Atmospheric Condensation Research Articles

Mars atmospheric CO2 condensation above the north and south poles as revealed by radio occultation, climate sounder, and laser ranging observations

We study the condensation of CO2 in Mars' atmosphere using temperature profiles retrieved from radio occultation measurements from Mars Global Surveyor (MGS) as well as the climate sounding instrument onboard the Mars Reconnaissance Orbiter (MRO), and detection of reflective clouds by the MGS Mars Orbiter Laser Altimeter (MOLA). We find 11 events in 1999 where MGS temperature profiles indicate CO2 condensation and MOLA simultaneously detects reflective clouds. We thus provide causal evidence that MOLA non‐ground returns are associated with CO2 condensation, which strongly indicates their nature being CO2 clouds. The MGS and MRO temperature profiles together reveal the seasonal expansion and shrinking of the area and the vertical extent of atmospheric saturation. The occurrence rate of atmospheric saturation is maximized at high latitudes in the middle of winter. The atmospheric saturation in the northern polar region exhibits more intense seasonal variation than in the southern polar region. In particular, a shrinking of saturation area and thickness from LS ∼ 270° to ∼300° in 2007 is found; this is probably related to a planet‐encircling dust storm. Furthermore, we integrate the condensation area and the condensation occurrence rate to estimate cumulative masses of CO2 condensates deposited onto the northern and southern seasonal polar caps. The precipitation flux is approximated by the particle settling flux which is estimated using the impulse responses of MOLA filter channels. With our approach, the total atmospheric condensation mass can be estimated from these observational data sets with average particle size as the only free parameter. By comparison with the seasonal polar cap masses inferred from the time‐varying gravity of Mars, our estimates indicate that the average condensate particle radius is 8–22 μm in the northern hemisphere and 4–13 μm in the southern hemisphere. Our multi‐instrument data analysis provides new constraints on modeling the global climate of Mars.

Factors and sources influencing ionic composition of atmospheric condensate during winter season in lower troposphere over Delhi, India

Atmospheric condensate (AC) and rainwater samples were collected during 2010-2011 winter season from Delhi and characterized for major cations and anions. The observed order of abundance of cations and anions in AC samples was NH (4) (+) > Ca(2+) > Na(+) > K(+) > Mg(2+) and HCO (3) (-) > SO (4) (2-) > Cl(-) > NO (2) (-) > NO (3) (-) > F(-), respectively. All samples were alkaline in nature and Σ (cation)/Σ (anion) ratio was found to be close to one. NH (4) (+) emissions followed by Ca(2+) and Mg(2+) were largely responsible for neutralization of acidity caused by high NO( x ) and SO(2) emissions from vehicles and thermal power plants in the region. Interestingly, AC samples show low nitrate content compared with its precursor nitrite, which is commonly reversed in case of rainwater. It could be due to (1) slow light-mediated oxidation of HONO; (2) larger emission of NO(2) and temperature inversion conditions entrapping them; and (3) formation and dissociation of ammonium nitrite, which seems to be possible as both carry close correlation in our data set. Principal component analysis indicated three factors (marine mixed with biomass burning, anthropogenic and terrestrial, and carbonates) for all ionic species. Significantly higher sulfate/nitrate ratio indicates greater anthropogenic contributions in AC samples compared with rainwater. Compared with rainwater, AC samples show higher abundance of all ionic species except SO(4), NO(3), and Ca suggesting inclusion of these ions by wash out process during rain events. Ionic composition and related variations in AC and rainwater samples indicate that two represent different processes in time and space coordinates. AC represents the near-surface interaction whereas rainwater chemistry is indicative of regional patterns. AC could be a suitable way to understand atmospheric water interactions with gas and solid particle species in the lower atmosphere.

Short term temporal variability in the photochemically mediated alteration of chromophoric dissolved organic matter (CDOM) in rainwater

Abstract The goal of the research presented here was to determine the impact of photochemistry on the abundance and spectral qualities of chromophoric dissolved organic matter (CDOM) in precipitation. The relationship between sunlight and CDOM in rainwater was complex with both production and photobleaching of optical properties occurring simultaneously in different regions of the fluorescence excitation emission spectra (EEMs) over relatively short time scales. Spectral slope was inversely correlated with the observed changes in total integrated fluorescence suggesting that photo-induced modifications in the molecular weight of CDOM were occurring along with fluctuations in its optical properties. Atmospheric condensate collected near a high traffic roadway had a response to sunlight similar to authentic rainwater suggesting some fraction of the CDOM in atmospheric waters is derived from local anthropogenic gas phase sources. There was a dramatic increase in fluorescence in two samples photolyzed with photosynthetically active radiation only (PAR; 400–700 nm) compared to analogous samples exposed to full spectrum sunlight indicating that this less energetic light is capable of producing photochemically labile compounds in rainwater. The observed temporal variability in the molecular level response of CDOM to sunlight is important because it may alter the spectral attenuation and the amount of solar radiation reaching the earth’s surface.

A Parameterized Method for Air-Quality Diagnosis and Its Applications

A parameterized method is developed to diagnose the air quality in Beijing and other cities with an index termed (parameters linking air-quality to meteorological elements PLAM) derived from a correlation between PM10and relevant weather elements based on the data between 2000 and 2007. Key weather factors for diagnosing the air pollution intensity are identified and included in PLAM that include atmospheric condensation of water vapour, wet potential equivalent temperature, and wind velocity. It is found that the poor air quality days with elevated PM10are usually associated with higher PLAM values, featuring higher temperature, humidity, lower wind velocity, and higher stability compared to the averaged values in the same period. Both 24 h and 72 h forecasts provided useful services for the day of the opening ceremony of the Beijing Olympic Games and subsequent sport events. A correlation coefficient of 0.82 was achieved between the forecasts and (air pollution index API) and 0.59 between the forecasts and observed PM10, all reaching the significant level of 0.001, for the summer period. A correction factor was also introduced to enable the PLAM to diagnose the observed PM10concentrations all year round.

HNO3−NHx, H2SO4−NHx, CH(O)OH−NHx, and CH3C(O)OH−NHx complexes and their role in the formation of condensation nuclei

The formation of sulfuric acid (H(2)SO(4)), nitric acid (HNO(3)), acetic acid (CH(3)C(O)OH), and formic acid (HC(O))H) complexes with ammonia (NH(3)), amidogen radical (NH(2)), and imidogen radical (NH) was studied using natural bond orbital calculations. The equilibrium structures, binding energies, and harmonic frequencies were calculated for each acid-NH(x) complex using hybrid density functional (B3LYP) and second-order Møller-Plesset perturbation approximation methods with the 6-311++G(3df,3pd) basis set. The results presented here suggest that the effect of NH(2) on the formation of new condensation nuclei will be similar to that of NH(3), but to a lesser degree and confined primarily to complexes with H(2)SO(4) and HNO(3). The NH radical is not expected to play a significant role in the formation of new atmospheric condensation nuclei.

On the characterization of nanoparticles emitted from combustion sources related to understanding their effects on health and climate

This work describes the use of well-controlled laboratory flames to produce aerosols of organic carbon (OC) as model particles representative of the OC fraction of combustion-generated particulate matter emissions in fresh exhausts. Water–particle interactions are explored in two specific cases. In the first case, particles are exposed to saturated environments and come into direct contact with liquid water by bubbling flame samples through a column of water. This case is representative of particle–liquid interactions relevant to wet removal routes by particle interception by rain or fog droplets or in biological systems covered with biological fluids composed mostly of water. In the second case, the particles are exposed to sub-saturated vapors with H2O concentrations representative of cloud-forming atmospheres. The particles’ capacity to serve as atmospheric cloud condensation nuclei (CCN) by rapid growth to droplets was measured and compared to NaCl particles, which are highly soluble particles with well known activation diameters. The results show measureable interactions with water in highly saturated conditions. However, in sub-saturated environments, no growth by water condensation was observed, and fresh emissions of OC nanoparticles are not likely to act as CCN in atmospherically relevant humidity.

Testing and evaluation of a method for locating potentially hazardous sites of eventual microdestruction and detecting marks of ISS RS hull leakage

In 2008, two experiments – BAR and EXPERT – were performed on the Russian segment (ISS RS) during ISS missions 16 and 17 using diagnostic equipment BAR. The experiments were aimed to enhance ISS safety by proposing means and methods of detecting leaks due to many factors including microdestruction of pressurized modules of the vehicle. The BAR experiment was designed to assess the ultraviolet background in 56 potentially dangerous locations identified by RS ISS designers and engineers. The method for locating sites carrying the risk of microdestruction of pressurized structure was verified. The study showed that the rate of microdestruction is highly affected by level of ultrasound vibrations caused by onboard equipment. The ultrasound measurements in 200 RS ISS sites were performed within the BAR experiment. The method consists of looking for surfaces with atmospheric condensate in the areas of increased levels of ultrasound vibrations. Twenty six sites were added to the nomenclature of potentially risky sites to be monitored on the regular basis. Some of these sites were contaminated by fungi and bacteria.

A comparison of Martian north and south polar cold spots and the long‐term effects of the 2001 global dust storm

In the 1970s, Viking and Mariner observed areas in the polar regions of Mars with winter brightness temperatures below the expected kinetic temperatures for CO2 ice sublimation. These areas have since been termed “cold spots” and have been identified as surface deposits of CO2 atmospheric condensates and, occasionally, active CO2 storms. Three Mars years of data from the Mars Global Surveyor Thermal Emission Spectrometer were used to observe autumn and winter cold spot activity. In this study, cold spots that occur near and on the southern perennial cap were compared to those found near or on the northern perennial cap. On the southern perennial cap, cold spots associated with topographic features (induced by orographic lifting) were less common than cold spots independent of topography, similar to the north. However, the cold spots in the south lasted longer than those observed in the north. There is also evidence that cold spot formation in the south was affected by the global dust storm of 2001, even though the dust storm occurred during the southern spring and summer seasons. Prior to the dust storm, the amount of overall cold spot activity closer to the perennial cap increased and the average CO2 grain size for most of the cold spots increased as well. Following the dust storm, the majority of cold spots in the south increased in size and duration but they did not form north of 62°S latitude, whereas, in other years, cold spots formed as far north as 48°S.

Characteristics of Oxygen Stable Isotopic Ratio in Precipitations in Niigata Prefecture, Japan

Time-course of oxygen stable isotopic ratios(i.e., δ18O)as well as annual or seasonal variation of δ18O has been examined to investigate the sources, the passing route and characteristics of precipitations in Niigata Prefecture. The precipitation samples have been mainly collected with a filtrating bulk sampler at the rooftop of Niigata University from 1999 to 2008. Furthermore, backward trajectories analyses have been also conducted for these samples taken sequentially for a short period.Consequently, the following features have been mainly clarified for the precipitations in Niigata Prefecture. (1)The δ18O values varied between −25.14‰ and −1.60‰, while the mean value of δ18O in each year was from −8.37‰(in 2006)to −7.33‰(in 2001). (2)As for the comparison among sampling points, the mean value of δ18O at seaside spots(i.e., Niigata City and Joetsu City)or marine spots(i.e., Sado City)is larger than that of inland spots(Shitada Village and Nagaoka City). (3)δ18O value was generally small in the rainy season, and relatively large in summer, and small in winter. (4)Decreasing δ18O content with time, as predicted by Rayleigh models of atmospheric vapor condensation, is a predominant feature of sequentially sampled rainfalls, particularly for precipitations taken during passage of typhoons.

Mars Climate Sounder limb profile retrieval of atmospheric temperature, pressure, and dust and water ice opacity

The Mars Climate Sounder (MCS) onboard the Mars Reconnaissance Orbiter is the latest of a series of investigations devoted to improving the understanding of current Martian climate. MCS is a nine‐channel passive midinfrared and far‐infrared filter radiometer designed to measure thermal emission in limb and on‐planet geometries from which vertical profiles of atmospheric temperature, water vapor, dust, and condensates can be retrieved. Here we describe the algorithm that is used to retrieve atmospheric profiles from MCS limb measurements for delivery to the Planetary Data System. The algorithm is based on a modified Chahine method and uses a fast radiative transfer scheme based on the Curtis‐Godson approximation. It retrieves pressure and vertical profiles of atmospheric temperature, dust opacity, and water ice opacity. Water vapor retrievals involve a different approach and will be reported separately. Pressure can be retrieved to a precision of 1–2% and is used to establish the vertical coordinate. Temperature profiles are retrieved over a range from 5–10 to 80–90 km altitude with a typical altitude resolution of 4–6 km and a precision between 0.5 and 2 K over most of this altitude range. Dust and water ice opacity profiles also achieve vertical resolutions of about 5 km and typically have precisions of 10−4–10−5 km−1 at 463 cm−1 and 843 cm−1, respectively. Examples of temperature profiles as well as dust and water ice opacity profiles from the first year of the MCS mission are presented, and atmospheric features observed during periods employing different MCS operational modes are described. An intercomparison with historical temperature measurements from the Mars Global Surveyor mission shows good agreement.

AN AGE CONSTRAINT FOR THE VERY LOW MASS STELLAR/BROWN DWARF BINARY 2MASS J03202839–0446358AB

2MASS J03202839-0446358AB is a recently identified, late-type M dwarf/T dwarf spectroscopic binary system for which both the radial velocity orbit for the primary and spectral types for both components have been determined. By combining these measurements with predictions from four different sets of evolutionary models, we determine a minimum age of 2.0 {+-} 0.3 Gyr for this system, corresponding to minimum primary and secondary masses of 0.080 M {sub sun} and 0.053 M {sub sun}, respectively. We find broad agreement in the inferred age and mass constraints between the evolutionary models, including those that incorporate atmospheric condensate grain opacity; however, we are not able to independently assess their accuracy. The inferred minimum age agrees with the kinematics and absence of magnetic activity in this system, but not the rapid rotation of its primary, further evidence of a breakdown in angular momentum evolution trends amongst the lowest luminosity stars. Assuming a maximum age of 10 Gyr, we constrain the orbital inclination of this system to i {approx}> 53{sup 0}. More precise constraints on the orbital inclination and/or component masses of 2MASS 0320-0446AB, through either measurement of the secondary radial velocity orbit (optimally in the 1.2-1.3 {mu}m band) or detection of anmore » eclipse (only 0.3% probability based on geometric constraints), would yield a bounded age estimate for this system, and the opportunity to use it as an empirical test for brown dwarf evolutionary models at late ages.« less

Source apportionment of PM2.5: Comparing PMF and CMB results for four ambient monitoring sites in the southeastern United States

Two commonly used receptor models, positive matrix factorization (PMF) and chemical mass balance (CMB), are applied to 3-year PM2.5 data at two urban sites (Atlanta, GA and Birmingham, AL) and two rural sites (Yorkville, GA and Centreville, AL). Source apportionment results using the two receptor models are analyzed and compared. Both models are able to identify major sources at all sites, though the degree of agreements and correlations between source impacts estimated by PMF and CMB varies depending on sources and receptor sites. Estimated contributions of secondary inorganic particles are the most comparable and highly correlated. The lesser comparability and correlations of estimated contributions of other sources (mostly primary) may be attributed to several factors. Resolved source profiles in PMF have more processed (or aged) characteristics resulting in part from atmospheric mixing and condensation of oxidized compounds, whereas source profiles used in CMB are obtained from measurements of emission sources with minimum amount of atmospheric processing. The PMF profiles vary from site to site; both atmospheric processing and local source variability contribute. In comparison, the CMB profiles obtained from a limited number of emission measurements may not be locally representative even if they are regionally representative. The omission of possible known or unknown sources due to lack of proper source profiles or proper “marker” species may also cause the differences in the source apportionment results. In addition, the implication for PM time-series health study is discussed based on the results from this study.

Analysis of a potential “solar radiation dose–dimethylsulfide–cloud condensation nuclei” link from globally mapped seasonal correlations

The CLAW postulate states that an increase in solar irradiance or in the heat flux to the ocean can trigger a biogeochemical response to counteract the associated increase in temperature and available sunlight. This natural (negative) feedback mechanism would be based on a multistep response: first, an increase in seawater dimethylsulfide concentrations (DMSw) and therefore its fluxes to the atmosphere (DMSflux); second, an increase in the atmospheric cloud condensation nuclei (CCN) burden as a consequence of DMS oxidation to form biogenic CCN (CCNbio); and third, an increase in cloud albedo due to higher CCN numbers. Monthly global climatological fields of the solar radiation dose in the upper mixed layer (SRD), surface oceanic DMSw, model outputs of hydroxyl radical concentrations (OH), and satellite‐derived CCN numbers (CCNs) are analyzed in order to evaluate the proposed “solar radiation dose‐DMS‐CCN” link from a global point of view. OH is included as the main atmospheric oxidant of the estimated DMSflux to produce CCNbio. Global maps of seasonal correlations between the variables show that the solar radiation dose is highly (positively) correlated with seawater dimethylsulfide over most of the global ocean and that atmospheric DMS oxidation is highly (positively) correlated with CCNs over large regions. These couplings are stronger at high latitudes, whereas the regions with negative or no correlation are located at low latitudes around the equator. However, CCNbio estimates for 15 regions of the global ocean show that DMS oxidation can be an important contributor to the CCNs burden only over pollution‐free regions, while it would have a minor contribution over regions with high loads of continental aerosols. Globally, the mean annual contribution of CCNbio to total CCNs is estimated to be ≈30%. Our results support that an oceanic biogenic mechanism that modulates cloud formation and albedo can indeed occur, although its impact seems rather weak over regions under a strong influence of continental aerosols. Nevertheless, our approach does not fully rule out that the observed correlations are due to an independent seasonal variation of the studied variables; seasonal couplings are necessary but not sufficient conditions to prove the CLAW hypothesis.

Efficiency of cloud condensation nuclei formation from ultrafine particles

Abstract. Atmospheric cloud condensation nuclei (CCN) concentrations are a key uncertainty in the assessment of the effect of anthropogenic aerosol on clouds and climate. The ability of new ultrafine particles to grow to become CCN varies throughout the atmosphere and must be understood in order to understand CCN formation. We have developed the Probability of Ultrafine particle Growth (PUG) model to answer questions regarding which growth and sink mechanisms control this growth, how the growth varies between different parts of the atmosphere and how uncertainties with respect to the magnitude and size distribution of ultrafine emissions translates into uncertainty in CCN generation. The inputs to the PUG model are the concentrations of condensable gases, the size distribution of ambient aerosol, particle deposition timescales and physical properties of the particles and condensable gases. It was found in most cases that condensation is the dominant growth mechanism and coagulation with larger particles is the dominant sink mechanism for ultrafine particles. In this work we found that the probability of a new ultrafine particle generating a CCN varies from <0.1% to ~90% in different parts of the atmosphere, though in the boundary layer a large fraction of ultrafine particles have a probability between 1% and 40%. Some regions, such as the tropical free troposphere, are areas with high probabilities; however, variability within regions makes it difficult to predict which regions of the atmosphere are most efficient for generating CCN from ultrafine particles. For a given mass of primary ultrafine aerosol, an uncertainty of a factor of two in the modal diameter can lead to an uncertainty in the number of CCN generated as high as a factor for eight. It was found that no single moment of the primary aerosol size distribution, such as total mass or number, is a robust predictor of the number of CCN ultimately generated. Therefore, a complete description of the emissions size distribution is generally required for global aerosol microphysics models.

Solar trough concentration for fresh water production and waste water treatment

The present paper examines the concept of utilizing trough type solar concentration plants for water production, remediation and waste treatment. Solar trough plants are a mature technology which deserves to be diffused throughout the European Union and in the partner countries of the Mediterranean Area. The present study is intended to find applications of the solar through concentration technology beyond heat and refrigeration. At the present stage, a number of possibilities have been identified; the main ones which will be considered here are related to clean water production by processes such as solar distillation, atmospheric condensation, and waste processing. Although the technical feasibility of the proposed applications is not in discussion, before attempting to put such applications into practice, we’ll discuss their potential economical and environmental benefits in comparison to existing solutions.

The CLAW hypothesis: a review of the major developments

Environmental context. Understanding the role of clouds in the warming and the cooling of the planet and how that role alters in a warming world is one of the biggest uncertainties climate change researchers face. Important in this regard is the influence on cloud properties of cloud condensation nuclei, the tiny atmospheric particles necessary for the nucleation of every single cloud droplet. The anthropogenic contribution to cloud condensation nuclei is known to be large in some regions through knowledge of pollutant emissions; however, the natural processes that regulate cloud condensation nuclei over large parts of the globe are less well understood. The CLAW hypothesis provides a mechanism by which plankton may modify climate through the atmospheric sulfur cycle via the provision of sulfate cloud condensation nuclei. The CLAW hypothesis was published over 20 years ago and has stimulated a great deal of research. Abstract. The CLAW hypothesis has for 20 years provided the intriguing prospect of oceanic and atmospheric systems exhibiting in an intimately coupled way a capacity to react to changing climate in a manner that opposes the change. A great number of quality scientific papers has resulted, many confirming details of specific links between oceanic phytoplankton and dimethylsulfide (DMS) emission to the atmosphere, the importance of DMS oxidation products in regulation of marine atmospheric cloud condensation nucleus (CCN) populations, and a concomitant influence on marine stratocumulus cloud properties. However, despite various links in the proposed phytoplankton–DMS–CCN–cloud albedo climate feedback loop being affirmed, there has been no overall scientific synthesis capable of adequately testing the hypothesis at a global scale. Moreover, significant gaps and contradictions remain, such as a lack of quantitative understanding of new particle formation processes in the marine atmospheric boundary layer, and of the extent to which dynamical, rather than microphysical, cloud feedbacks exist. Nevertheless, considerable progress has been made in understanding ‘Earth System Science’ involving the integration of ocean and atmospheric systems inherent in the CLAW hypothesis. We present here a short review of this progress since the publication of the CLAW hypothesis.

Siderophile element patterns, PGE nuggets and vapour condensation effects in Ni-rich quench chromite-bearing microkrystite spherules, ∼ 3.24 Ga S3 impact unit, Barberton greenstone belt, Kaapvaal Craton, South Africa

Energy dispersive spectrometry (EDS), laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) track analyses of chlorite-dominated quench-textured microkrystite spherules and LA-ICPMS spot analyses of intra-spherule Ni-rich skeletal quench chromites from the 3243 ± 4 Ma Barberton S3 impact fallout unit (lower part of the Mapepe Formation, Fig Tree Group, Barberton greenstone belt, Kaapvaal Craton, South Africa) reveal fractionated siderophile and PGE trace element patterns corresponding to chondrite-contaminated komatiite/basalt compositions. The chlorites, interpreted as altered glass, contain sharp siderophile elements and PGE spikes inherited from decomposed metal and Ni-rich chromite particles. LA-ICPMS spot analysis identifies PGE-rich micronuggets in Ni–chromites (Ir ∼ 12–100 ppm, Os ∼ 9–86 ppm, Ru ∼ 5–43 ppm) and lower levels of the volatile PGEs (Rh ∼ 1–11 ppm, Pd ∼ 0.68–0.96 ppm). Previously reported PGE anomalies in the order of hundreds of ppb in some Barberton microkrystite spherules are accounted for in terms of disintegration of PGE-rich micronuggets. Replacement of the Ni-chromites by sulphide masks primary chondritic patterns and condensation element distribution effects. High refractory/volatile PGE ratios pertain to both the chlorites and the Ni-rich chromites, consistent with similar compositional relations in microkrystite spherules from other impact fallout units in the Barberton greenstone belt and the Pilbara Craton, Western Australia. The near-consistent low Pt/Re and high V/Cr and V/Sc ratios in chlorite of the spherules, relative to komatiites, are suggestive of selective atmospheric condensation of the spherules which favored the relatively more refractory Re and V. Selective condensation may also be supported by depletion in the volatile Yb relative to Sm. Ni–Cr relationships allow estimates of the proportion of precursor crustal and meteoritic components of the spherules. Mass balance calculations based on the iridium flux allow estimates of the order of magnitude of the diameter of the chondritic projectile.

Microbial functions in space: Mars transit to early planetary base exploration missions

Microbial processing of liquid and solid wastes may play a role in the advanced life support systems of nearer term human exploration missions such as transit vehicles to Mars or initial surface bases on either the Moon or Mars. Recycling wastewater (urine, atmospheric condensate, hygiene water) is a critical component of reducing storage and resupply requirements on such missions, and microbial treatment of all or part of the waste stream may improve overall treatment efficiency. As small-scale plant systems (i.e., 5– 10 m 2 person - 1 ) are used to supplement food storage, microbial processing of both wastewater and edible plant material will facilitate nutrient and water recycling through the biomass production systems.

Search for causes of the low epithermal neutron flux anomaly in the Arabia Terra region (Mars)

A geologic analysis of 274 images acquired by the high-resolution MOC camera onboard the Mars Global Surveyor spacecraft within the Arabia Terra low neutron flux anomaly (which is indicative of an anom- alously high abundance of hydrogen: up to 16 wt % of the equivalent amount of water) was performed. Corre- lation between the enhanced abundance of equivalent water with the presence of dust on the surface was found. Since dust plays a key role in condensation of water from the atmosphere, we suppose that the anomalies could result from the retention of atmospheric moisture. To analyze this suggestion, we performed a theoretical mod- eling that allowed us to map the planetary-scale distributions of several meteorological parameters responsible for the atmospheric moisture condensation. Two antipodal regions coinciding rather well with the Arabia Terra anomaly and the geographically antipodal anomaly southwest of Olympus Mons were found in the maps. This suggests that the anomalies are rather recent than ancient formations. They were probably formed by a sink of moisture from the atmosphere in the areas where present meteorological conditions support this sink. Geolog- ical parameters, primarily the presence of dust, only promote this process. We cannot exclude the possibility that the Martian cryosphere, rather than the atmosphere, supplied the studied anomalies with moisture during their formation: the thermodynamic conditions in the anomaly areas could block the moisture flux from the Martian interior in the upper regolith layer. The moisture coming from the atmosphere or from the interior is likely held as chemically bound water entering into the structure of water-bearing minerals (probably, hydrated magnesium sulfates) directly from the vapor; or the moisture precipitates as frost, penetrates into microfissures, and then is bound in minerals. Probably, another geologic factor—the magnesium sulfate abundance—works in the Arabia Terra anomaly.

Formation of cloud microstructure during hygroscopic seeding

The evolution of cloud microstructure initiated by hygroscopic seeding is studied on the basis of numerical simulation of cloud formation in the initial stage of condensation. The influence of both physicochemical properties of atmospheric aerosol and atmospheric conditions controlling the cloud type on the microstructure of a developing cloud (without hygroscopic seeding) is analyzed. It is shown that cloud seeding with additional particles whose sizes exceed the characteristic size of atmospheric condensation nuclei leads to a decrease in the concentration of cloud droplets and an increase in their sizes. This result of cloud seeding represents a positive effect for stimulation of precipitation from convective clouds. It is shown that this positive effect is achieved if there are some relationships between the parameters characterizing the hygroscopic particles and the atmospheric conditions. In particular, the maximum effect of action can be achieved at some optimal concentration of seeded particles. The decrease in the concentration of cloud droplets because of hygroscopic seeding is compared to the results of numerical simulations performed by other authors with allowance for coagulation processes in clouds. It is shown that this decrease can serve as an estimate for the effectiveness of hygroscopic seeding as a means for artificial intensification of precipitation from convective clouds.