A study of extended zodiacal structures

NASA Technical Reports Server (NTRS)

Sykes, Mark V.

1990-01-01

Observations of cometary dust trails and zodiacal dust bands, discovered by the Infrared Astronomical Satellite (IRAS) were analyzed in a continuing effort to understand their nature and relationship to comets, asteroids, and processes effecting those bodies. A survey of all trails observed by IRAS has been completed, and analysis of this phenomenon continues. A total of 8 trails have been associated with known short-period comets (Churyumov-Gerasimenko, Encke, Gunn, Kopff, Pons-Winnecke, Schwassmann-Wachmann 1, Tempel 1, and Tempel 2), and a few faint trails have been detected which are not associated with any known comet. It is inferred that all short-period comets may have trails, and that the trails detected were seen as a consequence of observational selection effects. Were IRAS launched today, it would likely observe a largely different set of trails. The Tempel 2 trail exhibits a small but significant excess in color temperature relative to a blackbody at the same heliocentric distance. This excess may be due to the presence of a population of small, low-beta particles deriving from large particles within the trail, or a temperature gradient over the surface of large trail particles. Trails represent the very first stage in the formation and evolution of a meteor stream, and may also be the primary mechanism by which comets contribute to the interplanetary dust complex. A mathematical model of the spatial distribution of orbitally evolved collisional debris was developed which reproduces the zodiacal dust band phenomena and was used in the analysis of dust band observations made by IRAS. This has resulted in the principal zodiacal dust bands being firmly related to the principal Hirayama asteroid families. In addition, evidence for the collisional diffusion of the orbital elements of the dust particles has been found in the case of dust generated in the Eos asteroid family.

Radar detectability studies of slow and small Zodiacal Dust Cloud Particles: I. The case of Arecibo 430 MHz meteor head echo observations

PubMed Central

Janches, D.; Plane, J.M.C.; Nesvorný, D.; Feng, W.; Vokrouhlický, D.; Nicolls, M.J.

2016-01-01

Recent model development of the Zodiacal Dust Cloud (ZDC) model (Nesvorný et al. 2010, 2011b) argue that the incoming flux of meteoric material into the Earth’s upper atmosphere is mostly undetected by radars because they cannot detect small extraterrestrial particles entering the atmosphere at low velocities due to the relatively small production of electrons. In this paper we present a new methodology utilizing meteor head echo radar observations that aims to constrain the ZDC physical model by ground-based measurements. In particular, for this work, we focus on Arecibo 430 MHz observations since this is the most sensitive radar utilized for this type of observations to date. For this, we integrate and employ existing comprehensive models of meteoroid ablation, ionization and radar detection to enable accurate interpretation of radar observations and show that reasonable agreement in the hourly rates is found between model predictions and Arecibo observations when: 1) we invoke the lower limit of the model predicted flux (~16 t/d) and 2) we estimate the ionization probability of ablating metal atoms using laboratory measurements of the ionization cross sections of high speed metal atom beams, resulting in values up to two orders of magnitude lower than the extensively utilized figure reported by Jones (1997) for low speeds meteors. However, even at this lower limit the model over predicts the slow portion of the Arecibo radial velocity distributions by a factor of 3, suggesting the model requires some revision. PMID:27642186

Radar Detectability Studies of Slow and Small Zodiacal Dust Cloud Particles: I. The Case of Arecibo 430 MHz Meteor Head Echo Observations

NASA Technical Reports Server (NTRS)

Janches, D.; Plane, J. M. C.; Nesvorny, D.; Feng, W.; Vokrouhlicky, D.; Nicolls, M. J.

2014-01-01

Recent model development of the Zodiacal Dust Cloud (ZDC) model (Nesvorny et al. 2010, 2011b) argue that the incoming flux of meteoric material into the Earth's upper atmosphere is mostly undetected by radars because they cannot detect small extraterrestrial particles entering the atmosphere at low velocities due to the relatively small production of electrons. In this paper we present a new methodology utilizing meteor head echo radar observations that aims to constrain the ZDC physical model by ground-based measurements. In particular, for this work, we focus on Arecibo 430 MHz observations since this is the most sensitive radar utilized for this type of observations to date. For this, we integrate and employ existing comprehensive models of meteoroid ablation, ionization and radar detection to enable accurate interpretation of radar observations and show that reasonable agreement in the hourly rates is found between model predictions and Arecibo observations when: 1) we invoke the lower limit of the model predicted flux (approximately 16 t/d) and 2) we estimate the ionization probability of ablating metal atoms using laboratory measurements of the ionization cross sections of high speed metal atom beams, resulting in values up to two orders of magnitude lower than the extensively utilized figure reported by Jones (1997) for low speeds meteors. However, even at this lower limit the model over predicts the slow portion of the Arecibo radial velocity distributions by a factor of 3, suggesting the model requires some revision.

Radar detectability studies of slow and small zodiacal dust cloud particles. I. The case of Arecibo 430 MHz meteor head echo observations

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

Janches, D.; Plane, J. M. C.; Feng, W.

2014-11-20

Recent model development of the Zodiacal Dust Cloud (ZDC) argues that the incoming flux of meteoric material into the Earth's upper atmosphere is mostly undetected by radars because they cannot detect small extraterrestrial particles entering the atmosphere at low velocities due to the relatively small production of electrons. In this paper, we present a new methodology utilizing meteor head echo radar observations that aims to constrain the ZDC physical model by ground-based measurements. In particular, for this work, we focus on Arecibo 430 MHz observations since this is the most sensitive radar utilized for this type of observations to date.more » For this, we integrate and employ existing comprehensive models of meteoroid ablation, ionization, and radar detection to enable accurate interpretation of radar observations and show that reasonable agreement in the hourly rates is found between model predictions and Arecibo observations when (1) we invoke the lower limit of the model predicted flux (∼16 t d{sup –1}) and (2) we estimate the ionization probability of ablating metal atoms using laboratory measurements of the ionization cross sections of high-speed metal atom beams, resulting in values up to two orders of magnitude lower than the extensively utilized figure reported by Jones for low-speed meteors. However, even at this lower limit, the model overpredicts the slow portion of the Arecibo radial velocity distributions by a factor of three, suggesting that the model requires some revision.« less

Exozodiacal Dust Workshop

NASA Technical Reports Server (NTRS)

Backman, D. E. (Editor); Caroff, L. J. (Editor); Sandford, S. A. (Editor); Wooden, D. H. (Editor)

1998-01-01

The purpose of the workshop was to understand what effect circumstellar dust clouds will have on NASA's proposed Terrestrial Planet Finder (TPF) mission's ability to search for terrestrial-sized planets orbiting stars in the solar neighborhood. The workshop participants reviewed the properties of TPF, summarized what is known about the local zodiacal cloud and about exozodiacal clouds, and determined what additional knowledge must be obtained to help design TPF for maximum effectiveness within its cost constraint. Recommendations were made for ways to obtain that additional knowledge, at minimum cost. The workshop brought together approximately 70 scientists, from four different countries. The active participants included astronomers involved in the study of the local zodiacal cloud, in the formation of stars and planetary systems, and in the technologies and techniques of ground- and space-based infrared interferometry. During the course of the meeting, 15 invited talks and 20 contributed poster papers were presented, and there were four working sessions. This is a collection of the invited talks, contributed poster papers, and summaries of the working sessions.

Exozodiacal clouds: hot and warm dust around main sequence stars

NASA Astrophysics Data System (ADS)

Kral, Quentin; Krivov, Alexander V.; Defrère, Denis; van Lieshout, Rik; Bonsor, Amy; Augereau, Jean-Charles; Thébault, Philippe; Ertel, Steve; Lebreton, Jérémy; Absil, Olivier

2017-04-01

A warm/hot dust component (at temperature $>$ 300K) has been detected around $\\sim$ 20% of stars. This component is called "exozodiacal dust" as it presents similarities with the zodiacal dust detected in our Solar System, even though its physical properties and spatial distribution can be significantly different. Understanding the origin and evolution of this dust is of crucial importance, not only because its presence could hamper future detections of Earth-like planets in their habitable zones, but also because it can provide invaluable information about the inner regions of planetary systems. In this review, we present a detailed overview of the observational techniques used in the detection and characterisation of exozodiacal dust clouds ("exozodis") and the results they have yielded so far, in particular regarding the incidence rate of exozodis as a function of crucial parameters such as stellar type and age, or the presence of an outer cold debris disc. We also present the important constraints that have been obtained, on dust size distribution and spatial location, by using state-of-the-art radiation transfer models on some of these systems. Finally, we investigate the crucial issue of how to explain the presence of exozodiacal dust around so many stars (regardless of their ages) despite the fact that such dust so close to its host star should disappear rapidly due to the coupled effect of collisions and stellar radiation pressure. Several potential mechanisms have been proposed to solve this paradox and are reviewed in detail in this paper. The review finishes by presenting the future of this growing field.

Sahara Dust Cloud

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site] Dust Particles Click on the image for Quicktime movie from 7/15-7/24

A continent-sized cloud of hot air and dust originating from the Sahara Desert crossed the Atlantic Ocean and headed towards Florida and the Caribbean. A Saharan Air Layer, or SAL, forms when dry air and dust rise from Africa's west coast and ride the trade winds above the Atlantic Ocean.

These dust clouds are not uncommon, especially during the months of July and August. They start when weather patterns called tropical waves pick up dust from the desert in North Africa, carry it a couple of miles into the atmosphere and drift westward.

In a sequence of images created by data acquired by the Earth-orbiting Atmospheric Infrared Sounder ranging from July 15 through July 24, we see the distribution of the cloud in the atmosphere as it swirls off of Africa and heads across the ocean to the west. Using the unique silicate spectral signatures of dust in the thermal infrared, AIRS can detect the presence of dust in the atmosphere day or night. This detection works best if there are no clouds present on top of the dust; when clouds are present, they can interfere with the signal, making it much harder to detect dust as in the case of July 24, 2005.

In the Quicktime movie, the scale at the bottom of the images shows +1 for dust definitely detected, and ranges down to -1 for no dust detected. The plots are averaged over a number of AIRS observations falling within grid boxes, and so it is possible to obtain fractional numbers. [figure removed for brevity, see original site] Total Water Vapor in the Atmosphere Around the Dust Cloud Click on the image for Quicktime movie

The dust cloud is contained within a dry adiabatic layer which originates over the Sahara Desert. This Saharan Air Layer (SAL) advances Westward over the Atlantic Ocean, overriding the cool, moist air nearer the surface. This burst of very dry air is visible in the

Dynamics of Solar System Dust

NASA Technical Reports Server (NTRS)

Dermott, Stanley F.

2002-01-01

The ongoing aim of the research is to investigate the dynamical and physical evolution of interplanetary dust particles in order to produce a detailed global model of the zodiacal cloud and its constituent components that is capable of predicting thermal fluxes in mid-infrared wave bands to an accuracy of 1% or better; with the additional aim of exploiting this research as a basis for predicting structure in exozodiacal clouds that may be signatures of unseen planets.

Interplanetary dust. [survey of last four years' research

NASA Technical Reports Server (NTRS)

Brownlee, D. E.

1979-01-01

Progress in the study of interplanetary dust during the past four years is reviewed. Attention is given to determinations of the relative contributions of interstellar dust grains, collisional debris from the asteroid belt and short-period comets to the interplanetary dust cloud. Effects of radiation pressure and collisions on particle dynamics are discussed, noting the discovery of the variation of the orbital parameters of dust particles at 1 AU with size and in situ measurements of dust density between 0.3 and 5 AU by the Helios and Pioneer spacecraft. The interpretation of the zodiacal light as produced by porous absorbing particles 10 to 100 microns in size is noted, and measurements of the Doppler shift, light-producing-particle density, UV spectrum, photometric axis and angular scattering function of the zodiacal light are reported. Results of analyses of lunar rock microcraters as to micrometeoroid density, flux rate, size distribution and composition are indicated and interplanetary dust particles collected from the stratosphere are discussed. Findings concerning the composition of fragile meteoroid types found as cosmic spherules in deep sea sediments are also presented.

On the Contribution of Asteroid Disruptions to the Interplanetary Dust Flux

NASA Astrophysics Data System (ADS)

Kehoe, T. J. J.; Kehoe, A. E.

2017-12-01

Recent modeling has shown the significant contribution of micron- to millimeter-sized particles released by the disruption of main-belt asteroids (MBAs) to the interplanetary dust particle (IDP) flux (e.g., Dermott et al., 2002; Nesvorný et al., 2003; Espy Kehoe et al., 2015). In this paper, we present the results of a study that indicates that the dust injected into the zodiacal cloud due to the catastrophic disruption of an asteroid is dominated by the release of its surface regolith particles. Our research suggests that disrupting a single asteroid with diameter O(100 km) will be enough to regenerate the entire zodiacal cloud. The breakup of smaller asteroids with diameters O(10 km) will likely produce more moderate, but still significant, changes in the dust environment of the inner solar system. As collisional disruptions of asteroids in this size range occur more frequently, it is important that we develop a better understanding of the injection of asteroidal material into the zodiacal cloud as a result of these type of events in order to determine the temporal evolution of the interplanetary dust flux. The results presented in this paper will lead to a better understanding of the threat to exploration activities due to the enhanced IDP flux resulting from the disruption of asteroidal regoliths. These findings can be employed to improve engineering models, for example, the NASA Meteoroid Engineering Model (MEM) that is widely utilized to assess the impact hazard to space hardware and activities in the inner solar system due to the natural meteoroid environment (McNamara et al., 2004). This is an important area of concern for current and future mission development purposes.

Sahara Dust Cloud

NASA Image and Video Library

2005-07-15

In July of 2005, a continent-sized cloud of hot air and dust originating from the Sahara Desert crossed the Atlantic Ocean and headed towards Florida and the Caribbean, captured by the Atmospheric Infrared Sounder onboard NASA Aqua satellite. A Saharan Air Layer, or SAL, forms when dry air and dust rise from Africa's west coast and ride the trade winds above the Atlantic Ocean. These dust clouds are not uncommon, especially during the months of July and August. They start when weather patterns called tropical waves pick up dust from the desert in North Africa, carry it a couple of miles into the atmosphere and drift westward. http://photojournal.jpl.nasa.gov/catalog/PIA00448

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

NASA Astrophysics Data System (ADS)

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

1998-04-01

There is a possible connection between structure in circumstellar dust clouds and the presence of planets, our own zodiacal cloud being the prime example. Asymmetries in such clouds could be diagnostic of planets which would be otherwise undetectable. One such feature is an offset of the center of symmetry of the disk with respect to the central star. The offset is caused by the forced eccentricities (ef) of particles in the cloud. The orbit of a particle can be described by a set of five orbital elements: the semi-major axis (a), eccentricity (e), inclination (I), longitude of ascending node (Omega) and the argument of pericenter (omega). In low order secular perturbation theory, osculating elements of small bodies are decomposed into proper and forced elements. The proper elements are dependent on initial conditions while the forced elements are imposed on the particle's orbit by the gravitational perturbations of the planets. This decomposition is still applicable in the presence of drag forces. We compare COBE observations of the variation in average polar brightness of the background cloud, (N + S)/2, with ecliptic longitude of Earth with those of a model cloud made of asteroidal particles which populate the inner solar system according to a 1/rgamma where (gamma) = 1 (Poynting Robertson light drag) distribution. The variation with ecliptic longitude of Earth in mean polar brightness is shown in for the 25 micron waveband. Sine curves are fit to both the COBE observations and the model. The variation in (N+S)/2 with ecliptic longitude of Earth can be represented as a superposition of two sine curves: one for the variation in (N + S)/2 due to the Earth's eccentric orbit and the other for the variation in (N + S)/2 due to the forced eccentricities of particles in the cloud. If the cloud were symmetric about the Sun (i.e., if there were no offset), the maximum and minimum brightnesses of the cloud would occur at perihelion and aphelion, respectively. Looking at

Astrophysical dust grains in stars, the interstellar medium, and the solar system

NASA Technical Reports Server (NTRS)

Gehrz, Robert D.

1991-01-01

Studies of astrophysical dust grains in circumstellar shells, the interstellar medium, and the solar system may provide information about stellar evolution and about physical conditions in the primitive solar nebula. The following subject areas are covered: (1) the cycling of dust in stellar evolution and the formation of planetary systems; (2) astrophysical dust grains in circumstellar environments; (3) circumstellar grain formation and mass loss; (4) interstellar dust grains; (5) comet dust and the zodiacal cloud; (6) the survival of dust grains during stellar evolution; and (7) establishing connections between stardust and dust in the solar system.

The Origin of the Excess Near-Infrared Diffuse Sky Brightness: Population III Stars or Zodiacal Light?

NASA Technical Reports Server (NTRS)

Dwek, Eli

2006-01-01

The intensity of the diffuse 1 to 5 micron sky emission from which solar system and Galactic foregrounds have been subtracted is in excess of that expected from energy released by galaxies and stars that formed during the z < 5 redshift interval. The spectral signature of this excess near-infrared background light (NIRBL) component is almost identical to that of reflected sunlight from the interplanetary dust cloud, and could therefore be the result of the incomplete subtraction of this foreground emission component from the diffuse sky maps. Alternatively, this emission component could be extragalactic. Its spectral signature is consistent with that of redshifted continuum and recombination line emission from H-II regions formed by the first generation of very massive stars. In this talk I will present the implications of this excess emission for our understanding of the zodiacal dust cloud, the formation rate of Pop III stars, and the TeV gamma-ray opacity to nearby blazars.

Dust evolution from comets

NASA Technical Reports Server (NTRS)

Sekanina, Z.

1976-01-01

The studies of the evolution of cometary debris are reviewed. The subject is divided into three major sections: (1) the developments in the immediate vicinity of the cometary nucleus, which is the source of the dust; (2) the formation of the dust tail; and (3) the blending of the debris with the dust component of interplanetary matter. The importance of the physical theory of comets is emphasized for the understanding of the early phase of evolution. A physico-dynamical model designed to analyze the particle-emission mechanism from the distribution of light in the dust tail is described and the results are presented. Increased attention is paid to large particles because of their importance for the evolution of the zodiacal cloud. Finally, implications are discussed for the future in situ investigations of comets.

Dust evolution from comets

NASA Technical Reports Server (NTRS)

Sekanina, Z.

1977-01-01

The studies of the evolution of cometary debris are reviewed. The subject is divided into three major sections: (1) the developments in the immediate vicinity of the cometary nucleus, which is the source of the dust; (2) the formation of the dust tail; and (3) the blending of the debris with the dust component of interplanetary matter. The importance of the physical theory of comets is emphasized for the understanding of the early phase of the evolution of cometary dust. A physico-dynamical model designed to analyze the particle-emission mechanism from the distribution of light in the dust tails is described and the results are presented. Increased attention is paid to large particles because of their importance for the evolution of the zodiacal cloud. Finally, implications are discussed for the future in situ investigations of comets.

Galactic and zodiacal light surface brightness measurements with the Atmosphere Explorer satellites

NASA Technical Reports Server (NTRS)

Abreu, V. J.; Hays, P. B.; Yee, J. H.

1982-01-01

Galactic and zodiacal light surface maps based on the Atmosphere Explorer-C, -D, and -E satellite data are presented at 7320, 6300, 5577, 5200, and 4278 A. A procedure used to generate these maps, which involves separation of the individual stars and diffuse starlight from the zodiacal light, is described in detail. The maps can be used in atmospheric emission studies to correct for galactic emissions which contaminate satellite as well as ground-based photometric observations. The zodiacal light maps show enhanced features which are important for understanding the nature of interplanetary dust.

Pioneer 10 observations of zodiacal light brightness near the ecliptic - Changes with heliocentric distance

NASA Technical Reports Server (NTRS)

Hanner, M. S.; Weinberg, J. L.; Beeson, D. E.; Sparrow, J. G.

1976-01-01

Sky maps made by the Pioneer 10 Imaging Photopolarimeter (IPP) at sun-spacecraft distances from 1 to 3 AU have been analyzed to derive the brightness of the zodiacal light near the ecliptic at elongations greater than 90 degrees. The change in zodiacal light brightness with heliocentric distance is compared with models of the spatial distribution of the dust. Use of background starlight brightnesses derived from IPP measurements beyond the asteroid belt, where the zodiacal light is not detected, and, especially, use of a corrected calibration lead to considerably lower values for zodiacal light than those reported by us previously.

Unraveling the Mystery of Exozodiacal Dust

NASA Astrophysics Data System (ADS)

Ertel, S.; Augereau, J.-C.; Thébault, P.; Absil, O.; Bonsor, A.; Defrère, D.; Kral, Q.; Le Bouquin, J.-B.; Lebreton, J.; Coudé du Foresto, V.

2014-01-01

Exozodiacal dust clouds are thought to be the extrasolar analogs of the Solar System's zodiacal dust. Studying these systems provides insights in the architecture of the innermost regions of planetary systems, including the Habitable Zone. Furthermore, the mere presence of the dust may result in major obstacles for direct imaging of earth-like planets. Our EXOZODI project aims to detect and study exozodiacal dust and to explain its origin. We are carrying out the first large, near-infrared interferometric survey in the northern (CHARA/FLUOR) and southern (VLTI/PIONIER) hemispheres. Preliminary results suggest a detection rate of up to 30% around A to K type stars and interesting trends with spectral type and age. We focus here on presenting the observational work carried out by our team.

Zodiac II: Debris Disk Science from a Balloon

NASA Technical Reports Server (NTRS)

Bryden, Geoffrey; Traub, Wesley; Roberts, Lewis C., Jr.; Bruno, Robin; Unwin, Stephen; Backovsky, Stan; Brugarolas, Paul; Chakrabarti, Supriya; Chen, Pin; Hillenbrand, Lynne;

Zodiac II: Debris Disk Science from a Balloon

NASA Technical Reports Server (NTRS)

Bryden, Geoffrey; Traub, Wesley; Roberts, Lewis C., Jr.; Bruno, Robin; Unwin, Stephen; Backovsky, Stan; Brugarolas, Paul; Chakrabarti, Supriya; Chen, Pin; Hillenbrand, Lynne;

Parameterization of cloud glaciation by atmospheric dust

NASA Astrophysics Data System (ADS)

Nickovic, Slobodan; Cvetkovic, Bojan; Madonna, Fabio; Pejanovic, Goran; Petkovic, Slavko

2016-04-01

The exponential growth of research interest on ice nucleation (IN) is motivated, inter alias, by needs to improve generally unsatisfactory representation of cold cloud formation in atmospheric models, and therefore to increase the accuracy of weather and climate predictions, including better forecasting of precipitation. Research shows that mineral dust significantly contributes to cloud ice nucleation. Samples of residual particles in cloud ice crystals collected by aircraft measurements performed in the upper tropopause of regions distant from desert sources indicate that dust particles dominate over other known ice nuclei such as soot and biological particles. In the nucleation process, dust chemical aging had minor effects. The observational evidence on IN processes has substantially improved over the last decade and clearly shows that there is a significant correlation between IN concentrations and the concentrations of coarser aerosol at a given temperature and moisture. Most recently, due to recognition of the dominant role of dust as ice nuclei, parameterizations for immersion and deposition icing specifically due to dust have been developed. Based on these achievements, we have developed a real-time forecasting coupled atmosphere-dust modelling system capable to operationally predict occurrence of cold clouds generated by dust. We have been thoroughly validated model simulations against available remote sensing observations. We have used the CNR-IMAA Potenza lidar and cloud radar observations to explore the model capability to represent vertical features of the cloud and aerosol vertical profiles. We also utilized the MSG-SEVIRI and MODIS satellite data to examine the accuracy of the simulated horizontal distribution of cold clouds. Based on the obtained encouraging verification scores, operational experimental prediction of ice clouds nucleated by dust has been introduced in the Serbian Hydrometeorological Service as a public available product.

Radar Detectability Studies of Slow and Small Zodiacal Dust Cloud Particles. III. The Role of Sodium and the Head Echo Size on the Probability of Detection

NASA Astrophysics Data System (ADS)

Janches, D.; Swarnalingam, N.; Carrillo-Sanchez, J. D.; Gomez-Martin, J. C.; Marshall, R.; Nesvorný, D.; Plane, J. M. C.; Feng, W.; Pokorný, P.

2017-07-01

We present a path forward on a long-standing issue concerning the flux of small and slow meteoroids, which are believed to be the dominant portion of the incoming meteoric mass flux into the Earth’s atmosphere. Such a flux, which is predicted by dynamical dust models of the Zodiacal Cloud, is not evident in ground-based radar observations. For decades this was attributed to the fact that the radars used for meteor observations lack the sensitivity to detect this population, due to the small amount of ionization produced by slow-velocity meteors. Such a hypothesis has been challenged by the introduction of meteor head echo (HE) observations with High Power and Large Aperture radars, in particular the Arecibo 430 MHz radar. Janches et al. developed a probabilistic approach to estimate the detectability of meteors by these radars and initially showed that, with the current knowledge of ablation and ionization, such particles should dominate the detected rates by one to two orders of magnitude compared to the actual observations. In this paper, we include results in our model from recently published laboratory measurements, which showed that (1) the ablation of Na is less intense covering a wider altitude range; and (2) the ionization probability, {β }{ip}, for Na atoms in the air is up to two orders of magnitude smaller for low speeds than originally believed. By applying these results and using a somewhat smaller size of the HE radar target we offer a solution that reconciles these observations with model predictions.

Radar Detectability Studies of Slow and Small Zodiacal Dust Cloud Particles. III. The Role of Sodium and the Head Echo Size on the Probability of Detection

NASA Technical Reports Server (NTRS)

Janches, D.; Swarnalingam, N.; Carrillo-Sanchez, J. D.; Gomez-Martin, J. C.; Marshall, R.; Nesvorny, D.; Plane, J. M. C.; Feng, W.; Pokorny, P.

2017-01-01

We present a path forward on a long-standing issue concerning the flux of small and slow meteoroids, which are believed to be the dominant portion of the incoming meteoric mass flux into the Earth's atmosphere. Such a flux, which is predicted by dynamical dust models of the Zodiacal Cloud, is not evident in ground-based radar observations. For decades this was attributed to the fact that the radars used for meteor observations lack the sensitivity to detect this population, due to the small amount of ionization produced by slow-velocity meteors. Such a hypothesis has been challenged by the introduction of meteor head echo (HE) observations with High Power and Large Aperture radars, in particular the Arecibo 430 MHz radar. Janches et al. developed a probabilistic approach to estimate the detectability of meteors by these radars and initially showed that, with the current knowledge of ablation and ionization, such particles should dominate the detected rates by one to two orders of magnitude compared to the actual observations. In this paper, we include results in our model from recently published laboratory measurements, which showed that (1) the ablation of Na is less intense covering a wider altitude range; and (2) the ionization probability, Beta ip, for Na atoms in the air is up to two orders of magnitude smaller for low speeds than originally believed. By applying these results and using a somewhat smaller size of the HE radar target we offer a solution that reconciles these observations with model predictions.

The Zodiacal Cloud Model applied to the Martian atmosphere. Diurnal variations in meteoric ion layers

NASA Astrophysics Data System (ADS)

Carrillo-Sánchez, J. D.; Plane, J. M. C.; Withers, P.; Fallows, K.; Nesvorny, D.; Pokorný, P.

2016-12-01

Sporadic metal layers have been detected in the Martian atmosphere by radio occultation measurements using the Mars Express Orbiter and Mars Global Surveyor spacecraft. More recently, metallic ion layers produced by the meteor storm event following the close encounter between Comet Siding Spring (C/2013 A1) and Mars were identified by the Imaging UltraViolet Spectrograph (IUVS) and the Neutral Gas and Ion Mass Spectrometer (NGIMS) on the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. Work is now in progress to detect the background metal layers produced by the influx of sporadic meteors. In this study we predict the likely appearance of these layers. The Zodiacal Dust Cloud (ZDC) model for particle populations released by asteroids (AST), and dust grains from Jupiter Family Comets (JFCs) and Halley-Type Comets (HTCs) has been combined with a Monte Carlo sampling method and the Chemical ABlation MODel (CABMOD) to predict the ablation rates of Na, K, Fe, Si, Mg, Ca and Al above 40 km altitude in the Martian atmosphere. CABMOD considers the standard treatment of meteor physics, including the balance of frictional heating by radiative losses and the absorption of heat energy through temperature increases, melting phase transitions and vaporization, as well as sputtering by inelastic collisions with the air molecules. The vertical injection profiles are input into the Leeds 1-D Mars atmospheric model which includes photo-ionization, and gas-phase ion-molecule and neutral chemistry, in order to explore the evolution of the resulting metallic ions and atoms. We conclude that the dominant contributor in the Martian's atmosphere is the JFCs over other sources. Finally, we explore the changes of the neutral and ionized Na, Mg and Fe layers over a diurnal cycle.

Clouds and Dust Storms

NASA Technical Reports Server (NTRS)

2004-01-01

[figure removed for brevity, see original site]

Released 2 July 2004 The atmosphere of Mars is a dynamic system. Water-ice clouds, fog, and hazes can make imaging the surface from space difficult. Dust storms can grow from local disturbances to global sizes, through which imaging is impossible. Seasonal temperature changes are the usual drivers in cloud and dust storm development and growth.

Eons of atmospheric dust storm activity has left its mark on the surface of Mars. Dust carried aloft by the wind has settled out on every available surface; sand dunes have been created and moved by centuries of wind; and the effect of continual sand-blasting has modified many regions of Mars, creating yardangs and other unusual surface forms.

This image was acquired during mid-spring near the North Pole. The linear water-ice clouds are now regional in extent and often interact with neighboring cloud system, as seen in this image. The bottom of the image shows how the interaction can destroy the linear nature. While the surface is still visible through most of the clouds, there is evidence that dust is also starting to enter the atmosphere.

Image information: VIS instrument. Latitude 68.4, Longitude 180 East (180 West). 38 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

Sources of cosmic dust in the Earth's atmosphere

NASA Astrophysics Data System (ADS)

Carrillo-Sánchez, J. D.; Nesvorný, D.; Pokorný, P.; Janches, D.; Plane, J. M. C.

2016-12-01

There are four known sources of dust in the inner solar system: Jupiter Family comets, asteroids, Halley Type comets, and Oort Cloud comets. Here we combine the mass, velocity, and radiant distributions of these cosmic dust populations from an astronomical model with a chemical ablation model to estimate the injection rates of Na and Fe into the Earth's upper atmosphere, as well as the flux of cosmic spherules to the surface. Comparing these parameters to lidar observations of the vertical Na and Fe fluxes above 87.5 km, and the measured cosmic spherule accretion rate at South Pole, shows that Jupiter Family Comets contribute (80 ± 17)% of the total input mass (43 ± 14 t d-1), in good accord with Cosmic Background Explorer and Planck observations of the zodiacal cloud.

On the Effect of Dust Particles on Global Cloud Condensation Nuclei and Cloud Droplet Number

NASA Technical Reports Server (NTRS)

Karydis, V. A.; Kumar, P.; Barahona, D.; Sokolik, I. N.; Nenes, A.

2011-01-01

Aerosol-cloud interaction studies to date consider aerosol with a substantial fraction of soluble material as the sole source of cloud condensation nuclei (CCN). Emerging evidence suggests that mineral dust can act as good CCN through water adsorption onto the surface of particles. This study provides a first assessment of the contribution of insoluble dust to global CCN and cloud droplet number concentration (CDNC). Simulations are carried out with the NASA Global Modeling Initiative chemical transport model with an online aerosol simulation, considering emissions from fossil fuel, biomass burning, marine, and dust sources. CDNC is calculated online and explicitly considers the competition of soluble and insoluble CCN for water vapor. The predicted annual average contribution of insoluble mineral dust to CCN and CDNC in cloud-forming areas is up to 40 and 23.8%, respectively. Sensitivity tests suggest that uncertainties in dust size distribution and water adsorption parameters modulate the contribution of mineral dust to CDNC by 23 and 56%, respectively. Coating of dust by hygroscopic salts during the atmospheric aging causes a twofold enhancement of the dust contribution to CCN; the aged dust, however, can substantially deplete in-cloud supersaturation during the initial stages of cloud formation and can eventually reduce CDNC. Considering the hydrophilicity from adsorption and hygroscopicity from solute is required to comprehensively capture the dust-warm cloud interactions. The framework presented here addresses this need and can be easily integrated in atmospheric models.

Understanding Asteroid Disruptions Using Very Young Dust Bands

NASA Astrophysics Data System (ADS)

Espy Kehoe, Ashley J.; Kehoe, T. J.; Colwell, J. E.; Dermott, S. F.

2013-10-01

Zodiacal dust bands are structures that result from the dynamical sculpting of the dust particles released in the catastrophic disruption of an asteroid. Partial dust bands are the recently discovered younger siblings of the dust bands, ones that are still forming and due to very recent disruptions within the last few hundred thousand years. During the early stages of formation, these structures retain information on the original catastrophic disruptions that produced them (since the dust has not yet been lost or significantly altered by orbital or collisional decay). The first partial dust band, at about 17 degrees latitude, was revealed using a very precise method of co-adding the IRAS data set. We have shown that these partial dust bands exhibit structure consistent with a forming band, can be used to constrain the original size distribution of the dust produced in the catastrophic disruption of an asteroid, and these very young structures also allow a much better estimate of the total amount of dust released in the disruption. In order to interpret the observations and constrain the parameters of the dust injected into the cloud following an asteroid disruption, we have developed detailed models of the dynamical evolution of the dust that makes up the band. We model the dust velocity distribution resulting from the initial impact and then track the orbital evolution of the dust under the effects of gravitational perturbations from all the planets as well as radiative forces of Poynting-Robertson drag, solar wind drag and radiation pressure and use these results to produce maps of the thermal emission. Through the comparison of our newly completed dynamical evolution models with the coadded observations, we can put constraints on the parameters of dust producing the band. We confirm the source of the band as the very young Emilkowalski cluster ( <250,000 years; Nesvorny et al., 2003) and present our most recent estimates of the size-distribution and cross

Cloud Ozone Dust Imager (CODI)

NASA Astrophysics Data System (ADS)

Clancy, R. Todd; Dusenbery, Paul; Wolff, Michael; James, Phil; Allen, Mark; Goguen, Jay; Kahn, Ralph; Gladstone, Rany; Murphy, Jim

1995-01-01

The Cloud Ozone Dust Imager (CODI) is proposed to investigate the current climatic balance of the Mars atmosphere, with particular emphasis on the important but poorly understood roles which dust and water ice aerosols play in this balance. The large atmospheric heating (20-50 K) resulting from global dust storms around Mars perihelion is well recognized. However, groundbased observations of Mars atmospheric temperatures, water vapor, and clouds since the Viking missions have identified a much colder, cloudier atmosphere around Mars aphelion that may prove as important as global dust storms in determining the interannual and long-term behavior of the Mars climate. The key climate issues CODI is designed to investigate are: 1) the degree to which non-linear interactions between atmospheric dust heating, water vapor saturation, and cloud nucleation influence the seasonal and interannual variability of the Mars atmosphere, and 2) whether the strong orbital forcing of atmospheric dust loading, temperatures and water vapor saturation determines the long-term balance of Mars water, as reflected in the north-south hemispheric asymmetries of atmospheric water vapor and polar water ice abundances. The CODI experiment will measure the daily, seasonal and (potentially) interannual variability of atmospheric dust and cloud opacities, and the key physical properties of these aerosols which determine their role in the climate cycles of Mars. CODI is a small (1.2 kg), fixed pointing camera, in which four wide-angle (+/- 70 deg) lenses illuminate fixed filters and CCD arrays. Simultaneous sky/surface imaging of Mars is obtained at an angular resolution of 0.28 deg/pixel for wavelengths of 255, 336, 502, and 673 nm (similar to Hubble Space Telescope filters). These wavelengths serve to measure atmospheric ozone (255 and 336 nm), discriminate ice and dust aerosols (336 and 673 nm), and construct color images (336, 502, and 673 nm). The CODI images are detected on four 512 x 512

Simulation of Asia Dust and Cloud Interaction Over Pacific Ocean During Pacdex

NASA Astrophysics Data System (ADS)

Long, X.; Huang, J.; Cheng, C.; Wang, W.

2007-12-01

The effect of dust plume on the Pacific cloud systems and the associated radiative forcing is an outstanding problem for understanding climate change. Many studies showing that dust aerosol might be a good absorber for solar radiation, at the same time dust aerosols could affect the cloud's formation and precipitation by its capability as cloud condensation nuclei (CCN) and ice forming nuclei (IFN). But the role of aerosols in clouds and precipitation is very complex. Simulation of interaction between cloud and dust aerosols requires recognition that the aerosol cloud system comprises coupled components of dynamics, aerosol and cloud microphysics, radiation processes. In this study, we investigated the interaction between dust aerosols and cloud with WRF which coupled with detailed cloud microphysics processes and dust process. The observed data of SACOL (Semi-Arid Climate and Environment Observatory of Lanzhou University) and PACDEX (Pacific Dust Experiment) is used as the initialization which include the vertical distributions and concentration of dust particles. Our results show that dust aerosol not only impacts cloud microphysical processes but also cloud microstructure; Dust aerosols can act as effective ice nuclei and intensify the ice-forming processes.

Sources of cosmic dust in the Earth's atmosphere.

PubMed

Carrillo-Sánchez, J D; Nesvorný, D; Pokorný, P; Janches, D; Plane, J M C

2016-12-16

There are four known sources of dust in the inner solar system: Jupiter Family comets, asteroids, Halley Type comets, and Oort Cloud comets. Here we combine the mass, velocity, and radiant distributions of these cosmic dust populations from an astronomical model with a chemical ablation model to estimate the injection rates of Na and Fe into the Earth's upper atmosphere, as well as the flux of cosmic spherules to the surface. Comparing these parameters to lidar observations of the vertical Na and Fe fluxes above 87.5 km, and the measured cosmic spherule accretion rate at South Pole, shows that Jupiter Family Comets contribute (80 ± 17)% of the total input mass (43 ± 14 t d -1 ), in good accord with Cosmic Background Explorer and Planck observations of the zodiacal cloud.

Sources of cosmic dust in the Earth's atmosphere

PubMed Central

Carrillo‐Sánchez, J. D.; Nesvorný, D.; Pokorný, P.; Janches, D.

2016-01-01

Abstract There are four known sources of dust in the inner solar system: Jupiter Family comets, asteroids, Halley Type comets, and Oort Cloud comets. Here we combine the mass, velocity, and radiant distributions of these cosmic dust populations from an astronomical model with a chemical ablation model to estimate the injection rates of Na and Fe into the Earth's upper atmosphere, as well as the flux of cosmic spherules to the surface. Comparing these parameters to lidar observations of the vertical Na and Fe fluxes above 87.5 km, and the measured cosmic spherule accretion rate at South Pole, shows that Jupiter Family Comets contribute (80 ± 17)% of the total input mass (43 ± 14 t d−1), in good accord with Cosmic Background Explorer and Planck observations of the zodiacal cloud. PMID:28275286

Dust Cloud, Mid Atlantic Ocean

NASA Technical Reports Server (NTRS)

1991-01-01

This view of a dust cloud from a Sahara Desert, North Africa dust storm was taken over the Mid Atlantic Ocean, some 1700 miles from the African coast (24.5N, 45.0W). Dust, sand and other particulate matter from arid regions is frequently stirred up by fast blowing desert winds and carried aloft to high altitudes where it may be transported great distances, sometimes as much as half way around the world.

CALIPSO Observations of Transatlantic Dust: Vertical Stratification and Effect of Clouds

NASA Technical Reports Server (NTRS)

Yang, Weidong; Marshak, Alexander; Varnai, Tamas; Kalashnikova, Olga V.; Kostinski, Alexander B.

2014-01-01

We use CALIOP nighttime measurements of lidar backscatter, color and depolarization ratios, as well as particulate retrievals during the summer of 2007 to study transatlantic dust properties downwind of Saharan sources, and to examine the influence of nearby clouds on dust. Our analysis suggests that (1) under clear skies, while lidar backscatter and color ratio do not change much with altitude and longitude in the Saharan Air Layer (SAL), depolarization ratio increases with altitude and decreases westward in the SAL (2) the vertical lapse rate of dust depolarization ratio, introduced here, increases within SAL as plumes move westward (3) nearby clouds barely affect the backscatter and color ratio of dust volumes within SAL but not so below SAL. Moreover, the presence of nearby clouds tends to decrease the depolarization of dust volumes within SAL. Finally, (4) the odds of CALIOP finding dust below SAL next to clouds are about of those far away from clouds. This feature, together with an apparent increase in depolarization ratio near clouds, indicates that particles in some dust volumes loose asphericity in the humid air near clouds, and cannot be identified by CALIPSO as dust.

The dust cloud of the century

NASA Astrophysics Data System (ADS)

Robock, A.

1983-02-01

The structure and composition of the dust cloud from the 4 April 1982 eruption of the El Chichon volcano in Chiapas state, Mexico, is examined and the possible effects of the dust cloud on the world's weather patterns are discussed. Observations of the cloud using a variety of methods are evaluated, including data from the GOES and NOAA-7 weather satellites, vertically pointing lidar measurements, the SME satellite, and the Nimbus-7 satellite. Studies of the gaseous and particulate composition of the cloud reveal the presence of large amounts of sulfuric acid particles, which have a long mean residence time in the atmosphere and have a large effect on the amount of solar radiation received at the earth's surface by scattering several percent of the radiation back to space. Estimates of the effect of this cloud on surface air temperature changes are presented based on findings from climate models.

Dust scattering from the Taurus Molecular Cloud

NASA Astrophysics Data System (ADS)

Narayan, Sathya; Murthy, Jayant; Karuppath, Narayanankutty

2017-04-01

We present an analysis of the diffuse ultraviolet emission near the Taurus Molecular Cloud based on observations made by the Galaxy Evolution Explorer. We used a Monte Carlo dust scattering model to show that about half of the scattered flux originates in the molecular cloud with 25 per cent arising in the foreground and 25 per cent behind the cloud. The best-fitting albedo of the dust grains is 0.3, but the geometry is such that we could not constrain the phase function asymmetry factor (g).

CALIPSO Observations of Transatlantic Dust: Vertical Stratification and Effect of Clouds

NASA Technical Reports Server (NTRS)

Yang, Weidong; Marshak, Alexander; Varnai, Tamas; Kalashnikova, Olga V.; Kostinski, Alexander B.

2012-01-01

CALIOP nighttime measurements of lidar backscatter, color and depolarization ratios during the summer of 2007 are used to study transatlantic dust properties downwind of Saharan sources, and to examine the interaction of clouds and dust. We discuss the following findings: (1) while lidar backscatter doesn't change much with altitude in the Saharan Air Layer (SAL), depolarization and color ratios both increase with altitude in the SAL; (2) lidar backscatter and color ratio increase as dust is transported westward in the SAL; (3) the vertical lapse rate of dust depolarization ratio increases within SAL as plumes move westward; (4) nearby clouds barely affect the backscatter and color ratio of dust volumes within SAL but not so below SAL. Finally, (5) the odds of CALIOP finding dust below SAL next to clouds are about 2/3 of those far away from clouds. This feature, together with an apparent increase in depolarization ratio near clouds, indicates that particles in some dusty volumes lose asphericity in the humid air near clouds, and cannot be identified by CALIPSO as dust.

Evidence of Mineral Dust Altering Cloud Microphysics and Precipitation

NASA Technical Reports Server (NTRS)

Min, Qilong; Li, Rui; Lin, Bing; Joseph, Everette; Wang, Shuyu; Hu, Yongxiang; Morris, Vernon; Chang, F.

2008-01-01

Multi-platform and multi-sensor observations are employed to investigate the impact of mineral dust on cloud microphysical and precipitation processes in mesoscale convective systems. It is clearly evident that for a given convection strength,small hydrometeors were more prevalent in the stratiform rain regions with dust than in those regions that were dust free. Evidence of abundant cloud ice particles in the dust sector, particularly at altitudes where heterogeneous nucleation process of mineral dust prevails, further supports the observed changes of precipitation. The consequences of the microphysical effects of the dust aerosols were to shift the precipitation size spectrum from heavy precipitation to light precipitation and ultimately suppressing precipitation.

Experiment S001: Zodiacal Light Photography

NASA Technical Reports Server (NTRS)

Ney, E. P.; Huch, W. F.

1971-01-01

Observations made during the Gemini 5, 9, and 10 missions in the context of their relation to ground-based and balloon-based experiments on dim-light phenomena are reported. Zodiacal light is the visible manifestation of dust grains in orbit around the sun. The negatives that were exposed on the Gemini 9 mission were studied by the use of an isodensitracer to produce intensity isophotes. Data on the following factors were obtained: (1) intensity distribution of the zodiacal light, both morning and evening; (2) the height and intensity of the airglow at various geographic positions; and (3) intensity distribution of the Milky Way in the region of the sky near Cygnus. Also, a previously unreported phenomenon was discovered. This phenomenon appeared as an upward extension of the normal 90-kilometer airglow layer. The extension was in the form of wisps or plumes approximately 5 deg wide and extending upward approximately 5 deg. The results obtained from pictures exposed on the Gemini 10 mission were of qualitative or geometrical value only.

The global impact of mineral dust on cloud droplet number concentration

NASA Astrophysics Data System (ADS)

Karydis, V.; Tsimpidi, A.; Bacer, S.; Pozzer, A.; Nenes, A.; Lelieveld, J.

2016-12-01

This study assesses the importance of mineral dust for cloud droplet formation by taking into account i) the adsorption of water on the surface of insoluble dust particles, ii) the coating of soluble material on the surface of mineral particles which augments their cloud condensation nuclei activity, and iii) the effect of dust on the inorganic aerosol concentrations through thermodynamic interactions with mineral cations. Simulations are carried out with the EMAC chemistry climate model that calculates the global atmospheric aerosol composition using the ISORROPIA-II thermodynamic equilibrium model and considers the gas phase interactions with K+-Ca2+-Mg2+-NH4+-Na+-SO42-NO3-Cl-H2O particle components. Emissions of the inert mineral dust and the reactive dust aerosol components are calculated online by taking into account the soil particle size distribution and chemical composition of different deserts worldwide (Karydis et al., 2016). We have implemented the "unified dust activation parameterization" (Kumar et al., 2011; Karydis et al., 2011) to calculate the droplet number concentration by taking into account the inherent hydrophilicity from adsorption and the acquired hygroscopicity from soluble salts by dust particles. Our simulations suggest that mineral dust significantly increases the cloud droplet number concentration (CDNC) over the main deserts and the adjacent oceans. However, over polluted areas the CDNC decreases significantly in the presence of dust. Furthermore, we investigate the role of adsorption activation of insoluble aerosols and the mineral dust thermodynamic interactions with inorganic anions on the cloud droplet formation. The CDNC sensitivity to the emission load, chemical composition, and inherent hydrophilicity of mineral dust is also tested. ReferencesKarydis, et al. (2011). "On the effect of dust particles on global cloud condensation nuclei and cloud droplet number." J. Geophys. Res. Atmos. 116. Karydis, et al. (2016). "Effects of

Inner mean-motion resonances with eccentric planets: a possible origin for exozodiacal dust clouds

NASA Astrophysics Data System (ADS)

Faramaz, V.; Ertel, S.; Booth, M.; Cuadra, J.; Simmonds, C.

2017-02-01

High levels of dust have been detected in the immediate vicinity of many stars, both young and old. A promising scenario to explain the presence of this short-lived dust is that these analogues to the zodiacal cloud (or exozodis) are refilled in situ through cometary activity and sublimation. As the reservoir of comets is not expected to be replenished, the presence of these exozodis in old systems has yet to be adequately explained. It was recently suggested that mean-motion resonances with exterior planets on moderately eccentric (ep ≳ 0.1) orbits could scatter planetesimals on to cometary orbits with delays of the order of several 100 Myr. Theoretically, this mechanism is also expected to sustain continuous production of active comets once it has started, potentially over Gyr time-scales. We aim here to investigate the ability of this mechanism to generate scattering on to cometary orbits compatible with the production of an exozodi on long time-scales. We combine analytical predictions and complementary numerical N-body simulations to study its characteristics. We show, using order of magnitude estimates, that via this mechanism, low-mass discs comparable to the Kuiper belt could sustain comet scattering at rates compatible with the presence of the exozodis which are detected around Solar-type stars, and on Gyr time-scales. We also find that the levels of dust detected around Vega could be sustained via our proposed mechanism if an eccentric Jupiter-like planet were present exterior to the system's cold debris disc.

IDE spatio-temporal impact fluxes and high time-resolution studies of multi-impact events and long-lived debris clouds

NASA Technical Reports Server (NTRS)

Mulholland, J. Derral; Singer, S. Fred; Oliver, John P.; Weinberg, Jerry L.; Cooke, William J.; Montague, Nancy L.; Wortman, Jim J.; Kassel, Phillip C.; Kinard, William H.

1992-01-01

The purpose of the Interplanetary Dust Experiment (IDE) on the Long Duration Exposure Facility (LDEF) was to sample the cosmic dust environment and to use the spatio-temporal aspect of the experiment to distinguish between the various components of the environment: zodiacal cloud, beta meteoroids, meteor streams, interstellar dust, and orbital debris. It was found that the introduction of precise time and even rudimentary directionality as co-lateral observables in sampling the particulate environment in near-Earth space produces an enormous qualitative improvement in the information content of the impact data. The orbital debris population is extremely clumpy, being dominated by persistent clouds in which the fluxes may rise orders of magnitude above the background. The IDE data suggest a strategy to minimize the damage to sensitive spacecraft components, using the observed characteristics of cloud encounters.

Large Interstellar Polarisation Survey. II. UV/optical study of cloud-to-cloud variations of dust in the diffuse ISM

NASA Astrophysics Data System (ADS)

Siebenmorgen, R.; Voshchinnikov, N. V.; Bagnulo, S.; Cox, N. L. J.; Cami, J.; Peest, C.

2018-03-01

It is well known that the dust properties of the diffuse interstellar medium exhibit variations towards different sight-lines on a large scale. We have investigated the variability of the dust characteristics on a small scale, and from cloud-to-cloud. We use low-resolution spectro-polarimetric data obtained in the context of the Large Interstellar Polarisation Survey (LIPS) towards 59 sight-lines in the Southern Hemisphere, and we fit these data using a dust model composed of silicate and carbon particles with sizes from the molecular to the sub-micrometre domain. Large (≥6 nm) silicates of prolate shape account for the observed polarisation. For 32 sight-lines we complement our data set with UVES archive high-resolution spectra, which enable us to establish the presence of single-cloud or multiple-clouds towards individual sight-lines. We find that the majority of these 35 sight-lines intersect two or more clouds, while eight of them are dominated by a single absorbing cloud. We confirm several correlations between extinction and parameters of the Serkowski law with dust parameters, but we also find previously undetected correlations between these parameters that are valid only in single-cloud sight-lines. We find that interstellar polarisation from multiple-clouds is smaller than from single-cloud sight-lines, showing that the presence of a second or more clouds depolarises the incoming radiation. We find large variations of the dust characteristics from cloud-to-cloud. However, when we average a sufficiently large number of clouds in single-cloud or multiple-cloud sight-lines, we always retrieve similar mean dust parameters. The typical dust abundances of the single-cloud cases are [C]/[H] = 92 ppm and [Si]/[H] = 20 ppm.

How large is the cosmic dust flux into the Earth's atmosphere?

NASA Astrophysics Data System (ADS)

Plane, John; Janches, Diego; Gomez-Martin, Juan Carlos; Bones, David; Diego Carrillo-Sanchez, Juan; James, Sandy; Nesvorny, David; Pokorny, Petr

2016-07-01

Cosmic dust particles are produced in the solar system from the sublimation of comets as they orbit close to the sun, and also from collisions between asteroids in the belt between Mars and Jupiter. Current estimates of the magnitude of the cosmic dust input rate into the Earth's atmosphere range from 2 to well over 100 tons per day, depending on whether the measurements are made in space, in the middle atmosphere, or at the surface in polar ice cores. This nearly 2 order-of-magnitude discrepancy indicates that there are serious flaws in the interpretation of observations that have been used to make the estimates. Dust particles enter the atmosphere at hyperthermal velocities (11 - 72 km s ^{-1}), and mostly ablate at heights between 80 and 120 km in a region of the atmosphere known as the mesosphere/lower thermosphere (MLT). The resulting metal vapours (Fe, Mg, Si and Na etc.) then oxidize and recondense to form nm-size particles, termed "meteoric smoke". These particles are too small to sediment downwards. Instead, they are transported by the general circulation of the atmosphere, taking roughly 5 years to reach the surface. There is great interest in the role smoke particles play as condensation nuclei of noctilucent ice clouds in the mesosphere, and polar stratospheric clouds in the lower stratosphere. Various new estimates of the dust input will be discussed. The first is from a zodiacal dust cloud model which predicts that more than 90% of the dust entering the atmosphere comes from Jupiter Family Comets; this model is constrained by observations of the zodiacal cloud using the IRAS, COBE and Planck satellites. The cometary dust is predicted to mostly be in a near-prograde orbit, entering the atmosphere with an average velocity around 14 km s ^{-1}. The total dust input should then be about 40 t d ^{-1}. However, relatively few of these particles are observed, even by the powerful Arecibo 430 MHz radar. Coupled models of meteoroid differential ablation

Influence of Saharan dust on cloud glaciation in southern Morocco during the Saharan Mineral Dust Experiment

NASA Astrophysics Data System (ADS)

Ansmann, A.; Tesche, M.; Althausen, D.; Müller, D.; Seifert, P.; Freudenthaler, V.; Heese, B.; Wiegner, M.; Pisani, G.; Knippertz, P.; Dubovik, O.

2008-02-01

Multiwavelength lidar, Sun photometer, and radiosonde observations were conducted at Ouarzazate (30.9°N, 6.9°W, 1133 m above sea level, asl), Morocco, in the framework of the Saharan Mineral Dust Experiment (SAMUM) in May-June 2006. The field site is close to the Saharan desert. Information on the depolarization ratio, backscatter and extinction coefficients, and lidar ratio of the dust particles, estimates of the available concentration of atmospheric ice nuclei at cloud level, profiles of temperature, humidity, and the horizontal wind vector as well as backward trajectory analysis are used to study cases of cloud formation in the dust with focus on heterogeneous ice formation. Surprisingly, most of the altocumulus clouds that form at the top of the Saharan dust layer, which reaches into heights of 4-7 km asl and has layer top temperatures of -8°C to -18°C, do not show any ice formation. According to the lidar observations the presence of a high number of ice nuclei (1-20 cm-3) does not automatically result in the obvious generation of ice particles, but the observations indicate that cloud top temperatures must typically reach values as low as -20°C before significant ice production starts. Another main finding is that liquid clouds are obviously required before ice crystals form via heterogeneous freezing mechanisms, and, as a consequence, that deposition freezing is not an important ice nucleation process. An interesting case with cloud seeding in the free troposphere above the dust layer is presented in addition. Small water clouds formed at about -30°C and produced ice virga. These virga reached water cloud layers several kilometers below the initiating cloud cells and caused strong ice production in these clouds at temperatures as high as -12°C to -15°C.

Agglomeration of dust in convective clouds initialized by nuclear bursts

NASA Astrophysics Data System (ADS)

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

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

Assessment of dust aerosol effect on cloud properties over Northwest China using CERES SSF data

NASA Astrophysics Data System (ADS)

Huang, J.; Wang, X.; Wang, T.; Su, J.; Minnis, P.; Lin, B.; Hu, Y.; Yi, Y.

Dust aerosols not only have direct effects on the climate through reflection and absorption of the short and long wave radiation but also modify cloud properties such as the number concentration and size of cloud droplets indirect effect and contribute to diabatic heating in the atmosphere that often enhances cloud evaporation and reduces the cloud water path In this study indirect and semi-direct effects of dust aerosols are analyzed over eastern Asia using two years June 2002 to June 2004 of CERES Clouds and the Earth s Radiant Energy Budget Scanner and MODIS MODerate Resolution Imaging Spectroradiometer Aqua Edition 1B SSF Single Scanner Footprint data sets The statistical analysis shows evidence for both indirect and semi-direct effect of Asia dust aerosols The dust appears to reduce the ice cloud effective particle diameter and increase high cloud amount On average ice cloud effective particle diameters of cirrus clouds under dust polluted conditions dusty cloud are 11 smaller than those derived from ice clouds in dust-free atmospheric environments The water paths of dusty clouds are also considerably smaller than those of dust-free clouds Dust aerosols could warm clouds thereby increasing the evaporation of cloud droplets resulting in reduced cloud water path semi-direct effect The semi-direct effect may be dominated the interaction between dust aerosols and clouds over arid and semi-arid areas and partly contribute to reduced precipitation

Saharan Dust Event Impacts on Cloud Formation and Radiation over Western Europe

NASA Technical Reports Server (NTRS)

Bangert, M.; Nenes, A.; Vogel, B.; Vogel, H.; Barahona, D.; Karydis, V. A.; Kumar, P.; Kottmeier, C.; Blahak, U.

2013-01-01

We investigated the impact of mineral dust particles on clouds, radiation and atmospheric state during a strong Saharan dust event over Europe in May 2008, applying a comprehensive online-coupled regional model framework that explicitly treats particle-microphysics and chemical composition. Sophisticated parameterizations for aerosol activation and ice nucleation, together with two-moment cloud microphysics are used to calculate the interaction of the different particles with clouds depending on their physical and chemical properties. The impact of dust on cloud droplet number concentration was found to be low, with just a slight increase in cloud droplet number concentration for both uncoated and coated dust. For temperatures lower than the level of homogeneous freezing, no significant impact of dust on the number and mass concentration of ice crystals was found, though the concentration of frozen dust particles reached up to 100 l-1 during the ice nucleation events. Mineral dust particles were found to have the largest impact on clouds in a temperature range between freezing level and the level of homogeneous freezing, where they determined the number concentration of ice crystals due to efficient heterogeneous freezing of the dust particles and modified the glaciation of mixed phase clouds. Our simulations show that during the dust events, ice crystals concentrations were increased twofold in this temperature range (compared to if dust interactions are neglected). This had a significant impact on the cloud optical properties, causing a reduction in the incoming short-wave radiation at the surface up to -75Wm-2. Including the direct interaction of dust with radiation caused an additional reduction in the incoming short-wave radiation by 40 to 80Wm-2, and the incoming long-wave radiation at the surface was increased significantly in the order of +10Wm-2. The strong radiative forcings associated with dust caused a reduction in surface temperature in the order of -0

Changes in Stratiform Clouds of Mesoscale Convective Complex Introduced by Dust Aerosols

NASA Technical Reports Server (NTRS)

Lin, B.; Min, Q.-L.; Li, R.

2010-01-01

Aerosols influence the earth s climate through direct, indirect, and semi-direct effects. There are large uncertainties in quantifying these effects due to limited measurements and observations of aerosol-cloud-precipitation interactions. As a major terrestrial source of atmospheric aerosols, dusts may serve as a significant climate forcing for the changing climate because of its effect on solar and thermal radiation as well as on clouds and precipitation processes. Latest satellites measurements enable us to determine dust aerosol loadings and cloud distributions and can potentially be used to reduce the uncertainties in the estimations of aerosol effects on climate. This study uses sensors on various satellites to investigate the impact of mineral dust on cloud microphysical and precipitation processes in mesoscale convective complex (MCC). A trans-Atlantic dust outbreak of Saharan origin occurring in early March 2004 is considered. For the observed MCCs under a given convective strength, small hydrometeors were found more prevalent in the dusty stratiform regions than in those regions that were dust free. Evidence of abundant cloud ice particles in the dust regions, particularly at altitudes where heterogeneous nucleation of mineral dust prevails, further supports the observed changes of clouds and precipitation. The consequences of the microphysical effects of the dust aerosols were to shift the size spectrum of precipitation-sized hydrometeors from heavy precipitation to light precipitation and ultimately to suppress precipitation and increase the lifecycle of cloud systems, especially over stratiform areas.

The temperature of large dust grains in molecular clouds

NASA Technical Reports Server (NTRS)

Clark, F. O.; Laureijs, R. J.; Prusti, T.

1991-01-01

The temperature of the large dust grains is calculated from three molecular clouds ranging in visual extinction from 2.5 to 8 mag, by comparing maps of either extinction derived from star counts or gas column density derived from molecular observations to I(100). Both techniques show the dust temperature declining into clouds. The two techniques do not agree in absolute scale.

Accretion of Interplanetary Dust Particles by the Earth

NASA Astrophysics Data System (ADS)

Kortenkamp, Stephen J.; Dermott, Stanley F.

1998-10-01

Analyses of hypervelocity micrometeoroid impact craters preserved in lunar material and on the panels of the Long Duration Exposure Facility (LDEF) indicate that each year Earth accretes about 3 × 107kg of interplanetary dust particles (IDPs) from the zodiacal cloud (E. Grünet al.1985,Astron. Astrophys.286, 915-924; S. G. Love and D. E. Brownlee, 1993,Science262, 550-553). The size distributions of these lunar and LDEF craters indicate that the mass distribution of IDPs encountering Earth peaks at about 200 μm diameter. This particle-size cutoff may be indicative of collisionally evolved asteroidal dust, where the collisional lifetime of dust particles larger than ∼100 μm is shorter than the time required for their orbits to decay under Poynting-Robertson light drag from the asteroid belt to Earth (B. Å. S. Gustafson, 1994,Annu. Rev. Earth Planet. Sci.22, 553-595). Additionally, analyses of IDPs collected from the stratosphere by high-flying aircraft reveal a diversity in chemical composition which is even narrower than that of the meteorites (G. J. Flynn, 1995,Nature376, 114). Together these findings suggest that IDPs present in the atmosphere and our collections may originate from very limited sources in the asteroid belt. The most abundant sources of dust to be unambiguously linked to the zodiacal cloud are the three asteroid families Eos, Themis, and Koronis-the progenitors of the ten-degree and low-latitude dust bands discovered by the Infrared Astronomical Satellite in 1984. We use direct numerical integration of the full equations of motion to model the orbital evolution of dust particles from these three families as well as from other nonfamily asteroids and from the population of known short period comets. Our simulations include gravitational perturbations from the planets, radiation pressure, and solar wind drag. We find that a large, and perhaps the dominant, fraction of the IDPs accreted by Earth comes from the asteroid families Eos, Themis, and

Atmospheric transport of mold spores in clouds of desert dust

USGS Publications Warehouse

Shinn, E.A.; Griffin, Dale W.; Seba, D.B.

2003-01-01

Fungal spores can be transported globally in clouds of desert dust. Many species of fungi (commonly known as molds) and bacteria--including some that are human pathogens--have characteristics suited to long-range atmospheric transport. Dust from the African desert can affect air quality in Africa, Europe, the Middle East, and the Americas. Asian desert dust can affect air quality in Asia, the Arctic, North America, and Europe. Atmospheric exposure to mold-carrying desert dust may affect human health directly through allergic induction of respiratory stress. In addition, mold spores within these dust clouds may seed downwind ecosystems in both outdoor and indoor environments.

Hydrodynamic model of a self-gravitating optically thick gas and dust cloud

NASA Astrophysics Data System (ADS)

Zhukova, E. V.; Zankovich, A. M.; Kovalenko, I. G.; Firsov, K. M.

2015-10-01

We propose an original mechanism of sustained turbulence generation in gas and dust clouds, the essence of which is the consistent provision of conditions for the emergence and maintenance of convective instability in the cloud. We considered a quasi-stationary one-dimensional model of a selfgravitating flat cloud with stellar radiation sources in its center. The material of the cloud is considered a two-component two-speed continuous medium, the first component of which, gas, is transparent for stellar radiation and is supposed to rest being in hydrostatic equilibrium, and the second one, dust, is optically dense and is swept out by the pressure of stellar radiation to the periphery of the cloud. The dust is specified as a set of spherical grains of a similar size (we made calculations for dust particles with radii of 0.05, 0.1, and 0.15 μm). The processes of scattering and absorption of UV radiation by dust particles followed by IR reradiation, with respect to which the medium is considered to be transparent, are taken into account. Dust-driven stellar wind sweeps gas outwards from the center of the cloud, forming a cocoon-like structure in the gas and dust. For the radiation flux corresponding to a concentration of one star with a luminosity of about 5 ×104 L ⊙ per square parsec on the plane of sources, sizes of the gas cocoon are equal to 0.2-0.4 pc, and for the dust one they vary from tenths of a parsec to six parsecs. Gas and dust in the center of the cavity are heated to temperatures of about 50-60 K in the model with graphite particles and up to 40 K in the model with silicate dust, while the background equilibrium temperature outside the cavity is set equal to 10 K. The characteristic dust expansion velocity is about 1-7 kms-1. Three structural elements define the hierarchy of scales in the dust cocoon. The sizes of the central rarefied cavity, the dense shell surrounding the cavity, and the thin layer inside the shell in which dust is settling provide

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

NASA Astrophysics Data System (ADS)

Kumar, Prashant

2011-12-01

Mineral dust is ubiquitous in the atmosphere and represents a dominant type of particulate matter by mass. Dust particles can serve as cloud condensation nuclei (CCN), giant CCN (GCCN), or ice nuclei (IN), thereby, affecting cloud microphysics, albedo, and lifetime. Despite its well-recognized importance, assessments of dust impacts on clouds and climate remain highly uncertain. This thesis addresses the role of dust as CCN and GCCN with the goal of improving our understanding of dust-warm cloud interactions and their representation in climate models. Most studies to date focus on the soluble fraction of aerosol particles when describing cloud droplet nucleation, and overlook the interactions of the hydrophilic insoluble fraction with water vapor. A new approach to include such interactions (expressed by the process of water vapor adsorption) is explored, by combining multilayer Frenkel-Halsey-Hill (FHH) physical adsorption isotherm and curvature (Kelvin) effects. The importance of adsorption activation theory (FHH-AT) is corroborated by measurements of CCN activity of mineral aerosols generated from clays, calcite, quartz, and desert soil samples from Northern Africa, East Asia/China, and Northern America. A new aerosol generation setup for CCN measurements was developed based on a dry generation technique capable of reproducing natural dust aerosol emission. Based on the dependence of critical supersaturation with particle dry diameter, it is found that the FHH-AT is a better framework for describing fresh (and unprocessed) dust CCN activity than the classical Kohler theory (KT). Ion Chromatography (IC) measurements performed on fresh regional dust samples indicate negligible soluble fraction, and support that water vapor adsorption is the prime source of CCN activity in the dust. CCN measurements with the commonly used wet generated mineral aerosol (from atomization of a dust aqueous suspension) are also carried out. Results indicate that the method is subject

Volcanic Plume from Mt. Unzen, Dust Cloud, cloud Vortices

NASA Image and Video Library

1991-12-01

Stable, south flowing air over the western Pacific Ocean (26.0N, 131.0E) is disturbed by islands south of Korea, resulting in sinuous clouds known as von Karman vortices. The smoke plume from Japan's Mount Unzen Volcano on Kyushu, is visible just west of the large cloud mass and extending southward. A very large, purple tinged dust pall, originating in Mongolia, can be seen on the Earth's Limb, covering eastern China and extending into the East China Sea.

The Evolution of the Surface of Symmetry of the Interplanetary Dust from 24° to 5° Elongation

NASA Astrophysics Data System (ADS)

Stenborg, Guillermo; Howard, Russell A.

2017-10-01

The white-light STEREO/SECCHI images include light scattered by dust in orbit about the Sun (the F-corona). We analyzed the evolution of the symmetry axis of the F-corona between 2007 and 2012 in the elongation range covered by the STEREO-A/HI-1 instrument (4°-24° elongation) to characterize the plane of symmetry of the zodiacal dust cloud. The symmetry axes both above and below the ecliptic plane were derived separately without assuming any particular functional form. No noticeable time dependence was observed. However, we did find an evolution with elongation of both the inclination I and the ascending node {{{Ω }}}A of the inferred plane of symmetry. Both parameters appeared fairly constant in the outer half of the elongation range studied (I=˜ 3\\buildrel{\\circ}\\over{.} 7,{{{Ω }}}A=˜ 83^\\circ ; values close to those of Venus’s orbit). Then, they start to evolve, becoming I=˜ 6^\\circ (I.e., a trend toward the solar equatorial plane) and {{{Ω }}}A=˜ 57^\\circ at about 5° elongation. This variation indicates that the zodiacal dust cloud exhibits a warped plane of symmetry, with an estimated center of symmetry at about 0.5 {R}⊙ from the Sun’s center on the side of the heliosphere containing Jupiter. We found a marginal difference between the inclination of the axes below and above the ecliptic. This is suggestive of an increased dust density distribution at certain fixed longitudes, which could be explained by the dust deposition of Kreutz Sun-grazing comets. We conjecture that the circumsolar dust is mainly affected by gravitational forces, other forces becoming dominant only where the more rapid changes occur.

Recent Asteroid Disruptions in the WISE Dataset - Constraining Asteroid Surface Properties Using Solar System Dust Bands

NASA Astrophysics Data System (ADS)

Kehoe, A. E.; Shaw, C.; Kehoe, T. J. J.

2017-12-01

Zodiacal dust bands are a fine-structure feature of the mid-IR emission profile of the zodiacal cloud. The dust bands have been studied for many years dating back to the InfraRed Astronomical Satellite (IRAS) data of the 1980's. The recent discovery and modeling (Espy et al., 2009; 2010; Espy Kehoe et al., 2015) of a very young, still-forming dust band structure has shown that, in the early stages following an asteroid disruption, much information on the dust parameters of the original disruption is retained in the band. Partial dust bands allow a never-before-seen observational look at the size distribution and cross-sectional area of dust produced in an asteroidal disruption, before it has been lost or significantly altered by orbital and collisional decay. The study of these partial band structures reveals information on the way asteroids disrupt and allow us to reconstruct the surface properties of the parent asteroid, including the depth of the surface regolith and the size distribution of particles composing the regolith. Using the greatly increased sensitivity of the Wide-field Infrared Survey Explorer (WISE), we can now detect much fainter (and thus younger) dust bands. The WISE data also reveals much better longitudinal resolution of the bands, allowing a better constraint on the source and age of the disruption. We will present our newest results from the WISE dataset, including detection of faint partial dust bands, improved models of more prominent bands, and our constraints on the asteroid surface properties from modeling these structures.

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

NASA Astrophysics Data System (ADS)

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

2018-03-01

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

The Coupled Mars Dust and Water Cycles: Understanding How Clouds Affect the Vertical Distribution and Meridional Transport of Dust and Water.

NASA Technical Reports Server (NTRS)

Kahre, M. A.

2015-01-01

The dust and water cycles are crucial to the current Martian climate, and they are coupled through cloud formation. Dust strongly impacts the thermal structure of the atmosphere and thus greatly affects atmospheric circulation, while clouds provide radiative forcing and control the hemispheric exchange of water through the modification of the vertical distributions of water and dust. Recent improvements in the quality and sophistication of both observations and climate models allow for a more comprehensive understanding of how the interaction between the dust and water cycles (through cloud formation) affects the dust and water cycles individually. We focus here on the effects of clouds on the vertical distribution of dust and water, and how those vertical distributions control the net meridional transport of water. For this study, we utilize observations of temperature, dust and water ice from the Mars Climate Sounder (MCS) on the Mars Reconnaissance Orbiter (MRO) combined with the NASA ARC Mars Global Climate Model (MGCM). We demonstrate that the magnitude and nature of the net meridional transport of water between the northern and southern hemispheres during NH summer is sensitive to the vertical structure of the simulated aphelion cloud belt. We further examine how clouds influence the atmospheric thermal structure and thus the vertical structure of the cloud belt. Our goal is to identify and understand the importance of radiative/dynamic feedbacks due to the physical processes involved with cloud formation and evolution on the current climate of Mars.

Orbital Evolution of Dust Particles in the Sublimation Zone near the Sun

NASA Astrophysics Data System (ADS)

Shestakova, L. I.; Demchenko, B. I.

2018-03-01

We have performed the calculations of the orbital evolution of dust particles from volcanic glass ( p-obsidian), basalt, astrosilicate, olivine, and pyroxene in the sublimation zone near the Sun. The sublimation (evaporation) rate is determined by the temperature of dust particles depending on their radius, material, and distance to the Sun. All practically important parameters that characterize the interaction of spherical dust particles with the radiation are calculated using the Mie theory. The influence of radiation and solar wind pressure, as well as the Poynting-Robertson drag force effects on the dust dynamics, are also taken into account. According to the observations (Shestakova and Demchenko, 2016), the boundary of the dust-free zone is 7.0-7.6 solar radii for standard particles of the zodiacal cloud and 9.1-9.2 solar radii for cometary particles. The closest agreement is obtained for basalt particles and certain kinds of olivine, pyroxene, and volcanic glass.

Microgravity combustion of dust clouds: Quenching distance measurements

NASA Technical Reports Server (NTRS)

Goroshin, S.; Kleine, H.; Lee, J. H. S.; Frost, D.

1995-01-01

The current level of physical understanding of dust combustion phenomena is still in a rudimentary state compared with the understanding of gas combustion processes. The reason for such a lack of fundamental understanding is partially based on the complexity of multiphase combustion and the enormous diversity of chemical-physical properties of heterogeneous combustible mixtures but is largely due to difficulties in the experimental investigation of dust combustion. The influence of gravity on a dust suspension is the main reason. First of all, when particulates (either solid particles or liquid droplets) with a characteristic size of the order of tens of microns are suspended, they rapidly settle in the gravitational field. To maintain a particulate suspension for a time duration adequate to carry out combustion experiments invariably requires continuous convection of particulates at or in excess of the gravitational settling velocity. Of necessity, this makes the experiments turbulent in character and makes it impossible to study laminar dust flames. For particle sizes of the order of microns a stable laminar dust flow can be maintained only for relatively small dust concentrations (e.g., for low fuel equivalence ratios) at normal gravity conditions. High dust loading leads to gravitational instability of the dust cloud and to the formation of recirculation cells in a dust suspension in a confined volume, or to the rapid sedimentation of the dense dust cloud as a whole in an unconfined volume. In addition, many important solid fuels such as low volatile coal, carbon, and boron have low laminar flame speeds (of the order of several centimeters per second). Gravitational convection that occurs in combustion products due to the buoyancy forces disrupts low speed dust flames and, therefore, makes observation of such flames at normal gravity impossible. The only way to carry out 'clean' fundamental experiments in dust combustion over a wide range of dust cloud

The Mars Dust and Water Cycles: Investigating the Influence of Clouds on the Vertical Distribution and Meridional Transport of Dust and Water.

NASA Technical Reports Server (NTRS)

Kahre, M. A.; Haberle, R. M.; Hollingsworth, J. L.; Brecht, A. S.; Urata, R.

2015-01-01

The dust and water cycles are critical to the current Martian climate, and they interact with each other through cloud formation. Dust modulates the thermal structure of the atmosphere and thus greatly influences atmospheric circulation. Clouds provide radiative forcing and control the net hemispheric transport of water through the alteration of the vertical distributions of water and dust. Recent advancements in the quality and sophistication of both climate models and observations enable an increased understanding of how the coupling between the dust and water cycles (through cloud formation) impacts the dust and water cycles. We focus here on the effects of clouds on the vertical distributions of dust and water and how those vertical distributions control the net meridional transport of water. We utilize observations of temperature, dust and water ice from the Mars Climate Sounder (MCS) on the Mars Reconnaissance Orbiter (MRO) and the NASA ARC Mars Global Climate Model (MGCM) to show that the magnitude and nature of the hemispheric exchange of water during NH summer is sensitive to the vertical structure of the simulated aphelion cloud belt. Further, we investigate how clouds influence atmospheric temperatures and thus the vertical structure of the cloud belt. Our goal is to isolate and understand the importance of radiative/dynamic feedbacks due to the physical processes involved with cloud formation and evolution on the current climate of Mars.

The Mars Dust and Water Cycles: Investigating the Influence of Clouds on the Vertical Distribution and Meridional Transport of Dust and Water

NASA Astrophysics Data System (ADS)

Kahre, Melinda A.; Haberle, Robert M.; Hollingsworth, Jeffery L.; Brecht, Amanda S.; Urata, Richard A.

2015-11-01

The dust and water cycles are critical to the current Martian climate, and they interact with each other through cloud formation. Dust modulates the thermal structure of the atmosphere and thus greatly influences atmospheric circulation. Clouds provide radiative forcing and control the net hemispheric transport of water through the alteration of the vertical distributions of water and dust. Recent advancements in the quality and sophistication of both climate models and observations enable an increased understanding of how the coupling between the dust and water cycles (through cloud formation) impacts the dust and water cycles. We focus here on the effects of clouds on the vertical distributions of dust and water and how those vertical distributions control the net meridional transport of water. We utilize observations of temperature, dust and water ice from the Mars Climate Sounder (MCS) on the Mars Reconnaissance Orbiter (MRO) and the NASA ARC Mars Global Climate Model (MGCM) to show that the magnitude and nature of the hemispheric exchange of water during NH summer is sensitive to the vertical structure of the simulated aphelion cloud belt. Further, we investigate how clouds influence atmospheric temperatures and thus the vertical structure of the cloud belt. Our goal is to isolate and understand the importance of radiative/dynamic feedbacks due to the physical processes involved with cloud formation and evolution on the current climate of Mars.

Impact-generated dust clouds around planetary satellites: asymmetry effects

NASA Astrophysics Data System (ADS)

Sremčević, Miodrag; Krivov, Alexander V.; Spahn, Frank

2003-06-01

In a companion paper (Krivov et al., Impact-generated dust clouds around planetary satellites: spherically symmetric case, Planet. Space. Sci. 2003, 51, 251-269) an analytic model of an impact-generated, steady-state, spherically symmetric dust cloud around an atmosphereless planetary satellite (or planet - Mercury, Pluto) has been developed. This paper lifts the assumption of spherical symmetry and focuses on the asymmetry effects that result from the motion of the parent body through an isotropic field of impactors. As in the spherically symmetric case, we first consider the dust production from the surface and then derive a general phase-space distribution function of the ensemble of ejected dust motes. All quantities of interest, such as particle number densities and fluxes, can be obtained by integrating this phase-space distribution function. As an example, we calculate an asymmetric distribution of dust number density in a cloud. It is found that the deviation from the symmetric case can be accurately described by a cosine function of the colatitude measured from the apex of the satellite motion. This property of the asymmetry is rather robust. It is shown that even an extremely asymmetric dust production at the surface, when nearly all dust is ejected from the leading hemisphere, turns rapidly into the cosine modulation of the number density at distances larger than a few satellite radii. The amplitude of the modulation depends on the ratio of the moon orbital velocity to the speed of impactors and on the initial angular distribution of the ejecta. Furthermore, regardless of the functional form of the initial angular distribution, the number density distribution of the dust cloud is only sensitive to the mean ejecta angle. When the mean angle is small - ejection close to the normal of the surface - the initial dust production asymmetry remains persistent even far from the satellite, but when this angle is larger than about 45°, the asymmetry coefficient

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

NASA Technical Reports Server (NTRS)

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

2005-01-01

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

Ignition of Combustible Dust Clouds by Strong Capacitive Electric Sparks of Short Discharge Times

NASA Astrophysics Data System (ADS)

Eckhoff, Rolf K.

2017-10-01

It has been known for more than half a century that the discharge times of capacitive electric sparks can influence the minimum ignition energies of dust clouds substantially. Experiments by various workers have shown that net electric-spark energies for igniting explosive dust clouds in air were reduced by a factor of the order of 100 when spark discharge times were increased from a few μs to 0.1-1 ms. Experiments have also shown that the disturbance of the dust cloud by the shock/blast wave emitted by "short" spark discharges is a likely reason for this. The disturbance increases with increasing spark energy. In this paper a hitherto unpublished comprehensive study of this problem is presented. The work was performed about 50 years ago, using sparks of comparatively high energies (strong sparks). Lycopodium was used as test dust. The experiments were conducted in a brass vessel of 1 L volume. A transient dust cloud was generated in the vessel by a blast of compressed air. Synchronization of appearance of dust cloud and spark discharge was obtained by breaking the spark gap down by the dust cloud itself. This may in fact also be one possible synchronization mechanism in accidental industrial dust explosions initiated by electrostatic sparks. The experimental results for various spark energies were expressed as the probability of ignition, based on 100 replicate experiments, as a function of the nominal dust concentration. All probabilities obtained were 0%dust cloud for ignition to occur was a function of spark energy and nominal dust concentration, and that the stochastic element was the statistical distribution of the time interval between spark appearance and re-establishment of contact between spark channel and dust

Global impact of mineral dust on cloud droplet number concentration

NASA Astrophysics Data System (ADS)

Karydis, Vlassis A.; Tsimpidi, Alexandra P.; Bacer, Sara; Pozzer, Andrea; Nenes, Athanasios; Lelieveld, Jos

2017-05-01

The importance of wind-blown mineral dust for cloud droplet formation is studied by considering (i) the adsorption of water on the surface of insoluble particles, (ii) particle coating by soluble material (atmospheric aging) which augments cloud condensation nuclei (CCN) activity, and (iii) the effect of dust on inorganic aerosol concentrations through thermodynamic interactions with mineral cations. The ECHAM5/MESSy Atmospheric Chemistry (EMAC) model is used to simulate the composition of global atmospheric aerosol, while the ISORROPIA-II thermodynamic equilibrium model treats the interactions of K+-Ca2+-Mg2+-NH4+-Na+-SO42--NO3--Cl--H2O aerosol with gas-phase inorganic constituents. Dust is considered a mixture of inert material with reactive minerals and its emissions are calculated online by taking into account the soil particle size distribution and chemical composition of different deserts worldwide. The impact of dust on droplet formation is treated through the unified dust activation parameterization that considers the inherent hydrophilicity from adsorption and acquired hygroscopicity from soluble salts during aging. Our simulations suggest that the presence of dust increases cloud droplet number concentration (CDNC) over major deserts (e.g., up to 20 % over the Sahara and the Taklimakan desert) and decreases CDNC over polluted areas (e.g., up to 10 % over southern Europe and 20 % over northeastern Asia). This leads to a global net decrease in CDNC by 11 %. The adsorption activation of insoluble aerosols and the mineral dust chemistry are shown to be equally important for the cloud droplet formation over the main deserts; for example, these effects increase CDNC by 20 % over the Sahara. Remote from deserts the application of adsorption theory is critically important since the increased water uptake by the large aged dust particles (i.e., due to the added hydrophilicity by the soluble coating) reduce the maximum supersaturation and thus cloud droplet

Nulling interferometry: impact of exozodiacal clouds on the performance of future life-finding space missions

NASA Astrophysics Data System (ADS)

Defrère, D.; Absil, O.; den Hartog, R.; Hanot, C.; Stark, C.

2010-01-01

Context. Earth-sized planets around nearby stars are being detected for the first time by ground-based radial velocity and space-based transit surveys. This milestone is opening the path toward the definition of instruments able to directly detect the light from these planets, with the identification of bio-signatures as one of the main objectives. In that respect, both the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA) have identified nulling interferometry as one of the most promising techniques. The ability to study distant planets will however depend on the amount of exozodiacal dust in the habitable zone of the target stars. Aims: We assess the impact of exozodiacal clouds on the performance of an infrared nulling interferometer in the Emma X-array configuration. The first part of the study is dedicated to the effect of the disc brightness on the number of targets that can be surveyed and studied by spectroscopy during the mission lifetime. In the second part, we address the impact of asymmetric structures in the discs such as clumps and offset which can potentially mimic the planetary signal. Methods: We use the DarwinSIM software which was designed and validated to study the performance of space-based nulling interferometers. The software has been adapted to handle images of exozodiacal discs and to compute the corresponding demodulated signal. Results: For the nominal mission architecture with 2-m aperture telescopes, centrally symmetric exozodiacal dust discs about 100 times denser than the solar zodiacal cloud can be tolerated in order to survey at least 150 targets during the mission lifetime. Considering modeled resonant structures created by an Earth-like planet orbiting at 1 AU around a Sun-like star, we show that this tolerable dust density goes down to about 15 times the solar zodiacal density for face-on systems and decreases with the disc inclination. Conclusions: Whereas the disc brightness only affects

On the size and velocity distribution of cosmic dust particles entering the atmosphere

PubMed Central

Carrillo‐Sánchez, J. D.; Feng, W.; Nesvorný, D.; Janches, D.

2015-01-01

Abstract The size and velocity distribution of cosmic dust particles entering the Earth's atmosphere is uncertain. Here we show that the relative concentrations of metal atoms in the upper mesosphere, and the surface accretion rate of cosmic spherules, provide sensitive probes of this distribution. Three cosmic dust models are selected as case studies: two are astronomical models, the first constrained by infrared observations of the Zodiacal Dust Cloud and the second by radar observations of meteor head echoes; the third model is based on measurements made with a spaceborne dust detector. For each model, a Monte Carlo sampling method combined with a chemical ablation model is used to predict the ablation rates of Na, K, Fe, Mg, and Ca above 60 km and cosmic spherule production rate. It appears that a significant fraction of the cosmic dust consists of small (<5 µg) and slow (<15 km s−1) particles. PMID:27478282

COSMIC INFRARED BACKGROUND FLUCTUATIONS AND ZODIACAL LIGHT

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

Arendt, Richard G.; Kashlinsky, A.; Moseley, S. H.

We performed a specific observational test to measure the effect that the zodiacal light can have on measurements of the spatial fluctuations of the near-IR background. Previous estimates of possible fluctuations caused by zodiacal light have often been extrapolated from observations of the thermal emission at longer wavelengths and low angular resolution or from IRAC observations of high-latitude fields where zodiacal light is faint and not strongly varying with time. The new observations analyzed here target the COSMOS field at low ecliptic latitude where the zodiacal light intensity varies by factors of ∼2 over the range of solar elongations atmore » which the field can be observed. We find that the white-noise component of the spatial power spectrum of the background is correlated with the modeled zodiacal light intensity. Roughly half of the measured white noise is correlated with the zodiacal light, but a more detailed interpretation of the white noise is hampered by systematic uncertainties that are evident in the zodiacal light model. At large angular scales (≳100″) where excess power above the white noise is observed, we find no correlation of the power with the modeled intensity of the zodiacal light. This test clearly indicates that the large-scale power in the infrared background is not being caused by the zodiacal light.« less

Cosmic Infrared Background Fluctuations and Zodiacal Light

NASA Astrophysics Data System (ADS)

Arendt, Richard G.; Kashlinsky, A.; Moseley, S. H.; Mather, J.

2016-06-01

We performed a specific observational test to measure the effect that the zodiacal light can have on measurements of the spatial fluctuations of the near-IR background. Previous estimates of possible fluctuations caused by zodiacal light have often been extrapolated from observations of the thermal emission at longer wavelengths and low angular resolution or from IRAC observations of high-latitude fields where zodiacal light is faint and not strongly varying with time. The new observations analyzed here target the COSMOS field at low ecliptic latitude where the zodiacal light intensity varies by factors of ˜2 over the range of solar elongations at which the field can be observed. We find that the white-noise component of the spatial power spectrum of the background is correlated with the modeled zodiacal light intensity. Roughly half of the measured white noise is correlated with the zodiacal light, but a more detailed interpretation of the white noise is hampered by systematic uncertainties that are evident in the zodiacal light model. At large angular scales (≳100″) where excess power above the white noise is observed, we find no correlation of the power with the modeled intensity of the zodiacal light. This test clearly indicates that the large-scale power in the infrared background is not being caused by the zodiacal light.

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

NASA Astrophysics Data System (ADS)

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

2012-12-01

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

Rain chemistry and cloud composition and microphysics in a Caribbean tropical montane cloud forest under the influence of African dust

NASA Astrophysics Data System (ADS)

Torres-Delgado, Elvis; Valle-Diaz, Carlos J.; Baumgardner, Darrel; McDowell, William H.; González, Grizelle; Mayol-Bracero, Olga L.

2015-04-01

It is known that huge amounts of mineral dust travels thousands of kilometers from the Sahara and Sahel regions in Africa over the Atlantic Ocean reaching the Caribbean, northern South America and southern North America; however, not much is understood about how the aging process that takes place during transport changes dust properties, and how the presence of this dust affects cloud's composition and microphysics. This African dust reaches the Caribbean region mostly in the summer time. In order to improve our understanding of the role of long-range transported African dust (LRTAD) in cloud formation processes in a tropical montane cloud forest (TMCF) in the Caribbean region we had field campaigns measuring dust physical and chemical properties in summer 2013, as part of the Puerto Rico African Dust and Cloud Study (PRADACS), and in summer 2014, as a part of the Luquillo Critical Zone Observatory (LCZO) and in collaboration with the Saharan Aerosol Long-Range Transport and Aerosol-Cloud-Interaction Experiment (SALTRACE). Measurements were performed at the TMCF of Pico del Este (PE, 1051 masl) and at the nature reserve of Cabezas de San Juan (CSJ, 60 masl). In both stations we monitored meteorological parameters (e.g., temperature, wind speed, wind direction). At CSJ, we measured light absorption and scattering at three wavelengths (467, 528 and 652 nm). At PE we collected cloud and rainwater and monitored cloud microphysical properties (e.g., liquid water content, droplet size distribution, droplet number concentration, effective diameter and median volume diameter). Data from aerosol models, satellites, and back-trajectories were used together with CSJ measurements to classify air masses and samples collected at PE in the presence or absence of dust. Soluble ions, insoluble trace metals, pH and conductivity were measured for cloud and rainwater. Preliminary results for summer 2013 showed that in the presence of LRTAD (1) the average conductivity of cloud water

Evaluating the effect of soil dust particles from semi-arid areas on clouds and climate

NASA Astrophysics Data System (ADS)

Kristjansson, J. E.; Hummel, M.; Lewinschal, A.; Grini, A.

2016-12-01

Primary ice production in mixed-phase clouds predominantly takes place by heterogeneous freezing of mineral dust particles. Therefore, mineral dust has a large impact on cloud properties. Organic matter attached to mineral dust particles can expand their already good freezing ability further to warmer subzero temperatures. These dust particles are called "soil dust". Dusts emitted from deserts contribute most to the total dust concentration in the atmosphere and they can be transported over long distances. Soil dust is emitted from semi-arid regions, e.g. agricultural areas. Besides wind erosion, human activities like tillage or harvest might be a large source for soil dust release into the atmosphere. In this study, we analyze the influence of soil dust particles on clouds with the Norwegian Earth System Model (NorESM; Bentsen et al., 2013: GMD). The parameterization of immersion freezing on soil dust is based on findings from the AIDA cloud chamber (Steinke et al., in prep.). Contact angle and activation energy for soil dust are estimated in order to be used in the dust immersion freezing scheme of the model, which is based on classical nucleation theory. Our first results highlight the importance of soil dust for ice nucleation on a global scale. Its influence is expected to be highest in the northern hemisphere due to its higher area for soil dust emission. The immersion freezing rates due to additional soil dust can on average increase by a factor of 1.2 compared to a mineral dust-only simulation. Using a budget tool for NorESM, influences of soil dust ice nuclei on single tendencies of the cloud microphysics can be identified. For example, accretion to snow is sensitive to adding soil dust ice nuclei. This can result in changes e.g. in the ice water path and cloud radiative properties.

Cosmic Infrared Background Fluctuations and Zodiacal Light

NASA Technical Reports Server (NTRS)

Arendt, Richard G.; Kashlinsky, A.; Moseley, S. H.; Mather, J.

2017-01-01

We performed a specific observational test to measure the effect that the zodiacal light can have on measurements of the spatial fluctuations of the near-IR (near-infrared)background. Previous estimates of possible fluctuations caused by zodiacal light have often been extrapolated from observations of the thermal emission at longer wavelengths and low angular resolution or from IRAC (Infrared Array Camera) observations of high-latitude fields where zodiacal light is faint and not strongly varying with time. The new observations analyzed here target the COSMOS (Cosmic Evolution Survey) field at low ecliptic latitude where the zodiacal light intensity varies by factors of approximately 2 over the range of solar elongations at which the field can be observed. We find that the white-noise component of the spatial power spectrum of the background is correlated with the modeled zodiacal light intensity. Roughly half of the measured white noise is correlated with the zodiacal light, but a more detailed interpretation of the white noise is hampered by systematic uncertainties that are evident in the zodiacal light model. At large angular scales (greater than or approximately equal to 100 arcseconds) where excess power above the white noise is observed, we find no correlation of the power with the modeled intensity of the zodiacal light. This test clearly indicates that the large-scale power in the infrared background is not being caused by the zodiacal light.

Velocity Distributions of Interplanetary Dust Derived from Astronomical Sky Spectra

NASA Astrophysics Data System (ADS)

Huestis, D. L.; Ali, S.; Cosby, P. C.; Slanger, T. G.

2001-11-01

Characterization of interplanetary dust is important for understanding the creation by accretion of planets and moons, the development of planetary atmospheres, and, potentially, for the initiation of prebiotic chemistry. The recent COBE mission has provided a profile in ecliptic coordinates of the distribution of interplanetary dust particles through their thermal infrared emission. Additional information about interplanetary dust can be extracted from its visible spectrum of scattered sunlight, called Zodiacal Light. Night sky spectra taken at large-aperture telescopes using high-resolution echelle spectrographs reveal Fraunhofer absorption features in the Zodiacal Light spectrum of scattered sunlight, a nuisance in subtraction from the spectrum of the extraterrestrial object under investigation. We are analyzing the intensity modulations and Doppler shifts of solar Fraunhofer absorption lines in the Zodiacal Light component of sky spectra, donated by collaborating astronomers using Keck/HIRES and other high-performance astronomical facilities. Our objectives include velocity distributions of interplanetary dust and improved separation of terrestrial and extraterrestrial sources in sky spectra. Participation of S. Ali was made possible by a grant from the NSF Physics Research Experiences for Undergraduates (REU) program.

Results of observations of the dust distribution in the F-corona of the sun

NASA Astrophysics Data System (ADS)

Shestakova, L. I.; Demchenko, B. I.

2016-03-01

The results of modeling of the distribution of dust in the circumsolar zone are presented. The dust distribution was retrieved from observations of the line-of-sight velocities in the F-corona to the distances of 7-11 solar radii during the total eclipses of the Sun in different years: on July 31, 1981; August 11, 1991; March 29, 2006; and August 1, 2008. Comparison of the results has shown that the dust composition varies from year to year and the dust is dynamically nonuniform. In addition to the dust related to the zodiacal cloud and concentrating to the ecliptic plane, the dust of retrograde motion and the ejections and accretion in the polar regions are observed. From the results of observations of eclipses on July 31, 1981, August 11, 1991, and August 1, 2008, the east-west asymmetry in a sign of the line-of-sight velocities was detected: they are negative to the east of the Sun and positive to the west. Such distribution of the velocities is indicative of the nearecliptic orbital dust motion, whose direction coincides with that of the motion of the planets. In the course of the eclipse of March 29, 2006, almost no dynamical connection with the zodiacal cloud was found. At the same time, the direction, where the observed velocities are largest in value and opposite in sign on opposite sides of the Sun, was determined, which provides evidence of the orbital motion deviating from the ecliptic plane. The results of observations in 2006 reveal a clear genetic connection of the observed orbital motion of dust with the parent comets of the Kreutz family found near the Sun close to the eclipse date. The velocities observed near the symmetry line in the plane of the sky grow by absolute value with increasing the elongation, which may take place, if the line of sight croßses an empty zone that is free of dust. The modeling of the data of observations near the symmetry plane allowed the parameters of the dust distribution near the sublimation zone to be obtained. In

Dust in the Small Magellanic Cloud

NASA Technical Reports Server (NTRS)

Rodrigues, C. V.; Coyne, G. V.; Magalhaes, A. M.

1995-01-01

We discuss simultaneous dust model fits to our extinction and polarization data for the Small Magellanic Cloud (SMC) using existing dust models. Dust model fits to the wavelength dependent polarization are possible for stars with small lambda(sub max). They generally imply size distributions which are narrower and have smaller average sizes compared to those in the Galaxy. The best fits for the extinction curves are obtained with a power law size distribution. The typical, monotonic SMC extinction curve can be well fit with graphite and silicate grains if a small fraction of the SMC carbon is locked up in the grains. Amorphous carbon and silicate grains also fit the data well.

Satellite remote sensing of dust aerosol indirect effects on ice cloud formation.

PubMed

Ou, Steve Szu-Cheng; Liou, Kuo-Nan; Wang, Xingjuan; Hansell, Richard; Lefevre, Randy; Cocks, Stephen

2009-01-20

We undertook a new approach to investigate the aerosol indirect effect of the first kind on ice cloud formation by using available data products from the Moderate-Resolution Imaging Spectrometer (MODIS) and obtained physical understanding about the interaction between aerosols and ice clouds. Our analysis focused on the examination of the variability in the correlation between ice cloud parameters (optical depth, effective particle size, cloud water path, and cloud particle number concentration) and aerosol optical depth and number concentration that were inferred from available satellite cloud and aerosol data products. Correlation results for a number of selected scenes containing dust and ice clouds are presented, and dust aerosol indirect effects on ice clouds are directly demonstrated from satellite observations.

Possible influences of Asian dust aerosols on cloud properties and radiative forcing observed from MODIS and CERES

NASA Astrophysics Data System (ADS)

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

2006-03-01

The effects of dust storms on cloud properties and Radiative Forcing (RF) are analyzed over Northwestern China from April 2001 to June 2004 using data collected by the MODerate Resolution Imaging Spectroradiometer (MODIS) and Clouds and the Earth's Radiant Energy System (CERES) instruments on the Aqua and Terra satellites. On average, ice cloud effective particle diameter, optical depth and ice water path of cirrus clouds under dust polluted conditions are 11%, 32.8%, and 42% less, respectively, than those derived from ice clouds in dust-free atmospheric environments. Due to changes in cloud microphysics, the instantaneous net RF is increased from -161.6 W/m2 for dust-free clouds to -118.6 W/m2 for dust-contaminated clouds.

Cosmic dust and space debris; Proceedings of the Topical Meetings and Workshop 6 of the 26th COSPAR Plenary Meeting, Toulouse, France, June 30-July 11, 1986

NASA Technical Reports Server (NTRS)

Mcdonnell, J. A. M. (Editor); Hanner, M. S. (Editor); Kessler, D. J. (Editor)

1986-01-01

These proceedings encompass topics in the fields of extraterrestrial material samples, IRAS solar system and dust model results, and earth orbit debris. Attention is given to chemical fractionation during high velocity impact, particle deceleration and survival in multiple thin foil targets, and IRAS studies of asteroids, comets, cometary tails, the zodiacal background, and the three-dimensional modeling of interplanetary dust. Also discussed are the evolution of an earth orbit debris cloud, orbital debris due to future space activities, collision probabilities in geosynchronous orbits, and a bitelescopic survey of low altitude orbital debris.

Distribution of Dust from Kuiper Belt Objects

NASA Technical Reports Server (NTRS)

Gorkavyi, Nick N.; Ozernoy, Leonid; Taidakova, Tanya; Mather, John C.; Fisher, Richard (Technical Monitor)

2000-01-01

Using an efficient computational approach, we have reconstructed the structure of the dust cloud in the Solar system between 0.5 and 100 AU produced by the Kuiper belt objects. Our simulations offer a 3-D physical model of the 'kuiperoidal' dust cloud based on the distribution of 280 dust particle trajectories produced by 100 known Kuiper belt objects; the resulting 3-D grid consists of 1.9 x 10' cells containing 1.2 x 10" particle positions. The following processes that influence the dust particle dynamics are taken into account: 1) gravitational scattering on the eight planets (neglecting Pluto); 2) planetary resonances; 3) radiation pressure; and 4) the Poynting-Robertson (P-R) and solar wind drags. We find the dust distribution highly non-uniform: there is a minimum in the kuiperoidal dust between Mars and Jupiter, after which both the column and number densities of kuiperoidal dust sharply increase with heliocentric distance between 5 and 10 AU, and then form a plateau between 10 and 50 AU. Between 25 and 45 AU, there is an appreciable concentration of kuiperoidal dust in the form of a broad belt of mostly resonant particles associated with Neptune. In fact, each giant planet possesses its own circumsolar dust belt consisting of both resonant and gravitationally scattered particles. As with the cometary belts simulated in our related papers, we reveal a rich and sophisticated resonant structure of the dust belts containing families of resonant peaks and gaps. An important result is that both the column and number dust density are more or less flat between 10 and 50 AU, which might explain the surprising data obtained by Pioneers 10 & 11 and Voyager that the dust number density remains approximately distance-independent in this region. The simulated kuiperoidal dust, in addition to asteroidal and cometary dust, might represent a third possible source of the zodiacal light in the Solar system.

A Chinese Zodiac Mathematical Structure.

ERIC Educational Resources Information Center

Lamb, John F., Jr.

2000-01-01

Helps students identify the animal that corresponds to the year of their birth according to the Chinese zodiac. Defines the structure of the Chinese zodiac so that the subsets of compatibles and opposites form closed substructures with interesting mathematical properties. (ASK)

Zodiac II: Debris Disk Imaging Potential

NASA Technical Reports Server (NTRS)

Traub Wesley; Bryden, Geoff; Stapelfeldt, Karl; Chen, Pin; Trauger, John

2011-01-01

Zodiac II is a proposed coronagraph on a balloon-borne platform, for the purpose of observing debris disks around nearby stars. Zodiac II will have a 1.2-m diameter telescope mounted in a balloon-borne gondola capable of arcsecond quality pointing, and with the capability to make long-duration (several week) flights. Zodiac II will have a coronagraph able to make images of debris disks, meaning that its scattered light speckles will be at or below an average contrast level of about 10(exp -7) in three narrow (7 percent) bands centered on the V band, and one broad (20%) one at I band. We will discuss the potential science to be done with Zodiac II.

Dust in brown dwarfs. III. Formation and structure of quasi-static cloud layers

NASA Astrophysics Data System (ADS)

Woitke, P.; Helling, Ch.

2004-01-01

In this paper, first solutions of the dust moment equations developed in (Woitke & Helling \\cite{wh2003a}) for the description of dust formation and precipitation in brown dwarf and giant gas planet atmospheres are presented. We consider the special case of a static brown dwarf atmosphere, where dust particles continuously nucleate from the gas phase, grow by the accretion of molecules, settle gravitationally and re-evaporate thermally. Mixing by convective overshoot is assumed to replenish the atmosphere with condensable elements, which is necessary to counterbalance the loss of condensable elements by dust formation and gravitational settling (no dust without mixing). Applying a kinetic description of the relevant microphysical and chemical processes for TiO2-grains, the model makes predictions about the large-scale stratification of dust in the atmosphere, the depletion of molecules from the gas phase, the supersaturation of the gas in the atmosphere as well as the mean size and the mass fraction of dust grains as function of depth. Our results suggest that the presence of relevant amounts of dust is restricted to a layer, where the upper boundary (cloud deck) is related to the requirement of a minimum mixing activity (mixing time-scale τmix ≈ 10 6 s) and the lower boundary (cloud base) is determined by the thermodynamical stability of the grains. The nucleation occurs around the cloud deck where the gas is cool, strongly depleted, but nevertheless highly supersaturated (S ≫ 1). These particles settle gravitationally and populate the warmer layers below, where the in situ formation (nucleation) is ineffective or even not possible. During their descent, the particles grow and reach mean radii of ≈30 \\mum ... 400 \\mum at the cloud base, but the majority of the particles in the cloud layer remains much smaller. Finally, the dust grains sink into layers which are sufficiently hot to cause their thermal evaporation. Hence, an effective transport mechanism

Cosmic dust in the earth's atmosphere.

PubMed

Plane, John M C

2012-10-07

This review discusses the magnitude of the cosmic dust input into the earth's atmosphere, and the resulting impacts from around 100 km to the earth's surface. Zodiacal cloud observations and measurements made with a spaceborne dust detector indicate a daily mass input of interplanetary dust particles ranging from 100 to 300 tonnes, which is in agreement with the accumulation rates of cosmic-enriched elements (Ir, Pt, Os and super-paramagnetic Fe) in polar ice cores and deep-sea sediments. In contrast, measurements in the middle atmosphere - by radar, lidar, high-flying aircraft and satellite remote sensing - indicate that the input is between 5 and 50 tonnes per day. There are two reasons why this huge discrepancy matters. First, if the upper range of estimates is correct, then vertical transport in the middle atmosphere must be considerably faster than generally believed; whereas if the lower range is correct, then our understanding of dust evolution in the solar system, and transport from the middle atmosphere to the surface, will need substantial revision. Second, cosmic dust particles enter the atmosphere at high speeds and undergo significant ablation. The resulting metals injected into the atmosphere are involved in a diverse range of phenomena, including: the formation of layers of metal atoms and ions; the nucleation of noctilucent clouds, which are a sensitive marker of climate change; impacts on stratospheric aerosols and O(3) chemistry, which need to be considered against the background of a cooling stratosphere and geo-engineering plans to increase sulphate aerosol; and fertilization of the ocean with bio-available Fe, which has potential climate feedbacks.

Effect of Thin Cirrus Clouds on Dust Optical Depth Retrievals From MODIS Observations

NASA Technical Reports Server (NTRS)

Feng, Qian; Hsu, N. Christina; Yang, Ping; Tsay, Si-Chee

2011-01-01

The effect of thin cirrus clouds in retrieving the dust optical depth from MODIS observations is investigated by using a simplified aerosol retrieval algorithm based on the principles of the Deep Blue aerosol property retrieval method. Specifically, the errors of the retrieved dust optical depth due to thin cirrus contamination are quantified through the comparison of two retrievals by assuming dust-only atmospheres and the counterparts with overlapping mineral dust and thin cirrus clouds. To account for the effect of the polarization state of radiation field on radiance simulation, a vector radiative transfer model is used to generate the lookup tables. In the forward radiative transfer simulations involved in generating the lookup tables, the Rayleigh scattering by atmospheric gaseous molecules and the reflection of the surface assumed to be Lambertian are fully taken into account. Additionally, the spheroid model is utilized to account for the nonsphericity of dust particles In computing their optical properties. For simplicity, the single-scattering albedo, scattering phase matrix, and optical depth are specified a priori for thin cirrus clouds assumed to consist of droxtal ice crystals. The present results indicate that the errors in the retrieved dust optical depths due to the contamination of thin cirrus clouds depend on the scattering angle, underlying surface reflectance, and dust optical depth. Under heavy dusty conditions, the absolute errors are comparable to the predescribed optical depths of thin cirrus clouds.

Infrared emission from isolated dust clouds in the presence of very small dust grains

NASA Technical Reports Server (NTRS)

Lis, Dariusz C.; Leung, Chun M.

1991-01-01

Models of the effects of small grain-generated temperature fluctuations on the IR spectrum and surface brightness of externally heated interstellar dust clouds are presently constructed on the basis of a continuum radiation transport computer code which encompasses the transient heating of small dust grains. The models assume a constant fractional abundance of large and small grains throughout the given cloud. A comparison of model results with IRAS observations indicates that the observed 12-25 micron band emissions are associated with about 10-A radius grains, while the 60-100 micron emission is primarily due to large grains which are heated under the equilibrium conditions.

Dust clouds and plasmoids in Saturn's magnetosphere as seen with four Cassini instruments

NASA Astrophysics Data System (ADS)

Khalisi, Emil

2017-03-01

We revisit the evidence for a ;dust cloud; observed by the Cassini spacecraft at Saturn in 2006. The data of four instruments are simultaneously compared to interpret the signatures of a coherent swarm of dust that would have remained near the equatorial plane for as long as six weeks. The conspicuous pattern, as seen in the dust counters of the Cosmic Dust Analyser (CDA), clearly repeats on three consecutive revolutions of the spacecraft. That particular cloud is estimated to about 1.36 Saturnian radii in size, and probably broadening. We also present a reconnection event from the magnetic field data (MAG) that leave behind several plasmoids like those reported from the Voyager flybys in the early 1980s. That magnetic bubbles happened at the dawn side of Saturn's magnetosphere. At their nascency, the magnetic field showed a switchover of its alignment, disruption of flux tubes and a recovery on a time scale of about 30 days. However, we cannot rule out that different events might have taken place. Empirical evidence is shown at another occasion when a plasmoid was carrying a cloud of tiny dust particles such that a connection between plasmoids and coherent dust clouds is probable.

Mars dust and cloud opacities and scattering properties

NASA Technical Reports Server (NTRS)

Clancy, R. T.; Lee, S. W.

1992-01-01

We have recently completed an analysis of the visible emission-phase function (EPF) sequences obtained with the solar-band channel of the Infrared Thermal Mapping (IRTM) instrument onboard the two Viking Orbiters. Roughly 100 of these EPF sequences were gathered during the 1977-1980 period, in which the total broadband (.3-3.0 microns) reflectances of the atmosphere/surface above specific locations on Mars were measured versus emission angle as the spacecraft passed overhead. A multiple scattering radiative transfer program was employed to model the EPF observations in terms of the optical depths of dust/clouds, their single scattering albedos and phase functions, and the Lambert albedos and phase coefficient of the underlying surfaces. Due to the predominance of atmospheric scattering at large atmospheric pathlengths and/or large dust opacities, we were able to obtain strong constraints on the scattering properties of dust/clouds and their opacities for a wide range of latitudes, longitudes, and seasons on Mars.

Pyrophoric sulfides influence over the minimum ignition temperature of dust cloud

NASA Astrophysics Data System (ADS)

Prodan, Maria; Lupu, Leonard Andrei; Ghicioi, Emilian; Nalboc, Irina; Szollosi-Mota, Andrei

2017-12-01

The dust cloud is the main form of existence of combustible dust in the production area and together with the existence of effective ignition sources are the main causes of dust explosions in production processes. The minimum ignition temperature has an important role in the process of selecting the explosion-protected electrical equipment when performing the explosion risk assessment of combustible dusts. The heated surfaces are able to ignite the dust clouds that can form in process industry. The oil products usually contain hydrogen sulfide and thus on the pipe walls iron sulfides can form, which can be very dangerous from health and safety point of view. In order to study the influence of the pyrophoric sulfide over the minimum ignition temperature of combustible dusts for this work were performed several experiments on a residue collected from the oil pipes contaminated with commercially iron sulfide.

The implications of dust ice nuclei effect on cloud top temperature in a complex mesoscale convective system.

PubMed

Li, Rui; Dong, Xue; Guo, Jingchao; Fu, Yunfei; Zhao, Chun; Wang, Yu; Min, Qilong

2017-10-23

Mineral dust is the most important natural source of atmospheric ice nuclei (IN) which may significantly mediate the properties of ice cloud through heterogeneous nucleation and lead to crucial impacts on hydrological and energy cycle. The potential dust IN effect on cloud top temperature (CTT) in a well-developed mesoscale convective system (MCS) was studied using both satellite observations and cloud resolving model (CRM) simulations. We combined satellite observations from passive spectrometer, active cloud radar, lidar, and wind field simulations from CRM to identify the place where ice cloud mixed with dust particles. For given ice water path, the CTT of dust-mixed cloud is warmer than that in relatively pristine cloud. The probability distribution function (PDF) of CTT for dust-mixed clouds shifted to the warmer end and showed two peaks at about -45 °C and -25 °C. The PDF for relatively pristine cloud only show one peak at -55 °C. Cloud simulations with different microphysical schemes agreed well with each other and showed better agreement with satellite observations in pristine clouds, but they showed large discrepancies in dust-mixed clouds. Some microphysical schemes failed to predict the warm peak of CTT related to heterogeneous ice formation.

Satellite-Based Assessment of Possible Dust Aerosols Semi-Direct Effect on Cloud Water Path over East Asia

NASA Technical Reports Server (NTRS)

Huang, Jianping; Lin, Bing; Minnis, Patrick; Wang, Tainhe; Wang, Xin; Hu, Yongxiang; Yi, Yuhong; Ayers, J. Kirk

2006-01-01

The semi-direct effects of dust aerosols are analyzed over eastern Asia using 2 years (June 2002 to June 2004) of data from the Clouds and the Earth s Radiant Energy System (CERES) scanning radiometer and MODerate Resolution Imaging Spectroradiometer (MODIS) on the Aqua satellite, and 18 years (1984 to 2001) of International Satellite Cloud Climatology Project (ISCCP) data. The results show that the water path of dust-contaminated clouds is considerably smaller than that of dust-free clouds. The mean ice water path (IWP) and liquid water path (LWP) of dusty clouds are less than their dust-free counterparts by 23.7% and 49.8%, respectively. The long-term statistical relationship derived from ISCCP also confirms that there is significant negative correlation between dust storm index and ISCCP cloud water path. These results suggest that dust aerosols warm clouds, increase the evaporation of cloud droplets and further reduce cloud water path, the so-called semi-direct effect. The semi-direct effect may play a role in cloud development over arid and semi-arid areas of East Asia and contribute to the reduction of precipitation.

The Mars Dust Cycle: Investigating the Effects of Radiatively Active Water Ice Clouds on Surface Stresses and Dust Lifting Potential with the NASA Ames Mars General Circulation Model

NASA Technical Reports Server (NTRS)

Kahre, Melinda A.; Hollingsworth, Jeffery

2012-01-01

The dust cycle is a critically important component of Mars' current climate system. Dust is present in the atmosphere of Mars year-round but the dust loading varies with season in a generally repeatable manner. Dust has a significant influence on the thermal structure of the atmosphere and thus greatly affects atmospheric circulation. The dust cycle is the most difficult of the three climate cycles (CO2, water, and dust) to model realistically with general circulation models. Until recently, numerical modeling investigations of the dust cycle have typically not included the effects of couplings to the water cycle through cloud formation. In the Martian atmosphere, dust particles likely provide the seed nuclei for heterogeneous nucleation of water ice clouds. As ice coats atmospheric dust grains, the newly formed cloud particles exhibit different physical and radiative characteristics. Thus, the coupling between the dust and water cycles likely affects the distributions of dust, water vapor and water ice, and thus atmospheric heating and cooling and the resulting circulations. We use the NASA Ames Mars GCM to investigate the effects of radiatively active water ice clouds on surface stress and the potential for dust lifting. The model includes a state-of-the-art water ice cloud microphysics package and a radiative transfer scheme that accounts for the radiative effects of CO2 gas, dust, and water ice clouds. We focus on simulations that are radiatively forced by a prescribed dust map, and we compare simulations that do and do not include radiatively active clouds. Preliminary results suggest that the magnitude and spatial patterns of surface stress (and thus dust lifting potential) are substantial influenced by the radiative effects of water ice clouds.

Optimization of high-inclination orbits using planetary flybys for a zodiacal light-imaging mission

NASA Astrophysics Data System (ADS)

Soto, Gabriel; Lloyd, James; Savransky, Dmitry; Grogan, Keith; Sinha, Amlan

2017-09-01

The zodiacal light caused by interplanetary dust grains is the second-most luminous source in the solar system. The dust grains coalesce into structures reminiscent of early solar system formation; their composition has been predicted through simulations and some edge-on observations but better data is required to validate them. Scattered light from these dust grains presents challenges to exoplanet imaging missions: resolution of their stellar environment is hindered by exozodiacal emissions and therefore sets the size and scope of these imaging missions. Understanding the composition of this interplanetary dust in our solar system requires an imaging mission from a vantage point above the ecliptic plane. The high surface brightness of the zodiacal light requires only a small aperture with moderate sensitivity; therefore a 3cm camera is enough to meet the science goals of the mission at an orbital height of 0.1AU above the ecliptic. A 6U CubeSat is the target mass for this mission which will be a secondary payload detaching from an existing interplanetary mission. Planetary flybys are utilized to produce most of the plane change Δv deep space corrective maneuvers are implemented to optimize each planetary flyby. We developed an algorithm which determines the minimum Δv required to place the CubeSat on a transfer orbit to a planet's sphere of influence and maximizes the resultant orbital height with respect to the ecliptic plane. The satellite could reach an orbital height of 0.22 AU with an Earth gravity assist in late 2024 by boarding the Europa Clipper mission.

Dust Destruction Rates and Lifetimes in the Magellanic Clouds

NASA Technical Reports Server (NTRS)

Temim, Tea; Dwek, Eli; Tchernyshyov, Kirill; Boyer, Martha L.; Meixner, Margaret; Gall, Christa; Roman-Duval, Julia

2015-01-01

The nature, composition, abundance, and size distribution of dust in galaxies is determined by the rate at which it is created in the different stellar sources and destroyed by interstellar shocks. Because of their extensive wavelength coverage, proximity, and nearly face-on geometry, the Magellanic Clouds (MCs) provide a unique opportunity to study these processes in great detail. In this paper we use the complete sample of supernova remnants (SNRs) in the MCs to calculate the lifetime and destruction efficiencies of silicate and carbon dust in these galaxies. We find dust lifetimes of 22+/-13 Myr (30+/-17 Myr) for silicate (carbon) grains in the LMC, and 54 +/- 32 Myr (72 +/- 43 Myr) for silicate (carbon) grains in the SMC. The significantly shorter lifetimes in the MCs, as compared to the Milky Way, are explained as the combined effect of their lower total dust mass, and the fact that the dust-destroying isolated SNe in the MCs seem to be preferentially occurring in regions with higher than average dust-to-gas (D2G) mass ratios. We also calculate the supernova rate and the current star formation rate in the MCs, and use them to derive maximum dust injection rates by asymptotic giant branch (AGB) stars and core collapse supernovae (CCSNe). We find that the injection rates are an order of magnitude lower than the dust destruction rates by the SNRs. This supports the conclusion that, unless the dust destruction rates have been considerably overestimated, most of the dust must be reconstituted from surviving grains in dense molecular clouds. More generally, we also discuss the dependence of the dust destruction rate on the local D2G mass ratio and the ambient gas density and metallicity, as well as the application of our results to other galaxies and dust evolution models.

Water clouds and dust aerosols observations with PFS MEX at Mars

NASA Astrophysics Data System (ADS)

Zasova, L.; Formisano, V.; Moroz, V.; Grassi, D.; Ignatiev, N.; Giuranna, M.; Hansen, G.; Blecka, M.; Ekonomov, A.; Lellouch, E.; Fonti, S.; Grigoriev, A.; Hirsch, H.; Khatuntsev, I.; Mattana, A.; Maturilli, A.; Moshkin, B.; Patsaev, D.; Piccioni, G.; Rataj, M.; Saggin, B.

2005-08-01

Observations of water ice clouds and dust are among the main scientific goals of the Planetary Fourier Spectrometer (PFS), a payload instrument of the European Mars Express mission. We report some results, obtained in three orbits: 37, 41 and 68. The temperature profile, and dust and water ice cloud opacities are retrieved from the thermal infrared (long-wavelength channel of PFS) in a self-consistent way using the same spectrum. Orographic ice clouds are identified above Olympus (orbit 37) and Ascraeus Mons (orbit 68). Both volcanoes were observed near noon at Ls=337° and 342°, respectively. The effective radius of ice particles is preliminary estimated as 1-3 μm, changing along the flanks. The corresponding visual opacity changes in the interval 0.2-0.4 above Olympus and 0.1-0.6 above Ascraeus Mons. In the case of Ascraeus Mons, the ice clouds were observed mainly above the Southern flank of the volcano with maximum opacity near the summit. In the case of Olympus, the clouds were found above both sides of the top. A different type of ice cloud is observed at latitudes above 50°N (orbit 68) in the polar hood: the effective particle radius is estimated to be 4 μm. Below the 1 mb level an inversion in the temperature profiles is found with maximum temperature at around 0.6 mb. Along orbit 68 it appears above Alba Patera, then it increases to the north and decreases above the CO 2 polar cap. Beginning from latitude 20°S above Tharsis (orbit 68), the ice clouds and dust contribute equally to the spectral shape. Further on, the ice clouds are found everywhere along orbit 68 up to the Northern polar cap, except the areas between the Northern flank of Ascraeus Mons (below 10 km) and the edge of Alba Patera. Orbit 41 is shifted from the orbit 68 by roughly 180° longitude and passes through Hellas. Ice clouds are not visible in this orbit at latitudes below 80°S. The dust opacity is anticorrelated with the surface altitude. From 70°S to 25°N latitude the vertical

Modeling Dust in the Magellanic Clouds

NASA Astrophysics Data System (ADS)

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

2015-09-01

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

Experimental study on the minimum ignition temperature of coal dust clouds in oxy-fuel combustion atmospheres.

PubMed

Wu, Dejian; Norman, Frederik; Verplaetsen, Filip; Van den Bulck, Eric

2016-04-15

BAM furnace apparatus tests were conducted to investigate the minimum ignition temperature of coal dusts (MITC) in O2/CO2 atmospheres with an O2 mole fraction from 20 to 50%. Three coal dusts: Indonesian Sebuku coal, Pittsburgh No.8 coal and South African coal were tested. Experimental results showed that the dust explosion risk increases significantly with increasing O2 mole fraction by reducing the minimum ignition temperature for the three tested coal dust clouds dramatically (even by 100°C). Compared with conventional combustion, the inhibiting effect of CO2 was found to be comparatively large in dust clouds, particularly for the coal dusts with high volatile content. The retardation effect of the moisture content on the ignition of dust clouds was also found to be pronounced. In addition, a modified steady-state mathematical model based on heterogeneous reaction was proposed to interpret the observed experimental phenomena and to estimate the ignition mechanism of coal dust clouds under minimum ignition temperature conditions. The analysis revealed that heterogeneous ignition dominates the ignition mechanism for sub-/bituminous coal dusts under minimum ignition temperature conditions, but the decrease of coal maturity facilitates homogeneous ignition. These results improve our understanding of the ignition behaviour and the explosion risk of coal dust clouds in oxy-fuel combustion atmospheres. Copyright © 2015 Elsevier B.V. All rights reserved.

IRAS observations of dust heating and energy balance in the Rho Ophiuchi dark cloud

NASA Technical Reports Server (NTRS)

Greene, Thomas P.; Young, Erick T.

1989-01-01

The equilibrium process dust emission in the Rho Ophiuchi dark cloud is studied. The luminosity of the cloud is found to closely match the luminosity of the clouds's known embedded and external radiation sources. There is no evidence for a large population of undetected low-luminosity sources within the cloud and unknown external heating is also only a minor source of energy. Most of the cloud's luminosity is emitted in the mid-to-far-IR. Dust temperature maps indicate that the dust is not hot enough to heat the gas to observed temperatures. A simple cloud model with a radiation field composed of flux HD 147889, S1, and Sco OB2 associations predicts the observed IRAS 60 to 100 micron in-band flux ratios for a mean cloud density n(H2) = 1400. Flattened 12 and 25 micron observations show much extended emission in these bands, suggesting stochastic heating of very small grains or large molecules.

The potential influence of Asian and African mineral dust on ice, mixed-phase and liquid water clouds

NASA Astrophysics Data System (ADS)

Wiacek, A.; Peter, T.; Lohmann, U.

2010-02-01

This modelling study explores the availability of mineral dust particles as ice nuclei for interactions with ice, mixed-phase and liquid water clouds, also tracking the particles' history of cloud-processing. We performed 61 320 one-week forward trajectory calculations originating near the surface of major dust emitting regions in Africa and Asia using high-resolution meteorological analysis fields for the year 2007. Without explicitly modelling dust emission and deposition processes, dust-bearing trajectories were assumed to be those coinciding with known dust emission seasons. We found that dust emissions from Asian deserts lead to a higher potential for interactions with high clouds, despite being the climatologically much smaller dust emission source. This is due to Asian regions experiencing significantly more ascent than African regions, with strongest ascent in the Asian Taklimakan desert at ~25%, ~40% and 10% of trajectories ascending to 300 hPa in spring, summer and fall, respectively. The specific humidity at each trajectory's starting point was transported in a Lagrangian manner and relative humidities with respect to water and ice were calculated in 6-h steps downstream, allowing us to estimate the formation of liquid, mixed-phase and ice clouds. Practically none of the simulated air parcels reached regions where homogeneous ice nucleation can take place (T≲-40 °C) along trajectories that have not experienced water saturation first. By far the largest fraction of cloud forming trajectories entered conditions of mixed-phase clouds, where mineral dust will potentially exert the biggest influence. The majority of trajectories also passed through regions supersaturated with respect to ice but subsaturated with respect to water, where "warm" (T≳-40 °C) ice clouds may form prior to supercooled water or mixed-phase clouds. The importance of "warm" ice clouds and the general influence of dust in the mixed-phase cloud region are highly uncertain due to

Size Dependence of Dust Distribution around the Earth Orbit

NASA Astrophysics Data System (ADS)

Ueda, Takahiro; Kobayashi, Hiroshi; Takeuchi, Taku; Ishihara, Daisuke; Kondo, Toru; Kaneda, Hidehiro

2017-05-01

In the solar system, interplanetary dust particles (IDPs) originating mainly from asteroid collisions and cometary activities drift to Earth orbit due to Poynting-Robertson drag. We analyzed the thermal emission from IDPs that was observed by the first Japanese infrared astronomical satellite, AKARI. The observed surface brightness in the trailing direction of the Earth orbit is 3.7% greater than that in the leading direction in the 9 μm band and 3.0% in the 18 μm band. In order to reveal dust properties causing leading-trailing surface brightness asymmetry, we numerically integrated orbits of the Sun, the Earth, and a dust particle as a restricted three-body problem including radiation from the Sun. The initial orbits of particles are determined according to the orbits of main-belt asteroids or Jupiter-family comets. Orbital trapping in mean motion resonances results in a significant leading-trailing asymmetry so that intermediate sized dust (˜10-100 μm) produces a greater asymmetry than zodiacal light. The leading-trailing surface brightness difference integrated over the size distribution of the asteroidal dust is obtained to be 27.7% and 25.3% in the 9 μm and 18 μm bands, respectively. In contrast, the brightness difference for cometary dust is calculated as 3.6% and 3.1% in the 9 μm and 18 μm bands, respectively, if the maximum dust radius is set to be s max = 3000 μm. Taking into account these values and their errors, we conclude that the contribution of asteroidal dust to the zodiacal infrared emission is less than ˜10%, while cometary dust of the order of 1 mm mainly accounts for the zodiacal light in infrared.

Size Dependence of Dust Distribution around the Earth Orbit

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

Ueda, Takahiro; Takeuchi, Taku; Kobayashi, Hiroshi

In the solar system, interplanetary dust particles (IDPs) originating mainly from asteroid collisions and cometary activities drift to Earth orbit due to Poynting–Robertson drag. We analyzed the thermal emission from IDPs that was observed by the first Japanese infrared astronomical satellite, AKARI . The observed surface brightness in the trailing direction of the Earth orbit is 3.7% greater than that in the leading direction in the 9 μ m band and 3.0% in the 18 μ m band. In order to reveal dust properties causing leading–trailing surface brightness asymmetry, we numerically integrated orbits of the Sun, the Earth, and amore » dust particle as a restricted three-body problem including radiation from the Sun. The initial orbits of particles are determined according to the orbits of main-belt asteroids or Jupiter-family comets. Orbital trapping in mean motion resonances results in a significant leading–trailing asymmetry so that intermediate sized dust (∼10–100 μ m) produces a greater asymmetry than zodiacal light. The leading–trailing surface brightness difference integrated over the size distribution of the asteroidal dust is obtained to be 27.7% and 25.3% in the 9 μ m and 18 μ m bands, respectively. In contrast, the brightness difference for cometary dust is calculated as 3.6% and 3.1% in the 9 μ m and 18 μ m bands, respectively, if the maximum dust radius is set to be s {sub max} = 3000 μ m. Taking into account these values and their errors, we conclude that the contribution of asteroidal dust to the zodiacal infrared emission is less than ∼10%, while cometary dust of the order of 1 mm mainly accounts for the zodiacal light in infrared.« less

Do Cloud Properties in a Puerto Rican Tropical Montane Cloud Forest Depend on Occurrence of Long-Range Transported African Dust?

NASA Astrophysics Data System (ADS)

Spiegel, Johanna K.; Buchmann, Nina; Mayol-Bracero, Olga L.; Cuadra-Rodriguez, Luis A.; Valle Díaz, Carlos J.; Prather, Kimberly A.; Mertes, Stephan; Eugster, Werner

2014-09-01

We investigated cloud properties of warm clouds in a tropical montane cloud forest at Pico del Este (1,051 m a.s.l.) in the northeastern part of Puerto Rico to address the question of whether cloud properties in the Caribbean could potentially be affected by African dust transported across the Atlantic Ocean. We analyzed data collected during 12 days in July 2011. Cloud droplet size spectra were measured using the FM-100 fog droplet spectrometer that measured droplet size distributions in the range from 2 to 49 µm, primarily during fog events. The droplet size spectra revealed a bimodal structure, with the first peak ( D < 6 µm) being more pronounced in terms of droplet number concentrations, whereas the second peak (10 µm < D < 20 µm) was found to be the one relevant for total liquid water content (LWC) of the cloud. We identified three major clusters of characteristic droplet size spectra by means of hierarchical clustering. All clusters differed significantly from each other in droplet number concentration (), effective diameter (ED), and median volume diameter (MVD). For the cluster comprising the largest droplets and the lowest droplet number concentrations, we found evidence of inhomogeneous mixing in the cloud. Contrastingly, the other two clusters revealed microphysical behavior, which could be expected under homogeneous mixing conditions. For those conditions, an increase in cloud condensation nuclei—e.g., from processed African dust transported to the site—is supposed to lead to an increased droplet concentration. In fact, one of these two clusters showed a clear shift of cloud droplet size spectra towards smaller droplet diameters. Since this cluster occurred during periods with strong evidence for the presence of long-range transported African dust, we hypothesize a link between the observed dust episodes and cloud characteristics in the Caribbean at our site, which is similar to the anthropogenic aerosol indirect effect.

Laboratory Studies of the Cloud Droplet Activation Properties and Corresponding Chemistry of Saline Playa Dust.

PubMed

Gaston, Cassandra J; Pratt, Kerri A; Suski, Kaitlyn J; May, Nathaniel W; Gill, Thomas E; Prather, Kimberly A

2017-02-07

Playas emit large quantities of dust that can facilitate the activation of cloud droplets. Despite the potential importance of playa dusts for cloud formation, most climate models assume that all dust is nonhygroscopic; however, measurements are needed to clarify the role of dusts in aerosol-cloud interactions. Here, we report measurements of CCN activation from playa dusts and parameterize these results in terms of both κ-Köhler theory and adsorption activation theory for inclusion in atmospheric models. κ ranged from 0.002 ± 0.001 to 0.818 ± 0.094, whereas Frankel-Halsey-Hill (FHH) adsorption parameters of A FHH = 2.20 ± 0.60 and B FHH = 1.24 ± 0.14 described the water uptake properties of the dusts. Measurements made using aerosol time-of-flight mass spectrometry (ATOFMS) revealed the presence of halite, sodium sulfates, and sodium carbonates that were strongly correlated with κ underscoring the role that mineralogy, including salts, plays in water uptake by dust. Predictions of κ made using bulk chemical techniques generally showed good agreement with measured values. However, several samples were poorly predicted suggesting that chemical heterogeneities as a function of size or chemically distinct particle surfaces can determine the hygroscopicity of playa dusts. Our results further demonstrate the importance of dust in aerosol-cloud interactions.

Cosmic rays, gas and dust in nearby anticentre clouds. I. CO-to-H2 conversion factors and dust opacities

NASA Astrophysics Data System (ADS)

Remy, Q.; Grenier, I. A.; Marshall, D. J.; Casandjian, J. M.

2017-05-01

Aims: We aim to explore the capabilities of dust emission and γ rays for probing the properties of the interstellar medium in the nearby anti-centre region, using γ-ray observations with the Fermi Large Area Telescope (LAT), and the thermal dust optical depth inferred from Planck and IRAS observations. We also aim to study massive star-forming clouds including the well known Taurus, Auriga, Perseus, and California molecular clouds, as well as a more diffuse structure which we refer to as Cetus. In particular, we aim at quantifying potential variations in cosmic-ray density and dust properties per gas nucleon across the different gas phases and different clouds, and at measuring the CO-to-H2 conversion factor, XCO, in different environments. Methods: We have separated six nearby anti-centre clouds that are coherent in velocities and distances, from the Galactic-disc background in H I 21-cm and 12CO 2.6-mm line emission. We have jointly modelled the γ-ray intensity recorded between 0.4 and 100 GeV, and the dust optical depth τ353 at 353 GHz as a combination of H I-bright, CO-bright, and ionised gas components. The complementary information from dust emission and γ rays was used to reveal the gas not seen, or poorly traced, by H I, free-free, and 12CO emissions, namely (I) the opaque H iand diffuse H2 present in the Dark Neutral Medium at the atomic-molecular transition, and (II) the dense H2 to be added where 12CO lines saturate. Results: The measured interstellar γ-ray spectra support a uniform penetration of the cosmic rays with energies above a few GeV through the clouds, from the atomic envelopes to the 12CO-bright cores, and with a small ± 9% cloud-to-cloud dispersion in particle flux. We detect the ionised gas from the H iiregion NGC 1499 in the dust and γ-ray emissions and measure its mean electron density and temperature. We find a gradual increase in grain opacity as the gas (atomic or molecular) becomes more dense. The increase reaches a factor of

Cloud Ozone Dust Imager (CODI). Volume 1; Investigation and Technical Plan

NASA Technical Reports Server (NTRS)

Clancy, R. Todd; Dusenbery, Paul; Wolff, Michael; James, Phil; Allen, Mark; Goguen, Jay; Kahn, Ralph; Gladstone, Rany; Murphy, Jim

1995-01-01

The Cloud Ozone Dust Imager (CODI) is proposed to investigate the current climatic balance of the Mars atmosphere, with particular emphasis on the important but poorly understood roles which dust and water ice aerosols play in this balance. The large atmospheric heating (20-50 K) resulting from global dust storms around Mars perihelion is well recognized. However, groundbased observations of Mars atmospheric temperatures, water vapor, and clouds since the Viking missions have identified a much colder, cloudier atmosphere around Mars aphelion that may prove as important as global dust storms in determining the interannual and long-term behavior of the Mars climate. The key climate issues CODI is designed to investigate are: 1) the degree to which non-linear interactions between atmospheric dust heating, water vapor saturation, and cloud nucleation influence the seasonal and interannual variability of the Mars atmosphere, and 2) whether the strong orbital forcing of atmospheric dust loading, temperatures and water vapor saturation determines the long-term balance of Mars water, as reflected in the north-south hemispheric asymmetries of atmospheric water vapor and polar water ice abundances. The CODI experiment will measure the daily, seasonal and (potentially) interannual variability of atmospheric dust and cloud opacities, and the key physical properties of these aerosols which determine their role in the climate cycles of Mars. CODI is a small (1.2 kg), fixed pointing camera, in which four wide-angle (+/- 70 deg) lenses illuminate fixed filters and CCD arrays. Simultaneous sky/surface imaging of Mars is obtained at an angular resolution of 0.28 deg/pixel for wavelengths of 255, 336, 502, and 673 nm (similar to Hubble Space Telescope filters). These wavelengths serve to measure atmospheric ozone (255 and 336 nm), discriminate ice and dust aerosols (336 and 673 nm), and construct color images (336, 502, and 673 nm). The CODI images are detected on four 512 x 512

Results from Automated Cloud and Dust Devil Detection Onboard the MER

NASA Technical Reports Server (NTRS)

Chien, Steve; Castano, Rebecca; Bornstein, Benjamin; Fukunaga, Alex; Castano, Andres; Biesiadecki, Jeffrey; Greeley, Ron; Whelley, Patrick; Lemmon, Mark

2008-01-01

We describe a new capability to automatically detect dust devils and clouds in imagery onboard rovers, enabling downlink of just the images with the targets or only portions of the images containing the targets. Previously, the MER rovers conducted campaigns to image dust devils and clouds by commanding a set of images be collected at fixed times and downloading the entire image set. By increasing the efficiency of the campaigns, more campaigns can be executed. Software for these new capabilities was developed, tested, integrated, uploaded, and operationally checked out on both rovers as part of the R9.2 software upgrade. In April 2007 on Sol 1147 a dust devil was automatically detected onboard the Spirit rover for the first time. We discuss the operational usage of the capability and present initial dust devil results showing how this preliminary application has demonstrated the feasibility and potential benefits of the approach.

A study of zodiacal light models

NASA Technical Reports Server (NTRS)

Gary, G. A.; Craven, P. D.

1973-01-01

A review is presented of the basic equations used in the analysis of photometric observations of zodiacal light. A survey of the methods used to model the zodiacal light in and out of the ecliptic is given. Results and comparison of various models are presented, as well as recent results by the authors.

Laboratory Studies of the Cloud Droplet Activation Properties and Corresponding Chemistry of Saline Playa Dust

NASA Astrophysics Data System (ADS)

Gaston, C.; Pratt, K.; Suski, K. J.; May, N.; Gill, T. E.; Prather, K. A.

2016-12-01

Saline playas (dried lake beds) emit large quantities of dust that can facilitate the activation of cloud droplets. Despite the potential importance of playa dust for cloud formation, several models assume that dust is non-hygroscopic highlighting the need for measurements to clarify the role of dust from multiple sources in aerosol-cloud-climate interactions. Here we present water uptake measurements onto playa dust represented by the hygroscopicity parameter κ, which ranged from 0.002 ± 0.001 to 0.818 ± 0.094. Single-particle measurements made using an aircraft-aerosol time-of-flight mass spectrometer (A-ATOFMS) revealed the presence of halite, sodium sulfates, and sodium carbonates that were strongly correlated with κ underscoring the role that dust composition plays in water uptake. Predictions of κ made using bulk chemical techniques generally showed good agreement with measured values; however, several samples were poorly predicted using bulk particle composition. The lack of measurements/model agreement using this method and the strong correlations between κ and single-particle data are suggestive of chemical heterogeneities as a function of particle size and/or chemically distinct particle surfaces that dictate the water uptake properties of playa dust particles. Overall, our results highlight the ability of playa dust particles to act as cloud condensation nuclei that should be accounted for in models.

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

Natural mineral dust from desert regions is known to be the most important contributor to atmospheric ice-nucleating particles (INP) which induce heterogeneous ice nucleation in mixed-phase clouds. Its ability to nucleate ice effectively is shown by various laboratory (Hoose and Möhler 2012) and field results (DeMott et al. 2015) and its abundance in ice crystal residuals has also been shown (Cziczo et al. 2013). Thus it is an important player when representing mixed-phase clouds in climate models. MODIS satellite data indicate that 1 /4 of the global dust emission originates from semi-arid areas rather than from arid deserts (Ginoux et al. 2012). Here, organic components can mix with minerals within the soil and get into the atmosphere. These so-called 'soil dust' particles are ice-nucleating active at high sub-zero temperatures, i.e. at higher temperatures than pure desert dust (Steinke et al. 2016). In this study, soil dust is incorporated into the Norwegian Earth System Model (NorESM, Bentsen et al. 2013) and applied to a modified ice nucleation parameterization (Steinke et al. 2016). Its influence on the cloud ice phase is evaluated by comparing a control run, where only pure desert dust is considered, and a sensitivity experiment, where a fraction of the dust emissions are classified as soil dust. Both simulations are nudged to ERA-interim meteorology and they have the same loading of dust emissions. NorESM gives a lower annual soil dust emission flux compared to Ginoux et al. (2012), but the desert dust flux is similar to the MODIS-retrieved data. Although soil dust concentrations are much lower than desert dust, the NorESM simulations indicate that the annual INP concentrations from soil dust are on average lower by a just a factor of 4 than INP concentrations from pure desert dust. The highest soil dust INP concentrations occur at a lower height than for desert dust, i.e at warmer temperatures inside mixed-phase clouds. Furthermore, soil dust INP

The origin and evolution of dust clouds in Central Asia

USGS Publications Warehouse

Smirnov, V.V.; Gillette, Dale A.; Golitsyn, G.S.; MacKinnon, D.J.

1994-01-01

Data from a high resolution radiometer AVHRR (580-680 nm optical lengthwaves) installed on the "NOAA-11" satellite as well as TV (500-700 nm) and IR (8000-12000 nm) equipment of the Russia satellite "Meteor-2/16" were used to study the evolution of dust storms for 1-30 September 1989 in Tajikistan, Uzbekistan, Turkmenistan and Afghanistan. These data help to validate the hypothesis, that long-term dusted boundary layer (duration of the order of a day or more), but of comparatively not high optical density (4-10 km meteorological visibility range at the 20-50 km background), is formed after the northwest intrusions into a region of intensive cold fronts at the surface wind velocities of 7-15 m/s. Stability of dust clouds of vertical power to 3-3.5 km (up to an inversion level) is explained by an action of collective buoyancy factors at heating the dust particles of 2-4 ??m in mean diameter by solar radiation. The more intensive intrusions stimulate a formation of simultaneously dust and water clouds. The last partially reduce the solar radiation (by the calculations of the order of 30-50%) and decrease the role of buoyancy factors. Thus, initiated is the intensive but short-term dusted boundary layer at horizontal visibility of 50-200 m. ?? 1994.

Gathering dust: A galaxy-wide study of dust emission from cloud complexes in NGC 300

NASA Astrophysics Data System (ADS)

Riener, M.; Faesi, C. M.; Forbrich, J.; Lada, C. J.

2018-05-01

Aims: We use multi-band observations by the Herschel Space Observatory to study the dust emission properties of the nearby spiral galaxy NGC 300. We compile a first catalogue of the population of giant dust clouds (GDCs) in NGC 300, including temperature and mass estimates, and give an estimate of the total dust mass of the galaxy. Methods: We carried out source detection with the multiwavelength source extraction algorithm getsources. We calculated physical properties, including mass and temperature, of the GDCs from five-band Herschel PACS and SPIRE observations from 100 to 500 μm; the final size and mass estimates are based on the observations at 250 μm that have an effective spatial resolution of 170 pc. We correlated our final catalogue of GDCs to pre-existing catalogues of HII regions to infer the number of GDCs associated with high-mass star formation and determined the Hα emission of the GDCs. Results: Our final catalogue of GDCs includes 146 sources, 90 of which are associated with known HII regions. We find that the dust masses of the GDCs are completely dominated by the cold dust component and range from 1.1 × 103 to 1.4 × 104 M⊙. The GDCs have effective temperatures of 13-23 K and show a distinct cold dust effective temperature gradient from the centre towards the outer parts of the stellar disk. We find that the population of GDCs in our catalogue constitutes 16% of the total dust mass of NGC 300, which we estimate to be about 5.4 × 106 M⊙. At least about 87% of our GDCs have a high enough average dust mass surface density to provide sufficient shielding to harbour molecular clouds. We compare our results to previous pointed molecular gas observations in NGC 300 and results from other nearby galaxies and also conclude that it is very likely that most of our GDCs are associated with complexes of giant molecular clouds. The catalogue is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http

Spectral shifting strongly constrains molecular cloud disruption by radiation pressure on dust

NASA Astrophysics Data System (ADS)

Reissl, Stefan; Klessen, Ralf S.; Mac Low, Mordecai-Mark; Pellegrini, Eric W.

2018-03-01

Aim. We aim to test the hypothesis that radiation pressure from young star clusters acting on dust is the dominant feedback agent disrupting the largest star-forming molecular clouds and thus regulating the star-formation process. Methods: We performed multi-frequency, 3D, radiative transfer calculations including both scattering and absorption and re-emission to longer wavelengths for model clouds with masses of 104-107 M⊙, containing embedded clusters with star formation efficiencies of 0.009-91%, and varying maximum grain sizes up to 200 μm. We calculated the ratio between radiative and gravitational forces to determine whether radiation pressure can disrupt clouds. Results: We find that radiation pressure acting on dust almost never disrupts star-forming clouds. Ultraviolet and optical photons from young stars to which the cloud is optically thick do not scatter much. Instead, they quickly get absorbed and re-emitted by the dust at thermal wavelengths. As the cloud is typically optically thin to far-infrared radiation, it promptly escapes, depositing little momentum in the cloud. The resulting spectrum is more narrowly peaked than the corresponding Planck function, and exhibits an extended tail at longer wavelengths. As the opacity drops significantly across the sub-mm and mm wavelength regime, the resulting radiative force is even smaller than for the corresponding single-temperature blackbody. We find that the force from radiation pressure falls below the strength of gravitational attraction by an order of magnitude or more for either Milky Way or moderate starbust conditions. Only for unrealistically large maximum grain sizes, and star formation efficiencies far exceeding 50% do we find that the strength of radiation pressure can exceed gravity. Conclusions: We conclude that radiation pressure acting on dust does not disrupt star-forming molecular clouds in any Local Group galaxies. Radiation pressure thus appears unlikely to regulate the star

A physically-based approach of treating dust-water cloud interactions in climate models

NASA Astrophysics Data System (ADS)

Kumar, P.; Karydis, V.; Barahona, D.; Sokolik, I. N.; Nenes, A.

2011-12-01

All aerosol-cloud-climate assessment studies to date assume that the ability of dust (and other insoluble species) to act as a Cloud Condensation Nuclei (CCN) is determined solely by their dry size and amount of soluble material. Recent evidence however clearly shows that dust can act as efficient CCN (even if lacking appreciable amounts of soluble material) through adsorption of water vapor onto the surface of the particle. This "inherent" CCN activity is augmented as the dust accumulates soluble material through atmospheric aging. A comprehensive treatment of dust-cloud interactions therefore requires including both of these sources of CCN activity in atmospheric models. This study presents a "unified" theory of CCN activity that considers both effects of adsorption and solute. The theory is corroborated and constrained with experiments of CCN activity of mineral aerosols generated from clays, calcite, quartz, dry lake beds and desert soil samples from Northern Africa, East Asia/China, and Northern America. The unified activation theory then is included within the mechanistic droplet activation parameterization of Kumar et al. (2009) (including the giant CCN correction of Barahona et al., 2010), for a comprehensive treatment of dust impacts on global CCN and cloud droplet number. The parameterization is demonstrated with the NASA Global Modeling Initiative (GMI) Chemical Transport Model using wind fields computed with the Goddard Institute for Space Studies (GISS) general circulation model. References Barahona, D. et al. (2010) Comprehensively Accounting for the Effect of Giant CCN in Cloud Activation Parameterizations, Atmos.Chem.Phys., 10, 2467-2473 Kumar, P., I.N. Sokolik, and A. Nenes (2009), Parameterization of cloud droplet formation for global and regional models: including adsorption activation from insoluble CCN, Atmos.Chem.Phys., 9, 2517- 2532

Formation of iron nanoparticles and increase in iron reactivity in mineral dust during simulated cloud processing.

PubMed

Shi, Zongbo; Krom, Michael D; Bonneville, Steeve; Baker, Alex R; Jickells, Timothy D; Benning, Liane G

2009-09-01

The formation of iron (Fe) nanoperticles and increase in Fe reactivity in mineral dust during simulated cloud processing was investigated using high-resolution microscopy and chemical extraction methods. Cloud processing of dust was experimentally simulated via an alternation of acidic (pH 2) and circumneutral conditions (pH 5-6) over periods of 24 h each on presieved (<20 microm) Saharan soil and goethite suspensions. Microscopic analyses of the processed soil and goethite samples reveal the neo-formation of Fe-rich nanoparticle aggregates, which were not found initially. Similar Fe-rich nanoparticles were also observed in wet-deposited Saharen dusts from the western Mediterranean but not in dry-deposited dust from the eastern Mediterranean. Sequential Fe extraction of the soil samples indicated an increase in the proportion of chemically reactive Fe extractable by an ascorbate solution after simulated cloud processing. In addition, the sequential extractions on the Mediterranean dust samples revealed a higher content of reactive Fe in the wet-deposited dust compared to that of the dry-deposited dust These results suggestthat large variations of pH commonly reported in aerosol and cloud waters can trigger neo-formation of nanosize Fe particles and an increase in Fe reactivity in the dust

The Dynamic Community of Interest and Its Realization in ZODIAC

DTIC Science & Technology

2009-10-01

the ZODIAC project. ZODIAC is a network architecture that puts security first and foremost, with security broken down into confidentiality, integrity...hosts, a unified solution for MANETs will work for hosts or routers as well. DYNAMIC COMMUNITIES OF INTEREST The basis of the ZODIAC design is a new dis...narrow scope of each DCoI limits attack propagation, and supports confidentiality ABSTRACT The ZODIAC project has been exploring a security first

The potential influence of Asian and African mineral dust on ice, mixed-phase and liquid water clouds

NASA Astrophysics Data System (ADS)

Wiacek, A.; Peter, T.; Lohmann, U.

2010-09-01

This modelling study explores the availability of mineral dust particles as ice nuclei for interactions with ice, mixed-phase and liquid water clouds, also tracking the particles' history of cloud-processing. We performed 61 320 one-week forward trajectory calculations originating near the surface of major dust emitting regions in Africa and Asia using high-resolution meteorological analysis fields for the year 2007. Dust-bearing trajectories were assumed to be those coinciding with known dust emission seasons, without explicitly modelling dust emission and deposition processes. We found that dust emissions from Asian deserts lead to a higher potential for interactions with high ice clouds, despite being the climatologically much smaller dust emission source. This is due to Asian regions experiencing significantly more ascent than African regions, with strongest ascent in the Asian Taklimakan desert at ~25%, ~40% and 10% of trajectories ascending to 300 hPa in spring, summer and fall, respectively. The specific humidity at each trajectory's starting point was transported in a Lagrangian manner and relative humidities with respect to water and ice were calculated in 6-h steps downstream, allowing us to estimate the formation of liquid, mixed-phase and ice clouds. Downstream of the investigated dust sources, practically none of the simulated air parcels reached conditions of homogeneous ice nucleation (T≲-40 °C) along trajectories that have not experienced water saturation first. By far the largest fraction of cloud forming trajectories entered conditions of mixed-phase clouds, where mineral dust will potentially exert the biggest influence. The majority of trajectories also passed through atmospheric regions supersaturated with respect to ice but subsaturated with respect to water, where so-called "warm ice clouds" (T≳-40 °C) theoretically may form prior to supercooled water or mixed-phase clouds. The importance of "warm ice clouds" and the general influence

PROGRA2 experiment: new results for dust clouds and regoliths

NASA Astrophysics Data System (ADS)

Renard, J.-B.; Hadamcik, E.; Worms, J.-C.; Levasseur-Regourd, A.-C.; Daugeron, D.

With the CNES-sponsored PROGRA2 facility, linear polarization of scattered light is performed on various types of dust clouds in microgravity during parabolic flights onboard the CNES- and ESA-sponsored A300 Zéro-G aircraft. Clouds of fluffy aggregates are also studied on the ground when lifted by an air-draught. The effect of the physical properties of the particles, such as the grains size and size distribution, the real part of the refractive index, and the structure is currently being studied. The size distribution of the agglomerates is measured in the field of view from the polarized component images. The large number of phase curves already obtained in the various conditions of measurements, in order to build a database (about 160 curves) allows us to better connect the physical properties with the observed polarization of the dust in the clouds. The aim is to compare these curves with those obtained in the solar system by remote-sensing and in-situ techniques for interplanetary dust, cometary coma, and solid particles in planetary atmospheres (Renard et al., 2003). Measurements on layers of particles (i.e. on the ground) are then compared with remote measurements on asteroidal regoliths and planetary surfaces. New phase curves will be presented and discussed i.e. for quartz samples, crystals, fluffy mixtures of alumina and silica, and a high porosity ``regolith'' analogue made of micron-sized silica spheres. This work will contribute to the choice of the samples to be studied with the IMPACT/ICAPS instrument onboard the ISS. J.-B. Renard, E. Hadamcik, T. Lemaire, J.-C. Worms and A.-C. Levasseur-Regourd (2003). Polarization imaging of dust cloud particles: improvement and applications of the PROGRA2 instrument, ASR 31, 12, 2511-2518.

Mapping the three-dimensional dust extinction towards the supernova remnant S147 - the S147 dust cloud

NASA Astrophysics Data System (ADS)

Chen, B.-Q.; Liu, X.-W.; Ren, J.-J.; Yuan, H.-B.; Huang, Y.; Yu, B.; Xiang, M.-S.; Wang, C.; Tian, Z.-J.; Zhang, H.-W.

2017-12-01

We present a three-dimensional (3D) extinction analysis in the region towards the supernova remnant (SNR) S147 (G180.0-1.7) using multiband photometric data from the Xuyi Schmidt Telescope Photometric Survey of the Galactic Anticentre (XSTPS-GAC), 2MASS and WISE. We isolate a previously unrecognized dust structure likely to be associated with SNR S147. The structure, which we term as 'S147 dust cloud', is estimated to have a distance d = 1.22 ± 0.21 kpc, consistent with the conjecture that S147 is associated with pulsar PSR J0538 + 2817. The cloud includes several dense clumps of relatively high extinction that locate on the radio shell of S147 and coincide spatially with the CO and gamma-ray emission features. We conclude that the usage of CO measurements to trace the SNR associated MCs is unavoidably limited by the detection threshold, dust depletion and the difficulty of distance estimates in the outer Galaxy. 3D dust extinction mapping may provide a better way to identify and study SNR-MC interactions.

Evolution of Cometary Dust Particles to the Orbit of the Earth: Particle Size, Shape, and Mutual Collisions

NASA Astrophysics Data System (ADS)

Yang, Hongu; Ishiguro, Masateru

2018-02-01

In this study, we numerically investigated the orbital evolution of cometary dust particles, with special consideration of the initial size–frequency distribution (SFD) and different evolutionary tracks according to the initial orbit and particle shape. We found that close encounters with planets (mostly Jupiter) are the dominating factor determining the orbital evolution of dust particles. Therefore, the lifetimes of cometary dust particles (∼250,000 yr) are shorter than the Poynting–Robertson lifetime, and only a small fraction of large cometary dust particles can be transferred into orbits with small semimajor axes. The exceptions are dust particles from 2P/Encke and, potentially, active asteroids that have little interaction with Jupiter. We also found that the effects of dust shape, mass density, and SFD were not critical in the total mass supply rate to the interplanetary dust particle (IDP) cloud complex when these quantities are confined by observations of zodiacal light brightness and SFD around the Earth’s orbit. When we incorporate a population of fluffy aggregates discovered in the Earth’s stratosphere and the coma of 67P/Churyumov–Gerasimenko within the initial ejection, the initial SFD measured at the comae of comets (67P and 81P/Wild 2) can produce the observed SFD around the Earth’s orbit. Considering the above effects, we derived the probability of mutual collisions among dust particles within the IDP cloud for the first time in a direct manner via numerical simulation and concluded that mutual collisions can mostly be ignored.

Size-resolved Chemical Composition of Cloud and Rain Water Collected during the Puerto Rico African Dust and Clouds Study (PRADACS) Campaign

NASA Astrophysics Data System (ADS)

Torres, E.; Valle Diaz, C. J.; Zurcher, F.; Lee, T.; Collett, J. L.; Fitzgerald, E.; Cuadra, L.; Prather, K. A.; Mayol-Bracero, O. L.

2011-12-01

The underlying physico-chemical processes of dust-aerosol interactions are poorly understood; even less understood is how aging impacts cloud properties and climate as the particles travel from Africa to the Caribbean region. Caribbean landmasses have tropical montane cloud forests (TMCFs) that are tightly coupled to the atmospheric hydrologic cycle. Small-scale shifts in temperature and precipitation could have serious ecological consequences. Therefore, this makes TMCFs an interesting ecosystem to see the effects African Dust (AD) might have on cloud formation and precipitation. As part of the Puerto Rico African Dust and Clouds Study (PRADACS) cloud and rain water samples for subsequent chemical analysis were collected at Pico del Este (PE) station in Luquillo, PR (1051 masl) during summer 2011. At PE, two cloud collectors (i.e., single stage (Aluminum version) and 2-stage (Teflon version) Caltech Active Strand Cloudwater Collector (CASCC)), and a rainwater collector were operated. Measurements such as the liquid water content (LWC), pH, conductivity., and composition of single particles using an aerosol time of flight mass spectrometer (ATOFMS) were performed. Preliminary results showed that days with the influence of African dust (AD), had LWC values that ranged from 300 to 500 mg/m3, pH values up to 5.7,, and conductivity up to 180 μS/cm. The ATOFMS showed titanium and iron ions, suggesting the presence of AD as well as, occasionally, sulfate and nitrate ions suggesting the influence of anthropogenic pollution. Results on the chemical composition and the physical properties of cloud, rainwater, and aerosol for the inorganic as well as the organic fraction and how these properties change for the different air masses observed will also be presented.

Estimation of Asian Dust Aerosol Effect on Cloud Radiation Forcing Using Fu-Liou Radiative Model and CERES Measurements

NASA Technical Reports Server (NTRS)

Su, Jing; Huang, Jianping; Fu, Qiang; Minnis, Patrick; Ge, Jinming; Bi, Jianrong

2008-01-01

The impact of Asian dust on cloud radiative forcing during 2003-2006 is studied by using the Earth's Radiant Energy Budget Scanner (CERES) data and the Fu-Liou radiative transfer model. Analysis of satellite data shows that the dust aerosol significantly reduced the cloud cooling effect at TOA. In dust contaminated cloudy regions, the 4-year mean values of the instantaneous shortwave, longwave and net cloud radiative forcing are -138.9, 69.1, and -69.7 Wm(sup -2), which are 57.0, 74.2, and 46.3%, respectively, of the corresponding values in more pristine cloudy regions. The satellite-retrieved cloud properties are significantly different in the dusty regions and can influence the radiative forcing indirectly. The contributions to the cloud radiation forcing by the dust direct, indirect and semi-direct effects are estimated using combined satellite observations and Fu-Liou model simulation. The 4-year mean value of combination of indirect and semi-direct shortwave radiative forcing (SWRF) is 82.2 Wm(sup -2), which is 78.4% of the total dust effect. The direct effect is only 22.7 Wm(sup -2), which is 21.6% of the total effect. Because both first and second indirect effects enhance cloud cooling, the aerosol-induced cloud warming is mainly the result of the semi-direct effect of dust.

A Near-Infrared Spectrometer to Measure Zodiacal Light Absorption Spectrum

NASA Technical Reports Server (NTRS)

Kutyrev, A. S.; Arendt, R.; Dwek, E.; Kimble, R.; Moseley, S. H.; Rapchun, D.; Silverberg, R. F.

2010-01-01

We have developed a high throughput infrared spectrometer for zodiacal light fraunhofer lines measurements. The instrument is based on a cryogenic dual silicon Fabry-Perot etalon which is designed to achieve high signal to noise Fraunhofer line profile measurements. Very large aperture silicon Fabry-Perot etalons and fast camera optics make these measurements possible. The results of the absorption line profile measurements will provide a model free measure of the zodiacal Light intensity in the near infrared. The knowledge of the zodiacal light brightness is crucial for accurate subtraction of zodiacal light foreground for accurate measure of the extragalactic background light after the subtraction of zodiacal light foreground. We present the final design of the instrument and the first results of its performance.

The determination of cloud masses and dust characteristics from submillimetre thermal emission

NASA Technical Reports Server (NTRS)

Hildebrand, R. H.

1983-01-01

The principles by which the dust and masses and total masses of interstellar clouds and certain characteristics of interstellar dust grains can be derived from observations of far infrared and submillimeter thermal emission are reviewed. To the extent possible, the discussion will be independent of particular grain models.

Interstellar Explorer Observations of the Solar System's Debris Disks

NASA Astrophysics Data System (ADS)

Lisse, C. M.; McNutt, R. L., Jr.; Brandt, P. C.

2017-12-01

Planetesimal belts and debris disks full of dust are known as the "signposts of planet formation" in exosystems. The overall brightness of a disk provides information on the amount of sourcing planetesimal material, while asymmetries in the shape of the disk can be used to search for perturbing planets. The solar system is known to house two such belts, the Asteroid belt and the Kuiper Belt; and at least one debris cloud, the Zodiacal Cloud, sourced by planetisimal collisions and Kuiper Belt comet evaporative sublimation. However these are poorly understood in toto because we live inside of them. E.g., while we know of the two planetesimal belt systems, it is not clear how much, if any, dust is produced from the Kuiper belt since the near-Sun comet contributions dominate near-Earth space. Understanding how much dust is produced in the Kuiper belt would give us a much better idea of the total number of bodies in the belt, especially the smallest ones, and their dynamical collisional state. Even for the close in Zodiacal cloud, questions remain concerning its overall shape and orientation with respect to the ecliptic and invariable planes of the solar system - they aren't explainable from the perturbations caused by the known planets alone. In this paper we explore the possibilities of using an Interstellar Explorer telescope placed at 200 AU from the sun to observe the brightness, shape, and extent of the solar system's debris disk(s). We should be able to measure the entire extent of the inner, near-earth zodiacal cloud; whether it connects smoothly into an outer cloud, or if there is a second outer cloud sourced by the Kuiper belt and isolated by the outer planets, as predicted by Stark & Kuchner (2009, 2010) and Poppe et al. (2012, 2016; Figure 1). VISNIR imagery will inform about the dust cloud's density, while MIR cameras will provide thermal imaging photometry related to the cloud's dust particle size and composition. Observing at high phase angle by looking

Heterogeneous chemistry of atmospheric mineral dust particles and their resulting cloud-nucleation properties

NASA Astrophysics Data System (ADS)

Sullivan, Ryan Christopher

Mineral dust particles are a major component of tropospheric aerosol mass and affect regional and global atmospheric chemistry and climate. Dust particles experience heterogeneous reactions with atmospheric gases that alter the gas and particle-phase chemistry. These in turn influence the warm and cold cloud nucleation ability and optical properties of the dust particles. This dissertation investigates the atmospheric chemistry of mineral dust particles and their role in warm cloud nucleation through a combination of synergistic field measurements, laboratory experiments, and theoretical modeling. In-situ measurements made with a single-particle mass spectrometer during the ACE-Asia field campaign in 2001 provide the motivation for this work. The observed mixing state of the individual ambient particles with secondary organic and inorganic components is described in Chapter 2. A large Asian dust storm occurred during the campaign and produced dramatic changes in the aerosol's composition and mixing state. The effect of particle size and mineralogy on the atmospheric processing of individual dust particles is explored in Chapters 3 & 4. Sulfate was found to accumulate preferentially in submicron iron and aluminosilicate-rich dust particles, while nitrate and chloride were enriched in supermicron calcite-rich dust. The mineral dust (and sea salt particles) were also enriched in oxalic acid, the dominant component of water soluble organic carbon. Chapter 5 explores the roles of gas-phase photochemistry and partitioning of the diacids to the alkaline particles in producing this unique behavior. The effect of the dust's mixing state with secondary organic and inorganic components on the dust particles' solubility, hygroscopicity, and thus warm cloud nucleation properties is explored experimentally and theoretically in Chapter 6. Cloud condensation nucleation (CCN) activation curves revealed that while calcium nitrate and calcium chloride particles were very hygroscopic

Impact of Saharan dust on North Atlantic marine stratocumulus clouds: importance of the semidirect effect

NASA Astrophysics Data System (ADS)

Amiri-Farahani, Anahita; Allen, Robert J.; Neubauer, David; Lohmann, Ulrike

2017-05-01

One component of aerosol-cloud interactions (ACI) involves dust and marine stratocumulus clouds (MSc). Few observational studies have focused on dust-MSc interactions, and thus this effect remains poorly quantified. We use observations from multiple sensors in the NASA A-Train satellite constellation from 2004 to 2012 to obtain estimates of the aerosol-cloud radiative effect, including its uncertainty, of dust aerosol influencing Atlantic MSc off the coast of northern Africa between 45° W and 15° E and between 0 and 35° N. To calculate the aerosol-cloud radiative effect, we use two methods following Quaas et al. (2008) (Method 1) and Chen et al. (2014) (Method 2). These two methods yield similar results of -1.5 ± 1.4 and -1.5 ± 1.6 W m-2, respectively, for the annual mean aerosol-cloud radiative effect. Thus, Saharan dust modifies MSc in a way that acts to cool the planet. There is a strong seasonal variation, with the aerosol-cloud radiative effect switching from significantly negative during the boreal summer to weakly positive during boreal winter. Method 1 (Method 2) yields -3.8 ± 2.5 (-4.3 ± 4.1) during summer and 1 ± 2.9 (0.6 ± 1) W m-2 during winter. In Method 1, the aerosol-cloud radiative effect can be decomposed into two terms, one representing the first aerosol indirect effect and the second representing the combination of the second aerosol indirect effect and the semidirect effect (i.e., changes in liquid water path and cloud fraction in response to changes in absorbing aerosols and local heating). The first aerosol indirect effect is relatively small, varying from -0.7 ± 0.6 in summer to 0.1 ± 0.5 W m-2 in winter. The second term, however, dominates the overall radiative effect, varying from -3.2 ± 2.5 in summer to 0.9 ± 2.9 W m-2 during winter. Studies show that the semidirect effect can result in a negative (i.e., absorbing aerosol lies above low clouds like MSc) or positive (i.e., absorbing aerosol lies within low clouds) aerosol-cloud

Link between interplanetary & cometary dust: Polarimetric observations and space studies with Rosetta & Eye-Sat

NASA Astrophysics Data System (ADS)

Levasseur-Regourd, Anny-Chantal; Gaboriaud, Alain; Buil, Christian; Ressouche, Antoine; Lasue, J.; Palun, Adrien; Apper, Fabien; Elmaleh, Marc

in 2016 [7]. Its main purpose is to study the zodiacal light intensity and polarization from a Sun-synchronous orbit, for the first time at the high spatial resolution of 1° over a wide portion of the sky and at four different wavelengths (in the visible and near-IR domains). The instrumental choices and new on-board technologies will be summarized, together with the results that may be expected on local properties of the interplanetary dust particles and thus on their similarities and differences with cometary dust particles. Support from CNES is warmly acknowledged. [1] Leinert, C., Bowyer, S., Haikala, L.K., et al. The 1997 reference of diffuse night sky brightness, Astron. Astrophys. Supp., 127, 1-99, 1998. [2] Levasseur-Regourd, A.C., Mann, I., Dumont, R., et al. Optical and thermal properties of interplanetary dust. In Interplanetary dust (Grün, E. et al. Eds), 57-94, Springer-Verlag, Berlin, 2001. [3] Lasue, J., Levasseur-Regourd, A.C., Fray, N., et al. Inferring the interplanetary dust properties from remote observations and simulations, Astron. Astrophys., 473, 641-649, 2007. [4] Nesvorny, D., Jenniskens, P., Levison, H.F., et al. Cometary origin of the zodiacal cloud and carbonaceous micrometeorites: implications for hot debris disks. Astrophys. J. 713, 816-836, 2010. [5] Levasseur-Regourd, A.C., Mukai, T., Lasue, J., et al. Physical properties of cometary and interplanetary dust, Planet. Space Sci., 55, 1010-1020, 2007. [6] Hadamcik, E., Sen, A.K., Levasseur-Regourd, A.C., et al., Astron. Astrophys., 517, A86, 2010. [7] CNES internal report. Eye-Sat end of phase A internal review, EYESAT-PR-0-022-CNES, 2013.

Estimating the dust production rate of carbon stars in the Small Magellanic Cloud

NASA Astrophysics Data System (ADS)

Nanni, Ambra; Marigo, Paola; Girardi, Léo; Rubele, Stefano; Bressan, Alessandro; Groenewegen, Martin A. T.; Pastorelli, Giada; Aringer, Bernhard

2018-02-01

We employ newly computed grids of spectra reprocessed by dust for estimating the total dust production rate (DPR) of carbon stars in the Small Magellanic Cloud (SMC). For the first time, the grids of spectra are computed as a function of the main stellar parameters, i.e. mass-loss rate, luminosity, effective temperature, current stellar mass and element abundances at the photosphere, following a consistent, physically grounded scheme of dust growth coupled with stationary wind outflow. The model accounts for the dust growth of various dust species formed in the circumstellar envelopes of carbon stars, such as carbon dust, silicon carbide and metallic iron. In particular, we employ some selected combinations of optical constants and grain sizes for carbon dust that have been shown to reproduce simultaneously the most relevant colour-colour diagrams in the SMC. By employing our grids of models, we fit the spectral energy distributions of ≈3100 carbon stars in the SMC, consistently deriving some important dust and stellar properties, i.e. luminosities, mass-loss rates, gas-to-dust ratios, expansion velocities and dust chemistry. We discuss these properties and we compare some of them with observations in the Galaxy and Large Magellanic Cloud. We compute the DPR of carbon stars in the SMC, finding that the estimates provided by our method can be significantly different, between a factor of ≈2-5, than the ones available in the literature. Our grids of models, including the spectra and other relevant dust and stellar quantities, are publicly available at http://starkey.astro.unipd.it/web/guest/dustymodels.

Coupling the Mars Dust and Water Cycles: Investigating the Role of Clouds in Controlling the Vertical Distribution of Dust During N. H. Summer

NASA Technical Reports Server (NTRS)

Kahre, M. A.; Haberle, R. M.; Hollingsworth, J. L.; Wilson, R. J.

2014-01-01

The dust cycle is critically important for the current climate of Mars. The radiative effects of dust impact the thermal and dynamical state of the atmosphere (Gierasch and Goody, 1968; Haberle et al., 1982; Zurek et al., 1992). Although dust is present in the Martian atmosphere throughout the year, the level of dustiness varies with season. The atmosphere is generally the dustiest during northern fall and winter and the least dusty during northern spring and summer (Smith, 2004). Dust particles are lifted into the atmosphere by dust storms that range in size from meters to thousands of kilometers across (Cantor et al., 2001). During some years, regional storms combine to produce hemispheric or planet encircling dust clouds that obscure the surface and raise atmospheric temperatures by as much as 40 K (Smith et al., 2002). Key recent observations of the vertical distribution of dust indicate that elevated layers of dust exist in the tropics and sub-tropics throughout much of the year (Heavens et al., 2011). These observations have brought particular focus on the processes that control the vertical distribution of dust in the Martian atmosphere. The goal of this work is to further our understanding of how clouds in particular control the vertical distribution of dust, particularly during N. H. spring and summer

Observations of the zodiacal light from the ecliptic to the poles.

NASA Technical Reports Server (NTRS)

Sparrow, J. G.; Ney, E. P.

1972-01-01

The brightness and polarization of the zodiacal light have been measured from the satellite OSO-5, using two photometers of effective wavelengths 4180 and 6820 A. The satellite configuration restricts the observations to ecliptic longitudes close to 90 deg, but measurements have been made from the ecliptic to the poles. On the ecliptic, the intensity of the zodiacal light was found to be 117 S10 (blue) and 315 S10 (red) with polarizations of 16.5 and 15 per cent, respectively. At the ecliptic poles the zodiacal intensity was 35 S10 (blue) with 20 per cent polarization. No temporal changes in zodiacal light have been found nor any significant differences in the intensities in the two hemispheres. The direction of polarization of the zodiacal light has been shown to be H-pass radial.

Dynamical Model for the Zodiacal Cloud and Sporadic Meteors

NASA Astrophysics Data System (ADS)

Nesvorný, David; Janches, Diego; Vokrouhlický, David; Pokorný, Petr; Bottke, William F.; Jenniskens, Peter

2011-12-01

The solar system is dusty, and would become dustier over time as asteroids collide and comets disintegrate, except that small debris particles in interplanetary space do not last long. They can be ejected from the solar system by Jupiter, thermally destroyed near the Sun, or physically disrupted by collisions. Also, some are swept by the Earth (and other planets), producing meteors. Here we develop a dynamical model for the solar system meteoroids and use it to explain meteor radar observations. We find that the Jupiter Family Comets (JFCs) are the main source of the prominent concentrations of meteors arriving at the Earth from the helion and antihelion directions. To match the radiant and orbit distributions, as measured by the Canadian Meteor Orbit Radar (CMOR) and Advanced Meteor Orbit Radar (AMOR), our model implies that comets, and JFCs in particular, must frequently disintegrate when reaching orbits with low perihelion distance. Also, the collisional lifetimes of millimeter particles may be longer (gsim 105 yr at 1 AU) than postulated in the standard collisional models (~104 yr at 1 AU), perhaps because these chondrule-sized meteoroids are stronger than thought before. Using observations of the Infrared Astronomical Satellite to calibrate the model, we find that the total cross section and mass of small meteoroids in the inner solar system are (1.7-3.5) × 1011 km2 and ~4 × 1019 g, respectively, in a good agreement with previous studies. The mass input required to keep the zodiacal cloud in a steady state is estimated to be ~104-105 kg s-1. The input is up to ~10 times larger than found previously, mainly because particles released closer to the Sun have shorter collisional lifetimes and need to be supplied at a faster rate. The total mass accreted by the Earth in particles between diameters D = 5 μm and 1 cm is found to be ~15,000 tons yr-1 (factor of two uncertainty), which is a large share of the accretion flux measured by the Long Term Duration

Lidars for smoke and dust cloud diagnostics

NASA Astrophysics Data System (ADS)

Fujimura, S. F.; Warren, R. E.; Lutomirski, R. F.

1980-11-01

An algorithm that integrates a time-resolved lidar signature for use in estimating transmittance, extinction coefficient, mass concentration, and CL values generated under battlefield conditions is applied to lidar signatures measured during the DIRT-I tests. Estimates are given for the dependence of the inferred transmittance and extinction coefficient on uncertainties in parameters such as the obscurant backscatter-to-extinction ratio. The enhanced reliability in estimating transmittance through use of a target behind the obscurant cloud is discussed. It is found that the inversion algorithm can produce reliable estimates of smoke or dust transmittance and extinction from all points within the cloud for which a resolvable signal can be detected, and that a single point calibration measurement can convert the extinction values to mass concentration for each resolvable signal point.

Emission from small dust particles in diffuse and molecular cloud medium

NASA Technical Reports Server (NTRS)

Bernard, J. P.; Desert, X.

1990-01-01

Infrared Astronomy Satellite (IRAS) observations of the whole galaxy has shown that long wavelength emission (100 and 60 micron bands) can be explained by thermal emission from big grains (approx 0.1 micron) radiating at their equilibrium temperature when heated by the InterStellar Radiation Field (ISRF). This conclusion has been confirmed by continuum sub-millimeter observations of the galactic plane made by the EMILIE experiment at 870 microns (Pajot et al. 1986). Nevertheless, shorter wavelength observations like 12 and 25 micron IRAS bands, show an emission from the galactic plane in excess with the long wavelength measurements which can only be explained by a much hotter particles population. Because dust at equilibrium cannot easily reach high temperatures required to explain this excess, this component is thought to be composed of very small dust grains or big molecules encompassing thermal fluctuations. Researchers present here a numerical model that computes emission, from Near Infrared Radiation (NIR) to Sub-mm wavelengths, from a non-homogeneous spherical cloud heated by the ISRF. This model fully takes into account the heating of dust by multi-photon processes and back-heating of dust in the Visual/Infrared Radiation (VIS-IR) so that it is likely to describe correctly emission from molecular clouds up to large A sub v and emission from dust experiencing temperature fluctuations. The dust is a three component mixture of polycyclic aromatic hydrocarbons, very small grains, and classical big grains with independent size distributions (cut-off and power law index) and abundances.

Evolution of the Edgeworth-Kuiper Belt and Kuiperoidal Dust

NASA Astrophysics Data System (ADS)

Ozernoy, L. M.; Ipatov, S. I.

Evolution of orbits of Edgeworth-Kuiper belt objects (EKBOs) under the gravitational influence of the giant planets has been studied by a number of authors (e.g., Duncan & Levison; Budd; Ozernoy, Gorkavyi & Taidakova). Here we show that the gravitational interactions of EKBOs can also play a certain role in their orbital evolution. For instance, during the last 4 Gyr as many as several percents of EKBOs could change their semimajor axes by more than 1 AU due to close encounters with other EKBOs. Even small variations in orbital elements of EKBOs caused by their mutual collisions coupled with the mutual gravitational influence can cause large variations in the orbital elements due to the gravitational influence of planets. About 6% of Neptune-crossers can reach the orbit of the Earth, with the average time in Earth-crossing orbits of about 5× 103 yr. The portion of former EKBOs now moving in Earth-crossing orbits can exceed 20% of all Earth-crossers. Evaporation of the volatile material from the EKBOs surfaces, due to mutual EKBO collisions, along with the Solar wind and the heating by the Sun, are the sources of the dust in the outer Solar system. The evolution and structure of the interplanetary dust cloud computed, in some approximations, by Gorkavyi, Ozernoy, Mather, & Taidakova offers a preliminary 3-D physical model of the cloud, which includes three dust components (asteroidal, cometary, and kuiperoidal), which is fairly consistent with the available data of Pioneer and Voyager dust detectors and contribution of the zodiacal light into the COBE/DIRBE data. We acknowledge support of this work by NASA grant NAG5-10776, the Russian Federal Program ``Astronomy'' (section 1.9.4.1), RFBR (01-02-17540), and INTAS (00-240).

Aerosol Impacts on California Winter Clouds and Precipitation during CalWater 2011: Local Pollution versus Long-Range Transported Dust

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

Fan, Jiwen; Leung, Lai-Yung R.; DeMott, Paul J.

2014-01-03

Mineral dust aerosols often observed over California in winter and spring, associated with long-range transport from Asia and Sahara, have been linked to enhanced precipitation based on observations. Local anthropogenic pollution, on the other hand, was shown in previous observational and modeling studies to reduce precipitation. Here we incorporate recent developments in ice nucleation parameterizations to link aerosols with ice crystal formation in a spectral-bin cloud microphysical model coupled with the Weather Research and Forecasting (WRF) model, to examine the relative and combined impacts of dust and local pollution particles on cloud properties and precipitation type and intensity. Simulations aremore » carried out for two cloud cases with contrasting meteorology and cloud dynamics that occurred on February 16 (FEB16) and March 02 (MAR02) from the CalWater 2011 field campaign. In both cases, observations show the presence of dust and biological particles in a relative pristine environment. The simulated cloud microphysical properties and precipitation show reasonable agreement with aircraft and surface measurements. Model sensitivity experiments indicate that in the pristine environment, the dust and biological aerosol layers increase the accumulated precipitation by 10-20% from the Central Valley to the Sierra Nevada Mountains for both FEB16 and MAR02 due to a ~40% increase in snow formation, validating the observational hypothesis. Model results show that local pollution increases precipitation over the windward slope of the mountains by few percent due to increased snow formation when dust is present but reduces precipitation by 5-8% if dust is removed on FEB16. The effects of local pollution on cloud microphysics and precipitation strongly depend on meteorology including the strength of the Sierra Barrier Jet, and cloud dynamics. This study further underscores the importance of the interactions between local pollution, dust, and environmental

Properties of dust and clouds in the Mars atmosphere: Analysis of Viking IRTM emission phase function sequences

NASA Technical Reports Server (NTRS)

Clancy, R. T.; Lee, S. W.

1991-01-01

An analysis of emission-phase-function (EPF) observations from the Viking Orbiter Infrared Thermal Mapper (IRTM) yields a wide variety of results regarding dust and cloud scattering in the Mars atmosphere and atmospheric-corrected albedos for the surface of Mars. A multiple scattering radiative transfer model incorporating a bidirectional phase function for the surface and atmospheric scattering by dust and clouds is used to derive surface albedos and dust and ice optical properties and optical depths for these various conditions on Mars.

DUST AND GAS IN THE MAGELLANIC CLOUDS FROM THE HERITAGE HERSCHEL KEY PROJECT. II. GAS-TO-DUST RATIO VARIATIONS ACROSS INTERSTELLAR MEDIUM PHASES

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

Roman-Duval, Julia; Gordon, Karl D.; Meixner, Margaret

2014-12-20

The spatial variations of the gas-to-dust ratio (GDR) provide constraints on the chemical evolution and lifecycle of dust in galaxies. We examine the relation between dust and gas at 10-50 pc resolution in the Large and Small Magellanic Clouds (LMC and SMC) based on Herschel far-infrared (FIR), H I 21 cm, CO, and Hα observations. In the diffuse atomic interstellar medium (ISM), we derive the GDR as the slope of the dust-gas relation and find GDRs of 380{sub −130}{sup +250} ± 3 in the LMC, and 1200{sub −420}{sup +1600} ± 120 in the SMC, not including helium. The atomic-to-molecular transition is locatedmore » at dust surface densities of 0.05 M {sub ☉} pc{sup –2} in the LMC and 0.03 M {sub ☉} pc{sup –2} in the SMC, corresponding to A {sub V} ∼ 0.4 and 0.2, respectively. We investigate the range of CO-to-H{sub 2} conversion factor to best account for all the molecular gas in the beam of the observations, and find upper limits on X {sub CO} to be 6 × 10{sup 20} cm{sup –2} K{sup –1} km{sup –1} s in the LMC (Z = 0.5 Z {sub ☉}) at 15 pc resolution, and 4 × 10{sup 21} cm{sup –2} K{sup –1} km{sup –1} s in the SMC (Z = 0.2 Z {sub ☉}) at 45 pc resolution. In the LMC, the slope of the dust-gas relation in the dense ISM is lower than in the diffuse ISM by a factor ∼2, even after accounting for the effects of CO-dark H{sub 2} in the translucent envelopes of molecular clouds. Coagulation of dust grains and the subsequent dust emissivity increase in molecular clouds, and/or accretion of gas-phase metals onto dust grains, and the subsequent dust abundance (dust-to-gas ratio) increase in molecular clouds could explain the observations. In the SMC, variations in the dust-gas slope caused by coagulation or accretion are degenerate with the effects of CO-dark H{sub 2}. Within the expected 5-20 times Galactic X {sub CO} range, the dust-gas slope can be either constant or decrease by a factor of several across ISM phases. Further

[Signs of the zodiac and personality].

PubMed

Angst, J; Scheidegger, P

1976-01-01

3074 young men resident in the canton of Zurich, representing 50% of the 19 year old male population, form the fully representative sample of our large scale investigation. We investigated whether personality traits measured by means of the differentiated "Freiburger personality inventory" (FPI) could in any way be correlated to the signs of the zodiac under which the young men were born. The statistical analysis did not reveal any correlation between signs of the zodiac and personality. The claim made by astrologers that people can be characterized according to their sign of the zodiac (sagitarius, taurus, cancer, scorpion) must be refuted. Of course the astrologically founded description of human personality does not base itself on the position of the sun only, however the latter does form a very essential part of the astrological evaluation of people. This, at any rate has been shown to be without any scientific basis. The fact that astrological evaluation of human personality is so popular nowadays can be explained by the fact that even modern people are inclined towards magical thinking.

The competition between mineral dust and soot ice nuclei in mixed-phase clouds (Invited)

NASA Astrophysics Data System (ADS)

Murray, B. J.; Atkinson, J.; Umo, N.; Browse, J.; Woodhouse, M. T.; Whale, T.; Baustian, K. J.; Carslaw, K. S.; Dobbie, S.; O'Sullivan, D.; Malkin, T. L.

2013-12-01

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. In this talk our recent laboratory and global aerosol modelling work on mineral dust and soot ice nuclei will be presented. We have performed immersion mode experiments to quantify ice nucleation by the individual minerals which make up desert mineral dusts and have shown that the feldspar component, rather than the clay component, is most important for ice nucleation (Atkinson et al. 2013). Experiments with well-characterised soot generated with eugenol, an intermediate in biomass burning, and n-decane show soot has a significant ice nucleation activity in mixed-phase cloud conditions. Our results for soot are in good agreement with previous results for acetylene soot (DeMott, 1990), but extend the efficiency to much higher temperatures. We then use a global aerosol model (GLOMAP) to map the distribution of soot and feldspar particles on a global basis. We show that below about -15oC that dust and soot together can explain most observed ice nuclei in the Earth's atmosphere, while at warmer temperatures other ice nuclei types are needed. We show that in some regions soot is the most important ice nuclei (below -15oC), while in others feldspar dust dominates. Our results suggest that there is a strong anthropogenic contribution to the ice nuclei population, since a large proportion of soot aerosol in the atmosphere results from human activities. Atkinson, J. D., Murray, B. J., Woodhouse, M. T., Carslaw, K. S., Whale, T. F., Baustian, K. J., Dobbie, S., O'Sullivan, D., and Malkin, T. L.: The importance of feldspar for ice nucleation by mineral dust in mixed-phase clouds, Nature, 10.1038/nature12278, (2013). Demott, P. J. 1990. An Exploratory-Study of Ice Nucleation by Soot

Hubble space telescope imaging of decoupled dust clouds in the ram pressure stripped Virgo spirals NGC 4402 and NGC 4522

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

Abramson, Anne; Kenney, Jeffrey D. P., E-mail: anne.abramson@yale.edu, E-mail: jeff.kenney@yale.edu

We present the highest-resolution study to date of the interstellar medium (ISM) in galaxies undergoing ram pressure stripping, using Hubble Space Telescope BVI imaging of NGC 4522 and NGC 4402, Virgo Cluster spirals that are well known to be experiencing intracluster medium (ICM) ram pressure. We find that throughout most of both galaxies, the main dust lane has a fairly well-defined edge, with a population of giant molecular cloud (GMC) sized (tens- to hundreds-of-pc scale), isolated, highly extincting dust clouds located up to ∼1.5 kpc radially beyond it. Outside of these dense clouds, the area has little or no diffusemore » dust extinction, indicating that the clouds have decoupled from the lower-density ISM material that has already been stripped. Several of the dust clouds have elongated morphologies that indicate active ram pressure, including two large (kpc scale) filaments in NGC 4402 that are elongated in the projected ICM wind direction. We calculate a lower limit on the H I + H{sub 2} masses of these clouds based on their dust extinctions and find that a correction factor of ∼10 gives cloud masses consistent with those measured in CO for clouds of similar diameters, probably due to the complicating factors of foreground light, cloud substructure, and resolution limitations. Assuming that the clouds' actual masses are consistent with those of GMCs of similar diameters (∼10{sup 4}-10{sup 5} M {sub ☉}), we estimate that only a small fraction (∼1%-10%) of the original H I + H{sub 2} remains in the parts of the disks with decoupled clouds. Based on Hα images, a similar fraction of star formation persists in these regions, 2%-3% of the estimated pre-stripping star formation rate. We find that the decoupled cloud lifetimes may be up to 150-200 Myr.« less

THE 1.1 mm CONTINUUM SURVEY OF THE SMALL MAGELLANIC CLOUD: PHYSICAL PROPERTIES AND EVOLUTION OF THE DUST-SELECTED CLOUDS

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

Takekoshi, Tatsuya; Minamidani, Tetsuhiro; Sorai, Kazuo

The first 1.1 mm continuum survey toward the Small Magellanic Cloud (SMC) was performed using the AzTEC instrument installed on the ASTE 10 m telescope. This survey covered 4.5 deg{sup 2} of the SMC with 1 σ noise levels of 5–12 mJy beam{sup −1}, and 44 extended objects were identified. The 1.1 mm extended emission has good spatial correlation with Herschel 160 μ m, indicating that the origin of the 1.1 mm extended emission is thermal emission from a cold dust component. We estimated physical properties using the 1.1 mm and filtered Herschel data (100, 160, 250, 350, and 500more » μ m). The 1.1 mm objects show dust temperatures of 17–45 K and gas masses of 4 × 10{sup 3}–3 × 10{sup 5} M {sub ⊙}, assuming single-temperature thermal emission from the cold dust with an emissivity index, β , of 1.2 and a gas-to-dust ratio of 1000. These physical properties are very similar to those of giant molecular clouds (GMCs) in our galaxy and the Large Magellanic Cloud. The 1.1 mm objects also displayed good spatial correlation with the Spitzer 24 μ m and CO emission, suggesting that the 1.1 mm objects trace the dense gas regions as sites of massive star formation. The dust temperature of the 1.1 mm objects also demonstrated good correlation with the 24 μ m flux connected to massive star formation. This supports the hypothesis that the heating source of the cold dust is mainly local star-formation activity in the 1.1 mm objects. The classification of the 1.1 mm objects based on the existence of star-formation activity reveals the differences in the dust temperature, gas mass, and radius, which reflects the evolution sequence of GMCs.« less

The 1.1 mm Continuum Survey of the Small Magellanic Cloud: Physical Properties and Evolution of the Dust-selected Clouds

NASA Astrophysics Data System (ADS)

Takekoshi, Tatsuya; Minamidani, Tetsuhiro; Komugi, Shinya; Kohno, Kotaro; Tosaki, Tomoka; Sorai, Kazuo; Muller, Erik; Mizuno, Norikazu; Kawamura, Akiko; Onishi, Toshikazu; Fukui, Yasuo; Ezawa, Hajime; Oshima, Tai; Scott, Kimberly S.; Austermann, Jason E.; Matsuo, Hiroshi; Aretxaga, Itziar; Hughes, David H.; Kawabe, Ryohei; Wilson, Grant W.; Yun, Min S.

2017-01-01

The first 1.1 mm continuum survey toward the Small Magellanic Cloud (SMC) was performed using the AzTEC instrument installed on the ASTE 10 m telescope. This survey covered 4.5 deg2 of the SMC with 1σ noise levels of 5-12 mJy beam-1, and 44 extended objects were identified. The 1.1 mm extended emission has good spatial correlation with Herschel 160 μm, indicating that the origin of the 1.1 mm extended emission is thermal emission from a cold dust component. We estimated physical properties using the 1.1 mm and filtered Herschel data (100, 160, 250, 350, and 500 μm). The 1.1 mm objects show dust temperatures of 17-45 K and gas masses of 4 × 103-3 × 105 M⊙, assuming single-temperature thermal emission from the cold dust with an emissivity index, β, of 1.2 and a gas-to-dust ratio of 1000. These physical properties are very similar to those of giant molecular clouds (GMCs) in our galaxy and the Large Magellanic Cloud. The 1.1 mm objects also displayed good spatial correlation with the Spitzer 24 μm and CO emission, suggesting that the 1.1 mm objects trace the dense gas regions as sites of massive star formation. The dust temperature of the 1.1 mm objects also demonstrated good correlation with the 24 μm flux connected to massive star formation. This supports the hypothesis that the heating source of the cold dust is mainly local star-formation activity in the 1.1 mm objects. The classification of the 1.1 mm objects based on the existence of star-formation activity reveals the differences in the dust temperature, gas mass, and radius, which reflects the evolution sequence of GMCs. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Saharan Dust as a Causal Factor of Significant Cloud Cover Along the Saharan Air Layer in the Atlantic Ocean

NASA Technical Reports Server (NTRS)

Kishcha, Pavel; Da Silva, Arlindo M.; Starobinet, Boris; Alpert, Pinhas

2016-01-01

The tropical Atlantic is frequently affected by Saharan dust intrusions. Based on MODIS cloud fraction (CF) data during the ten-year study period, we found that these dust intrusions contribute to significant cloud cover along the Saharan Air Layer (SAL). Below the temperature inversion at the SAL's base, the presence of large amounts of settling dust particles, together with marine aerosols, produces meteorological conditions suitable for the formation of shallow stratocumulus clouds. The significant cloud fraction along the SAL together with clouds over the Atlantic Inter-tropical Convergence Zone contributes to the 20% hemispheric CF asymmetry between the tropical North and South Atlantic. This leads to the imbalance in strong solar radiation, which reaches the sea surface between the tropical North and South Atlantic, and, consequently, affects climate formation in the tropical Atlantic. Therefore, despite the fact that, over the global ocean, there is no noticeable hemispheric asymmetry in cloud fraction, over the significant area such as the tropical Atlantic the hemispheric asymmetry in CF takes place. Saharan dust is also the major contributor to hemispheric aerosol asymmetry over the tropical Atlantic. The NASA GEOS-5 model with aerosol data assimilation was used to extend the MERRA reanalysis with five atmospheric aerosol species (desert dust, sulfates, organic carbon, black carbon, and sea-salt). The obtained ten-year (2002 - 2012) MERRA-driven aerosol reanalysis dataset (aka MERRAero) showed that, over the tropical Atlantic, dust and carbonaceous aerosols were distributed asymmetrically relative to the equator, while other aerosol species were distributed more symmetrically.

COLLISIONAL GROOMING MODELS OF THE KUIPER BELT DUST CLOUD

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

Kuchner, Marc J.; Stark, Christopher C., E-mail: Marc.Kuchner@nasa.go, E-mail: starkc@umd.ed

2010-10-15

We modeled the three-dimensional structure of the Kuiper Belt (KB) dust cloud at four different dust production rates, incorporating both planet-dust interactions and grain-grain collisions using the collisional grooming algorithm. Simulated images of a model with a face-on optical depth of {approx}10{sup -4} primarily show an azimuthally symmetric ring at 40-47 AU in submillimeter and infrared wavelengths; this ring is associated with the cold classical KB. For models with lower optical depths (10{sup -6} and 10{sup -7}), synthetic infrared images show that the ring widens and a gap opens in the ring at the location of Neptune; this feature ismore » caused by trapping of dust grains in Neptune's mean motion resonances. At low optical depths, a secondary ring also appears associated with the hole cleared in the center of the disk by Saturn. Our simulations, which incorporate 25 different grain sizes, illustrate that grain-grain collisions are important in sculpting today's KB dust, and probably other aspects of the solar system dust complex; collisions erase all signs of azimuthal asymmetry from the submillimeter image of the disk at every dust level we considered. The model images switch from being dominated by resonantly trapped small grains ('transport dominated') to being dominated by the birth ring ('collision dominated') when the optical depth reaches a critical value of {tau} {approx} v/c, where v is the local Keplerian speed.« less

Dynamical Model for the Zodiacal Cloud and Sporadic Meteors

NASA Technical Reports Server (NTRS)

Nesvorny, David; Janches, Diego; Vokrouhlicky, David; Pokorny, Petr; Bottke, William F.; Jenniskens, Peter

2011-01-01

The solar system is dusty, and would become dustier over time as asteroids collide and comets disintegrate, except that small debris particles in interplanetary space do not last long. They can be ejected from the solar system by Jupiter, thermally destroyed near the Sun, or physically disrupted by collisions. Also, some are swept by the Earth (and other planets), producing meteors. Here we develop a dynamical model for the solar system meteoroids and use it to explain meteor radar observations. We find that the Jupiter Family Comets (JFCs) are the main source of the prominent concentrations of meteors arriving to the Earth from the helion and antihelion directions. To match the radiant and orbit distributions, as measured by the Canadian Meteor Orbit Radar (CMOR) and Advanced Meteor Orbit Radar (AMOR), our model implies that comets, and JFCs in particular, must frequently disintegrate when reaching orbits with low perihelion distance. Also, the collisional lifetimes of millimeter particles may be longer (approx. > 10(exp 5) yr at 1 AU) than postulated in the standard collisional models (approx 10(exp 4) yr at 1 AU), perhaps because these chondrule-sized meteoroids are stronger than thought before. Using observations of the Infrared Astronomical Satellite (IRAS) to calibrate the model, we find that the total cross section and mass of small meteoroids in the inner solar system are (1.7-3.5) 10(exp 11) sq km and approx. 4 10(exp 19) g, respectively, in a good agreement with previous studies. The mass input required to keep the Zodiacal Cloud (ZC) in a steady state is estimated to be approx. 10(exp 4)-10(exp 5) kg/s. The input is up to approx 10 times larger than found previously, mainly because particles released closer to the Sun have shorter collisional lifetimes, and need to be supplied at a faster rate. The total mass accreted by the Earth in particles between diameters D = 5 micron and 1 cm is found to be approx 15,000 tons/yr (factor of 2 uncertainty), which is

DYNAMICAL MODEL FOR THE ZODIACAL CLOUD AND SPORADIC METEORS

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

Nesvorny, David; Vokrouhlicky, David; Pokorny, Petr

2011-12-20

The solar system is dusty, and would become dustier over time as asteroids collide and comets disintegrate, except that small debris particles in interplanetary space do not last long. They can be ejected from the solar system by Jupiter, thermally destroyed near the Sun, or physically disrupted by collisions. Also, some are swept by the Earth (and other planets), producing meteors. Here we develop a dynamical model for the solar system meteoroids and use it to explain meteor radar observations. We find that the Jupiter Family Comets (JFCs) are the main source of the prominent concentrations of meteors arriving atmore » the Earth from the helion and antihelion directions. To match the radiant and orbit distributions, as measured by the Canadian Meteor Orbit Radar (CMOR) and Advanced Meteor Orbit Radar (AMOR), our model implies that comets, and JFCs in particular, must frequently disintegrate when reaching orbits with low perihelion distance. Also, the collisional lifetimes of millimeter particles may be longer ({approx}> 10{sup 5} yr at 1 AU) than postulated in the standard collisional models ({approx}10{sup 4} yr at 1 AU), perhaps because these chondrule-sized meteoroids are stronger than thought before. Using observations of the Infrared Astronomical Satellite to calibrate the model, we find that the total cross section and mass of small meteoroids in the inner solar system are (1.7-3.5) Multiplication-Sign 10{sup 11} km{sup 2} and {approx}4 Multiplication-Sign 10{sup 19} g, respectively, in a good agreement with previous studies. The mass input required to keep the zodiacal cloud in a steady state is estimated to be {approx}10{sup 4}-10{sup 5} kg s{sup -1}. The input is up to {approx}10 times larger than found previously, mainly because particles released closer to the Sun have shorter collisional lifetimes and need to be supplied at a faster rate. The total mass accreted by the Earth in particles between diameters D = 5 {mu}m and 1 cm is found to be {approx

Raman lidar measurement of water vapor and ice clouds associated with Asian dust layer over Tsukuba, Japan

NASA Astrophysics Data System (ADS)

Sakai, Tetsu; Nagai, Tomohiro; Nakazato, Masahisa; Matsumura, Takatsugu

2004-03-01

The vertical distributions of particle extinction, backscattering, depolarization, and water vapor mixing ratio were measured using a Raman lidar over Tsukuba (36.1°N, 140.1°E), Japan, on 23-24 April 2001. Ice clouds associated with the Asian dust layer were observed at an altitude of ~6-9 km. The relative humidities in the cloud layer were close to the ice saturation values and the temperature at the top of the cloud layer was ~-35°C, suggesting that the Asian dust acted as ice nuclei at the high temperatures. The meteorological analysis suggested that the ice-saturated region was formed near the top of the dust layer where the moist air ascended in slantwise fashion above the cold-frontal zone associated with extratropical cyclone.

OAO-2 observations of the zodiacal light

NASA Technical Reports Server (NTRS)

Lillie, C. F.

1972-01-01

Photometric measurements of the night sky brightness have been obtained at twelve wavelengths between 1000 A and 4300 A from above the earth's atmosphere. A preliminary analysis of the data reveals a component of the sky brightness with ecliptic symmetry and an intensity distribution similar to that of the zodiacal light. The ultraviolet spectrum of the zodiacal light can be closely approximated with a two component model in which one component has an albedo proportional to the wavelength lambda and the other component has a scattering efficiency proportional to lambda to lbe minus 19 power.

Positive low cloud and dust feedbacks amplify tropical North Atlantic Multidecadal Oscillation

DOE PAGES

Yuan, Tianle; Oreopoulos, Lazaros; Zelinka, Mark; ...

2016-02-04

The Atlantic Multidecadal Oscillation (AMO) is characterized by a horseshoe pattern of sea surface temperature (SST) anomalies and has a wide range of climatic impacts. While the tropical arm of AMO is responsible for many of these impacts, it is either too weak or completely absent in many climate model simulations. Here we show, using both observational and model evidence, that the radiative effect of positive low cloud and dust feedbacks is strong enough to generate the tropical arm of AMO, with the low cloud feedback more dominant. The feedbacks can be understood in a consistent dynamical framework: weakened tropicalmore » trade wind speed in response to a warm middle latitude SST anomaly reduces dust loading and low cloud fraction over the tropical Atlantic, which warms the tropical North Atlantic SST. Together they contribute to the appearance of the tropical arm of AMO. Most current climate models miss both the critical wind speed response and two positive feedbacks though realistic simulations of them may be essential for many climatic studies related to the AMO.« less

Positive Low Cloud and Dust Feedbacks Amplify Tropical North Atlantic Multidecadal Variability

NASA Technical Reports Server (NTRS)

Yuan, Tianle; Oraiopoulos, Lazaros; Zelinka, Mark; Yu, Hongbin; Norris, Joel R.; Chin, Mian; Platnick, Steven; Meyer, Kerry

2016-01-01

The Atlantic Multidecadal Oscillation (AMO) is characterized by a horseshoe pattern of sea surface temperature (SST) anomalies and has a wide range of climatic impacts. While the tropical arm of AMO is responsible for many of these impacts, it is either too weak or completely absent in many climate model simulations. Here we show, using both observational and model evidence, that the radiative effect of positive low cloud and dust feedbacks is strong enough to generate the tropical arm of AMO, with the low cloud feedback more dominant. The feedbacks can be understood in a consistent dynamical framework: weakened tropical trade wind speed in response to a warm middle latitude SST anomaly reduces dust loading and low cloud fraction over the tropical Atlantic, which warms the tropical North Atlantic SST. Together they contribute to appearance of the tropical arm of AMO. Most current climate models miss both the critical wind speed response and two positive feedbacks though realistic simulations of them may be essential for many climatic studies related to the AMO.

Estimating dust production rate of carbon-rich stars in the Small Magellanic Cloud

NASA Astrophysics Data System (ADS)

Nanni, A.; Marigo, P.; Groenewegen, M. A. T.; Aringer, B.; Pastorelli, G.; Rubele, S.; Girardi, L.; Bressan, A.; Bladh, S.

We compute a grid of spectra describing dusty Circumstellar Envelopes of Thermally Pulsing Asymptotic Giant Branch carbon-rich stars by employing a physically grounded description for dust growth. The optical constants for carbon dust have been selected in order to reproduce simultaneously the most important color-color diagrams in the Near and Mid Infrared bands. We fit the Spectral Energy Distribution of ≈2000 carbon-rich in the Small Magellanic Cloud and we compute their total dust production rate. We compare our results with the ones in the literature. Different choices of the dust-to-gas ratio and outflow expansion velocity adopted in different works, yield, in some cases, a total dust budget about three times lower than the one derived from our scheme, with the same optical data set for carbon dust.

Dust in a compact, cold, high-velocity cloud: A new approach to removing foreground emission

NASA Astrophysics Data System (ADS)

Lenz, D.; Flöer, L.; Kerp, J.

2016-02-01

Context. Because isolated high-velocity clouds (HVCs) are found at great distances from the Galactic radiation field and because they have subsolar metallicities, there have been no detections of dust in these structures. A key problem in this search is the removal of foreground dust emission. Aims: Using the Effelsberg-Bonn H I Survey and the Planck far-infrared data, we investigate a bright, cold, and clumpy HVC. This cloud apparently undergoes an interaction with the ambient medium and thus has great potential to form dust. Methods: To remove the local foreground dust emission we used a regularised, generalised linear model and we show the advantages of this approach with respect to other methods. To estimate the dust emissivity of the HVC, we set up a simple Bayesian model with mildly informative priors to perform the line fit instead of an ordinary linear least-squares approach. Results: We find that the foreground can be modelled accurately and robustly with our approach and is limited mostly by the cosmic infrared background. Despite this improvement, we did not detect any significant dust emission from this promising HVC. The 3σ-equivalent upper limit to the dust emissivity is an order of magnitude below the typical values for the Galactic interstellar medium.

Dust cloud evolution in sub-stellar atmospheres via plasma deposition and plasma sputtering

NASA Astrophysics Data System (ADS)

Stark, C. R.; Diver, D. A.

2018-04-01

Context. In contemporary sub-stellar model atmospheres, dust growth occurs through neutral gas-phase surface chemistry. Recently, there has been a growing body of theoretical and observational evidence suggesting that ionisation processes can also occur. As a result, atmospheres are populated by regions composed of plasma, gas and dust, and the consequent influence of plasma processes on dust evolution is enhanced. Aim. This paper aims to introduce a new model of dust growth and destruction in sub-stellar atmospheres via plasma deposition and plasma sputtering. Methods: Using example sub-stellar atmospheres from DRIFT-PHOENIX, we have compared plasma deposition and sputtering timescales to those from neutral gas-phase surface chemistry to ascertain their regimes of influence. We calculated the plasma sputtering yield and discuss the circumstances where plasma sputtering dominates over deposition. Results: Within the highest dust density cloud regions, plasma deposition and sputtering dominates over neutral gas-phase surface chemistry if the degree of ionisation is ≳10-4. Loosely bound grains with surface binding energies of the order of 0.1-1 eV are susceptible to destruction through plasma sputtering for feasible degrees of ionisation and electron temperatures; whereas, strong crystalline grains with binding energies of the order 10 eV are resistant to sputtering. Conclusions: The mathematical framework outlined sets the foundation for the inclusion of plasma deposition and plasma sputtering in global dust cloud formation models of sub-stellar atmospheres.

Zodiacal light and the asteroid belt - The view from Pioneer 10

NASA Technical Reports Server (NTRS)

Hanner, M. S.; Weinberg, J. L.; Deshields, L. M., II; Green, B. A.; Toller, G. N.

1974-01-01

Brightnesses measured by the Pioneer 10 imaging photopolarimeter in two regions of sky were compared on sky maps at sun-spacecraft distances from 2.4 to 4.8 AU to determine the spatial extent of the zodiacal light. Data in the ecliptic at elongations greater than 90 deg show negligible contribution to the zodiacal light beyond 3.3 AU, the 2:1 Jupiter resonance. The zodiacal light brightness at 2.4 AU is less than 10% of that observed at 1 AU.

Water Ice Clouds and Dust in the Martian Atmosphere Observed by Mars Climate Sounder

NASA Technical Reports Server (NTRS)

Benson, Jennifer L.; Kass, David; Heavens, Nicholas; Kleinbohl, Armin

2011-01-01

The water ice clouds are primarily controlled by the temperature structure and form at the water condensation level. Clouds in all regions presented show day/night differences. Cloud altitude varies between night and day in the SPH and tropics: (1) NPH water ice opacity is greater at night than day at some seasons (2) The diurnal thermal tide controls the daily variability. (3) Strong day/night changes indicate that the amount of gas in the atmosphere varies significantly. See significant mixtures of dust and ice at the same altitude planet-wide (1) Points to a complex radiative and thermal balance between dust heating (in the visible) and ice heating or cooling in the infrared. Aerosol layering: (1) Early seasons reveal a zonally banded spatial distribution (2) Some localized longitudinal structure of aerosol layers (3) Later seasons show no consistent large scale organization

The fundamentally different dynamics of dust and gas in molecular clouds

NASA Astrophysics Data System (ADS)

Hopkins, Philip F.; Lee, Hyunseok

2016-03-01

We study the behaviour of large dust grains in turbulent molecular clouds (MCs). In primarily neutral regions, dust grains move as aerodynamic particles, not necessarily with the gas. We therefore directly simulate, for the first time, the behaviour of aerodynamic grains in highly supersonic, magnetohydrodynamic turbulence typical of MCs. We show that, under these conditions, grains with sizes a ≳ 0.01 micron exhibit dramatic (exceeding factor ˜1000) fluctuations in the local dust-to-gas ratio (implying large small-scale variations in abundances, dust cooling rates, and dynamics). The dust can form highly filamentary structures (which would be observed in both dust emission and extinction), which can be much thinner than the characteristic width of gas filaments. Sometimes, the dust and gas filaments are not even in the same location. The `clumping factor' < n_dust2 > / < n_dust > 2 of the dust (critical for dust growth/coagulation/shattering) can reach ˜100, for grains in the ideal size range. The dust clustering is maximized around scales ˜ 0.2 pc (a/μm) (ngas/100 cm- 3)- 1, and is `averaged out' on larger scales. However, because the density varies widely in supersonic turbulence, the dynamic range of scales (and interesting grain sizes) for these fluctuations is much broader than in the subsonic case. Our results are applicable to MCs of essentially all sizes and densities, but we note how Lorentz forces and other physics (neglected here) may change them in some regimes. We discuss the potentially dramatic consequences for star formation, dust growth and destruction, and dust-based observations of MCs.

High-latitude dust clouds LDN 183 and LDN 169: distances and extinctions

NASA Astrophysics Data System (ADS)

Straižys, V.; Boyle, R. P.; Zdanavičius, J.; Janusz, R.; Corbally, C. J.; Munari, U.; Andersson, B.-G.; Zdanavičius, K.; Kazlauskas, A.; Maskoliūnas, M.; Černis, K.; Macijauskas, M.

2018-03-01

Interstellar extinction is investigated in a 2°× 2° area containing the dust and molecular clouds LDN 183 (MBM 37) and LDN 169, which are located at RA = 15h 54m, Dec = - 3°. The study is based on a photometric classification in spectral and luminosity classes of 782 stars selected from the catalogs of 1299 stars down to V = 20 mag observed in the Vilnius seven-color system. For control, the MK types for the 18 brightest stars with V between 8.5 and 12.8 mag were determined spectroscopically. For 14 stars, located closer than 200 pc, distances were calculated from trigonometric parallaxes taken from the Gaia Data Release 1. For about 70% of the observed stars, two-dimensional spectral types, interstellar extinctions AV, and distances were determined. Using 57 stars closer than 200 pc, we estimate that the front edge of the clouds begins at 105 ± 8 pc. The extinction layer in the vicinities of the clouds can be about 20 pc thick. In the outer parts of the clouds and between the clouds, the extinction is 0.5-2.0 mag. Behind the Serpens/Libra clouds, the extinction range does not increase; this means that the dust layer at 105 pc is a single extinction source. Full Tables 1 and 2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/611/A9

Dust Aerosol, Clouds, and the Atmospheric Optical Depth Record over 5 Mars Years of the Mars Exploration Rover Mission

NASA Technical Reports Server (NTRS)

Lemmon, Mark T.; Wolff, Michael J.; Bell, James F., III; Smith, Michael D.; Cantor, Bruce A.; Smith, Peter H.

2014-01-01

Dust aerosol plays a fundamental role in the behavior and evolution of the Martian atmosphere. The first five Mars years of Mars Exploration Rover data provide an unprecedented record of the dust load at two sites. This record is useful for characterization of the atmosphere at the sites and as ground truth for orbital observations. Atmospheric extinction optical depths have been derived from solar images after calibration and correction for time-varying dust that has accumulated on the camera windows. The record includes local, regional, and globally extensive dust storms. Comparison with contemporaneous thermal infrared data suggests significant variation in the size of the dust aerosols, with a 1 micrometer effective radius during northern summer and a 2 micrometer effective radius at the onset of a dust lifting event. The solar longitude (L (sub s)) 20-136 degrees period is also characterized by the presence of cirriform clouds at the Opportunity site, especially near LS = 50 and 115 degrees. In addition to water ice clouds, a water ice haze may also be present, and carbon dioxide clouds may be present early in the season. Variations in dust opacity are important to the energy balance of each site, and work with seasonal variations in insolation to control dust devil frequency at the Spirit site.

Sensitivity Studies of Dust Ice Nuclei Effect on Cirrus Clouds with the Community Atmosphere Model CAM5

NASA Technical Reports Server (NTRS)

Liu, Xiaohong; Zhang, Kai; Jensen, Eric J.; Gettelman, Andrew; Barahona, Donifan; Nenes, Athanasios; Lawson, Paul

2012-01-01

In this study the effect of dust aerosol on upper tropospheric cirrus clouds through heterogeneous ice nucleation is investigated in the Community Atmospheric Model version 5 (CAM5) with two ice nucleation parameterizations. Both parameterizations consider homogeneous and heterogeneous nucleation and the competition between the two mechanisms in cirrus clouds, but differ significantly in the number concentration of heterogeneous ice nuclei (IN) from dust. Heterogeneous nucleation on dust aerosol reduces the occurrence frequency of homogeneous nucleation and thus the ice crystal number concentration in the Northern Hemisphere (NH) cirrus clouds compared to simulations with pure homogeneous nucleation. Global and annual mean shortwave and longwave cloud forcing are reduced by up to 2.0+/-0.1Wm (sup-2) (1 uncertainty) and 2.4+/-0.1Wm (sup-2), respectively due to the presence of dust IN, with the net cloud forcing change of -0.40+/-0.20W m(sup-2). Comparison of model simulations with in situ aircraft data obtained in NH mid-latitudes suggests that homogeneous ice nucleation may play an important role in the ice nucleation at these regions with temperatures of 205-230 K. However, simulations overestimate observed ice crystal number concentrations in the tropical tropopause regions with temperatures of 190- 205 K, and overestimate the frequency of occurrence of high ice crystal number concentration (greater than 200 L(sup-1) and underestimate the frequency of low ice crystal number concentration (less than 30 L(sup-1) at NH mid-latitudes. These results highlight the importance of quantifying the number concentrations and properties of heterogeneous IN (including dust aerosol) in the upper troposphere from the global perspective.

The effect of temperature mixing on the observable (T, β)-relation of interstellar dust clouds

NASA Astrophysics Data System (ADS)

Juvela, M.; Ysard, N.

2012-03-01

Context. Detailed studies of the shape of dust emission spectra are possible thanks to the current instruments capable of simultaneous observations in several sub-millimetre bands (e.g., Herschel and Planck). The relationship between the observed spectra and the intrinsic dust grain properties is known to be affected by the noise and the line-of-sight temperature variations. However, some controversy remains even on the basic effects resulting from the mixing of temperatures along the line-of-sight or within the instrument beam. Aims: Regarding the effect of temperature variations, previous studies have suggested either a positive or a negative correlation between the colour temperature TC and the observed spectral index βObs. Our aim is to show that both cases are possible and to determine the principal factors leading to either behaviour. Methods: We start by studying the behaviour of the sum of two or three modified black bodies at different temperatures. Then, with radiative transfer models of spherical clouds, we examine the probability distributions of the dust mass as a function of the physical dust temperature. With these results as a guideline, we examine the (TC, βobs) relations for different sets of clouds. Results: Even in the simple case of models consisting of two blackbodies at temperatures T0 and T0 + ΔT0, the correlation between TC and βobs can be either positive or negative. If one compares models where the temperature difference ΔT0 between the two blackbodies is varied, the correlation is negative. If the models differ in their mean temperature T0 rather than in ΔT0, the correlation remains positive. Radiative transfer models show that externally heated clouds have different mean temperatures but the widths of their temperature distributions are rather similar. Thus, in observations of samples of such clouds the correlation between TC and βObs is expected to be positive. The same result applies to clouds illuminated by external radiation

The Dust Cloud TGU H1192 (LDN 1525) in Auriga. II

NASA Astrophysics Data System (ADS)

Boyle, Richard P.; Janusz, Robert; Straizys, Vytautas; Zdanavicius, Kazimieras; Maskoliunas, Marius; Kazlauskas, Algirdas

2016-01-01

The results of a new investigation of interstellar extinction in the direction of the emission nebulae Sh2-231 and Sh2-235 are presented. The investigation is based on CCD photometry and photometric MK classification in seven areas of 12' by 12' size in the Vilnius seven-color photometric system down to V = 19 mag. Additionally, for the same task we applied 519 red clump giants identified in the surrounding 1.5 deg. by 1.5 deg. area using the results of photometry in the 2MASS and WISE surveys. The dependence of the extinction run with distance allows determining distances to dust clouds and their extinctions. We comparethese new more detailed results with the preliminary results described in our previous paper (V. Straizys et al. 2010, Baltic Astronomy, 19, 169) and the AAS communication at the AAS Meeting No. 219 (Austin), 349.12. The relation of the TGU H1192 dust cloud with the Auriga OB1 association is discussed.

Metals and dust in the neutral ISM: the Galaxy, Magellanic Clouds, and damped Lyman-α absorbers

NASA Astrophysics Data System (ADS)

De Cia, Annalisa

2018-05-01

Context. The presence of dust in the neutral interstellar medium (ISM) dramatically changes the metal abundances that we measure. Understanding the metal content in the neutral ISM, and a direct comparison between different environments, has been hampered to date because of the degeneracy to the observed ISM abundances caused by the effects of metallicity, the presence of dust, and nucleosynthesis. Aims: We study the metal and dust content in the neutral ISM consistently in different environments, and assess the universality of recently discovered sequences of relative abundances. We also intend to assess the validity of [Zn/Fe] as a tracer of dust in the ISM. This has recently been cast into doubt based on observations of stellar abundances, and needs to be addressed before we can safely use it to study the ISM. Methods: In this letter we present a simple comparison of relative abundances observed in the neutral ISM in the Galaxy, the Magellanic Clouds, and damped Lyman-α absorbers (DLAs). The main novelty in this comparison is the inclusion of the Magellanic Clouds. Results: The same sequences of relative abundances are valid for the Galaxy, Magellanic Clouds, and DLAs. These sequences are driven by the presence of dust in the ISM and seem "universal". Conclusions: The metal and dust properties in the neutral ISM appear to follow a similar behaviour in different environments. This suggests that a dominant fraction of the dust budget is built up from grain growth in the ISM depending of the physical conditions and regardless of the star formation history of the system. In addition, the DLA gas behaves like the neutral ISM, at least from a chemical point of view. Finally, despite the deviations in [Zn/Fe] observed in stellar abundances, [Zn/Fe] is a robust dust tracer in the ISM of different environments, from the Galaxy to DLAs.

Size and density distribution of very small dust grains in the Barnard 5 cloud

NASA Technical Reports Server (NTRS)

Lis, Dariusz C.; Leung, Chun Ming

1991-01-01

The effects of the temperature fluctuations in small graphite grains on the energy spectrum and the IR surface brightness of an isolated dust cloud heated externally by the interstellar radiation field were investigated using a series of models based on a radiation transport computer code. This code treats self-consistently the thermal coupling between the transient heating of very small dust grains and the equilibrium heating of conventional large grains. The model results were compared with the IRAS observations of the Barnard 5 (B5) cloud, showing that the 25-micron emission of the cloud must be produced by small grains with a 6-10 A radius, which also contribute about 50 percent to the observed 12-micron emission. The remaining 12 micron flux may be produced by the polycyclic aromatic hydrocarbons. The 60-and 100-micron radiation is dominated by emission from large grains heated under equilibrium conditions.

H2, CO, and dust absorption through cold molecular clouds

NASA Astrophysics Data System (ADS)

Lacy, John H.; Sneden, Chris; Kim, Hwihyun; Jaffe, Daniel Thomas

2017-06-01

We have made observations with IGRINS on the Harlan J. Smith telescope at McDonald Observatory of near-infrared absorption by H2, CO, and dust toward stars behind molecular clouds, primarily the TMC. Prior to these observations, the abundance of H2 in molecular clouds, relative to the commonly used tracer CO, had only been measured toward a few embedded stars, which may be surrounded by atypical gas. The new observations provide a representative sample of these molecules in cold molecular gas. We find N(H2)/Av ~ 0.9e+21, N(CO)/Av ~ 1.6e+17, and H2/CO ~ 6000. The measured H2/CO ratio is consistent with that measured toward embedded stars in various molecular clouds, but half that derived from mm-wave observations of CO emission and star counts or other determinations of Av.

The optical depth sensor (ODS) for column dust opacity measurements and cloud detection on martian atmosphere

NASA Astrophysics Data System (ADS)

Toledo, D.; Rannou, P.; Pommereau, J.-P.; Foujols, T.

2016-08-01

A lightweight and sophisticated optical depth sensor (ODS) able to measure alternatively scattered flux at zenith and the sum of the direct flux and the scattered flux in blue and red has been developed to work in martian environment. The principal goals of ODS are to perform measurements of the daily mean dust opacity and to retrieve the altitude and optical depth of high altitude clouds at twilight, crucial parameters in the understanding of martian meteorology. The retrieval procedure of dust opacity is based on the use of radiative transfer simulations reproducing observed changes in the solar flux during the day as a function of 4 free parameters: dust opacity in blue and red, and effective radius and effective width of dust size distribution. The detection of clouds is undertaken by looking at the time variation of the color index (CI), defined as the ratio between red and blue ODS channels, at twilight. The retrieval of altitude and optical depth of clouds is carried out using a radiative transfer model in spherical geometry to simulate the CI time variation at twilight. Here the different retrieval procedures to analyze ODS signals, as well as the results obtained in different sensitivity analysis are presented and discussed.

Dust and Gas in the Magellanic Clouds from the Heritage Herschel Key Project. I. Dust Properties and Insights into the Origin of the Submm (Submillimeter) Excess Emission

NASA Technical Reports Server (NTRS)

Gordon, Karl D.; Roman-Duval, Julia; Bot, Caroline; Meixner, Margaret; Babler, Brian; Bernard, Jean-Philippe; Bolatto, Alberto; Boyer, Martha L.; Clayton, Geoffrey C.; Engelbracht, Charles;

Voyages of the Zodiac, an Impenitent Traveller across Lands and Ages

NASA Astrophysics Data System (ADS)

Belmonte, Juan Antonio

2015-05-01

The zodiac is one of humankind's oldest astronomical heritages. Indeed, it has a long history and had an impressive cultural influence in the past that could be traced from the steppes of Mesopotamia to the wilderness of the Roman frontiers in Great Britain. In the present essay, we will discuss the origin of the zodiacal constellations in ancient Mesopotamia from their possible prehistoric ancestors in the pre-ceramic context of the 10,000-year-old site of Göbleki Tepe. Later on, we will discuss the role that the zodiac played in the development of the new cult established by King Antiochos I of Commagene in his hierothesion at Nemrud Dag, where a planetary conjunction in Leo has played a role in the clues to understand the enigmas of such an impressive monument. This will be followed by the analysis of its southwards travel to the Valley of the Nile, where we will study the famous Zodiac of Dendera. Then we will travel westwards to discuss the astronomical aspects of a new religion where astronomical eras and the zodiac ought to play a most relevant role, Mithraism. Finally, new ideas for future research in this most interesting topic will briefly be sketched.

Retrieving cloud, dust and ozone abundances in the Martian atmosphere using SPICAM/UV nadir spectra

NASA Astrophysics Data System (ADS)

Willame, Y.; Vandaele, A. C.; Depiesse, C.; Lefèvre, F.; Letocart, V.; Gillotay, D.; Montmessin, F.

2017-08-01

We present the retrieval algorithm developed to analyse nadir spectra from SPICAM/UV aboard Mars-Express. The purpose is to retrieve simultaneously several parameters of the Martian atmosphere and surface: the dust optical depth, the ozone total column, the cloud opacity and the surface albedo. The retrieval code couples the use of an existing complete radiative transfer code, an inversion method and a cloud detection algorithm. We describe the working principle of our algorithm and the parametrisation used to model the required absorption, scattering and reflection processes of the solar UV radiation that occur in the Martian atmosphere and at its surface. The retrieval method has been applied on 4 Martian years of SPICAM/UV data to obtain climatologies of the different quantities under investigation. An overview of the climatology is given for each species showing their seasonal and spatial distributions. The results show a good qualitative agreement with previous observations. Quantitative comparisons of the retrieved dust optical depths indicate generally larger values than previous studies. Possible shortcomings in the dust modelling (altitude profile) have been identified and may be part of the reason for this difference. The ozone results are found to be influenced by the presence of clouds. Preliminary quantitative comparisons show that our retrieved ozone columns are consistent with other results when no ice clouds are present, and are larger for the cases with clouds at high latitude. Sensitivity tests have also been performed showing that the use of other a priori assumptions such as the altitude distribution or some scattering properties can have an important impact on the retrieval.

Chemical Speciation of Water Soluble Ions and Metals of Cloud and Rain Water During the Puerto Rico African Dust and Clouds Study (PRADACS) Campaigns

NASA Astrophysics Data System (ADS)

Torres, E.; Valle Diaz, C. J.; Lee, T.; Collett, J. L.; Fitzgerald, E.; Cuadra-Rodriguez, L. A.; Prather, K. A.; Sánchez, M.; McDowell, W. H.; Mayol-Bracero, O. L.

2013-05-01

The underlying physico-chemical processes of dust particles interactions are poorly understood; even less understood is how aging impacts cloud properties and climate as the particles travel from Africa to the Caribbean region. Caribbean landmasses have tropical montane cloud forests (TMCFs) that are tightly coupled to the atmospheric hydrologic cycle. TMCFs are ecosystems to study the effects African Dust (AD) on cloud formation and precipitation as these are very sensitive ecosystems that respond to small changes in climate. As part of the Puerto Rico African Dust and Clouds Study (PRADACS), chemical analyses were performed on cloud and rain water samples collected at Pico del Este (PE) station in Luquillo, PR (1051 masl) during campaigns held from 2010 to 2012. At PE, two cloud collectors (i.e., single stage (Aluminum version), a 2-stage (Teflon version) Caltech Active Strand Cloudwater Collector (CASCC)), a rainwater collector, and anAerosol Time-Of-Flight Mass Spectrometer (ATOFMS) were operated. Chemical analyses performed on collected samples include pH, conductivity, ion chromatography (IC), and inductive coupled plasma (ICP). Results from these campaigns showed that on days that had air masses with the influence of AD, cloud water samples had higher conductivity and pH values on average (up to 5.7 and 180μS/cm, respectively) than those with air masses without AD influence. An increase in the concentrations of water-soluble ions like non-sea salt calcium and magnesium, and metals like magnesium, calcium and aluminum was observed and the appearance of iron was seen on ICP analyses. The ATOFMS, showed an increase on the amount of particles during AD influence with composition of aluminum, silicates, potassium, iron and titanium aerosols. The increase on the aforementioned species was constant in the three years of sampling, which give us confidence in the identification of the chemical species that are present during the influence of AD.

Examination of the potential impacts of dust and pollution aerosol acting as cloud nucleating aerosol on water resources in the Colorado River Basin

NASA Astrophysics Data System (ADS)

Jha, Vandana

In this study we examine the cumulative effect of dust acting as cloud nucleating aerosol (cloud condensation nuclei (CCN), giant cloud condensation nuclei (GCCN), and ice nuclei (IN)) along with anthropogenic aerosol pollution acting primarily as CCN, over the entire Colorado Rocky Mountains from the months of October to April in the year 2004-2005; the snow year. This ˜6.5 months analysis provides a range of snowfall totals and variability in dust and anthropogenic aerosol pollution. The specific objectives of this research is to quantify the impacts of both dust and pollution aerosols on wintertime precipitation in the Colorado Mountains using the Regional Atmospheric Modeling System (RAMS). In general, dust enhances precipitation primarily by acting as IN, while aerosol pollution reduces water resources in the CRB via the so-called "spill-over" effect, by enhancing cloud droplet concentrations and reducing riming rates. Dust is more episodic and aerosol pollution is more pervasive throughout the winter season. Combined response to dust and aerosol pollution is a net reduction of water resources in the CRB. The question is by how much are those water resources affected? Our best estimate is that total winter-season precipitation loss for for the CRB the 2004-2005 winter season due to the combined influence of aerosol pollution and dust is 5,380,00 acre-feet of water. Sensitivity studies for different cases have also been run for the specific cases in 2004-2005 winter season to analyze the impact of changing dust and aerosol ratios on precipitation in the Colorado River Basin. The dust is varied from 3 to 10 times in the experiments and the response is found to be non monotonic and depends on various environmental factors. The sensitivity studies show that adding dust in a wet system increases precipitation when IN affects are dominant. For a relatively dry system high concentrations of dust can result in over-seeding the clouds and reductions in precipitation

Modeling dust emission in the Magellanic Clouds with Spitzer and Herschel

NASA Astrophysics Data System (ADS)

Chastenet, Jérémy; Bot, Caroline; Gordon, Karl D.; Bocchio, Marco; Roman-Duval, Julia; Jones, Anthony P.; Ysard, Nathalie

2017-05-01

Context. Dust modeling is crucial to infer dust properties and budget for galaxy studies. However, there are systematic disparities between dust grain models that result in corresponding systematic differences in the inferred dust properties of galaxies. Quantifying these systematics requires a consistent fitting analysis. Aims: We compare the output dust parameters and assess the differences between two dust grain models, the DustEM model and THEMIS. In this study, we use a single fitting method applied to all the models to extract a coherent and unique statistical analysis. Methods: We fit the models to the dust emission seen by Spitzer and Herschel in the Small and Large Magellanic Clouds (SMC and LMC). The observations cover the infrared (IR) spectrum from a few microns to the sub-millimeter range. For each fitted pixel, we calculate the full n-D likelihood based on a previously described method. The free parameters are both environmental (U, the interstellar radiation field strength; αISRF, power-law coefficient for a multi-U environment; Ω∗, the starlight strength) and intrinsic to the model (YI: abundances of the grain species I; αsCM20, coefficient in the small carbon grain size distribution). Results: Fractional residuals of five different sets of parameters show that fitting THEMIS brings a more accurate reproduction of the observations than the DustEM model. However, independent variations of the dust species show strong model-dependencies. We find that the abundance of silicates can only be constrained to an upper-limit and that the silicate/carbon ratio is different than that seen in our Galaxy. In the LMC, our fits result in dust masses slightly lower than those found in the literature, by a factor lower than 2. In the SMC, we find dust masses in agreement with previous studies.

Semidirect Dynamical and Radiative Impact of North African Dust Transport on Lower Tropospheric Clouds over the Subtropical North Atlantic in CESM 1.0

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

DeFlorio, Mike; Ghan, Steven J.; Singh, Balwinder

This study uses a century length pre-industrial climate simulation by the Community Earth System Model (CESM 1.0) to explore statistical relationships between dust, clouds and atmospheric circulation, and to suggest a dynamical, rather than microphysical, mechanism linking subtropical North Atlantic lower tropospheric cloud cover with North African dust transport. The length of the run allows us to account for interannual variability of dust emissions and transport downstream of North Africa in the model. CESM’s mean climatology and probability distribution of aerosol optical depth in this region agrees well with available AERONET observations. In addition, CESM shows strong seasonal cycles ofmore » dust burden and lower tropospheric cloud fraction, with maximum values occurring during boreal summer, when a strong correlation between these two variables exists downstream of North Africa over the subtropical North Atlantic. Calculations of Estimated Inversion Strength (EIS) and composites of EIS on high and low downstream North Africa dust months during boreal summer reveal that dust is likely increasing inversion strength over this region due to both solar absorption and reflection. We find no evidence for a microphysical link between dust and lower tropospheric clouds in this region. These results yield new insight over an extensive period of time into the complex relationship between North African dust and lower tropospheric clouds over the open ocean, which has previously been hindered by spatiotemporal constraints of observations. Our findings lay a framework for future analyses using sub-monthly data over regions with different underlying dynamics.« less

Atmospheric movement of microorganisms in clouds of desert dust and implications for human health

USGS Publications Warehouse

Griffin, Dale W.

2007-01-01

Billions of tons of desert dust move through the atmosphere each year. The primary source regions, which include the Sahara and Sahel regions of North Africa and the Gobi and Takla Makan regions of Asia, are capable of dispersing significant quantities of desert dust across the traditionally viewed oceanic barriers. While a considerable amount of research by scientists has addressed atmospheric pathways and aerosol chemistry, very few studies to determine the numbers and types of microorganisms transported within these desert dust clouds and the roles that they may play in human health have been conducted. This review is a summary of the current state of knowledge of desert dust microbiology and the health impact that desert dust and its microbial constituents may have in downwind environments both close to and far from their sources.

Atmospheric movement of microorganisms in clouds of desert dust and implications for human health.

PubMed

Griffin, Dale W

2007-07-01

Billions of tons of desert dust move through the atmosphere each year. The primary source regions, which include the Sahara and Sahel regions of North Africa and the Gobi and Takla Makan regions of Asia, are capable of dispersing significant quantities of desert dust across the traditionally viewed oceanic barriers. While a considerable amount of research by scientists has addressed atmospheric pathways and aerosol chemistry, very few studies to determine the numbers and types of microorganisms transported within these desert dust clouds and the roles that they may play in human health have been conducted. This review is a summary of the current state of knowledge of desert dust microbiology and the health impact that desert dust and its microbial constituents may have in downwind environments both close to and far from their sources.

Impact of aerosols, dust, water vapor and clouds on fair weather PG and implications for the Carnegie curve

NASA Astrophysics Data System (ADS)

Kourtidis, Konstantinos; Georgoulias, Aristeidis

2017-04-01

We studied the impact of anthropogenic aerosols, fine mode natural aerosols, Saharan dust, atmospheric water vapor, cloud fraction, cloud optical depth and cloud top height on the magnitude of fair weather PG at the rural station of Xanthi. Fair weather PG was measured in situ while the other parameters were obtained from the MODIS instrument onboard the Terra and Aqua satellites. All of the above parameteres were found to impact fair weather PG magnitude. Regarding aerosols, the impact was larger for Saharan dust and fine mode natural aerosols whereas regarding clouds the impact was larger for cloud fraction while less than that of aerosols. Water vapour and ice precipitable water were also found to influence fair weather PG. Since aerosols and water are ubiquitous in the atmosphere and exhibit large spatial and temporal variability, we postulate that our understanding of the Carnegie curve might need revision.

Planck intermediate results: XXVIII. Interstellar gas and dust in the Chamaeleon clouds as seen by Fermi LAT and Planck $$\\star$$

DOE PAGES

Ade, P. A. R.; Aghanim, N.; Aniano, G.; ...

2015-09-30

The nearby Chamaeleon clouds have been observed in γ rays by the Fermi Large Area Telescope (LAT) and in thermal dust emission by Planck and IRAS. Cosmic rays and large dust grains, if smoothly mixed with gas, can jointly serve with the H i and 12CO radio data to (i) map the hydrogen column densities, N H, in the different gas phases, in particular at the dark neutral medium (DNM) transition between the H i-bright and CO-bright media; (ii) constrain the CO-to-H 2 conversion factor, X CO; and (iii) probe the dust properties per gas nucleon in each phase andmore » map their spatial variations across the clouds. We have separated clouds at local, intermediate, and Galactic velocities in H i and 12CO line emission to model in parallel the γ-ray intensity recorded between 0.4 and 100 GeV; the dust optical depth at 353 GHz, τ 353; the thermal radiance of the large grains; and an estimate of the dust extinction, A VQ, empirically corrected for the starlight intensity. Furthermore, the dust and γ-ray models have been coupled to account for the DNM gas. The consistent γ-ray emissivity spectra recorded in the different phases confirm that the GeV–TeV cosmic rays probed by the LAT uniformly permeate all gas phases up to the 12CO cores. The dust and cosmic rays both reveal large amounts of DNM gas, with comparable spatial distributions and twice as much mass as in the CO-bright clouds. We give constraints on the H i-DNM-CO transitions for five separate clouds. CO-dark H 2 dominates the molecular columns up to AV ≃ 0.9 and its mass often exceeds the one-third of the molecular mass expected by theory. The corrected A VQ extinction largely provides the best fit to the total gas traced by the γ rays. Nevertheless, we find evidence for a marked rise in A VQ/N H with increasing N H and molecular fraction, and with decreasing dust temperature. The rise in τ 353/NH is even steeper. Here, we observe variations of lesser amplitude and orderliness for the specific power of

SIGNATURES OF RECENT ASTEROID DISRUPTIONS IN THE FORMATION AND EVOLUTION OF SOLAR SYSTEM DUST BANDS

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

Kehoe, A. J. Espy; Colwell, J. E.; Kehoe, T. J. J.

We have performed detailed dynamical modeling of the structure of a faint dust band observed in coadded InfraRed Astronomical Satellite data at an ecliptic latitude of 17° that convincingly demonstrates that it is the result of a relatively recent (significantly less than 1 Ma) disruption of an asteroid and is still in the process of forming. We show here that young dust bands retain information on the size distribution and cross-sectional area of dust released in the original asteroid disruption, before it is lost to orbital and collisional decay. We find that the Emilkowalski cluster is the source of thismore » partial band and that the dust released in the disruption would correspond to a regolith layer ∼3 m deep on the ∼10 km diameter source body's surface. The dust in this band is described by a cumulative size-distribution inverse power-law index with a lower bound of 2.1 (implying domination of cross-sectional area by small particles) for dust particles with diameters ranging from a few μm up to a few cm. The coadded observations show that the thermal emission of the dust band structure is dominated by large (mm–cm size) particles. We find that dust particle ejection velocities need to be a few times the escape velocity of the Emilkowalski cluster source body to provide a good fit to the inclination dispersion of the observations. We discuss the implications that such a significant release of material during a disruption has for the temporal evolution of the structure, composition, and magnitude of the zodiacal cloud.« less

The relationship between CO emission and visual extinction traced by dust emission in the Magellanic Clouds

NASA Astrophysics Data System (ADS)

Lee, Cheoljong; Leroy, Adam K.; Schnee, Scott; Wong, Tony; Bolatto, Alberto D.; Indebetouw, Remy; Rubio, Monica

2015-07-01

To test the theoretical understanding that finding bright CO emission depends primarily on dust shielding, we investigate the relationship between CO emission (ICO) and the amount of dust (estimated from infrared emission and expressed as `AV') across the Large Magellanic Cloud (LMC), the Small Magellanic Cloud, and the Milky Way. We show that at our common resolution of 10 pc scales, ICO given a fixed line of sight AV is similar across all three systems despite the difference in metallicity. We find some evidence for a secondary dependence of ICO on radiation field; in the LMC, ICO at a given AV is smaller in regions of high Tdust, perhaps because of an increased photodissociating radiation field. We suggest a simple but useful picture in which the CO-to-H2 conversion factor (XCO) depends on two separable factors: (1) the distribution of gas column densities, which maps to an extinction distribution via a dust-to-gas ratio; and (2) the dependence of ICO on AV. Assuming that the probability distribution function (PDF) of local Milky Way clouds is universal, this approach predicts a dependence of {X_CO} on Z between Z-1 and Z-2 above about a third solar metallicity. Below this metallicity, CO emerges from only the high column density parts of the cloud and so depends very sensitively on the adopted PDF and the H2/H I prescription. The PDF of low-metallicity clouds is thus of considerable interest and the uncertainty associated with even an ideal prescription for XCO at very low metallicity will be large.

Atmospheric Movement of Microorganisms in Clouds of Desert Dust and Implications for Human Health

PubMed Central

Griffin, Dale W.

2007-01-01

Billions of tons of desert dust move through the atmosphere each year. The primary source regions, which include the Sahara and Sahel regions of North Africa and the Gobi and Takla Makan regions of Asia, are capable of dispersing significant quantities of desert dust across the traditionally viewed oceanic barriers. While a considerable amount of research by scientists has addressed atmospheric pathways and aerosol chemistry, very few studies to determine the numbers and types of microorganisms transported within these desert dust clouds and the roles that they may play in human health have been conducted. This review is a summary of the current state of knowledge of desert dust microbiology and the health impact that desert dust and its microbial constituents may have in downwind environments both close to and far from their sources. PMID:17630335

Planck early results. XVII. Origin of the submillimetre excess dust emission in the Magellanic Clouds

NASA Astrophysics Data System (ADS)

Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Balbi, A.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Battaner, E.; Benabed, K.; Benoît, A.; Bernard, J.-P.; Bersanelli, M.; Bhatia, R.; Bock, J. J.; Bonaldi, A.; Bond, J. R.; Borrill, J.; Bot, C.; Bouchet, F. R.; Boulanger, F.; Bucher, M.; Burigana, C.; Cabella, P.; Cardoso, J.-F.; Catalano, A.; Cayón, L.; Challinor, A.; Chamballu, A.; Chiang, L.-Y.; Chiang, C.; Christensen, P. R.; Clements, D. L.; Colombi, S.; Couchot, F.; Coulais, A.; Crill, B. P.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Gasperis, G.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Delouis, J.-M.; Désert, F.-X.; Dickinson, C.; Dobashi, K.; Donzelli, S.; Doré, O.; Dörl, U.; Douspis, M.; Dupac, X.; Efstathiou, G.; Enßlin, T. A.; Finelli, F.; Forni, O.; Frailis, M.; Franceschi, E.; Fukui, Y.; Galeotta, S.; Ganga, K.; Giard, M.; Giardino, G.; Giraud-Héraud, Y.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Harrison, D.; Helou, G.; Henrot-Versillé, S.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hovest, W.; Hoyland, R. J.; Huffenberger, K. M.; Jaffe, A. H.; Jones, W. C.; Juvela, M.; Kawamura, A.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knox, L.; Kurki-Suonio, H.; Lagache, G.; Lähteenmäki, A.; Lamarre, J.-M.; Lasenby, A.; Laureijs, R. J.; Lawrence, C. R.; Leach, S.; Leonardi, R.; Leroy, C.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; MacTavish, C. J.; Madden, S.; Maffei, B.; Mandolesi, N.; Mann, R.; Maris, M.; Martínez-González, E.; Masi, S.; Matarrese, S.; Matthai, F.; Mazzotta, P.; Meinhold, P. R.; Melchiorri, A.; Mendes, L.; Mennella, A.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Munshi, D.; Murphy, A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; Onishi, T.; Osborne, S.; Pajot, F.; Paladini, R.; Paradis, D.; Pasian, F.; Patanchon, G.; Perdereau, O.; Perotto, L.; Perrotta, F.; Piacentini, F.; Piat, M.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Poutanen, T.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Reach, W. T.; Rebolo, R.; Reinecke, M.; Renault, C.; Ricciardi, S.; Riller, T.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rowan-Robinson, M.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Savini, G.; Scott, D.; Seiffert, M. D.; Smoot, G. F.; Starck, J.-L.; Stivoli, F.; Stolyarov, V.; Sudiwala, R.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Torre, J.-P.; Tristram, M.; Tuovinen, J.; Umana, G.; Valenziano, L.; Varis, J.; Vielva, P.; Villa, F.; Vittorio, N.; Wade, L. A.; Wandelt, B. D.; Wilkinson, A.; Ysard, N.; Yvon, D.; Zacchei, A.; Zonca, A.

2011-12-01

The integrated spectral energy distributions (SED) of the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) appear significantly flatter than expected from dust models based on their far-infrared and radio emission. The still unexplained origin of this millimetre excess is investigated here using the Planck data. The integrated SED of the two galaxies before subtraction of the foreground (Milky Way) and background (CMB fluctuations) emission are in good agreement with previous determinations, confirming the presence of the millimetre excess. In the context of this preliminary analysis we do not propose a full multi-component fitting of the data, but instead subtract contributions unrelated to the galaxies and to dust emission. The background CMB contribution is subtracted using an internal linear combination (ILC) method performed locally around the galaxies. The foreground emission from the Milky Way is subtracted as a Galactic Hi template, and the dust emissivity is derived in a region surrounding the two galaxies and dominated by Milky Way emission. After subtraction, the remaining emission of both galaxies correlates closely with the atomic and molecular gas emission of the LMC and SMC. The millimetre excess in the LMC can be explained by CMB fluctuations, but a significant excess is still present in the SMC SED. The Planck and IRAS-IRIS data at 100 μm are combined to produce thermal dust temperature and optical depth maps of the two galaxies. The LMC temperature map shows the presence of a warm inner arm already found with the Spitzer data, but which also shows the existence of a previously unidentified cold outer arm. Several cold regions are found along this arm, some of which are associated with known molecular clouds. The dust optical depth maps are used to constrain the thermal dust emissivity power-law index (β). The average spectral index is found to be consistent with β = 1.5 and β = 1.2 below 500μm for the LMC and SMC respectively

Interstellar and Cometary Dust

NASA Technical Reports Server (NTRS)

Mathis, John S.

1997-01-01

'Interstellar dust' forms a continuum of materials with differing properties which I divide into three classes on the basis of observations: (a) diffuse dust, in the low-density interstellar medium; (b) outer-cloud dust, observed in stars close enough to the outer edges of molecular clouds to be observed in the optical and ultraviolet regions of the spectrum, and (c) inner-cloud dust, deep within the cores of molecular clouds, and observed only in the infrared by means of absorption bands of C-H, C=O, 0-H, C(triple bond)N, etc. There is a surprising regularity of the extinction laws between diffuse- and outer-cloud dust. The entire mean extinction law from infrared through the observable ultraviolet spectrum can be characterized by a single parameter. There are real deviations from this mean law, larger than observational uncertainties, but they are much smaller than differences of the mean laws in diffuse- and outer-cloud dust. This fact shows that there are processes which operate over the entire distribution of grain sizes, and which change size distributions extremely efficiently. There is no evidence for mantles on grains in local diffuse and outer-cloud dust. The only published spectra of the star VI Cyg 12, the best candidate for showing mantles, does not show the 3.4 micro-m band which appreciable mantles would produce. Grains are larger in outer-cloud dust than diffuse dust because of coagulation, not accretion of extensive mantles. Core-mantle grains favored by J. M. Greenberg and collaborators, and composite grains of Mathis and Whiffen (1989), are discussed more extensively (naturally, I prefer the latter). The composite grains are fluffy and consist of silicates, amorphous carbon, and some graphite in the same grain. Grains deep within molecular clouds but before any processing within the solar system are presumably formed from the accretion of icy mantles on and within the coagulated outer-cloud grains. They should contain a mineral

Research studies using OSO-6 zodiacal light experiment data

NASA Technical Reports Server (NTRS)

1977-01-01

The results of research studies on the OSO-6 zodiacal light experiment, conducted during the period from May 1976 to October 1977 are described. A discussion is included of the instrument performance and the empirical calibrations developed. Main areas of the research performed, i.e., (1) zodiacal light variation analysis; (2) integrated starlight and diffuse galactic light; and (3) earth/moon libration region counterglow, are covered. Considerable data processing was performed during these studies and it is summarized. Recommendations for future research to complete the interim results are given.

Airborne Dust Cloud Measurements at the INL National Security Test Range

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

Michael L. Abbott; Norm Stanley; Larry Radke

2007-09-01

On July 11, 2007, a surface, high-explosive test (<20,000 lb TNT-equivalent) was carried out at the National Security Test Range (NSTR) on the Idaho National Laboratory (INL) Site. Aircraft-mounted rapid response (1-sec) particulate monitors were used to measure airborne PM-10 concentrations directly in the dust cloud and to develop a PM-10 emission factor that could be used for subsequent tests at the NSTR. The blast produced a mushroom-like dust cloud that rose approximately 2,500–3,000 ft above ground level, which quickly dissipated (within 5 miles of the source). In general, the cloud was smaller and less persistence than expected, or thatmore » might occur in other areas, likely due to the coarse sand and subsurface conditions that characterize the immediate NSTR area. Maximum short time-averaged (1-sec) PM-10 concentrations at the center of the cloud immediately after the event reached 421 µg m-3 but were rapidly reduced (by atmospheric dispersion and fallout) to near background levels (~10 µg m-3) after about 15 minutes. This occurred well within the INL Site boundary, about 8 km (5 miles) from the NSTR source. These findings demonstrate that maximum concentrations in ambient air beyond the INL Site boundary (closest is 11.2 km from NSTR) from these types of tests would be well within the 150 µg m-3 24-hour National Ambient Air Quality Standards for PM-10. Aircraft measurements and geostatistical techniques were used to successfully quantify the initial volume (1.64E+9 m3 or 1.64 km3) and mass (250 kg) of the PM-10 dust cloud, and a PM-10 emission factor (20 kg m-3 crater soil volume) was developed for this specific type of event at NSTR. The 250 kg of PM-10 mass estimated from this experiment is almost seven-times higher than the 36 kg estimated for the environmental assessment (DOE-ID 2007) using available Environmental Protection Agency (EPA 1995) emission factors. This experiment demonstrated that advanced aircraft-mounted instruments operated by

Variations between Dust and Gas in the Diffuse Interstellar Medium. III. Changes in Dust Properties

NASA Astrophysics Data System (ADS)

Reach, William T.; Bernard, Jean-Philippe; Jarrett, Thomas H.; Heiles, Carl

2017-12-01

We study infrared emission of 17 isolated, diffuse clouds with masses of order {10}2 {M}ȯ to test the hypothesis that grain property variations cause the apparently low gas-to-dust ratios that have been measured in those clouds. Maps of the clouds were constructed from Wide-field Infrared Survey Explorer (WISE) data and directly compared with the maps of dust optical depth from Planck. The mid-infrared emission per unit dust optical depth has a significant trend toward lower values at higher optical depths. The trend can be quantitatively explained by the extinction of starlight within the clouds. The relative amounts of polycyclic aromatic hydrocarbon and very small grains traced by WISE, compared with large grains tracked by Planck, are consistent with being constant. The temperature of the large grains significantly decreases for clouds with larger dust optical depth; this trend is partially due to dust property variations, but is primarily due to extinction of starlight. We updated the prediction for molecular hydrogen column density, taking into account variations in dust properties, and find it can explain the observed dust optical depth per unit gas column density. Thus, the low gas-to-dust ratios in the clouds are most likely due to “dark gas” that is molecular hydrogen.

Maintaining the Background Dust Opacity During Northern Hemisphere Summer Mars Using Wind Stress Based Dust Lifting

NASA Astrophysics Data System (ADS)

Jha, V.; Kahre, M. A.

2017-12-01

The Mars atmosphere has low levels of dust during Northern Hemisphere (NH) spring and summer (the non-dusty season) and increased levels during NH autumn and winter (the dusty season). In the absence of regional or global storms, dust devils and local storms maintain a background minimum dust loading during the non-dusty season. While observational surveys and Global Climate Model (GCM) studies suggest that dust devils are likely to be major contributors to the background haze during NH spring and summer, a complete understanding of the relative contribution of dust devils and local dust storms has not yet been achieved. We present preliminary results from an investigation that focuses on the effects of radiatively active water ice clouds on dust lifting processes during these seasons. Water ice clouds are known to affect atmospheric temperatures directly by absorption and emission of thermal infrared radiation and indirectly through dynamical feedbacks. Our goal is to understand how clouds affect the contribution by local (wind stress) dust storms to the background dust haze during NH spring and summer. The primary tool for this work is the NASA Ames Mars GCM, which contains physical parameterizations for a fully interactive dust cycle. Three simulations that included wind stress dust lifting were executed for a period of 5 Martian years: a case that included no cloud formation, a case that included radiatively inert cloud formation and a case that included radiatively active cloud (RAC) formation. Results show that when radiatively active clouds are included, the clouds in the aphelion cloud belt radiatively heat the atmosphere aloft in the tropics (Figure 1). This heating produces a stronger overturning circulation, which in turn produces an enhanced low-level flow in the Hadley cell return branch. The stronger low-level flow drives higher surface stresses and increased dust lifting in those locations. We examine how realistic these simulated results are by

The Lunar Dust Environment

NASA Astrophysics Data System (ADS)

Szalay, Jamey Robert

Planetary bodies throughout the solar system are continually bombarded by dust particles, largely originating from cometary activities and asteroidal collisions. Surfaces of bodies with thick atmospheres, such as Venus, Earth, Mars and Titan are mostly protected from incoming dust impacts as these particles ablate in their atmospheres as 'shooting stars'. However, the majority of bodies in the solar system have no appreciable atmosphere and their surfaces are directly exposed to the flux of high speed dust grains. Impacts onto solid surfaces in space generate charged and neutral gas clouds, as well as solid secondary ejecta dust particles. Gravitationally bound ejecta clouds forming dust exospheres were recognized by in situ dust instruments around the icy moons of Jupiter and Saturn, and had not yet been observed near bodies with refractory regolith surfaces before NASA's Lunar Dust and Environment Explorer (LADEE) mission. In this thesis, we first present the measurements taken by the Lunar Dust Explorer (LDEX), aboard LADEE, which discovered a permanently present, asymmetric dust cloud surrounding the Moon. The global characteristics of the lunar dust cloud are discussed as a function of a variety of variables such as altitude, solar longitude, local time, and lunar phase. These results are compared with models for lunar dust cloud generation. Second, we present an analysis of the groupings of impacts measured by LDEX, which represent detections of dense ejecta plumes above the lunar surface. These measurements are put in the context of understanding the response of the lunar surface to meteoroid bombardment and how to use other airless bodies in the solar system as detectors for their local meteoroid environment. Third, we present the first in-situ dust measurements taken over the lunar sunrise terminator. Having found no excess of small grains in this region, we discuss its implications for the putative population of electrostatically lofted dust.

Teeth and numerology from zodiac signs. A correlative study.

PubMed

Kudva, S; Bhat, A P

2000-01-01

Comparative anatomical descriptions have been time and again mentioned in the literature. Based on these aspects, an attempt is made to correlate the morphological features of the human teeth, the zodiac sun signs and numerology. This unique study (first ever of its kind) is also done with a purpose as to whether a particular 'Zodiac Sunsign' or numerology can predict about an individual dental health, the same way the future predictions are being made. It was quite interesting to note that there are few definite attributable dental morphological traits and health to the specific sun signs and numerology.

Changes of Dust Opacity with Density in the Orion A Molecular Cloud

NASA Astrophysics Data System (ADS)

Roy, Arabindo; Martin, Peter G.; Polychroni, Danae; Bontemps, Sylvain; Abergel, Alain; André, Philippe; Arzoumanian, Doris; Di Francesco, James; Hill, Tracey; Konyves, Vera; Nguyen-Luong, Quang; Pezzuto, Stefano; Schneider, Nicola; Testi, Leonardo; White, Glenn

2013-01-01

We have studied the opacity of dust grains at submillimeter wavelengths by estimating the optical depth from imaging at 160, 250, 350, and 500 μm from the Herschel Gould Belt Survey and comparing this to a column density obtained from the Two Micron All Sky Survey derived color excess E(J - K s). Our main goal was to investigate the spatial variations of the opacity due to "big" grains over a variety of environmental conditions and thereby quantify how emission properties of the dust change with column (and volume) density. The central and southern areas of the Orion A molecular cloud examined here, with N H ranging from 1.5 × 1021 cm-2 to 50 × 1021 cm-2, are well suited to this approach. We fit the multi-frequency Herschel spectral energy distributions (SEDs) of each pixel with a modified blackbody to obtain the temperature, T, and optical depth, τ1200, at a fiducial frequency of 1200 GHz (250 μm). Using a calibration of N H/E(J - Ks ) for the interstellar medium (ISM) we obtained the opacity (dust emission cross-section per H nucleon), σe(1200), for every pixel. From a value ~1 × 10-25 cm2 H-1 at the lowest column densities that is typical of the high-latitude diffuse ISM, σe(1200) increases as N 0.28 H over the range studied. This is suggestive of grain evolution. Integrating the SEDs over frequency, we also calculated the specific power P (emission power per H) for the big grains. In low column density regions where dust clouds are optically thin to the interstellar radiation field (ISRF), P is typically 3.7 × 10-31 W H-1, again close to that in the high-latitude diffuse ISM. However, we find evidence for a decrease of P in high column density regions, which would be a natural outcome of attenuation of the ISRF that heats the grains, and for localized increases for dust illuminated by nearby stars or embedded protostars.

Gas, dust, stars, star formation, and their evolution in M 33 at giant molecular cloud scales

NASA Astrophysics Data System (ADS)

Komugi, Shinya; Miura, Rie E.; Kuno, Nario; Tosaki, Tomoka

2018-06-01

We report on a multi-parameter analysis of giant molecular clouds (GMCs) in the nearby spiral galaxy M 33. A catalog of GMCs identifed in 12CO(J = 3-2) was used to compile associated 12CO(J = 1-0), dust, stellar mass, and star formation rate. Each of the 58 GMCs are categorized by their evolutionary stage. Applying the principal component analysis on these parameters, we construct two principal components, PC1 and PC2, which retain 75% of the information from the original data set. PC1 is interpreted as expressing the total interstellar matter content, and PC2 as the total activity of star formation. Young (< 10 Myr) GMCs occupy a distinct region in the PC1-PC2 plane, with lower interstellar medium (ISM) content and star formation activity compared to intermediate-age and older clouds. Comparison of average cloud properties in different evolutionary stages imply that GMCs may be heated or grow denser and more massive via aggregation of diffuse material in their first ˜ 10 Myr. The PCA also objectively identified a set of tight relations between ISM and star formation. The ratio of the two CO lines is nearly constant, but weakly modulated by massive star formation. Dust is more strongly correlated with the star formation rate than the CO lines, supporting recent findings that dust may trace molecular gas better than CO. Stellar mass contributes weakly to the star formation rate, reminiscent of an extended form of the Schmidt-Kennicutt relation with the molecular gas term substituted by dust.

Gas, dust, stars, star formation, and their evolution in M 33 at giant molecular cloud scales

NASA Astrophysics Data System (ADS)

Komugi, Shinya; Miura, Rie E.; Kuno, Nario; Tosaki, Tomoka

2018-04-01

We report on a multi-parameter analysis of giant molecular clouds (GMCs) in the nearby spiral galaxy M 33. A catalog of GMCs identifed in 12CO(J = 3-2) was used to compile associated 12CO(J = 1-0), dust, stellar mass, and star formation rate. Each of the 58 GMCs are categorized by their evolutionary stage. Applying the principal component analysis on these parameters, we construct two principal components, PC1 and PC2, which retain 75% of the information from the original data set. PC1 is interpreted as expressing the total interstellar matter content, and PC2 as the total activity of star formation. Young (< 10 Myr) GMCs occupy a distinct region in the PC1-PC2 plane, with lower interstellar medium (ISM) content and star formation activity compared to intermediate-age and older clouds. Comparison of average cloud properties in different evolutionary stages imply that GMCs may be heated or grow denser and more massive via aggregation of diffuse material in their first ˜ 10 Myr. The PCA also objectively identified a set of tight relations between ISM and star formation. The ratio of the two CO lines is nearly constant, but weakly modulated by massive star formation. Dust is more strongly correlated with the star formation rate than the CO lines, supporting recent findings that dust may trace molecular gas better than CO. Stellar mass contributes weakly to the star formation rate, reminiscent of an extended form of the Schmidt-Kennicutt relation with the molecular gas term substituted by dust.

Metal Evolution and TrAnsport in the Large Magellanic Cloud (METAL): Probing Dust Evolution in Star Forming Galaxies

NASA Astrophysics Data System (ADS)

Roman-Duval

2016-10-01

METAL is a large spectroscopic and imaging program with HST dedicated to the study of dust evolution in the Large Magellanic Cloud (LMC). The program will obtain FUV and NUV medium-resolution spectra of 33 massive stars in the LMC with STIS and COS complementing existing archival data to measure gas-phase and dust-phase (depletion) elemental abundances. With these spectra, we will subsequently directly measure the dust composition and abundance as a function of environment (surface density, radiation field, dynamical conditions, such as the proximity of supernova remnants or expanding HI shells). The depletion information will be complemented with dust UV extinction curves (i.e., the UV opacity of dust grains as a function of wavelength) derived from either archival IUE, or new COS and low-resolution STIS spectra acquired as part of this program. Together, the depletions and extinction curves will constrain how the dust abundance and properties (composition, size distribution) vary with environment at Z=0.5Zo. In parallel to the spectroscopic observations, we will obtain WFC3 NUV-NIR imaging to map dust extinction parameters (AV, RV) in the vicinity of our targets and calibrate the far-infrared (FIR) emissivity of dust. Our observations we will improve the accuracy of dust mass and extinction estimates in the local and high-redshift universe by up to an order of magnitude.METAL will complement a Cycle 23 HST/STIS program (GO-13778) focused on dust evolution in the Small Magellanic Cloud (SMC) at Z=0.2Zo, and previously published depletion studies in the Milky Way (Jenkins et al. 2009) to provide a comprehensive view of dust evolution as a function of metallicity.

Dust in the small Magellanic Cloud. 2: Dust models from interstellar polarization and extinction data

NASA Technical Reports Server (NTRS)

Rodrigues, C. V.; Magalhaes, A. M.; Coyne, G. V.

1995-01-01

We study the dust in the Small Magellanic Cloud using our polarization and extinction data (Paper 1) and existing dust models. The data suggest that the monotonic SMC extinction curve is related to values of lambda(sub max), the wavelength of maximum polarization, which are on the average smaller than the mean for the Galaxy. On the other hand, AZV 456, a star with an extinction similar to that for the Galaxy, shows a value of lambda(sub max) similar to the mean for the Galaxy. We discuss simultaneous dust model fits to extinction and polarization. Fits to the wavelength dependent polarization data are possible for stars with small lambda(sub max). In general, they imply dust size distributions which are narrower and have smaller mean sizes compared to typical size distributions for the Galaxy. However, stars with lambda(sub max) close to the Galactic norm, which also have a narrower polarization curve, cannot be fit adequately. This holds true for all of the dust models considered. The best fits to the extinction curves are obtained with a power law size distribution by assuming that the cylindrical and spherical silicate grains have a volume distribution which is continuous from the smaller spheres to the larger cylinders. The size distribution for the cylinders is taken from the fit to the polarization. The 'typical', monotonic SMC extinction curve can be fit well with graphite and silicate grains if a small fraction of the SMC carbon is locked up in the grain. However, amorphous carbon and silicate grains also fit the data well. AZV456, which has an extinction curve similar to that for the Galaxy, has a UV bump which is too blue to be fit by spherical graphite grains.

The influence of the Chinese zodiac on fertility in Hong Kong SAR.

PubMed

Yip, Paul S F; Lee, Joseph; Cheung, Y B

2002-11-01

The annual total of births in Hong Kong SAR fell substantially in the past 20 years; hence the total fertility rate (TFR) followed the downward trend and dropped to a low of 0.9 below replacement level in 2000. Despite the long-term downward trend, short-run increases in the annual total of births and the TFR were exhibited. Such temporary fertility increases are identified in the Dragon Years of 1988 and 2000. The phenomenon of fertility changes associated with zodiacal animal years is examined in this paper with a view to gaining some insight into whether Chinese cultural preferences and folklore beliefs might have influenced prospective parents' reproductive behaviour. The paper explains the underlying philosophy of the Chinese astrological tradition and discusses how zodiacal preferences affect fertility between 1976 and 2000. The paper also explores why zodiacal influences on Chinese fertility before 1976 did not exist. It is unquestionable that the Dragon Year preference exerts an influence on fertility of modern Chinese populations through zodiacal birth-timing motivations. Birth rate rise in the Dragon Year is due to changes in timing of births that will have little effect on cumulative fertility.

Planck early results. XXV. Thermal dust in nearby molecular clouds

NASA Astrophysics Data System (ADS)

Planck Collaboration; Abergel, A.; Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Balbi, A.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Battaner, E.; Benabed, K.; Benoît, A.; Bernard, J.-P.; Bersanelli, M.; Bhatia, R.; Bock, J. J.; Bonaldi, A.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bucher, M.; Burigana, C.; Cabella, P.; Cardoso, J.-F.; Catalano, A.; Cayón, L.; Challinor, A.; Chamballu, A.; Chiang, L.-Y.; Chiang, C.; Christensen, P. R.; Clements, D. L.; Colombi, S.; Couchot, F.; Coulais, A.; Crill, B. P.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Gasperis, G.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Delouis, J.-M.; Désert, F.-X.; Dickinson, C.; Dobashi, K.; Donzelli, S.; Doré, O.; Dörl, U.; Douspis, M.; Dupac, X.; Efstathiou, G.; Enßlin, T. A.; Eriksen, H. K.; Finelli, F.; Forni, O.; Frailis, M.; Franceschi, E.; Galeotta, S.; Ganga, K.; Giard, M.; Giardino, G.; Giraud-Héraud, Y.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Guillet, V.; Hansen, F. K.; Harrison, D.; Henrot-Versillé, S.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hovest, W.; Hoyland, R. J.; Huffenberger, K. M.; Jaffe, A. H.; Jones, A.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knox, L.; Kurki-Suonio, H.; Lagache, G.; Lamarre, J.-M.; Lasenby, A.; Laureijs, R. J.; Lawrence, C. R.; Leach, S.; Leonardi, R.; Leroy, C.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; MacTavish, C. J.; Maffei, B.; Mandolesi, N.; Mann, R.; Maris, M.; Marshall, D. J.; Martin, P.; Martínez-González, E.; Masi, S.; Matarrese, S.; Matthai, F.; Mazzotta, P.; McGehee, P.; Meinhold, P. R.; Melchiorri, A.; Mendes, L.; Mennella, A.; Mitra, S.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Munshi, D.; Murphy, A.; Naselsky, P.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; Osborne, S.; Pajot, F.; Paladini, R.; Pasian, F.; Patanchon, G.; Perdereau, O.; Perotto, L.; Perrotta, F.; Piacentini, F.; Piat, M.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Poutanen, T.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Reach, W. T.; Rebolo, R.; Reinecke, M.; Renault, C.; Ricciardi, S.; Riller, T.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Savini, G.; Scott, D.; Seiffert, M. D.; Shellard, P.; Smoot, G. F.; Starck, J.-L.; Stivoli, F.; Stolyarov, V.; Sudiwala, R.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Torre, J.-P.; Tristram, M.; Tuovinen, J.; Umana, G.; Valenziano, L.; Verstraete, L.; Vielva, P.; Villa, F.; Vittorio, N.; Wade, L. A.; Wandelt, B. D.; Yvon, D.; Zacchei, A.; Zonca, A.

2011-12-01

Planck allows unbiased mapping of Galactic sub-millimetre and millimetre emission from the most diffuse regions to the densest parts of molecular clouds. We present an early analysis of the Taurus molecular complex, on line-of-sight-averaged data and without component separation. The emission spectrum measured by Planck and IRAS can be fitted pixel by pixel using a single modified blackbody. Some systematic residuals are detected at 353 GHz and 143 GHz, with amplitudes around -7% and +13%, respectively, indicating that the measured spectra are likely more complex than a simple modified blackbody. Significant positive residuals are also detected in the molecular regions and in the 217 GHz and 100 GHz bands, mainly caused by the contribution of the J = 2 → 1 and J = 1 → 0 12CO and 13CO emission lines. We derive maps of the dust temperature T, the dust spectral emissivity index β, and the dust optical depth at 250 μm τ250. The temperature map illustrates the cooling of the dust particles in thermal equilibrium with the incident radiation field, from 16 - 17 K in the diffuse regions to 13 - 14 K in the dense parts. The distribution of spectral indices is centred at 1.78, with a standard deviation of 0.08 and a systematic error of 0.07. We detect a significant T - β anti-correlation. The dust optical depth map reveals the spatial distribution of the column density of the molecular complex from the densest molecular regions to the faint diffuse regions. We use near-infrared extinction and Hi data at 21-cm to perform a quantitative analysis of the spatial variations of the measured dust optical depth at 250 μm per hydrogen atom τ250/NH. We report an increase of τ250/NH by a factor of about 2 between the atomic phase and the molecular phase, which has a strong impact on the equilibrium temperature of the dust particles. Corresponding author: A. Abergel, e-mail: alain.abergel@ias.u-psud.fr

Migration of Interplanetary Dust and Comets

NASA Astrophysics Data System (ADS)

Ipatov, S. I.; Mather, J. C.

Our studies of migration of interplanetary dust and comets were based on the results of integration of the orbital evolution of 15,000 dust particles and 30,000 Jupiter-family comets (JFCs) [1-3]. For asteroidal and cometary particles, the values of the ratio β between the radiation pressure force and the gravitational force varied from <0.0004 to 0.4. For silicates, such values correspond to particle diameters between >1000 and 1 microns. The probability of a collision of a dust particle started from an asteroid or JFC with the Earth during a lifetime of the particle was maximum at diameter d ˜100 microns. For particles started from asteroids and comet 10P, this maximum probability was ˜0.01. Different studies of migration of dust particles and small bodies testify that the fraction of cometary dust particles of the overall dust population inside Saturn's orbit is considerable and can be dominant: (1) Cometary dust particles produced both inside and outside Jupiter's orbit are needed to explain the observed constant number density of dust particles at 3-18 AU. The number density of migrating trans-Neptunian particles near Jupiter's orbit is smaller by a factor of several than that beyond Saturn's orbit. Only a small fraction of asteroidal particles can get outside Jupiter's orbit. (2) Some (less than 0.1%) JFCs can reach typical near-Earth object orbits and remain there for millions of years. Dynamical lifetimes of most of the former JFCs that have typical near-Earth object orbits are about 106 -109 yr, so during most of these times they were extinct comets. Such former comets could disintegrate and produce a lot of mini-comets and dust. (3) Comparison of the velocities of zodiacal dust particles (velocities of MgI line) based on the distributions of particles over their orbital elements obtained in our runs [3-4] with the velocities obtained at the WHAM observations shows that only asteroidal dust particles cannot explain these observations, and particles

Skylab experiment SO73: Gegenschein/zodiacal light. [electrophotometry of surface brightness and polarization

NASA Technical Reports Server (NTRS)

Weinberg, J. L.

1976-01-01

A 10 color photoelectric polarimeter was used to measure the surface brightness and polarization associated with zodiacal light, background starlight, and spacecraft corona during each of the Skylab missions. Fixed position and sky scanning observations were obtained during Skylab missions SL-2 and SL-3 at 10 wavelenghts between 4000A and 8200A. Initial results from the fixed-position data are presented on the spacecraft corona and on the polarized brightness of the zodiacal light. Included among the fixed position regions that were observed are the north celestial pole, south ecliptic pole, two regions near the north galactic pole, and 90 deg from the sun in the ecliptic. The polarized brightness of the zodiacal light was found to have the color of the sun at each of these positions. Because previous observations found the total brightness to have the color of the sun from the near ultraviolet out to 2.4 micrometers, the degree of polarization of the zodiacal light is independent of wavelength from 4000A to 8200A.

Attenuation of Ultraviolet Radiation by Dust in Interstellar Clouds

NASA Astrophysics Data System (ADS)

Escalante, V.

1994-07-01

Se han obtenido soluciones de la ecuación de transporte para la dispersión coherente, no conservativa y anisotrópica para estimar la precisión de métodos aproximados, usados en modelos de nubes en que la luz es atenuada principalmente por el polvo. En los cálculos se ha aplicado el metodo de armónicos esféricos para distintos parámetros del polvo. Se ha explorado la posibilidad de descubrir cambios en las caracterísiticas del polvo mediante observaciones de regiones fotodisociadas. Se muestra que para altos valores del albedo de dispersión simple y del parametro de asimetria de Ia función de fase que son adecuados para el polvo galáctico, no es posible determinar variaciones de más de un factor de 2 en el cociente de gas a polvo. Solutions to the transfer equation for coherent, non-conservative, anisotropic scattering have been obtained in order to estimate the accuracy of approximate methods used in models of clouds where light is attenuated mostly by dust. In the calculations the spherical harmonic method has been applied for different grain parameters. The possibility of discovering changes of dust characteristics through observations of photodissociation regions has been considered. It is shown that for the high values of the single scattering albedo and the asymmetry parameter of the phase function for redistribution that appear to be appropriate for galactic dust, it is not possible to determine variations of more than a factor of 2 in the gas to dust ratio.

Condition for dust evacuation from the first galaxies

NASA Astrophysics Data System (ADS)

Fukushima, Hajime; Yajima, Hidenobu; Omukai, Kazuyuki

2018-06-01

Dust enables low-mass stars to form from low-metallicity gas by inducing fragmentation of clouds via cooling by thermal emission. Dust may, however, be evacuated from star-forming clouds due to the radiation force from massive stars. We study here the condition for dust evacuation by comparing the dust evacuation time with the time of cloud destruction due to either expansion of H II regions or supernovae. The cloud destruction time has a weak dependence on cloud radius, while the dust evacuation time is shorter for a cloud with a smaller radius. Dust evacuation, thus, occurs in compact star-forming clouds whose column density is NH ≃ 1024-1026 cm-2. The critical halo mass above which dust evacuation occurs is lower for higher formation red shift, e.g. ˜109 M⊙ at red shift z ˜ 3 and ˜107 M⊙ at z ˜ 9. In addition, the metallicity of the gas should be less than ˜10-2 Z⊙, otherwise attenuation by dust reduces the radiation force significantly. From the dust-evacuated gas, massive stars are likely to form, even with a metallicity above ˜10-5 Z⊙, the critical value for low-mass star formation due to dust cooling. This can explain the dearth of ultra-metal-poor stars with a metallicity lower than ˜10-4 Z⊙.

PROGRA2 experiment: New results for dust clouds and regoliths analogs

NASA Astrophysics Data System (ADS)

Hadamcik, E.; Renard, J.-B.; Levasseur-Regourd, A. C.; Worms, J.-C.

2006-01-01

With the PROGRA2 experience, linear polarization of scattered light is measured on various types of dust clouds lifted by microgravity, or by an air-draught. The aim is to compare the phase curves for dust analogs with those obtained in the Solar System (cometary comae, and solid particles in planetary atmospheres) by remote-sensing and in situ techniques. Measurements are also performed on layers of particles (on the ground) and compared with remote measurements on asteroidal regoliths and planetary surfaces. New phase curves have been obtained, e.g., for quartz samples, crystals, fluffy mixtures of silica and carbon blacks and a high porosity regolith analog made of micron-sized silica spheres. This work will contribute to the choice of the samples to be studied with the ICAPS experiment onboard the ISS and on the precursor experiment.

Limb clouds and dust on Mars from images obtained by the Visual Monitoring Camera (VMC) onboard Mars Express

NASA Astrophysics Data System (ADS)

Sánchez-Lavega, A.; Chen-Chen, H.; Ordoñez-Etxeberria, I.; Hueso, R.; del Río-Gaztelurrutia, T.; Garro, A.; Cardesín-Moinelo, A.; Titov, D.; Wood, S.

2018-01-01

The Visual Monitoring Camera (VMC) onboard the Mars Express (MEx) spacecraft is a simple camera aimed to monitor the release of the Beagle-2 lander on Mars Express and later used for public outreach. Here, we employ VMC as a scientific instrument to study and characterize high altitude aerosols events (dust and condensates) observed at the Martian limb. More than 21,000 images taken between 2007 and 2016 have been examined to detect and characterize elevated layers of dust in the limb, dust storms and clouds. We report a total of 18 events for which we give their main properties (areographic location, maximum altitude, limb projected size, Martian solar longitude and local time of occurrence). The top altitudes of these phenomena ranged from 40 to 85 km and their horizontal extent at the limb ranged from 120 to 2000 km. They mostly occurred at Equatorial and Tropical latitudes (between ∼30°N and 30°S) at morning and afternoon local times in the southern fall and northern winter seasons. None of them are related to the orographic clouds that typically form around volcanoes. Three of these events have been studied in detail using simultaneous images taken by the MARCI instrument onboard Mars Reconnaissance Orbiter (MRO) and studying the properties of the atmosphere using the predictions from the Mars Climate Database (MCD) General Circulation Model. This has allowed us to determine the three-dimensional structure and nature of these events, with one of them being a regional dust storm and the two others water ice clouds. Analyses based on MCD and/or MARCI images for the other cases studied indicate that the rest of the events correspond most probably to water ice clouds.

Division F Commission 22: Meteors, Meteorites, and Interplanetary Dust

NASA Astrophysics Data System (ADS)

Jenniskens, Peter; Borovička, Jiří; Watanabe, Jun-Ichi; Jopek, Tadeusz; Abe, Shinsuke; Consolmagno, Guy J.; Ishiguro, Masateru; Janches, Diego; Ryabova, Galina O.; Vaubaillon, Jérémie; Zhu, Jin

2016-04-01

Commission 22 (Meteors, Meteorites and Interplanetary Dust) was established at the first IAU General Assembly held in Rome in 1922, with William Frederick Denning as its first President. Denning was an accountant by profession, but as an amateur astronomer he contributed extensively to meteor science. Commission 22 thus established a pattern that has continued to this day that non-professional astronomers were welcomed and valued and could play a significant role in its affairs. The field of meteors, meteorites and interplanetary dust has played a disproportional role in the astronomical perception of the general public through the majestic displays of our annual meteor showers. Those in the field deployed many techniques uncommon in other fields of astronomy, studying the ``vermin of space'', the small solid bodies that pervade interplanetary space and impact Earth's atmosphere, the surface of the Moon, and that of our satellites in orbit. Over time, the field has tackled a wide array of problems, from predicting the encounter with meteoroid streams, to the origin of our meteorites and the nature of the zodiacal cloud. Commission 22 has played an important role in organizing the field through dedicated meetings, a data centre, and working groups that developed professional-amateur relationships and that organized the nomenclature of meteor showers. The contribution of Commission 22 to the field is perhaps most readily seen in the work of the presidents that followed in the footsteps of Denning.

Optical Depth Sensor (ODS) for the measurement of dust and clouds properties in the Mars atmosphere

NASA Astrophysics Data System (ADS)

Toledo, D.; Rannou, P.; Pommereau, J.-P.; Sarkissian, A.; Foujols, T.

2014-04-01

A small and sophisticated optical depth sensor (ODS) has been designed to work in both Martian and Earth environments. The principal goal of ODS is to carry out the opacity due to the Martian dust as well as to characterize the high altitude clouds at twilight, crucial parameters in understanding of Martian meteorology. The instrument was initially designed for the failed MARS96 Russian mission, and also was included in the payload of several other missions [1]. Until recently, it was selected (NASA/ESA AO) in the payload of the atmospheric package DREAMS onboard the MARS 2016 mission. But following a decision of the CNES, it is no more included in the payload. In order to study the performance of ODS under a wide range of conditions as well as its capable to provide daily measurements of both dust optical thickness and high altitude clouds properties, the instrument has participated in different terrestrial campaigns. A good performance of ODS prototype (Figure 1) on cirrus clouds detection and in dust opacity estimation was previously archived in Africa during 2004-2005 and in Brasil from 2012 to nowadays. Moreover, a campaign in the arctic is expected before 2016 where fifteen ODSs will be part of an integrated observing system over the Arctic Ocean, allowing test the ODS performance in extreme conditions. In this presentation we present main principle of the retrieval, the instrumental concept, the result of the tests performed and the principal objectives of ODS in Mars.

Simulation of the Processes of Formation of a Dust Cloud in a Vacuum and in the Absence of Gravitation

NASA Astrophysics Data System (ADS)

Avdeev, A. V.; Boreisho, A. S.; Ivakin, S. V.; Moiseev, A. A.; Savin, A. V.; Sokolov, E. I.; Smirnov, P. G.

2018-01-01

This article is devoted to the simulation of the processes of formation of dust clouds in the absence of gravitation, which is necessary for understanding the processes proceeding in dust clusters in outer space, upper planetary atmosphere, and on the surface of space objects, as well as for evaluating the possibilities of creating disperse structures with given properties. The chief aim of the simulation is to determine the general laws of the dynamics of the dust cloud at the initial stage of its formation. With the use of the original approach based on the particle-in-cell method that permits investigating the mechanics of large ensembles of particles on contemporary computational platforms, we consider the mechanics of a dusty medium in the process of its excitation in a closed container due to the vibration of the walls, and then in the process of particle scattering when the container opens in outer space. The main formation mechanisms of a dust formation have been elucidated, and the possibilities of mathematical simulation for predicting spatial and time characteristics of disperse structures have been shown.

Overview for the reanalysis of Mariner 9 UV spectrometer data for ozone, cloud, and dust abundances, and their interaction over climate timescales

NASA Technical Reports Server (NTRS)

Lindner, Bernhard Lee

1992-01-01

Mariner 9 UV spectrometer data were reinverted for the ozone abundance, cloud abundance, dust abundance, and polar-cap albedo. The original reduction of the spectra ignored the presence of atmospheric dust and clouds, even though their abundance is substantial and can mask appreciable amounts of ozone if not accounted for (Lindner, 1988). The Mariner 9 ozone data has been used as a benchmark in all theoretical models of atmospheric composition, escape, and photochemistry. A second objective is to examine the data for the interrelationship of the ozone cycle, dust cycle, and cloud cycle, on an annual, inter-annual, and climatic basis, testing predictions by Lindner (1988). This also has implications for many terrestrial ozone studies, such as the ozone hole, acid rain, and ozone-smog. A third objective is to evaluate the efficacy of the reflectance spectroscopy technique at retrieving the ozone abundance on Mars. This would be useful for planning ozone observations on future Mars missions or the terrestrial troposphere.

The Primeval Zodiac: Its Social, Religious, and Mythological Background

NASA Astrophysics Data System (ADS)

Verderame, L.

2009-08-01

In this brief paper we try to draw the lines of the possible development of the originary iconographic and symbolic repertoire of the Mesopotamian zodiac, which through the Greeks was adopted in the Western world.

Foehn-induced effects on dust pollution, frontal clouds and solar radiation in the Dead Sea valley

NASA Astrophysics Data System (ADS)

Kishcha, Pavel; Starobinets, Boris; Alpert, Pinhas; Kaplan, Michael

2017-04-01

The significant drying up of the Dead Sea over the past 40 years has led to an increase in an exposed area contributing to local dust pollution. Measurements show that, sometimes, in the Dead Sea valley, dust pollution can reach extreme concentrations up to several thousands of micrograms per cubic meters. Our analysis of a meteorological situation shows that a foehn phenomenon can be a causal factor for the aforementioned extreme local dust concentration. This foehn phenomenon creates strong warm and dry winds, which are accompanied by air turbulence and temperature inversion. In our study, foehn-induced effects on dust pollution, frontal clouds and solar radiation were analyzed over the Judean Mountains ( 1000 m) and over the Dead Sea valley (-420 m), using high-resolution numerical simulations and in-situ observations at meteorological stations located across the mountain ridge. An extreme dust episode occurring on March 22, 2013, was analyzed, which was characterized by measured surface dust concentrations of up to 7000 µg m-3 in the Dead Sea valley. We simulated this foehn phenomenon with the 3-km resolution COSMO-ART model. Our analysis has shown that the foehn phenomenon could be observed even over the relatively low Judean Mountains. This analysis was based on various meteorological, pyranometer, radar, and aerosol measurements together with high-resolution model data. In the Dead Sea valley, the maximum aerosol optical depth (AOD) did not coincide with the maximum surface dust concentration. This lack of coincidence indicates difficulties in using satellite-based AOD for initializing dust concentration within numerical forecast systems over this region with complex terrain. In the western Dead Sea valley, strong foehn winds of over 20 m/s were accompanied by maximal air turbulence leading to maximal local dust emissions. Thus, the model showed that, by creating significant turbulence, the foehn phenomenon intensified the saltation (bombardment) mechanism

Sahara Dust

Atmospheric Science Data Center

2013-04-15

article title:  Casting Light and Shadows on a Saharan Dust Storm     ... ocean and dust layer, which are visible in shades of blue and tan, respectively. In the lower panel, heights derived from automated ... cast by the cirrus clouds onto the dust (indicated by blue and cyan pixels) provide sufficient spatial contrast for a retrieval of ...

Ten-color Gegenschein-zodiacal light photometer. [onboard Skylab

NASA Technical Reports Server (NTRS)

Sparrow, J. G.; Weinberg, J. L.; Hahn, R. C.

1977-01-01

A ten-color Fabry photometer was used during Skylab missions SL-2 and SL-3 to measure sky brightness and polarization associated with zodiacal light, background starlight, F region airglow, and spacecraft corona. A brief description is given of the design, calibration, and performance of the instrument.

Analysis of Aerosols and Fallout from High-Explosive Dust Clouds. Volume 2

DTIC Science & Technology

1977-03-01

to the situation at hand, where S is an absolute error, AIV- 30 Rio • N(i, - N(i,2) It is to be noted, however, that the Poisson formula specifies the...sphere TNT detonation near Grand Junction, Colorado, on November 13, 1972. Data from the resulting dust cloud was collected by two aircraft and includes...variations. rio Measurements of carbon monoxide were inconclusive due to an unusually high noise level (6 to 8 ppm or considerably higher than the carbon

Dust particle radial confinement in a dc glow discharge.

PubMed

Sukhinin, G I; Fedoseev, A V; Antipov, S N; Petrov, O F; Fortov, V E

2013-01-01

A self-consistent nonlocal model of the positive column of a dc glow discharge with dust particles is presented. Radial distributions of plasma parameters and the dust component in an axially homogeneous glow discharge are considered. The model is based on the solution of a nonlocal Boltzmann equation for the electron energy distribution function, drift-diffusion equations for ions, and the Poisson equation for a self-consistent electric field. The radial distribution of dust particle density in a dust cloud was fixed as a given steplike function or was chosen according to an equilibrium Boltzmann distribution. The balance of electron and ion production in argon ionization by an electron impact and their losses on the dust particle surface and on the discharge tube walls is taken into account. The interrelation of discharge plasma and the dust cloud is studied in a self-consistent way, and the radial distributions of the discharge plasma and dust particle parameters are obtained. It is shown that the influence of the dust cloud on the discharge plasma has a nonlocal behavior, e.g., density and charge distributions in the dust cloud substantially depend on the plasma parameters outside the dust cloud. As a result of a self-consistent evolution of plasma parameters to equilibrium steady-state conditions, ionization and recombination rates become equal to each other, electron and ion radial fluxes become equal to zero, and the radial component of electric field is expelled from the dust cloud.

Ice Nucleation of Bare and Sulfuric Acid-coated Mineral Dust Particles and Implication for Cloud Properties

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

Kulkarni, Gourihar R.; Sanders, Cassandra N.; Zhang, Kai

2014-08-27

Ice nucleation properties of different dust species coated with soluble material are not well understood. We determined the ice nucleation ability of bare and sulfuric acid coated mineral dust particles as a function of temperature (-25 to -35 deg C) and relative humidity with respect to water (RHw). Five different mineral dust species: Arizona test dust (ATD), illite, montmorillonite, quartz and kaolinite were dry dispersed and size-selected at 150 nm and exposed to sulfuric acid vapors in the coating apparatus. The condensed sulfuric acid soluble mass fraction per particle was estimated from the cloud condensation nuclei activated fraction measurements. Themore » fraction of dust particles nucleating ice at various temperatures and RHw was determined using a compact ice chamber. In water-subsaturated conditions, compared to bare dust particles, we found that only coated ATD particles showed suppression of ice nucleation ability while other four dust species did not showed the effect of coating on the fraction of particles nucleating ice. The results suggest that interactions between the dust surface and sulfuric acid vapor are important, such that interactions may or may not modify the surface via chemical reactions with sulfuric acid. At water-supersaturated conditions we did not observed the effect of coating, i.e. the bare and coated dust particles had similar ice nucleation behavior.« less

Limb clouds and dust on Mars from VMC-Mars Express images

NASA Astrophysics Data System (ADS)

Sanchez-Lavega, Agustin; Chen, Hao Chen; Ordoñez-Etxeberria, Iñaki; Hueso, Ricardo; Cardesin, Alejandro; Titov, Dima; Wood, Simon

2016-10-01

We have used the large image database generated by the Visual Monitoring Camera (VMC) onboard Mars Express to first search and then study, the properties of projected features (dust and water clouds) on the planet limb. VMC is a small camera serving since 2007 for public education and outreach (Ormston et al., 2011). The camera consists of a CMOS sensor with a Bayer filter mosaic providing color images in the wavelength range 400-900 nm. Since the observations were performed in an opportunistic mode (nor planned on a science base) the captured events occurred in a random mode. In total 17 limb features were observed in the period spanning from April 2007 to August 2015. Their extent at limb varies from about 100 km for the smaller ones to 2,000 km for the major ones. They showed a rich morphology consisting in series of patchy elements with a uniform top layer located at altitudes ranging from 30 to 85 km. The features are mostly concentrated between latitudes 45 deg North and South covering most longitudes although a greater concentration occurs around -90 to +90 deg. from the reference meridian (i.e. longitude 0 degrees, East or West). Most events in the southern hemisphere occurred for orbital longitudes 0-90 degrees (autumnal season) and in the north for orbital longitudes 330-360 (winter season). We present a detailed study of two of these events, one corresponding to a dust storm observed also with the MARCI instrument onboard Mars Reconnaissance Orbiter, and a second one corresponding to a water cloud.

Forecast errors in dust vertical distributions over Rome (Italy): Multiple particle size representation and cloud contributions

NASA Astrophysics Data System (ADS)

Kishcha, P.; Alpert, P.; Shtivelman, A.; Krichak, S. O.; Joseph, J. H.; Kallos, G.; Katsafados, P.; Spyrou, C.; Gobbi, G. P.; Barnaba, F.; Nickovic, S.; PéRez, C.; Baldasano, J. M.

2007-08-01

In this study, forecast errors in dust vertical distributions were analyzed. This was carried out by using quantitative comparisons between dust vertical profiles retrieved from lidar measurements over Rome, Italy, performed from 2001 to 2003, and those predicted by models. Three models were used: the four-particle-size Dust Regional Atmospheric Model (DREAM), the older one-particle-size version of the SKIRON model from the University of Athens (UOA), and the pre-2006 one-particle-size Tel Aviv University (TAU) model. SKIRON and DREAM are initialized on a daily basis using the dust concentration from the previous forecast cycle, while the TAU model initialization is based on the Total Ozone Mapping Spectrometer aerosol index (TOMS AI). The quantitative comparison shows that (1) the use of four-particle-size bins in the dust modeling instead of only one-particle-size bins improves dust forecasts; (2) cloud presence could contribute to noticeable dust forecast errors in SKIRON and DREAM; and (3) as far as the TAU model is concerned, its forecast errors were mainly caused by technical problems with TOMS measurements from the Earth Probe satellite. As a result, dust forecast errors in the TAU model could be significant even under cloudless conditions. The DREAM versus lidar quantitative comparisons at different altitudes show that the model predictions are more accurate in the middle part of dust layers than in the top and bottom parts of dust layers.

Evolution of trace elements in the planetary boundary layer in southern China: Effects of dust storms and aerosol-cloud interactions

NASA Astrophysics Data System (ADS)

Li, Tao; Wang, Yan; Zhou, Jie; Wang, Tao; Ding, Aijun; Nie, Wei; Xue, Likun; Wang, Xinfeng; Wang, Wenxing

2017-03-01

Aerosols and cloud water were analyzed at a mountaintop in the planetary boundary layer in southern China during March-May 2009, when two Asian dust storms occurred, to investigate the effects of aerosol-cloud interactions (ACIs) on chemical evolution of atmospheric trace elements. Fe, Al, and Zn predominated in both coarse and fine aerosols, followed by high concentrations of toxic Pb, As, and Cd. Most of these aerosol trace elements, which were affected by dust storms, exhibited various increases in concentrations but consistent decreases in solubility. Zn, Fe, Al, and Pb were the most abundant trace elements in cloud water. The trace element concentrations exhibited logarithmic inverse relationships with the cloud liquid water content and were found highly pH dependent with minimum concentrations at the threshold of pH 5.0. The calculation of Visual MINTEQ model showed that 80.7-96.3% of Fe(II), Zn(II), Pb(II), and Cu(II) existed in divalent free ions, while 71.7% of Fe(III) and 71.5% of Al(III) were complexed by oxalate and fluoride, respectively. ACIs could markedly change the speciation distributions of trace elements in cloud water by pH modification. The in-cloud scavenging of aerosol trace elements likely reached a peak after the first 2-3 h of cloud processing, with scavenging ratios between 0.12 for Cr and 0.57 for Pb. The increases of the trace element solubility (4-33%) were determined in both in-cloud aerosols and postcloud aerosols. These results indicated the significant importance of aerosol-cloud interactions to the evolution of trace elements during the first several cloud condensation/evaporation cycles.

Dust in brown dwarfs and extra-solar planets. I. Chemical composition and spectral appearance of quasi-static cloud layers

NASA Astrophysics Data System (ADS)

Helling, Ch.; Woitke, P.; Thi, W.-F.

2008-07-01

Aims: Brown dwarfs are covered by dust cloud layers which cause inhomogeneous surface features and move below the observable τ = 1 level during the object's evolution. The cloud layers have a strong influence on the structure and spectral appearance of brown dwarfs and extra-solar planets, e.g. by providing high local opacities and by removing condensable elements from the atmosphere causing a sub-solar metalicity in the atmosphere. We aim at understanding the formation of cloud layers in quasi-static substellar atmospheres that consist of dirty grains composed of numerous small islands of different solid condensates. Methods: The time-dependent description is a kinetic model describing nucleation, growth and evaporation. It is extended to treat gravitational settling and is applied to the static-stationary case of substellar model atmospheres. From the solution of the dust moments, we determine the grain size distribution function approximately which, together with the calculated material volume fractions, provides the basis for applying effective medium theory and Mie theory to calculate the opacities of the composite dust grains. Results: The cloud particles in brown dwarfs and hot giant-gas planets are found to be small in the high atmospheric layers (a ≈ 0.01 μm), and are composed of a rich mixture of all considered condensates, in particular MgSiO3[s], Mg2SiO4[s] and SiO2[s]. As the particles settle downward, they increase in size and reach several 100 μm in the deepest layers. The more volatile parts of the grains evaporate and the particles stepwise purify to form composite particles of high-temperature condensates in the deeper layers, mainly made of Fe[s] and Al2O3[s]. The gas phase abundances of the elements involved in the dust formation process vary by orders of magnitudes throughout the atmosphere. The grain size distribution is found to be relatively broad in the upper atmospheric layers but strongly peaked in the deeper layers. This reflects

Theory of Dust Voids in Plasmas

NASA Technical Reports Server (NTRS)

Goree, J.; Morfill, G. E.; Tsytovich, V. N.; Vladimirov, S. V.

1999-01-01

Dusty plasmas in a gas discharge often feature a stable void, i.e., a dust-free region inside the dust cloud. This occurs under conditions relevant to both plasma processing discharges and plasma crystal experiments. The void results from a balance of the electrostatic and ion drag forces on a dust particle. The ion drag force is driven by a flow of ions outward from an ionization source and toward the surrounding dust cloud, which has a negative space charge. In equilibrium the force balance for dust particles requires that the boundary with the dust cloud be sharp, provided that the particles are cold and monodispersive. Numerical solutions of the one-dimensional nonlinear fluid equations are carried out including dust charging and dust-neutral collisions, but not ion-neutral collisions. The regions of parameter space that allow stable void equilibria are identified. There is a minimum ionization rate that can sustain a void. Spatial profiles of plasma parameters in the void are reported. In the absence of ion-neutral collisions, the ion flow enters the dust cloud's edge at Mach number M = 1. Phase diagrams for expanding or contracting voids reveal a stationary point corresponding to a single stable equilibrium void size, provided the ionization rate is constant. Large voids contract and small voids expand until they attain this stationary void size. On the other hand, if the ionization rate is not constant, the void size can oscillate. Results are compared to recent laboratory and microgravity experiments.

Scattering by ensembles of small particles experiment, theory and application

NASA Technical Reports Server (NTRS)

Gustafson, B. A. S.

1980-01-01

A hypothetical self consistent picture of evolution of prestellar intertellar dust through a comet phase leads to predictions about the composition of the circum-solar dust cloud. Scattering properties of thus resulting conglomerates with a bird's-nest type of structure are investigated using a micro-wave analogue technique. Approximate theoretical methods of general interest are developed which compared favorably with the experimental results. The principal features of scattering of visible radiation by zodiacal light particles are reasonably reproduced. A component which is suggestive of (ALPHA)-meteoroids is also predicted.

China Dust

Atmospheric Science Data Center

2013-04-16

... SpectroRadiometer (MISR) nadir-camera images of eastern China compare a somewhat hazy summer view from July 9, 2000 (left) with a ... arid and sparsely vegetated surfaces of Mongolia and western China pick up large quantities of yellow dust. Airborne dust clouds from the ...

Desert dust suppressing precipitation: A possible desertification feedback loop

PubMed Central

Rosenfeld, Daniel; Rudich, Yinon; Lahav, Ronen

2001-01-01

The effect of desert dust on cloud properties and precipitation has so far been studied solely by using theoretical models, which predict that rainfall would be enhanced. Here we present observations showing the contrary; the effect of dust on cloud properties is to inhibit precipitation. Using satellite and aircraft observations we show that clouds forming within desert dust contain small droplets and produce little precipitation by drop coalescence. Measurement of the size distribution and the chemical analysis of individual Saharan dust particles collected in such a dust storm suggest a possible mechanism for the diminished rainfall. The detrimental impact of dust on rainfall is smaller than that caused by smoke from biomass burning or anthropogenic air pollution, but the large abundance of desert dust in the atmosphere renders it important. The reduction of precipitation from clouds affected by desert dust can cause drier soil, which in turn raises more dust, thus providing a possible feedback loop to further decrease precipitation. Furthermore, anthropogenic changes of land use exposing the topsoil can initiate such a desertification feedback process. PMID:11353821

72. 451 MADISON AVENUE, GRAND STAIR, ZODIAC CLOCK WITH DECORATIVE ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

72. 451 MADISON AVENUE, GRAND STAIR, ZODIAC CLOCK WITH DECORATIVE CARVING BY STANFORD WHITE AND AUGUSTUS SAINT-GAUDENS - Villard Houses, 451-457 Madison Avenue & 24 East Fifty-first Street, New York County, NY

Investigating cloud absorption effects: Global absorption properties of black carbon, tar balls, and soil dust in clouds and aerosols

NASA Astrophysics Data System (ADS)

Jacobson, Mark Z.

2012-03-01

This study examines modeled properties of black carbon (BC), tar ball (TB), and soil dust (SD) absorption within clouds and aerosols to understand better Cloud Absorption Effects I and II, which are defined as the effects on cloud heating of absorbing inclusions in hydrometeor particles and of absorbing aerosol particles interstitially between hydrometeor particles at their actual relative humidity (RH), respectively. The globally and annually averaged modeled 550 nm aerosol mass absorption coefficient (AMAC) of externally mixed BC was 6.72 (6.3-7.3) m2/g, within the laboratory range (6.3-8.7 m2/g). The global AMAC of internally mixed (IM) BC was 16.2 (13.9-18.2) m2/g, less than the measured maximum at 100% RH (23 m2/g). The resulting AMAC amplification factor due to internal mixing was 2.41 (2-2.9), with highest values in high RH regions. The global 650 nm hydrometeor mass absorption coefficient (HMAC) due to BC inclusions was 17.7 (10.6-19) m2/g, ˜9.3% higher than that of the IM-AMAC. The 650 nm HMACs of TBs and SD were half and 1/190th, respectively, that of BC. Modeled aerosol absorption optical depths were consistent with data. In column tests, BC inclusions in low and mid clouds (CAE I) gave column-integrated BC heating rates ˜200% and 235%, respectively, those of interstitial BC at the actual cloud RH (CAE II), which itself gave heating rates ˜120% and ˜130%, respectively, those of interstitial BC at the clear-sky RH. Globally, cloud optical depth increased then decreased with increasing aerosol optical depth, consistent with boomerang curves from satellite studies. Thus, CAEs, which are largely ignored, heat clouds significantly.

Contact freezing of supercooled cloud droplets on collision with mineral dust particles: effect of particle size

NASA Astrophysics Data System (ADS)

Hoffmann, Nadine; Duft, Denis; Kiselev, Alexei; Leisner, Thomas

2013-04-01

The contact freezing of supercooled cloud droplets is one of the potentially important and the least investigated heterogeneous mechanism of ice formation in the tropospheric clouds [1]. On the time scales of cloud lifetime the freezing of supercooled water droplets via contact mechanism may occur at higher temperature compared to the same IN immersed in the droplet. However, the laboratory experiments of contact freezing are very challenging due to the number of factors affecting the probability of ice formation. In our experiment we study single water droplets freely levitated in the laminar flow of mineral dust particles acting as the contact freezing nuclei. By repeating the freezing experiment sufficient number of times we are able to reproduce statistical freezing behavior of large ensembles of supercooled droplets and measure the average rate of freezing events. We show that the rate of freezing at given temperature is governed only by the rate of droplet -particle collision and by the properties of the contact ice nuclei. In this contribution we investigate the relationship between the freezing probability and the size of mineral dust particle (represented by illite) and show that their IN efficiency scales with the particle size. Based on this observation, we discuss the similarity between the freezing of supercooled water droplets in immersion and contact modes and possible mechanisms of apparent enhancement of the contact freezing efficiency. [1] - K.C. Young, The role of contact nucleation in ice phase initiation in clouds, Journal of the Atmospheric Sciences 31, 1974

Coupling Mars' Dust and Water Cycles: Effects on Dust Lifting Vigor, Spatial Extent and Seasonality

NASA Technical Reports Server (NTRS)

Kahre, M. A.; Hollingsworth, J. L.; Haberle, R. M.; Montmessin, F.

2012-01-01

The dust cycle is an important component of Mars' current climate system. Airborne dust affects the radiative balance of the atmosphere, thus greatly influencing the thermal and dynamical state of the atmosphere. Dust raising events on Mars occur at spatial scales ranging from meters to planet-wide. Although the occurrence and season of large regional and global dust storms are highly variable from one year to the next, there are many features of the dust cycle that occur year after year. Generally, a low-level dust haze is maintained during northern spring and summer, while elevated levels of atmospheric dust occur during northern autumn and winter. During years without global-scale dust storms, two peaks in total dust loading were observed by MGS/TES: one peak occurred before northern winter solstice at Ls 200-240, and one peak occurred after northern winter solstice at L(sub s) 305-340. These maxima in dust loading are thought to be associated with transient eddy activity in the northern hemisphere, which has been observed to maximize pre- and post-solstice. Interactive dust cycle studies with Mars General Circulation Models (MGCMs) have included the lifting, transport, and sedimentation of radiatively active dust. Although the predicted global dust loadings from these simulations capture some aspects of the observed dust cycle, there are marked differences between the simulated and observed dust cycles. Most notably, the maximum dust loading is robustly predicted by models to occur near northern winter solstice and is due to dust lifting associated with down slope flows on the flanks of the Hellas basin. Thus far, models have had difficulty simulating the observed pre- and post- solstice peaks in dust loading. Interactive dust cycle studies typically have not included the formation of water ice clouds or their radiative effects. Water ice clouds can influence the dust cycle by scavenging dust from atmosphere and by interacting with solar and infrared radiation

Interstellar Dust: Contributed Papers

NASA Technical Reports Server (NTRS)

Tielens, Alexander G. G. M. (Editor); Allamandola, Louis J. (Editor)

1989-01-01

A coherent picture of the dust composition and its physical characteristics in the various phases of the interstellar medium was the central theme. Topics addressed included: dust in diffuse interstellar medium; overidentified infrared emission features; dust in dense clouds; dust in galaxies; optical properties of dust grains; interstellar dust models; interstellar dust and the solar system; dust formation and destruction; UV, visible, and IR observations of interstellar extinction; and quantum-statistical calculations of IR emission from highly vibrationally excited polycyclic aromatic hydrocarbon (PAH) molecules.

Testing the sensitivity of past climates to the indirect effects of dust

NASA Astrophysics Data System (ADS)

Sagoo, Navjit; Storelvmo, Trude

2017-06-01

Mineral dust particles are important ice nuclei (IN) and as such indirectly impact Earth's radiative balance via the properties of cold clouds. Using the Community Earth System Model version 1.0.6, and Community Atmosphere Model version 5.1, and a new empirical parameterization for ice nucleation on dust particles, we investigate the radiative forcing induced by dust IN for different dust loadings. Dust emissions are representative of global conditions for the Last Glacial Maximum and the mid-Pliocene Warm Period. Increased dust leads to smaller and more numerous ice crystals in mixed phase clouds, impacting cloud opacity, lifetime, and precipitation. This increases the shortwave cloud radiative forcing, resulting in significant surface temperature cooling and polar amplification—which is underestimated in existing studies relative to paleoclimate archives. Large hydrological changes occur and are linked to an enhanced dynamical response. We conclude that dust indirect effects could potentially have a significant impact on the model-data mismatch that exists for paleoclimates.