in supercooled clouds.

  15. Understanding Ice Supersaturation, Particle Growth, and Number Concentration in Cirrus Clouds

    NASA Technical Reports Server (NTRS)

    Comstock, Jennifer M.; Lin, Ruei-Fong; Starr, David O'C.; Yang, Ping

    2008-01-01

    Many factors control the ice supersaturation and microphysical properties in cirrus clouds. We explore the effects of dynamic forcing, ice nucleation mechanisms, and ice crystal growth rate on the evolution and distribution of water vapor and cloud properties in nighttime cirrus clouds using a one-dimensional cloud model with bin microphysics and remote sensing measurements obtained at the Department of Energy's Atmospheric Radiation Measurement (ARM) Climate Research Facility located near Lamont, OK. We forced the model using both large-scale vertical ascent and, for the first time, mean mesoscale velocity derived from radar Doppler velocity measurements. Both heterogeneous and homogeneous nucleation processes are explored, where a classical theory heterogeneous scheme is compared with empirical representations. We evaluated model simulations by examining both bulk cloud properties and distributions of measured radar reflectivity, lidar extinction, and water vapor profiles, as well as retrieved cloud microphysical properties. Our results suggest that mesoscale variability is the primary mechanism needed to reproduce observed quantities. Model sensitivity to the ice growth rate is also investigated. The most realistic simulations as compared with observations are forced using mesoscale waves, include fast ice crystal growth, and initiate ice by either homogeneous or heterogeneous nucleation. Simulated ice crystal number concentrations (tens to hundreds particles per liter) are typically two orders of magnitude smaller than previously published results based on aircraft measurements in cirrus clouds, although higher concentrations are possible in isolated pockets within the nucleation zone.

  16. Understanding Ice Supersaturation, Particle Growth, and Number Concentration in Cirrus Clouds

    NASA Technical Reports Server (NTRS)

    Comstock, Jennifer M.; Lin, Ruei-Fong; Starr, David O'C.; Yang, Ping

    2008-01-01

    Many factors control the ice supersaturation and microphysical properties in cirrus clouds. We explore the effects of dynamic forcing, ice nucleation mechanisms, and ice crystal growth rate on the evolution and distribution of water vapor and cloud properties in nighttime cirrus clouds using a one-dimensional cloud model with bin microphysics and remote sensing measurements obtained at the Department of Energy's Atmospheric Radiation Measurement (ARM) Climate Research Facility located near Lamont, OK. We forced the model using both large-scale vertical ascent and, for the first time, mean mesoscale velocity derived from radar Doppler velocity measurements. Both heterogeneous and homogeneous nucleation processes are explored, where a classical theory heterogeneous scheme is compared with empirical representations. We evaluated model simulations by examining both bulk cloud properties and distributions of measured radar reflectivity, lidar extinction, and water vapor profiles, as well as retrieved cloud microphysical properties. Our results suggest that mesoscale variability is the primary mechanism needed to reproduce observed quantities. Model sensitivity to the ice growth rate is also investigated. The most realistic simulations as compared with observations are forced using mesoscale waves, include fast ice crystal growth, and initiate ice by either homogeneous or heterogeneous nucleation. Simulated ice crystal number concentrations (tens to hundreds particles per liter) are typically two orders of magnitude smaller than previously published results based on aircraft measurements in cirrus clouds, although higher concentrations are possible in isolated pockets within the nucleation zone.

  17. Formation of wind-driven ice bridges in narrow straits

    NASA Astrophysics Data System (ADS)

    Rallabandi, Bhargav; Zheng, Zhong; Winton, Michael; Stone, Howard A.

    2016-11-01

    An ice bridge is a static arch made of tightly packed ice that can be formed when sea ice flows through a narrow strait between landmasses. The formation of a stable ice arch prevents the further flow of sea ice into warmer oceans, and therefore plays an important role in the regulation of the local climate and ecology and to an extent, the mass balance of Arctic ice. While ice bridges are a seasonal phenomenon in many parts of the Canadian Archipelago, the process of their formation and breakup is poorly understood. Using thin-layer theory along with dynamic sea ice models widely used in climate modeling, we develop a reduced-order description of wind-driven ice bridge formation in long, narrow straits. Our theory predicts a critical static condition for arrested flow that involves the ice properties (thickness and compactness), the geometry of the channel, and the magnitude of the wind stress. Further, we show that in a channel of varying shape and under a constant wind stress, a spatially uniform ice field evolves towards a steady state with discontinuities in its properties, consistent with observed mechanisms of ice bridge formation. The reduced-order model thus provides a predictive tool for the flow and stoppage of sea ice in straits.

  18. A model of sea ice formation in leads and polynyas

    NASA Astrophysics Data System (ADS)

    Heorton, Harry; Feltham, Daniel; Radia, Nikhil

    2017-04-01

    Cracks in the sea ice cover break the barrier between the ocean and atmosphere, exposing the ocean to the cold atmosphere during the winter. These cracks are known as leads within the continuous sea ice pack and polynyas near land or ice shelves. Sea ice formation starts with frazil ice crystals in supercooled waters, which grow and precipitate to the ocean surface to form grease ice, eventually consolidating into a layer of solid sea ice that grows downwards. In this study a numerical model is formulated to simulate the formation of sea ice in a lead or polynya from frazil ice to a layer of new sea ice. Our simulations show the refreezing of a lead within 48 hours of its opening. Grease ice covers the lead typically within 3 - 10 hours and consolidates into sea ice within 15 - 30 hours. We use our model to simulate an observed polynya event in the Laptev Sea showing the vertical distribution of frazil ice and water supercooling. Sensitivity studies are used to investigate the dependence of ice growth on the ambient environment with the surface wind speed shown to be of greatest importance to lead exposure time and total ice growth. The size and distribution of frazil crystals and the time taken for the lead to freeze over is shown to be highly dependent upon the ambient forcing and lead geometry.

  19. Observational evidence of high ice concentration in a shallow convective cloud embedded in stratiform cloud over North China

    NASA Astrophysics Data System (ADS)

    Yang, Jiefan; Lei, Hengchi; Hou, Tuanjie

    2017-04-01

    In this study we observed the microphysical properties, including the vertical and horizontal distributions of ice particles, liquid water content and ice habit, in different regions of a slightly supercooled stratiform cloud. Using aircraft instrument and radar data, the cloud top temperature was recorded as higher than -15°C, behind a cold front, on 9 September 2015 in North China. During the flight sampling, the high ice number concentration area was located in the supercooled part of a shallow convective cloud embedded in a stratiform cloud, where the ambient temperature was around -3°C. In this area, the maximum number concentrations of particles with diameter greater than 100 μm and 500 μm ( N 100 and N 500) exceeded 300 L-1 and 30 L-1, respectively, and were related to large supercooled water droplets with diameter greater than 24 μm derived from cloud-aerosol spectrometer probe measurements. The ice particles types in this region were predominantly columnar, needle, graupel, and some freezing drops, suggesting that the occurrence of high ice number concentrations was likely related to the Hallett-Mossop mechanism, although many other ice multiplication processes cannot be totally ruled out. The maximum ice number concentration obtained during the first penetration was around two to three orders of magnitude larger than that predicted by the Demott and Fletcher schemes when assuming the cloud top temperature was around -15°C. During the second penetration conducted within the stratiform cloud, N 100 and N 500 decreased by a factor of five to ten, and the presence of columnar and needle-like crystals became very rare.

  20. Thin Ice Clouds in Far IR Experiment: TICFIRE

    NASA Astrophysics Data System (ADS)

    Blanchet, Jean-Pierre

    The TICFIRE mission concept developed with the support of the Canadian Space Agency aims: 1) to improve measurements of water-vapor concentration in the low limit, where cold regions are most sensitive and 2) to determine the contribution of Thin Ice Clouds (TIC) to the energy balance and the role of their microphysical properties on atmospheric cooling. TICFIRE is a process-oriented mission on a micro-satellite platform dedicated to observe key parameters of TIC forming in the cold regions of the Poles and globally, in the upper troposphere. It locates cloud top profiles at the limb and measures at nadir the corresponding upwelling radiance of the atmosphere directly in the thermal window and in the Far Infrared (FIR) spectrum over cold geographical regions, precisely where most of the atmospheric thermal cooling takes place. Due to technological limitations, the FIR spectrum (17 to 50 m) is not regularly monitored by conventional sensors despite its major importance. This deficiency in key data also impacts operational weather forecasting. TICFIRE will provide on a global scale a needed contribution in calibrated radiance assimilation near the IR maximum emission to improve weather forecast. Therefore, TICFIRE is a science-driven mission with a strong operational component.

  1. Cold Cloud Infall and Galaxy Formation

    SciTech Connect

    Kaufmann, Tobias; Bullock, James S.; Fang Taotao; Maller, Ari

    2008-08-01

    We present a pair of high-resolution SPH (smoothed particle hydrodynamics) simulations that explore the nature of cool gas infall into galaxies, and the physical conditions necessary to support the type of gaseous halos that seem to be required by observations. Observations of local X-ray absorbers, high-velocity clouds, and distant quasar absorption line systems suggest that a significant fraction of baryons may reside in multi-phase, low-density, extended, {approx}100 kpc, gaseous halos around normal galaxies. The two simulations are identical other than their initial gas density distributions: one is initialized with a standard hot gas halo that traces the cuspy profile of the dark matter, and the other is initialized with a cored hot halo with a high central entropy, as might be expected in models with early pre-heating feedback. Galaxy formation proceeds in dramatically different fashions in these two cases. While the standard cuspy halo cools rapidly, primarily from the central region, the cored halo is quasi-stable for {approx}4 Gyr and eventually cools via the fragmentation and infall of clouds from {approx}100 kpc distances. After 10 Gyr of cooling, the X-ray luminosity of the standard halo is {approx}100 times current limits and the resultant disk galaxy is twice as massive as the Milky Way. In contrast, the cored halo has an X-ray luminosity that is in line with observations, an extended cloud population reminiscent of the high-velocity cloud population of the Milky Way, and a disk galaxy with half the mass and {approx}50% more specific angular momentum than the disk formed in the low-entropy simulation.

  2. Estimation of Instantaneous TOA Albedo at 670 nm over Ice Clouds from POLDER Multidirectional Measurements

    NASA Technical Reports Server (NTRS)

    Sun, W.; Loeb, N. G.; Kato, S.

    2003-01-01

    An algorithm that determines the 670-nm top-of-atmosphere (TOA) albedo of ice clouds over ocean using Polarization and Directionality of the Earth's Reflectance ( POLDER) multidirectional measurements is developed. A plane-parallel layer of ice cloud with various optical thicknesses and light scattering phase functions is assumed. For simplicity, we use a double Henyey-Greenstein phase function to approximate the volume-averaged phase function of the ice clouds. A multidirectional reflectance best-fit match between theoretical and POLDER reflectances is used to infer effective cloud optical thickness, phase function and TOA albedo. Sensitivity tests show that while the method does not provide accurate independent retrievals of effective cloud optical depth and phase function, TOA albedo retrievals are accurate to within similar to 3% for both a single layer of ice clouds or a multilayer system of ice clouds and water clouds. When the method is applied to POLDER measurements and retrieved albedos are compared with albedos based on empirical angular distribution models (ADMs), zonal albedo differences are generally smaller than similar to 3%. When albedos are compared with those on the POLDER-I ERB and Cloud product, the differences can reach similar to 15% at small solar zenith angles.

  3. Aphelion water-ice cloud mapping and property retrieval using the OMEGA imaging spectrometer onboard Mars Express

    NASA Astrophysics Data System (ADS)

    Madeleine, J.-B.; Forget, F.; Spiga, A.; Wolff, M. J.; Montmessin, F.; Vincendon, M.; Jouglet, D.; Gondet, B.; Bibring, J.-P.; Langevin, Y.; Schmitt, B.

    2012-05-01

    Mapping of the aphelion clouds over the Tharsis plateau and retrieval of their particle size and visible opacity are made possible by the OMEGA imaging spectrometer aboard Mars Express. Observations cover the period from MY26 Ls = 330° to MY29 Ls = 180° and are acquired at various local times, ranging from 8 AM to 6 PM. Cloud maps of the Tharsis region constructed using the 3.1 μm ice absorption band reveal the seasonal and diurnal evolution of aphelion clouds. Four distinct types of clouds are identified: morning hazes, topographically controlled hazes, cumulus clouds and thick hazes. The location and time of occurrence of these clouds are analyzed and their respective formation process is discussed. An inverse method for retrieving cloud particle size and opacity is then developed and can only be applied to thick hazes. The relative error of these measurements is less than 30% for cloud particle size and 20% for opacity. Two groups of particles can be distinguished. The first group is found over flat plains and is composed of relatively small particles, ranging in size from 2 to 3.5 μm. The second group is characterized by particle sizes of ˜5 μm which appear to be quite constant over Ls and local time. It is found west of Ascraeus and Pavonis Mons, and near Lunae Planum. These regions are preferentially exposed to anabatic winds, which may control the formation of these particles and explain their distinct properties. The water ice column is equal to 2.9 pr.μm on average, and can reach 5.2 pr.μm in the thickest clouds of Tharsis.

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

    NASA Technical Reports Server (NTRS)

    Bartkus, Tadas; Tsao, Jen-Ching; Struk, Peter

    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.

  5. 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.

  6. Remote Sensing of Ice Cloud Properties Using Combined Airborne Lidar-Radar Measurements

    NASA Astrophysics Data System (ADS)

    Ewald, F.; Gross, S.; Delanoë, J.; Cazenave, Q.

    2016-12-01

    Ice clouds play an essential role in the climate system since they have a large direct effect on the Earth's radiation budget. Their reaction to changes in water vapor concentrations and their interaction with aerosols still constitutes one of the largest uncertainties in climate change predictions. These uncertainties arise from uncertainties associated with the optical and microphysical properties of ice clouds as well as from insufficient knowledge about their spatial and temporal distribution. Substantial improvement of our understanding of the interconnection of aerosols, clouds and radiation is expected from the combination of multiple instruments exploiting sensitivities at different wavelengths. To this end, the upcoming ESA/JAXA satellite mission EarthCARE will combine a new generation spaceborne lidar system, a cloud radar, and a multi-spectral imager on one single platform. In our work, we investigate the potential to combine lidar and radar measurements to retrieve ice cloud microphysics. For the first time, this study combines the high spectral resolution (HSRL) and differential absorption (DIAL) lidar system WALES and the 35 GHz cloud radar onboard the German High Altitude and LOng range research aircraft to retrieve ice cloud properties. During flight experiments over Europe and over the extra-tropical North-Atlantic, collocated measurements with the spaceborne CALIPSO/CALIOP lidar and CloudSat radar are used to investigate the influence of different wavelengths and spatial resolutions on retrieved ice cloud properties. In our presentation, we will give first results of the synergistic approach using the differential sensitivity of the WALES lidar and the cloud radar to retrieve ice particle size and their concentration. Here, the central focus will be on the coordinated airborne and satellite measurements and on the comparison of retrieved ice cloud microphysics in preparation for the EarthCARE mission.

  7. Ice Cloud Optical Depth Retrievals from CRISM Multispectral Images

    NASA Astrophysics Data System (ADS)

    Klassen, David R.

    2014-11-01

    One set of data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on the Mars Reconnaissance Orbiter (MRO) is the multispectral survey that measured the visible-through-near-infrared reflectance of the entire planet of Mars at specific wavelengths. The spectral data from several sols were be combined to create multi-spectral maps of Mars. In addition, these maps can be zonally averaged to create a latitude vs season image cube of Mars. All of these image cubes can be fit using a full radiative transfer modeling in order to retrieve ice cloud optical depth—as a map for one of the particular dates, or as a latitude vs season record.To compare the data radiative transfer models, a measure of the actual surface reflectance is needed. There are several possible ways to model this, such as using a nearby region that is "close enough" or by looking at the same region at different times and assuming one of those is the actual surface reflectance. Neither of these is ideal for trying to process an entire map of data because aerosol clouds can be fairly extensive both spatially and temporally.Another technique is to assume that the surface can be modeled as a linear combination of a limited set of intrinsic spectral endmembers. A combination of Principal Component Analysis (PCA) and Target Transformation (TT) has been used to recover just such a set of spectral endmember shapes. The coefficients in the linear combination then become additional fitting parameters in the radiative transfer modeling of each map point—all parameters are adjusted until the RMS error between the model and the data is minimized. Based on previous work, the PCA of martian spectral image cubes is relatively consistent regardless of season, implying the underlying, large-scale, intrinsic traits that dominate the data variance are relatively constant. These overall PCA results can then be used to create a single set of spectral endmembers that can be used for any of the data

  8. Formation of gas and ice giant planets

    NASA Astrophysics Data System (ADS)

    Boss, Alan P.

    2003-10-01

    The only presently known example of a planetary system containing a terrestrial planet in the habitable zone of a main sequence star is the Solar System. If the Solar System's giant planets formed by the generally assumed mechanism of core accretion, the Solar System probably formed in a relatively long-lived protoplanetary disk in a quiescent region of star formation, such as in the Taurus molecular cloud. However, if the giant planets formed by the more radical disk instability mechanism, then the Solar System would have formed in a region of high mass star formation, similar to the Orion Nebula Cluster or the Carina Nebula. In the latter case, the number of extrasolar planetary systems strongly resembling our own is likely to be significantly larger than in the former case, with important implications for the design of Darwin/TPF.

  9. NASA Glenn Icing Research Tunnel: 2014 Cloud Calibration Procedure and Results

    NASA Technical Reports Server (NTRS)

    Van Zante, Judith F.; Ide, Robert F.; Steen, Laura E.; Acosta, Waldo J.

    2014-01-01

    The results of the December 2013 to February 2014 Icing Research Tunnel full icing cloud calibration are presented. The calibration steps included establishing a uniform cloud and conducting drop size and liquid water content calibrations. The goal of the calibration was to develop a uniform cloud, and to generate a transfer function from the inputs of air speed, spray bar atomizing air pressure and water pressure to the outputs of median volumetric drop diameter and liquid water content. This was done for both 14 CFR Parts 25 and 29, Appendix C ('typical' icing) and soon-to-be released Appendix O (supercooled large drop) conditions.

  10. Effects of ice-phase cloud microphysics in simulating wintertime precipitation

    SciTech Connect

    Kim, Jinwon; Cho, Han-Ru; Soong, Sy-Tzai

    1995-11-01

    We compare two numerical experiments to investigate the effects of ice-phase cloud microphysical processes on simulations of wintertime precipitation in the southwestern United States. Results of these simulations, one with and the other without ice-phase microphysics, suggest that an inclusion of ice-phase microphysics plays a crucial role in simulating wintertime precipitation. The simulation that employs both the ice and water-phase microphysics better reproduced the observed spatial distribution of precipitation compared to the one without ice-phase microphysics. The most significant effect of ice-phase microphysics appeared in local production of precipitating particles by collection processes, rather than in local condensation.

  11. Ice supersaturations exceeding 100% at the cold tropical tropopause: implications for cirrus formation and dehydration

    NASA Astrophysics Data System (ADS)

    Jensen, E. J.; Smith, J. B.; Pfister, L.; Pittman, J. V.; Weinstock, E. M.; Sayres, D. S.; Herman, R. L.; Troy, R. F.; Rosenlof, K.; Thompson, T. L.; Fridlind, A. M.; Hudson, P. K.; Cziczo, D. J.; Heymsfield, A. J.; Schmitt, C.; Wilson, J. C.

    2005-03-01

    Recent in situ measurements at tropical tropopause temperatures as low as 187 K indicate supersaturations with respect to ice exceeding 100% with little or no ice present. In contrast, models used to simulate cloud formation near the tropopause assume a supersaturation threshold for ice nucleation of about 65% based on laboratory measurements of aqueous aerosol freezing. The high supersaturations reported here, along with cloud simulations assuming a plausible range of temperature histories in the sampled air mass, indicate that the vast majority of aerosols in the air sampled on this flight must have had supersaturation thresholds for ice nucleation exceeding 100% (i.e. near liquid water saturation at these temperatures). Possible explanations for this high threshold are that (1) the expressions used for calculating vapor pressure over supercooled water at low temperatures give values are at least 20% too low, (2) organic films on the aerosol surfaces reduce their accommodation coefficient for uptake of water, resulting in aerosols with more concentrated solutions when moderate-rapid cooling occurs and correspondingly inhibited homogeneous freezing, and (3) if surface freezing dominates, organic coatings may increase the surface energy of the ice embryo/vapor interface resulting in suppressed ice nucleation. Simulations of in situ cloud formation in the tropical tropopause layer (TTL) throughout the tropics indicate that if decreased accommodation coefficients and resulting high thresholds for ice nucleation prevailed throughout the tropics, then the calculated occurrence frequency and areal coverage of TTL cirrus would be significantly suppressed. However, the simulations also show that even if in situ TTL cirrus form only over a very small fraction of the tropics in the western Pacific, enough air passes through them due to rapid horizontal transport such that they can still effectively freeze-dry air entering the stratosphere. The TTL cirrus simulations show

  12. ON THE FORMATION OF CO{sub 2} AND OTHER INTERSTELLAR ICES

    SciTech Connect

    Garrod, R. T.; Pauly, T.

    2011-07-01

    We investigate the formation and evolution of interstellar dust-grain ices under dark-cloud conditions, with a particular emphasis on CO{sub 2}. We use a three-phase model (gas/surface/mantle) to simulate the coupled gas-grain chemistry, allowing the distinction of the chemically active surface from the ice layers preserved in the mantle beneath. The model includes a treatment of the competition between barrier-mediated surface reactions and thermal-hopping processes. The results show excellent agreement with the observed behavior of CO{sub 2}, CO, and water ice in the interstellar medium. The reaction of the OH radical with CO is found to be efficient enough to account for CO{sub 2} ice production in dark clouds. At low visual extinctions, with dust temperatures {approx}>12 K, CO{sub 2} is formed by direct diffusion and reaction of CO with OH; we associate the resultant CO{sub 2}-rich ice with the observational polar CO{sub 2} signature. CH{sub 4} ice is well correlated with this component. At higher extinctions, with lower dust temperatures, CO is relatively immobile and thus abundant; however, the reaction of H and O atop a CO molecule allows OH and CO to meet rapidly enough to produce a CO:CO{sub 2} ratio in the range {approx}2-4, which we associate with apolar signatures. We suggest that the observational apolar CO{sub 2}/CO ice signatures in dark clouds result from a strongly segregated CO:H{sub 2}O ice, in which CO{sub 2} resides almost exclusively within the CO component. Observed visual-extinction thresholds for CO{sub 2}, CO, and H{sub 2}O are well reproduced by depth-dependent models. Methanol formation is found to be strongly sensitive to dynamical timescales and dust temperatures.

  13. THE EFFECTS OF GRAIN SIZE AND TEMPERATURE DISTRIBUTIONS ON THE FORMATION OF INTERSTELLAR ICE MANTLES

    SciTech Connect

    Pauly, Tyler; Garrod, Robin T.

    2016-02-01

    Computational models of interstellar gas-grain chemistry have historically adopted a single dust-grain size of 0.1 micron, assumed to be representative of the size distribution present in the interstellar medium. Here, we investigate the effects of a broad grain-size distribution on the chemistry of dust-grain surfaces and the subsequent build-up of molecular ices on the grains, using a three-phase gas-grain chemical model of a quiescent dark cloud. We include an explicit treatment of the grain temperatures, governed both by the visual extinction of the cloud and the size of each individual grain-size population. We find that the temperature difference plays a significant role in determining the total bulk ice composition across the grain-size distribution, while the effects of geometrical differences between size populations appear marginal. We also consider collapse from a diffuse to a dark cloud, allowing dust temperatures to fall. Under the initial diffuse conditions, small grains are too warm to promote grain-mantle build-up, with most ices forming on the mid-sized grains. As collapse proceeds, the more abundant, smallest grains cool and become the dominant ice carriers; the large population of small grains means that this ice is distributed across many grains, with perhaps no more than 40 monolayers of ice each (versus several hundred assuming a single grain size). This effect may be important for the subsequent processing and desorption of the ice during the hot-core phase of star formation, exposing a significant proportion of the ice to the gas phase, increasing the importance of ice-surface chemistry and surface–gas interactions.

  14. Study of Ice Particle Formation and Lifetime in Space Environment

    NASA Technical Reports Server (NTRS)

    Jeng, D.

    1972-01-01

    The ice particles are formed when liquid and/or humid gases vent to the space. These submicroscopic ice particles are potential contamination sources of the environments during Skylab operations. The critical size of ice particle and its nucleation rate based on the theory of homogeneous and heterogeneous nucleation by sublimation are analyzed. The equations which are pertinent for studying the growth and evaporation of the ice particles are formulated. The mechanisms affecting the lifetime of ice particle are discussed. The gas dynamic techniques for experimental study of ice particle formation are proposed.

  15. Water-Ice Clouds in the LMDs Martian General Circulation Model

    NASA Technical Reports Server (NTRS)

    Montmessin, F.; Forget, F.; Haberle, R. M.; Rannou, P.; Cabane, M.

    2003-01-01

    The interest for Martian water ice clouds has recently taken a new extent given their likely involvement both in climate and in the hydrological cycle. Previous related microphysical studies have already discussed the complex interactions between airborne dust and clouds [2]. Whereas water ice mantles upon dust cores enhance sedimentation rates and thus possibly change the vertical distribution of dust and water, the advection of clouds by winds could also modulate the geographical distribution of volatiles. Within this context, only 3D modeling based on the use of Martian General Circulation Models (MGCM) is able to give us a consistent clue of the global climatic aspects of Martian clouds.

  16. Microweve Radiative Transfer through Clouds Composed of Realistically Shaped Ice Crystals. Part II. Remote Sensing of Ice Clouds.

    NASA Astrophysics Data System (ADS)

    Evans, K. Franklin; Stephens, Graeme L.

    1995-06-01

    This paper presents the results of polarized microwave radiative transfer modeling of cirrus clouds containing five different particle shoes and 18 Gamma size distributions. Upwelling brightness temperatures for tropical and midlatitude winter atmospheres are simulated at 85.5, 157, 220, and 340 GHz using scattering properties computed with the discrete dipole approximation (described in Part I).The key parameter for the results is the sensitivity (Tb/IWP), which relates the modeled brightness temperature depression to the ice water path. It is shown that for the higher frequencies or distributions of larger particles (i.e., in the scattering regime) the sensitivity is nearly independent of cloud temperature and details of the underlying atmosphere. As expected from the single-scattering results, the characteristic particle size has a large effect on the sensitivity, while the distribution width has only a minor effect. The range in sensitivity over the five particle shapes is typically a factor of 2. The sensitivity for a size distribution of solid columns with a median of the third power of the dimension of 250 µm is about 0.1 K/g m2). Ratios of Tb's at adjacent frequencies can determine the characteristic size of the distribution, though the relationship is double valued for the most sensitive frequencies considered here. Ratios of Tb at horizontal to vertical polarization contain information about particle shape primarily via the aspect ratio. Ideas concerning the development of a specific cirrus retrieval algorithm are discussed.

  17. Seasonal Variation of Cloud Radiative Forcing Over Young Sea Ice During the N-ICE2015 Experiment

    NASA Astrophysics Data System (ADS)

    Murphy, S. Y.; Walden, V. P.; Cohen, L.; Hudson, S. R.

    2016-12-01

    There is a lack of comprehensive measurements of the seasonal variation of cloud and radiation properties over sea ice. The Norwegian Young Sea Ice experiment (N-ICE2015), conducted from January to June 2015, was the first experiment since SHEBA in 1997/1998 to measure cloud properties and all components of the surface energy balance. N-ICE2015 was also the first experiment that was focused on understanding the effects of the atmosphere specifically on thin, young sea ice near the edge of the Arctic ice pack. Here we present the variation of cloud radiative forcing (CRF) at the surface during the seasonal transition from winter to summer. Cloud macrophysical and microphysical properties were measured using a micropulse lidar and a ceilometer. Broadband radiometers were used to measure upwelling and downwelling shortwave and longwave radiative fluxes at the surface. These measurements are combined with radiative transfer calculations of clear-sky fluxes to determine cloud radiative forcing during the seasonal transition. During the winter, the CRF is determined by longwave radiation and averages about 20-30 W m-2, with a range of 0 to 60 W m-2. In spring, shortwave radiation creates a strong diurnal cycle in CRF with values ranging from about -40 to +60 W m-2, the values of which depend strongly on the cloud fraction. In summer, the CRF averages to about 50-60 W m-2 and is always positive with values ranging from 10 to 100 W m-2. Two case studies, one in winter and one in spring, will be highlighted, as well as the dependence of CRF on cloud phase.

  18. Covariance between Arctic sea ice and clouds within atmospheric state regimes at the satellite footprint level

    PubMed Central

    Kato, Seiji; Xu, Kuan‐Man; Cai, Ming

    2015-01-01

    Abstract Understanding the cloud response to sea ice change is necessary for modeling Arctic climate. Previous work has primarily addressed this problem from the interannual variability perspective. This paper provides a refined perspective of sea ice‐cloud relationship in the Arctic using a satellite footprint‐level quantification of the covariance between sea ice and Arctic low cloud properties from NASA A‐Train active remote sensing data. The covariances between Arctic low cloud properties and sea ice concentration are quantified by first partitioning each footprint into four atmospheric regimes defined using thresholds of lower tropospheric stability and midtropospheric vertical velocity. Significant regional variability in the cloud properties is found within the atmospheric regimes indicating that the regimes do not completely account for the influence of meteorology. Regional anomalies are used to account for the remaining meteorological influence on clouds. After accounting for meteorological regime and regional influences, a statistically significant but weak covariance between cloud properties and sea ice is found in each season for at least one atmospheric regime. Smaller average cloud fraction and liquid water are found within footprints with more sea ice. The largest‐magnitude cloud‐sea ice covariance occurs between 500 m and 1.2 km when the lower tropospheric stability is between 16 and 24 K. The covariance between low cloud properties and sea ice is found to be largest in fall and is accompanied by significant changes in boundary layer temperature structure where larger average near‐surface static stability is found at larger sea ice concentrations. PMID:27818851

  19. The Influence of Sea Ice on Arctic Low Cloud Properties and Radiative Effects

    NASA Technical Reports Server (NTRS)

    Taylor, Patrick C.

    2015-01-01

    The Arctic is one of the most climatically sensitive regions of the Earth. Climate models robustly project the Arctic to warm 2-3 times faster than the global mean surface temperature, termed polar warming amplification (PWA), but also display the widest range of surface temperature projections in this region. The response of the Arctic to increased CO2 modulates the response in tropical and extra-tropical regions through teleconnections in the atmospheric circulation. An increased frequency of extreme precipitation events in the northern mid-latitudes, for example, has been linked to the change in the background equator-to-pole temperature gradient implied by PWA. Understanding the Arctic climate system is therefore important for predicting global climate change. The ice albedo feedback is the primary mechanism driving PWA, however cloud and dynamical feedbacks significantly contribute. These feedback mechanisms, however, do not operate independently. How do clouds respond to variations in sea ice? This critical question is addressed by combining sea ice, cloud, and radiation observations from satellites, including CERES, CloudSAT, CALIPSO, MODIS, and microwave radiometers, to investigate sea ice-cloud interactions at the interannual timescale in the Arctic. Cloud characteristics are strongly tied to the atmospheric dynamic and thermodynamic state. Therefore, the sensitivity of Arctic cloud characteristics, vertical distribution and optical properties, to sea ice anomalies is computed within atmospheric dynamic and thermodynamic regimes. Results indicate that the cloud response to changes in sea ice concentration differs significantly between atmospheric state regimes. This suggests that (1) the atmospheric dynamic and thermodynamic characteristics and (2) the characteristics of the marginal ice zone are important for determining the seasonal forcing by cloud on sea ice variability.

  20. Parameterizations of Depositional Growth of Cloud Ice in a Bulk Microphysical Scheme

    NASA Technical Reports Server (NTRS)

    Braun, Scott A.; Ferrier, Brad S.; Tao, Wei-Kuo

    1999-01-01

    Two aspects of the cloud ice parameterization in the Goddard Cumulus Ensemble Model cloud physics parameterization are examined: the conversion of cloud ice to snow by depositional growth, designated PSFI, and the saturation adjustment scheme. The original formulation of PSFI is shown to produce excessive conversion of cloud ice to snow because of an implicit assumption that the relative humidity is 100% with respect to water even though the air may actually be quite less humid. Two possible corrections to this problem are proposed, the first involving application of a relative humidity dependent correction factor to the original formulation of PSFI, and the second involving a new formulation of PSFI based on the equation for depositional growth of cloud ice. The sensitivity of these formulations of PSFI to the assumed masses of the ice particles is examined. Possible problems associated with using a saturation adjustment scheme for cloud ice are discussed and simulations of a squall line with and without application of the adjustment scheme for ice are compared.

  1. Black carbon enrichment in atmospheric ice particle residuals observed in lower trophospheric mixed phase clouds

    SciTech Connect

    Cozic, J.; Mertes, S.; Verheggen, B.; Cziczo, Dan; Gallavardin, S. J.; Walter, S.; Baltensperger, Urs; Weingartner, E.

    2008-08-15

    The enrichment of black carbon (BC) in residuals of small ice particles was investigated during intensive experiments in winter 2004 and 2005 at the high alpine research station Jungfraujoch (3580 m asl, Switzerland). Two inlets were used to sample the bulk aerosol (residuals of cloud droplets and ice crystals as well as non-activated aerosol particles) and the residual particles of small ice crystals (diameter 5 - 20 m). An enrichment of the BC mass fraction in the ice particle residuals was observed by investigating the measured BC mass concentration as a fraction of the bulk (submicrometer) aerosol mass concentration sampled by the two inlets. On average, the BC mass fraction was 5% for the bulk aerosol and 14% for the ice particle residuals. The observed enrichment of BC in ice particle residuals suggests that BC may act as ice nuclei, with important implications for the indirect aerosol effect via glaciation of clouds.

  2. Black carbon enrichment in atmospheric ice particle residuals observed in lower tropospheric mixed phase clouds

    SciTech Connect

    Cozic, J.; Mertes, S.; Verheggen, B.; Cziczo, Daniel J.; Gallavardin, S. J.; Walter, S.; Baltensperger, Urs; Weingartner, E.

    2008-08-15

    The enrichment of black carbon (BC) in residuals of small ice crystals was investigated during intensive experiments in winter 2004 and 2005 at the high alpine research station Jungfraujoch (3580 m asl, Switzerland). Two inlets were used to sample the bulk aerosol (residuals of cloud droplets and ice crystals as well as non-activated aerosol particles) and the residual particles of small ice crystals (diameter 5 - 20 μm). An enrichment of the BC mass fraction in the ice particle residuals was observed by investigating the measured BC mass concentration as a fraction of the bulk (submicrometer) aerosol mass concentration sampled by the two inlets. On average, the BC mass fraction was 5% for the bulk aerosol and 27% for the ice particle residuals. The observed enrichment of BC in ice particle residuals suggests that BC containing particles preferentially act as ice nuclei, with important implications for the indirect aerosol effect via glaciation of clouds.

  3. The influence of organic-containing soil dust on ice nucleation and cloud properties

    NASA Astrophysics Data System (ADS)

    Hummel, Matthias; Grini, Alf; Berntsen, Terje K.; Ekman, Annica

    2017-04-01

    distributes only to a small extent towards subtropical regions, but does not expand further poleward than desert dust INP. Due to the current setup, with simulations nudged to ERA-Interim meteorology, only small changes in the cloud variables are possible. However, the experiment still shows clear influences of soil dust INP on the cloud ice phase. Due to an increased number of ice particles in regions with T<-15˚ C, the formation of precipitation particles is larger. Bentsen, M., Bethke, I., Debernard, J. B., Iversen, T., Kirkevåg, A., Seland, Ø., Drange, H., Roelandt, C., Seierstad, I. A., Hoose, C., and Kristjánsson, J. E.: The Norwegian Earth System Model, NorESM1-M - Part 1: Description and basic evaluation of the physical climate, Geosci. Model Dev., 6, 687-720, 10.5194/gmd-6-687-2013, 2013. Cziczo, D. J., Froyd, K. D., Hoose, C., Jensen, E. J., Diao, M., Zondlo, M. A., Smith, J. B., Twohy, C. H., and Murphy, D. M.: Clarifying the Dominant Sources and Mechanisms of Cirrus Cloud Formation, Science, 340, 1320-1324, 10.1126/science.1234145, 2013. DeMott, P. J., Prenni, A. J., McMeeking, G. R., Sullivan, R. C., Petters, M. D., Tobo, Y., Niemand, M., Möhler, O., Snider, J. R., Wang, Z., and Kreidenweis, S. M.: Integrating laboratory and field data to quantify the immersion freezing ice nucleation activity of mineral dust particles, Atmos. Chem. Phys., 15, 393-409, 10.5194/acp-15-393-2015, 2015. Ginoux, P., Prospero, J. M., Gill, T. E., Hsu, N. C., and Zhao, M.: Global-scale attribution of anthropogenic and natural dust sources and their emission rates based on MODIS Deep Blue aerosol products, Reviews of Geophysics, 50, RG3005, 10.1029/2012RG000388, 2012. Hoose, C., and Möhler, O.: Heterogeneous ice nucleation on atmospheric aerosols: a review of results from laboratory experiments, Atmos. Chem. Phys., 12, 9817-9854, 10.5194/acp-12-9817-2012, 2012. Steinke, I., Funk, R., Busse, J., Iturri, A., Kirchen, S., Leue, M., Möhler, O., Schwartz, T., Schnaiter, M., Sierau, B

  4. Vapor deposition of water on graphitic surfaces: Formation of amorphous ice, bilayer ice, ice I, and liquid water

    SciTech Connect

    Lupi, Laura; Kastelowitz, Noah; Molinero, Valeria

    2014-11-14

    Carbonaceous surfaces are a major source of atmospheric particles and could play an important role in the formation of ice. Here we investigate through molecular simulations the stability, metastability, and molecular pathways of deposition of amorphous ice, bilayer ice, and ice I from water vapor on graphitic and atomless Lennard-Jones surfaces as a function of temperature. We find that bilayer ice is the most stable ice polymorph for small cluster sizes, nevertheless it can grow metastable well above its region of thermodynamic stability. In agreement with experiments, the simulations predict that on increasing temperature the outcome of water deposition is amorphous ice, bilayer ice, ice I, and liquid water. The deposition nucleation of bilayer ice and ice I is preceded by the formation of small liquid clusters, which have two wetting states: bilayer pancake-like (wetting) at small cluster size and droplet-like (non-wetting) at larger cluster size. The wetting state of liquid clusters determines which ice polymorph is nucleated: bilayer ice nucleates from wetting bilayer liquid clusters and ice I from non-wetting liquid clusters. The maximum temperature for nucleation of bilayer ice on flat surfaces, T{sub B}{sup max} is given by the maximum temperature for which liquid water clusters reach the equilibrium melting line of bilayer ice as wetting bilayer clusters. Increasing water-surface attraction stabilizes the pancake-like wetting state of liquid clusters leading to larger T{sub B}{sup max} for the flat non-hydrogen bonding surfaces of this study. The findings of this study should be of relevance for the understanding of ice formation by deposition mode on carbonaceous atmospheric particles, including soot.

  5. Vapor deposition of water on graphitic surfaces: formation of amorphous ice, bilayer ice, ice I, and liquid water.

    PubMed

    Lupi, Laura; Kastelowitz, Noah; Molinero, Valeria

    2014-11-14

    Carbonaceous surfaces are a major source of atmospheric particles and could play an important role in the formation of ice. Here we investigate through molecular simulations the stability, metastability, and molecular pathways of deposition of amorphous ice, bilayer ice, and ice I from water vapor on graphitic and atomless Lennard-Jones surfaces as a function of temperature. We find that bilayer ice is the most stable ice polymorph for small cluster sizes, nevertheless it can grow metastable well above its region of thermodynamic stability. In agreement with experiments, the simulations predict that on increasing temperature the outcome of water deposition is amorphous ice, bilayer ice, ice I, and liquid water. The deposition nucleation of bilayer ice and ice I is preceded by the formation of small liquid clusters, which have two wetting states: bilayer pancake-like (wetting) at small cluster size and droplet-like (non-wetting) at larger cluster size. The wetting state of liquid clusters determines which ice polymorph is nucleated: bilayer ice nucleates from wetting bilayer liquid clusters and ice I from non-wetting liquid clusters. The maximum temperature for nucleation of bilayer ice on flat surfaces, T(B)(max) is given by the maximum temperature for which liquid water clusters reach the equilibrium melting line of bilayer ice as wetting bilayer clusters. Increasing water-surface attraction stabilizes the pancake-like wetting state of liquid clusters leading to larger T(B)(max) for the flat non-hydrogen bonding surfaces of this study. The findings of this study should be of relevance for the understanding of ice formation by deposition mode on carbonaceous atmospheric particles, including soot.

  6. 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

  7. Effects of ice number concentration on dynamics of a shallow mixed-phase stratiform cloud

    SciTech Connect

    Ovchinnikov, Mikhail; Korolev, Alexei; Fan, Jiwen

    2011-09-17

    Previous modeling studies have shown a high sensitivity of simulated properties of mixed-phase clouds to ice number concentration, Ni, with many models losing their ability to maintain the liquid phase as Ni increases. Although models differ widely at what Ni the mixed-phase cloud becomes unstable, the transition from a mixed-phase to an ice only cloud in many cases occurs over a narrow range of ice concentration. To gain better understanding of this non-linear model behavior, in this study, we analyze simulations of a mixed-phase stratiform Artic cloud observed on 26 April 2008 during recent Indirect and Semi-Direct Aerosol Campaign (ISDAC). The BASE simulation, in which Ni is constrained to match the measured value, produces a long-lived cloud in a quasi steady state similar to that observed. The simulation without the ice (NO_ICE) produces a comparable but slightly thicker cloud because more moisture is kept in the mixed layer due to lack of precipitation. When Ni is quadrupled relative to BASE (HI_ICE), the cloud starts loosing liquid water almost immediately and the liquid water path is reduced by half in less than two hours. The changes in liquid water are accompanied by corresponding reduction in the radiative cooling of the layer and a slow down in the vertical mixing, confirming the important role of interactions among microphysics, radiation and dynamics in this type of clouds. Deviations of BASE and HI_ICE from NO_ICE are used to explore the linearity of the model response to variation in Ni. It is shown that at early stages, changes in liquid and ice water as well as in radiative cooling/heating rates are proportional to the Ni change, while changes in the vertical buoyancy flux are qualitatively different in HI_ICE compared to BASE. Thus, while the positive feedback between the liquid water path and radiative cooling of the cloud layer is essential for glaciation of the cloud at higher Ni, the non-linear (with respect to Ni) reduction in positive

  8. Star formation triggered by cloud-cloud collisions

    NASA Astrophysics Data System (ADS)

    Balfour, S. K.; Whitworth, A. P.; Hubber, D. A.; Jaffa, S. E.

    2015-11-01

    We present the results of smoothed particle hydrodynamics simulations in which two clouds, each having mass MO = 500 M⊙ and radius RO = 2 pc, collide head-on at relative velocities of ΔvO = 2.4, 2.8, 3.2, 3.6 and 4.0 km s-1. There is a clear trend with increasing ΔvO. At low ΔvO, star formation starts later, and the shock-compressed layer breaks up into an array of predominantly radial filaments; stars condense out of these filaments and fall, together with residual gas, towards the centre of the layer, to form a single large-N cluster, which then evolves by competitive accretion, producing one or two very massive protostars and a diaspora of ejected (mainly low-mass) protostars; the pattern of filaments is reminiscent of the hub and spokes systems identified recently by observers. At high ΔvO, star formation occurs sooner and the shock-compressed layer breaks up into a network of filaments; the pattern of filaments here is more like a spider's web, with several small-N clusters forming independently of one another, in cores at the intersections of filaments, and since each core only spawns a small number of protostars, there are fewer ejections of protostars. As the relative velocity is increased, the mean protostellar mass increases, but the maximum protostellar mass and the width of the mass function both decrease. We use a Minimal Spanning Tree to analyse the spatial distributions of protostars formed at different relative velocities.

  9. Contrasting the impact of aerosols at northern and southern midlatitudes on heterogeneous ice formation

    NASA Astrophysics Data System (ADS)

    Kanitz, T.; Seifert, P.; Ansmann, A.; Engelmann, R.; Althausen, D.; Casiccia, C.; Rohwer, E. G.

    2011-09-01

    Three cloud data sets, each covering four months of observations, were recently recorded with a lidar at Punta Arenas (53°S), Chile, at Stellenbosch (34°S, near Cape Town), South Africa, and aboard the research vessel Polarstern during three north-south cruises. By comparing these observations with an 11-year cloud data set measured with a lidar at Leipzig (51°N), Germany, the occurrence of heterogeneous ice formation (as a function of cloud top temperature) for very different aerosol conditions in the northern and southern hemisphere is investigated. Large differences in the heterogeneous freezing behavior in the mostly layered clouds are found. For example, <20%, 30%-40% and around 70% of the cloud layers with cloud top temperatures from -15°C to -20°C, showed ice formation over Punta Arenas, Stellenbosch, and Leipzig, respectively. The observed strong contrast reflects the differences in the free tropospheric aerosol conditions at northern midlatitudes, that are controlled by anthropogenic pollution, mineral dust, forest fire smoke, terrestrial biological material and high southern midlatitudes with clean marine conditions.

  10. Spatial and temporal distributions of ice nucleating particles during the Atmospheric Radiation Measurement (ARM) Cloud Aerosol Precipitation Experiment (ACAPEX)

    NASA Astrophysics Data System (ADS)

    Levin, E. J.; DeMott, P. J.; Suski, K. J.; Boose, Y.; Hill, T. C. J.; McCluskey, C. S.; Schill, G. P.; Duncan, D.; Al-Mashat, H.; Prather, K. A.; Sedlacek, A. J., III; Tomlinson, J. M.; Mei, F.; Hubbe, J. M.; Pekour, M. S.; Leung, L. R.; Kreidenweis, S. M.

    2016-12-01

    California is currently under drought conditions and changes in precipitation due to future climate change scenarios are uncertain. Thus, understanding the controlling factors for precipitation in this region, and having the capability to accurately model these scenarios, is important. A crucial area in understanding precipitation is in the interplay between atmospheric moisture and aerosols. Specifically, ice nucleation in clouds is an important process controlling precipitation formation. A major component of CA's yearly precipitation comes from wintertime atmospheric river (AR) events which were the focus of the 2015 Atmospheric Radiation Measurement (ARM) Cloud Aerosol Precipitation Experiment (ACAPEX) and CalWater 2 campaigns. These two campaigns provided sampling platforms on four aircraft, including the ARM Aerial Facility G-1, as well as the NOAA Ron Brown research vessel and at a ground station at Bodega Bay, CA. Measurements of ice nucleating particles (INPs) were made with the Colorado State University (CSU) Continuous Flow Diffusion Chamber (CFDC) aboard the G-1 and at Bodega Bay, and using aerosol filter collections on these platforms as well as the Ron Brown for post-processing via immersion freezing in the CSU Ice Spectrometer. Aerosol composition was measured aboard the G-1 with the Aerosol Time-of-Flight Mass Spectrometer (ATOFMS). Both the CFDC and ATOFMS sampled off of an isokinetic inlet when flying in clear air and a counter-flow virtual impactor in clouds to capture ice crystal and cloud droplet residuals. In this presentation we present ice nucleating particle concentrations before, during and after an AR event from air, ground and ocean-based measurements. We also examine INP concentration variability in orographic clouds and in clear air at altitude along the Sierra Nevada range, in the marine boundary layer and through the Central Valley, and relate these INP measurements to other aerosol physical and chemical properties.

  11. CRISM Limb Observations of Coincident CO2 Ice Clouds and O2 Emission in the Mars Equatorial Mesosphere

    NASA Astrophysics Data System (ADS)

    Clancy, R. T.; Smith, Michael; Lefvère, Franck; Sandor, Brad; Wolff, Michael; McConnochie, Tim; Seelos, Kim; Nair, Hari; Toigo, Anthony; Murchie, Scott

    2015-11-01

    Limb observations with the CRISM visible/near IR (0.4-4 μm) imaging spectrometer (Murchie et al., 2009) onboard the Mars Reconnaissance Orbiter have supported a broad range of atmospheric airglow (1.27 μm O2, 1.45 and 2.9 μm OH) and aerosol (dust, H2O and CO2 ice) vertical profile retrievals. Most recently, CRISM limb observations over Ls=62-137° in MY32 (Dec 2013-May 2014) have obtained the first visible-to-near IR scattering spectra of CO2 ice clouds in the Mars equatorial mesosphere (i.e., 60-70 km altitudes, 10S-10N, over Ls=0-140° Clancy et al, 2007, Montemessin et al, 2007). These spectra are highly diagnostic of both the CO2 ice composition and cloud paritcle sizes (Reff=1-2 μm). The current report regards May 27, 2014 (Ls=137°) CRISM limb imaging observations of CO2 ice clouds centered near 10S,75W at an altitude of 60 km.What is distinct about the May 2014 observation is the coincidence of striking mesospheric O2(1Δg) 1.27 μm dayglow, indicative of very low H2O/temperature conditions, which lead to locally intense O3 enhancements (and 1.27 μm O2 emission associated with O3 photolysis). In this respect, we have an unique temperature indicator in the presence of CO2 ice clouds. Interestingly, LMD GCM photochemical simulations exhibit such localized O2 dayglow at the same location/season, associated with a thermal tide temperature minimum (the current best explanation for mesospheric CO2 ice cloud formation). We present CO2 cloud optical depth and particle size determinations, and discuss observed and modeled O2 mesospheric peak emissions in the context of very cold atmospheric temperatures implied by local CO2 ice formation and O2 emission.

  12. 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.

  13. On the Contribution of Clouds to Greenland Ice Sheet Mass Loss

    NASA Astrophysics Data System (ADS)

    Van Tricht, K.; Lhermitte, S.; Lenaerts, J.; Gorodetskaya, I.; L'Ecuyer, T. S.; Noel, B.; van den Broeke, M. R.; Turner, D. D.; Van Lipzig, N. P. M.

    2015-12-01

    The Greenland ice sheet (GrIS) has become one of the main contributors to global mean sea level rise, predominantly explained by a decreasing surface mass balance (SMB). Clouds are known to have a strong influence on the surface energy budget, which in consequence impacts the SMB. For example, the potentially important role of thin liquid-bearing clouds over Greenland in enhancing ice sheet melt has recently gained interest. Yet, current research is spatially and temporally limited, focusing on particular events and cloud types, while the large-scale impact of all clouds on the SMB remains unknown. Using a unique cloud product covering the entire GrIS over the period 2007-2010, consisting of active satellite remote sensing data, ground-based observations and climate model data, together with snow model simulations, we investigate the cloud radiative effect over the GrIS and the consequences for the SMB. We show a strong sensitivity of the GrIS to clouds, with a complex interplay between enhanced and reduced mass loss. We further distinguish between ice-only and liquid-bearing clouds, temporal and spatial variations in cloud impacts, and we demonstrate the large spread in simulated clouds by state-of-the-art climate models. Our results therefore urge the need for accurate cloud representations in climate models, to improve future projections of GrIS SMB and global sea level rise.

  14. West Antarctic Ice Sheet cloud cover and surface radiation budget from NASA A-Train satellites

    DOE PAGES

    Scott, Ryan C.; Lubin, Dan; Vogelmann, Andrew M.; ...

    2017-04-26

    Clouds are an essential parameter of the surface energy budget influencing the West Antarctic Ice Sheet (WAIS) response to atmospheric warming and net contribution to global sea-level rise. A four-year record of NASA A-Train cloud observations is combined with surface radiation measurements to quantify the WAIS radiation budget and constrain the three-dimensional occurrence frequency, thermodynamic phase partitioning, and surface radiative effect of clouds over West Antarctica (WA). The skill of satellite-modeled radiative fluxes is confirmed through evaluation against measurements at four Antarctic sites (WAIS Divide Ice Camp, Neumayer, Syowa, and Concordia Stations). And due to perennial high-albedo snow and icemore » cover, cloud infrared emission dominates over cloud solar reflection/absorption leading to a positive net all-wave cloud radiative effect (CRE) at the surface, with all monthly means and 99.15% of instantaneous CRE values exceeding zero. The annual-mean CRE at theWAIS surface is 34 W m-2, representing a significant cloud-induced warming of the ice sheet. Low-level liquid-containing clouds, including thin liquid water clouds implicated in radiative contributions to surface melting, are widespread and most frequent in WA during the austral summer. Clouds warm the WAIS by 26 W m-2, in summer, on average, despite maximum offsetting shortwave CRE. Glaciated cloud systems are strongly linked to orographic forcing, with maximum incidence on the WAIS continuing downstream along the Transantarctic Mountains.« less

  15. Ice formation and growth shape bacterial community structure in Baltic Sea drift ice.

    PubMed

    Eronen-Rasimus, Eeva; Lyra, Christina; Rintala, Janne-Markus; Jürgens, Klaus; Ikonen, Vilma; Kaartokallio, Hermanni

    2015-02-01

    Drift ice, open water and under-ice water bacterial communities covering several developmental stages from open water to thick ice were studied in the northern Baltic Sea. The bacterial communities were assessed with 16S rRNA gene terminal-restriction fragment length polymorphism and cloning, together with bacterial abundance and production measurements. In the early stages, open water and pancake ice were dominated by Alphaproteobacteria and Actinobacteria, which are common bacterial groups in Baltic Sea wintertime surface waters. The pancake ice bacterial communities were similar to the open-water communities, suggesting that the parent water determines the sea-ice bacterial community in the early stages of sea-ice formation. In consolidated young and thick ice, the bacterial communities were significantly different from water bacterial communities as well as from each other, indicating community development in Baltic Sea drift ice along with ice-type changes. The thick ice was dominated by typical sea-ice genera from classes Flavobacteria and Gammaproteobacteria, similar to those in polar sea-ice bacterial communities. Since the thick ice bacterial community was remarkably different from that of the parent seawater, results indicate that thick ice bacterial communities were recruited from the rarer members of the seawater bacterial community.

  16. The importance of feldspar for ice nucleation by mineral dust in mixed-phase clouds.

    PubMed

    Atkinson, James D; Murray, Benjamin J; Woodhouse, Matthew T; Whale, Thomas F; Baustian, Kelly J; Carslaw, Kenneth S; Dobbie, Steven; O'Sullivan, Daniel; Malkin, Tamsin L

    2013-06-20

    The amount of ice present in mixed-phase clouds, which contain both supercooled liquid water droplets and ice particles, affects cloud extent, lifetime, particle size and radiative properties. The freezing of cloud droplets can be catalysed by the presence of aerosol particles known as ice nuclei. One of the most important ice nuclei is thought to be mineral dust aerosol from arid regions. It is generally assumed that clay minerals, which contribute approximately two-thirds of the dust mass, dominate ice nucleation by mineral dust, and many experimental studies have therefore focused on these materials. Here we use an established droplet-freezing technique to show that feldspar minerals dominate ice nucleation by mineral dusts under mixed-phase cloud conditions, despite feldspar being a minor component of dust emitted from arid regions. We also find that clay minerals are relatively unimportant ice nuclei. Our results from a global aerosol model study suggest that feldspar ice nuclei are globally distributed and that feldspar particles may account for a large proportion of the ice nuclei in Earth's atmosphere that contribute to freezing at temperatures below about -15 °C.

  17. CloudSat-Constrained Cloud Ice Water Path and Cloud Top Height Retrievals from MHS 157 and 183.3 GHz Radiances

    NASA Technical Reports Server (NTRS)

    Gong, J.; Wu, D. L.

    2014-01-01

    Ice water path (IWP) and cloud top height (ht) are two of the key variables in determining cloud radiative and thermodynamical properties in climate models. Large uncertainty remains among IWP measurements from satellite sensors, in large part due to the assumptions made for cloud microphysics in these retrievals. In this study, we develop a fast algorithm to retrieve IWP from the 157, 183.3+/-3 and 190.3 GHz radiances of the Microwave Humidity Sounder (MHS) such that the MHS cloud ice retrieval is consistent with CloudSat IWP measurements. This retrieval is obtained by constraining the empirical forward models between collocated and coincident measurements of CloudSat IWP and MHS cloud-induced radiance depression (Tcir) at these channels. The empirical forward model is represented by a lookup table (LUT) of Tcir-IWP relationships as a function of ht and the frequency channel.With ht simultaneously retrieved, the IWP is found to be more accurate. The useful range of the MHS IWP retrieval is between 0.5 and 10 kg/sq m, and agrees well with CloudSat in terms of the normalized probability density function (PDF). Compared to the empirical model, current operational radiative transfer models (RTMs) still have significant uncertainties in characterizing the observed Tcir-IWP relationships. Therefore, the empirical LUT method developed here remains an effective approach to retrieving ice cloud properties from the MHS-like microwave channels.

  18. Final Technical Report for "Ice nuclei relation to aerosol properties: Data analysis and model parameterization for IN in mixed-phase clouds" (DOE/SC00002354)

    SciTech Connect

    Anthony Prenni; Kreidenweis, Sonia M.

    2012-09-28

    cloud-resolving model to compare predictions of ice crystal concentrations and other cloud properties to those observed in two intensive case studies of Arctic stratus during ISDAC. Our implementation included development of a prognostic scheme of ice activation using the IN parameterization so that the most realistic treatment of ice nuclei, including their budget (gains and losses), was achieved. Many cloud microphysical properties and cloud persistence were faithfully reproduced, despite a tendency to under-predict (by a few to several times) ice crystal number concentrations and cloud ice mass, in agreement with some other studies. This work serves generally as the basis for improving predictive schemes for cloud ice crystal activation in cloud and climate models, and more specifically as the basis for such a scheme to be used in a Multi-scale Modeling Format (MMF) that utilizes a connected system of cloud-resolving models on a global grid in an effort to better resolve cloud processes and their influence on climate.

  19. Improved identification of clouds and ice/snow covered surfaces in SCIAMACHY observations

    NASA Astrophysics Data System (ADS)

    Krijger, J. M.; Tol, P.; Istomina, L. G.; Schlundt, C.; Schrijver, H.; Aben, I.

    2011-10-01

    In the ultra-violet, visible and near infra-red wavelength range the presence of clouds can strongly affect the satellite-based passive remote sensing observation of constituents in the troposphere, because clouds effectively shield the lower part of the atmosphere. Therefore, cloud detection algorithms are of crucial importance in satellite remote sensing. However, the detection of clouds over snow/ice surfaces is particularly difficult in the visible wavelengths as both clouds an snow/ice are both white and highly reflective. The SCIAMACHY Polarisation Measurement Devices (PMD) Identification of Clouds and Ice/snow method (SPICI) uses the SCIAMACHY measurements in the wavelength range between 450 nm and 1.6 μm to make a distinction between clouds and ice/snow covered surfaces, specifically developed to identify cloud-free SCIAMACHY observations. For this purpose the on-board SCIAMACHY PMDs are used because they provide higher spatial resolution compared to the main spectrometer measurements. In this paper we expand on the original SPICI algorithm (Krijger et al., 2005a) to also adequately detect clouds over snow-covered forests which is inherently difficult because of the similar spectral characteristics. Furthermore the SCIAMACHY measurements suffer from degradation with time. This must be corrected for adequate performance of SPICI over the full SCIAMACHY time range. Such a correction is described here. Finally the performance of the new SPICI algorithm is compared with various other datasets, such as from FRESCO, MICROS and AATSR, focusing on the algorithm improvements.

  20. Development of Two-Moment Cloud Microphysics for Liquid and Ice Within the NASA Goddard Earth Observing System Model (GEOS-5)

    NASA Technical Reports Server (NTRS)

    Barahona, Donifan; Molod, Andrea M.; Bacmeister, Julio; Nenes, Athanasios; Gettelman, Andrew; Morrison, Hugh; Phillips, Vaughan,; Eichmann, Andrew F.

    2013-01-01

    This work presents the development of a two-moment cloud microphysics scheme within the version 5 of the NASA Goddard Earth Observing System (GEOS-5). The scheme includes the implementation of a comprehensive stratiform microphysics module, a new cloud coverage scheme that allows ice supersaturation and a new microphysics module embedded within the moist convection parameterization of GEOS-5. Comprehensive physically-based descriptions of ice nucleation, including homogeneous and heterogeneous freezing, and liquid droplet activation are implemented to describe the formation of cloud particles in stratiform clouds and convective cumulus. The effect of preexisting ice crystals on the formation of cirrus clouds is also accounted for. A new parameterization of the subgrid scale vertical velocity distribution accounting for turbulence and gravity wave motion is developed. The implementation of the new microphysics significantly improves the representation of liquid water and ice in GEOS-5. Evaluation of the model shows agreement of the simulated droplet and ice crystal effective and volumetric radius with satellite retrievals and in situ observations. The simulated global distribution of supersaturation is also in agreement with observations. It was found that when using the new microphysics the fraction of condensate that remains as liquid follows a sigmoidal increase with temperature which differs from the linear increase assumed in most models and is in better agreement with available observations. The performance of the new microphysics in reproducing the observed total cloud fraction, longwave and shortwave cloud forcing, and total precipitation is similar to the operational version of GEOS-5 and in agreement with satellite retrievals. However the new microphysics tends to underestimate the coverage of persistent low level stratocumulus. Sensitivity studies showed that the simulated cloud properties are robust to moderate variation in cloud microphysical parameters

  1. Cloud condensation nuclei and ice nucleation activity of hydrophobic and hydrophilic soot particles.

    PubMed

    Koehler, Kirsten A; DeMott, Paul J; Kreidenweis, Sonia M; Popovicheva, Olga B; Petters, Markus D; Carrico, Christian M; Kireeva, Elena D; Khokhlova, Tatiana D; Shonija, Natalia K

    2009-09-28

    contrast, GTS, TS, and TC1 re