bluuebunny/crossref_metadata_2025 huggingface dataset:
Tropical climate change recorded by a glacier in the central Andes during the last decades of the twentieth century: Chacaltaya, Bolivia, 16°S
Authors: Francou Bernard , Vuille Mathias , Wagnon Patrick , Mendoza Javier , Sicart Jean‐Emmanuel
Published: May 2003

The reasons for the accelerated glacier retreat observed since the early 1980s in the tropical Andes are analyzed based on the well‐documented Chacaltaya glacier (Bolivia). Monthly mass balance measurements available over the entire 1991–2001 decade are interpreted in the light of a recent energy balance study performed on nearby Zongo glacier and further put into a larger‐scale context by analyzing the relationship with ocean‐atmosphere dynamics over the tropical Pacific‐South American domain. The strong interannual variability observed in the mass balance is mainly dependent on variations in ablation rates during the austral summer months, in particular during DJF. Since high humidity levels during the summer allow melting to be distinctly predominant over sublimation, net all‐wave radiation, via albedo and incoming long‐wave radiation, is the main factor that governs ablation. Albedo depends on snowfall and a deficit during the transition period and in the core of the wet season (DJF) maintains low albedo surfaces of bare ice, which in turn leads to enhanced absorption of solar radiation and thus to increased melt rates. On a larger spatial scale, interannual glacier evolution is predominantly controlled by sea surface temperature anomalies (SSTA) in the eastern equatorial Pacific (Niño 1+2 region). The glacier mass balance is influenced by tropical Pacific SSTA primarily through changes in precipitation, which is significantly reduced during El Niño events. The more frequent occurrence of El Niño events and changes in the characteristics of its evolution, combined with an increase of near‐surface temperature in the Andes, are identified as the main factors responsible for the accelerated retreat of Chacaltaya glacier.
A new interactive chemistry‐climate model: 1. Present‐day climatology and interannual variability of the middle atmosphere using the model and 9 years of HALOE/UARS data
Authors: Steil B. , Brühl C. , Manzini E. , Crutzen P. J. , Lelieveld J. , Rasch P. J. , Roeckner E. , Krüger K.
Published: May 2003

The newly developed middle atmosphere general circulation model with interactive photochemistry, Middle Atmosphere European Centre/Hamburg Model 4 with Chemistry (MA‐ECHAM4‐CHEM), has been applied for several 20 year “time slice” experiments using fixed boundary conditions typical of the early and late 1990s, the 1960s, and the near future, including sensitivity runs to study effects of sea surface temperature and greenhouse gas concentration changes. In part 1 we compare the results for the early and late 1990s with 9 years of data of the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite, some presented for the first time, and other satellite and radiosonde data. We show a statistical analysis as well as snapshots of a set of chemical species for typical situations. The model captures the main features of temperature and ozone distributions including the interannual variability of the Arctic and Antarctic vortices and homogeneous and heterogeneous ozone destruction. A detailed comparison of modeled and observed chlorine and nitrogen species including denitrification and chlorine repartitioning in the polar vortices is presented, showing generally good agreement. This holds also for chemical ozone budgets derived from the model and from satellite data. Computed stratospheric and mesospheric water vapor agrees with the satellite data within about 10%, including dehydration in the Antarctic winter. However, in the tropical lower stratosphere, the concentrations of the source gases are underestimated, presumably because of numerical deficiencies in transport. It is shown that interactive photochemistry is important to get agreement with observed temperatures in the lower stratosphere in high‐latitude spring. Our coupled model provides a powerful tool to investigate chemical‐radiative‐dynamical feedback mechanisms of anthropogenic trace gas emissions and natural variability on climate and stratospheric ozone, at least for quasi‐steady‐state conditions.
Characterization of organic aerosols emitted from the combustion of biomass indigenous to South Asia
Authors: Sheesley Rebecca J. , Schauer James J. , Chowdhury Zohir , Cass Glen R. , Simoneit Bernd R. T.
Published: May 2003

Throughout South Asia biomass is commonly used as a fuel source for cooking and heating homes. The smoke from domestic use of these fuels is expected to be a major source of atmospheric particulate matter in the region and needs to be characterized for input in regional source apportionment models and global climate models. Biomass fuel samples including coconut leaves, rice straw, jackfruit branches, dried cowdung patties, and biomass briquettes manufactured from compressed biomass material were obtained from Bangladesh. The fuel samples were burned in a wood stove to collect and characterize the particulate matter emissions. The bulk chemical composition including total organic and elemental carbon, sulfate, nitrate, ammonium and chloride ions, and bulk elements such as potassium and sodium did not show conclusive differences among the biomass samples tested. Unique features, however, exist in the detailed organic characterization of the combustion smoke from the different sources. The organic compound fingerprints of the particulate matter are shown to be distinct from one another and distinct from North American wood fuels. Fecal stanols including 5β‐stigmastanol, coprostanol, and cholestanol are found to be good molecular markers for the combustion of cowdung. Additionally, the patterns of methoxyphenols and plant sterols provide a unique signature for each biomass sample and are conducive as source apportionment tracers.
Long‐term trends of inorganic chlorine from ground‐based infrared solar spectra: Past increases and evidence for stabilization
Authors: Rinsland C. P. , Mahieu E. , Zander R. , Jones N. B. , Chipperfield M. P. , Goldman A. , Anderson J. , Russell J. M. , Demoulin P. , Notholt J. , Toon G. C. , Blavier J.‐F. , Sen B. , Sussmann R. , Wood S. W. , Meier A. , Griffith D. W. T. , Chiou L. S. , Murcray F. J. , Stephen T. M. , Hase F. , Mikuteit S. , Schulz A. , Blumenstock T.
Published: May 2003

Long‐term time series of hydrogen chloride (HCl) and chlorine nitrate (ClONO2) total column abundances has been retrieved from high spectral resolution ground‐based solar absorption spectra recorded with infrared Fourier transform spectrometers at nine NDSC (Network for the Detection of Stratospheric Change) sites in both Northern and Southern Hemispheres. The data sets span up to 24 years and most extend until the end of 2001. The time series of Cly (defined here as the sum of the HCl and ClONO2 columns) from the three locations with the longest time‐span records show rapid increases until the early 1990s superimposed on marked day‐to‐day, seasonal and inter‐annual variability. Subsequently, the buildup in Cly slows and reaches a broad plateau after 1996, also characterized by variability. A similar time evolution is also found in the total chlorine concentration at 55 km altitude derived from Halogen Occultation Experiment (HALOE) global observations since 1991. The stabilization of inorganic chlorine observed in both the total columns and at 55 km altitude indicates that the near‐global 1993 organic chlorine (CCly) peak at the Earth's surface has now propagated over a broad altitude range in the upper atmosphere, though the time lag is difficult to quantify precisely from the current data sets, due to variability. We compare the three longest measured time series with two‐dimensional model calculations extending from 1977 to 2010, based on a halocarbon scenario that assumes past measured trends and a realistic extrapolation into the future. The model predicts broad Cly maxima consistent with the long‐term observations, followed by a slow Cly decline reaching 12–14% relative to the peak by 2010. The data reported here confirm the effectiveness of the Montreal Protocol and its Amendments and Adjustments in progressively phasing out the major man‐related perturbations of the stratospheric ozone layer, in particular, the anthropogenic chlorine‐bearing source gases.
A case study of the anomalous Arctic sea ice conditions during 1990: Insights from coupled and uncoupled regional climate model simulations
Authors: Rinke A. , Gerdes R. , Dethloff K. , Kandlbinder T. , Karcher M. , Kauker F. , Frickenhaus S. , Köberle C. , Hiller W.
Published: May 2003

The regional coupled atmosphere‐ice‐ocean model HIRHAM‐MOM has been developed to simulate the Arctic climate. The model has been applied for the year 1990, which was characterized by anomalous ice retreat along the eastern Arctic coasts. Many observed features of the anomalous atmospheric circulation and sea ice concentration pattern during spring to early summer are reproduced by the model. It was even able to generate the extreme summer sea ice conditions in the Eurasian Arctic and the associated high surface air temperatures. The model shows less success in simulating the large ice retreat in the Siberian Arctic in late summer. This is explained mainly by deviations in the simulated atmospheric circulations. Results from an ocean‐ice‐alone model confirm that the atmospheric forcing dominates the simulated ice retreat. On the other hand, a sensitivity study with the atmosphere‐alone model shows the impact of the sea ice conditions on the atmospheric circulation. Only with the accurate satellite‐derived sea ice data is the model able to reproduce the anomalous late summer atmospheric pressure patterns.
Volcanic rifting at Martian grabens
Authors: Mège Daniel , Cook Anthony C. , Garel Erwan , Lagabrielle Yves , Cormier Marie‐Hélène
Published: May 2003

A large fraction of surface extension on Mars occurred at segmented grabens having width/length ratios akin to oceanic rifts on Earth. Association with volcanic landforms such as pit craters clearly suggests interconnection between tectonic and magmatic processes. A Martian rift evolution model is proposed on the basis of new geomorphological and structural interpretations of imagery, high‐resolution digital elevation models (DEMs), scaled experimental modeling and three‐dimensional boundary element modeling of magmatic and tectonic processes, and a comparison with terrestrial rifts. The DEMs were obtained from Mars Observer Laser Altimeter, Viking Orbiter stereo images, or a combination of both. Comparison of terrestrial rifts included Afar, Iceland, and the East Pacific Rise. The ambient extensional stress field induced by regional body forces is combined at depth with decompression melting and mantle plume thermal anomaly, resulting in emplacement of elongated magma reservoirs along the grabens. Injection of dikes above the reservoirs and flood basalt eruption result in a reservoir underpressurization of up to hundreds of MPa and induces surface collapse. Each collapse event is associated with an eruption of volcanic volumes akin to those of individual flow eruptions in large terrestrial igneous provinces. The geometry and mechanisms of graben formation and surface collapse are described and used to infer reservoir depth and width. We conclude from this study that giant dike swarms akin to typical giant terrestrial dike swarms are unlikely to underlie the volcanic Martian grabens on the basis one graben‐one dike. Rather, every volcanic graben segment appears to own a local dike swarm perhaps analogous to the dike swarms in the Icelandic fissure zones.
Ground‐penetrating radar as a tool for probing the shallow subsurface of Mars
Authors: Grant John A. , Schutz Alan E. , Campbell Bruce A.
Published: May 2003

Design and testing of an impulse ground‐penetrating radar (GPR) for possible rover deployment on Mars in 2009 is well underway. The GPR has mass, power, volume, and data‐rate targets of 0.5 kg, 3 W (peak), 3400 cm3, and 0.3 Mb/d and will possess easily modified bistatic high‐frequency (e.g., 500–600 MHz) and monostatic “rat‐tail” (e.g., 100 MHz) antennas. The GPR should be capable of measuring in situ radar properties on Mars to depths of up to 10–20 m, thereby helping to constrain near‐surface geology and structure. Initial GPR tests at the site of the 2001 FIDO rover field trials near Cronese Lake, California, confirm the value of the instrument in defining local geologic setting and in providing context for data collected using other rover science payload elements. A rover‐deployed GPR may enable three‐dimensional mapping of local stratigraphy, which in turn can assist in evaluating the history of aqueous activity and the accessibility of near‐surface water.
Rock glaciers and protalus landforms: Analogous forms and ice sources on Earth and Mars
Authors: Whalley W. Brian , Azizi Fethi
Published: May 2003

The basic features and terminology of terrestrial “rock glaciers” are reviewed together with associated forms termed “protalus lobes” and “protalus ramparts.” Two basic models of rock glacier formation and flow invoke either the creep of ice derived from permafrost or glacial/former glacial activity; a third possible mechanism invokes landslide emplacement. Observations on terrestrial rock glaciers and similar forms suggest that the ice component can be produced via ground ice or from a glacier system. Finite element modeling of simple slope systems containing (1) a continuous ice layer buried by debris and (2) a mixture of ice and rigid blocks can both show creep but with very low rates, especially at low temperatures. Possible Martian examples of rock glacier and protalus lobe features are identified from Candor Chasma by wide‐angle Mars Orbiter Camera (MOC) imagery, although the topography does not allow unambiguous interpretation. Some possible ways in which MOC and Mars Orbiter Laser Altimeter (MOLA) and other Mars orbiter data could help future interpretation of rock glaciers, related protalus landforms, and ice presence are discussed.
Martian underground water detection: Thermal model and simulations of radar signal propagation
Authors: Shchuko Oleg B. , Kartashov Daniil V. , Picardi Giovanni , Orosei Roberto
Published: May 2003

The thermophysical conditions of ice/water existence in the upper Martian crust have been considered in the frame of a multilayer structurally inhomogeneous geological model. The water even at the equatorial site has been shown to exist only at depths below 1 km for any values of the upper layer emissivity and internal flux intensity. The radar signal propagation in the layered inhomogeneous medium has been studied. The possibility of the ice or water existence at deep layers has been considered by analyzing the reflected radar signal in the frequency band 1.9‐5.8 MHz.
Geomorphic analysis of lobate debris aprons on Mars at Mars Orbiter Camera scale: Evidence for ice sublimation initiated by fractures
Authors: Mangold N.
Published: May 2003

Lobate debris aprons, known to be geomorphic landform indicators of the presence of ground ice, are of special interest for future missions devoted to the research of water on Mars. Lobate debris aprons in fretted terrains of Deuteronilus and Protonilus Mensae (35°–50°N) show typical convex shapes interpreted to be the result of viscous deformation. At the scale of Mars Orbiter Camera (MOC) high‐resolution images the surface of these debris aprons shows complex patterns with small pits and buttes. These patterns can be explained by the mantling of dust, the accumulation of interstitial ice, and the subsequent removal of ice by sublimation. The sublimation of the ground ice is especially initiated and accelerated by subsurface heterogeneities like fractures. Theoretical quantification of sublimation rates therefore minimizes sublimation, which is not a homogeneous process, at least over the landforms studied. Crater counts show that the sublimation occurred in the last tens of millions of years up to the recent past. In the point of view of future searching of subsurface ice, only surface layers are submitted to sublimation favoring the conservation of ground ice in deeper layers since the formation of the landform. The geophysical survey of lobate debris aprons would give interesting insights into the subsurface distribution of ice and its seasonal variations, especially in order to measure current sublimation of ground ice.
Evaluation of melting process of the permafrost on Mars: Its implication for surface features
Authors: Ogawa Yoshiko , Yamagishi Yasuko , Kurita Kei
Published: May 2003

For supplying massive liquid water to the outflow channels, igneous melting of the permafrost layer could have played a significant role. We numerically simulate the melting process of the permafrost layer induced by magmatic intrusion. The point of our simulation is incorporation of thermal convection in porous media, which has not been modeled well in previous studies of the melting of the permafrost. Our results show that convection in the melted zone causes drastic change in heat transfer, which results in focusing in the growth of the melt region and enhancement of water generation. The resulting melt zone extends vertically up just next to the surface, like a plume with a single column (mushroom structure). The volume of meltwater is considerably more than that expected in the conduction case. These characteristics suggest that a substantial amount of water may exist very near the surface. In response to compaction, segregated liquid water may have erupted out of the ground to form the fluvial features. Such an event would certainly be accompanied by surface destruction, which we can see as chaotic terrain. We propose a consistent scenario of forming surface features around the outflow channels.
Subsurface investigation of a rock glacier using ground‐penetrating radar: Implications for locating stored water on Mars
Authors: Degenhardt John J. , Giardino John R.
Published: May 2003

The discovery of rock glacier‐like features on Mars suggests the presence of flowing, or once‐flowing, ice‐rock mixtures. These landforms, which include lobate debris aprons, concentric crater fill, and lineated valley fill, hold significant promise as reservoirs of stored water ice that could be used as fuel sources for human exploration of Mars and provide a frozen record of the climatic history of the planet. To understand the deformation and distribution of ice within these landforms, fundamental descriptions of their internal structure and development are required. To this end, a ground‐penetrating radar investigation was initiated using rock glaciers in the San Juan Mountains of Colorado as surrogates for similar Martian landforms. Results obtained from one of these rock glaciers show that the interior of the landform is composed of a layered permafrost matrix of ice, sediment, and ice lenses that comprise thicker depositional units formed through high‐magnitude debris falls. Folds in the uppermost layers correspond to the surface expression of ridges and furrows, suggesting that compressive stresses originating in the accumulation zone are transmitted downslope through the rock glacier. Rock glacier features on Mars may also consist of layered permafrost, which would suggest a history of development involving seasonal frost accumulation and/or water influx from below. In terms of water storage within Martian analogs, consideration must include the possibility that some water ice may be stored in relatively pure form within lenses and vein networks such as observed in the surrogate rock glacier of this study.
Timing of formation of Beta Regio and its geodynamical implications
Authors: Vezolainen A. V. , Solomatov V. S. , Head J. W. , Basilevsky A. T. , Moresi L.‐N.
Published: May 2003

Recent evidence suggests that the Beta Regio equatorial highland, generally considered to be a plume‐related structure, was emplaced over a relatively short period of time in the recent Venus history (100–400 m.y.). We perform numerical simulations which use this evidence as a new constraint on geodynamic models and find that it is difficult to satisfy simultaneously the constraint on the uplift rate and the constraints on gravity, topography, and rheology. One possible solution is that the effective viscosity contrast between the mantle and the lithosphere does not exceed about 104. If our simple models do capture the basic dynamics of formation of Beta Regio, this value implies that the viscosity of the lithosphere is softer than olivine at subsolidus temperatures and that the Venusian lithosphere may not be much stronger than the terrestrial one.
Mechanisms for the formation of benzene in the atmosphere of Titan
Authors: Wilson E. H. , Atreya S. K. , Coustenis A.
Published: May 2003

Polycyclic aromatic hydrocarbons (PAHs) are important interstellar species, and their precursor benzene (C6H6) has been detected in our solar system. In this study the possibility of benzene formation in the atmosphere of Titan is investigated. Benzene abundance in Titan's atmosphere is found to be rather highly dependent on the assumed mechanism for benzene production. Assuming reactions involved in this mechanism to proceed at the rate corresponding to 300 K, a value of 5.4 × 10−7 at 2 × 10−5 mbar is found for the mole fraction of benzene. The primary mechanism responsible for this benzene abundance involves the recombination of propargyl (C3H3) radicals. A source of benzene molecules through ion chemistry in the upper atmosphere is also investigated. The inclusion of heavy cyclic ions results in little change in the C6H6 abundance at the peak in mole fraction, where [C6H6] = 3.6 × 105 cm−3, but does produce about a factor of 2 increase in the benzene mole fraction at the 10−6 mbar level [C6H6] = 1 × 104 cm−3. This produces a negligible change in C6H6 column abundance below this microbar level. In the stratosphere, Infrared Space Observatory (ISO) measurements of the benzene abundance have been fit by our nominal profile multiplied by a factor of 3.0 ± 0.5. Taking the lower value of this factor, the ISO fit corresponds to an altitude‐dependent benzene profile with a value of 9.8 × 10−11 at 1 mbar. Benzene profiles determined in this study suggest an important path for the formation of higher‐order hydrocarbons, which may play a significant role in the formation of hazes in Titan's atmosphere.
Geologic settings of Martian gullies: Implications for their origins
Authors: Treiman Allan H.
Published: May 2003

Martian gullies are found on steep slopes of all origins, on all sorts of terrains of all ages, scattered across nearly all of Mars. Gullies are observed on all manner of substrates (layered, massive, shattered, rubble), with or without nearby mantling deposits. Gullies are most common in the southern midlatitudes but also occur in the northern hemisphere, in near polar terrain, on equatorial volcanoes, and on northern plains. Most gullies in the southern hemisphere are on south‐facing slopes, but they occur on slopes of all orientations. Gullies are among the youngest features on Mars but locally are overlain by eolian deposits and cut by faults. Old or eroded gullies are rare, and those found have been partially stripped from slopes, leaving no rock debris behind. Most gully deposits contain no detectable rocks. These data are inconsistent with published hypotheses of gully formation, including seeps and breakouts of water or brine, hydrothermal activity, cryovolcanism, and breakouts from liquid carbon dioxide. The data are consistent with gullies being dry flows of eolian material (dust and silt), comparable to climax snow avalanches on Earth. Eolian sedimentation should be correlated little with underlying geology: cause of slope, age of terrain, type of terrain, or the nature of the rocks. Eolian sedimentation should be correlated with wind deceleration (which will cause suspended sediment to drop), and areas with common gullies are those with strong wind deceleration (predicted by global circulation model). In such areas, sediment will be deposited preferentially in the lee of obstacles; for the gully‐rich areas of the southern midlatitudes, winds blow from the NNW, so that sediment is deposited on SSE‐facing slopes (i.e., poleward). These predictions are in accord with observations.
Methane and carbon dioxide hydrates on Mars: Potential origins, distribution, detection, and implications for future in situ resource utilization
Authors: Pellenbarg Robert E. , Max Michael D. , Clifford Stephen M.
Published: May 2003

There is high probability for the long‐term crustal accumulation of methane and carbon dioxide on Mars. These gases can arise from a variety of processes, including deep biosphere activity and abiotic mechanisms, or, like water, they could exist as remnants of planetary formation and by‐products of internal differentiation. CH4 and CO2 would tend to rise buoyantly toward the planet's surface, condensing with water under appropriate conditions of temperature and pressure to form gas hydrate. Gas hydrates are a class of materials created when gas molecules are trapped within a crystalline lattice of water‐ice. The hydrate stability fields of both CH4 and CO2 encompass a portion of the Martian crust that extends from within the water‐ice cryosphere, from a depth as shallow as ∼10–20 m to as great as a kilometer or more below the base of the Martian cryosphere. The presence and distribution of methane and carbon dioxide hydrates may be of critical importance in understanding the geomorphic evolution of Mars and the geophysical identification of water and other volatiles stored in the hydrates. Of critical importance, Martian gas hydrates would ensure the availability of key in situ resources for sustaining future robotic and human exploration, and the eventual colonization, of Mars.
Age relationship of basaltic and andesitic surface compositions on Mars: Analysis of high‐resolution TES observations of the northern hemisphere
Authors: Rogers Deanne , Christensen Philip R.
Published: May 2003

Previous Mars Global Surveyor Thermal Emission Spectrometer (TES) results have identified two principal surface compositions on Mars; basaltic surfaces are found primarily in the southern highlands, while andesitic surfaces are found in the northern lowlands and in smaller concentrations distributed throughout the southern highlands. In 1 pixel‐per‐degree composition maps, the exact boundary between the basaltic and andesitic compositions is obscured by large amounts of equatorial surface dust. In this work, high‐resolution TES surface spectral data are used to identify and characterize isolated regions of basalt within the equatorial dust regions and northern lowlands (generally between 20°S–60°N, 0–360°W) in an effort to better understand the nature of the boundary between the two compositions. The purpose of refining this boundary is to more accurately determine the relationship of the compositional dichotomy with global surface morphology and derived crustal thickness. Results show that the basaltic surface composition is closely associated with the ancient cratered terrain morphology but is not well correlated with crustal thickness. The northern extent of the TES basalt composition is also established. With four exceptions, there are no significant concentrations (>∼30% surface cover) of basalt greater than ∼400 km2 in area within the northern plains. Three are located within or adjacent to knobby terrain, which has been suggested to be erosional remnants of the cratered highlands. The fourth exception is in Milankovic crater and may represent a local basalt flow or basaltic material excavated during crater formation. Results from this work suggest that there is a stratigraphic relationship between the basaltic and andesitic surface compositions, with younger andesitic materials overlying older basaltic materials throughout the equatorial and northern plains regions.
Resurfacing time of terrestrial surfaces by the formation and maturation of polygonal patterned ground
Authors: Sletten R. S. , Hallet B. , Fletcher R. C.
Published: May 2003

To help interpret the polygonal patterned ground on Mars, we present recent findings about a similar form of patterned ground in a particularly cold and arid region on Earth, the Dry Valleys of Antarctica. In this region, distinct arrays of interconnected polygons, which we refer to herein simply as patterned ground, characterize many surfaces, reflecting a subsurface network of interconnected, subvertical wedges of sand that grow incrementally as sand progressively fills soil fractures. The fractures form initially as thermoelastic stresses arise during periods of rapid cooling of frozen ground, and they continue to open and close in response to thermal cycles. We describe the initiation and maturation of the patterned ground using data for the growth of sand wedges and for the evolution of crack patterns and microrelief over time scales ranging up to 106 years.
Stochastic forces in circumplanetary dust dynamics
Authors: Spahn Frank , Krivov Alexander V. , Sremčević Miodrag , Schwarz Udo , Kurths Jürgen
Published: May 2003

Charged dust grains in circumplanetary environments experience, beyond various deterministic forces, also stochastic perturbations caused, by fluctuations of the magnetic field, the charge of the grains, by chaotic rotation of aspherical grains, etc. Here we investigate the dynamics of a dust population in a circular orbit around a planet which is perturbed by a stochastic planetary magnetic field B′, modeled by an isotropically Gaussian white noise. The resulting perturbation equations give rise to a modified diffusion of the inclinations i and eccentricities e: 〈Δx2〉 ≈ D Δt (here x = e or i, t is time). The diffusion coefficient is found to be D ∝ ωG2 ∣Δn∣/n2, where the gyrofrequency, the Kepler frequency, and the synodic frequency are denoted by ωG, n, and Δn, respectively. This behavior has been checked against numerical simulations. We have chosen dust grains (1μm in radius) ejected from Jupiter's satellite Europa in circular equatorial orbits around Jupiter and integrated numerically their trajectories over their typical lifetimes (100 years). The particles were exposed to a Gaussian fluctuating magnetic field B′ with the same statistical properties as in the analytical treatment. These simulations have confirmed the analytical results. The theoretical studies showed the statistical properties of B′ to be of decisive importance. To estimate them, we analyzed the magnetic field data obtained by the Galileo spacecraft magnetometer at Jupiter and found almost Gaussian fluctuations of about 5% of the mean field and exponentially decaying correlations. This results in a diffusion of orbital inclinations and eccentricities of the dust grains of about ten percent over the lifetime of the particles. For smaller dusty motes or for close‐in particles (e.g., in Jovian gossamer rings) stochastics might well dominate the dynamics.
Spectroscopic mapping of Mars CO mixing ratio: Detection of north‐south asymmetry
Authors: Krasnopolsky Vladimir A.
Published: May 2003

The CO mixing ratio on Mars was mapped in early northern summer (LS = 112°) using the IRTF/CSHELL long‐slit spectrograph. The spatial resolution of 500 km is intermediate between those from the Phobos orbiter and the previous ground‐based observations. The spectral resolving power of 4 × 104 is high enough to measure equivalent widths of individual lines. The R8‐R13 lines of the CO (3‐0) band at 1.57 μm and some CO2 lines of comparable strength were observed. This made it possible to determine the CO mixing ratios and to cancel out the effects of air mass and dust opacity. Extraction of the CO and CO2 abundances from the observed line equivalent widths was made using the standard curve of growth approach with a special care for the CO2 lines with high lower level energies. Some formulas, which describe the effects of the low‐level energy on weak absorption lines in Mars' reflection spectra, have been derived. The MGS MOLA and TES data on the surface elevation and thermal structure of the atmosphere during the observation were applied to improve the uncertainty of the derived CO mixing ratios, which was equal to 28% for 520 individual points on the disk. Isolines of the CO mixing ratio on Mars' disk and the latitude‐longitude map were used to study the local time, elevation, and latitudinal variations of CO on Mars. The CO mixing ratio is constant within ±7% relative to local time from 700 to 1800. A decrease by a factor of 1.18 in the CO mixing ratio from elevation of −6 km to 3 km was observed. Probably, it is due to a systematic error. The most interesting result is the detection of a seasonal (winter‐summer) asymmetry in the CO mixing ratio. This asymmetry is displayed as a latitudinal increase in the CO mixing ratio from a constant value of 8.3 × 10−4 northward of the subsolar latitude at 23°N to the south from this latitude where CO reaches a value of 12.5 × 10−4 at 50°S. This asymmetry is explained by the intense condensation of CO2 on the south polar cap at LS = 112°. General circulation models predict a weak meridional circulation in southern winter, which cannot prevent the buildup of the CO mixing ratio. The amount of CO2 ice accumulated on the south polar cap is equal to ≈1 mbar of global‐mean CO2 gas according to the general circulation models of the polar processes. If this gas were released and mixed in the southern atmosphere up to the subsolar latitude, then the CO mixing ratio would be equal in both hemispheres. Photochemical accumulation of CO during the southern winter due to freezing out of water vapor does not exceed 4%, that is, an order of magnitude weaker than the observed effect. Further study of seasonal variations of the CO asymmetry should be made by observations and simulated by general circulation models.
Equatorial jets in the dusty Martian atmosphere
Authors: Lewis Stephen R. , Read Peter L.
Published: May 2003

We investigate the production of equatorial jets which demonstrate strong local superrotation in an atmospheric general circulation model of Mars. These westerly jets are driven by diurnal thermal tides, and their strength is shown to be closely related to the amount of dust in the atmosphere. The superrotating jets are strongest near to equinox and under conditions of high atmospheric dust loading. If there is sufficient dust, in amounts corresponding to dust storm conditions, the westerly equatorial jets can occur at any time of year and reach speeds of over 40 m/s, peaking between 10 and 20 km altitude. For more moderate dust amounts, typical of background levels on Mars, the jets are still strong when the subsolar point is close to the equator and latitudinally symmetric tidal modes are forced. Strong easterly retrograde winds are also found high above the equator, and it is shown that the thermal tides play a major role in their formation. This process is especially relevant close to equinox when the cross‐equatorial meridional circulation is weak.
Photometric anomalies of the lunar surface: Results from Clementine data
Authors: Kreslavsky M. A. , Shkuratov Y. G.
Published: May 2003

We mapped the photometric characteristics of the lunar surface for several small areas using Clementine UVVIS camera images. The maps of the phase function steepness showed several anomalous sites. Several small fresh impact craters have anomalous halos in these maps. The phase function within the halos is less steep than for the surrounding mare surface. We interpret these halos to be due to geologically recent impact‐caused alteration of the equilibrium millimeter‐scale regolith structure. This equilibrium structure is established through micrometeoritic bombardment at a geologically short timescale. An anomaly of the same signature was found at the Apollo 15 landing site. We interpret it as being a result of the regolith structure alteration with the lander jets. A unique photometric anomaly not correlated with albedo was found within the Reiner Gamma Formation. We suggest that this anomaly is genetically related to the formation, which indicates its young age. This favors the impact hypothesis for the nature of the Reiner Gamma Formation. Our study showed that mapping of photometric characteristics is a new powerful tool in studies of the surfaces of atmosphereless bodies. Future photometric studies of the Moon with existing and new data sets are promising for a search for traces of recent seismic events, studies of the recent population of meteoroids in the inner solar system, an advance in the understanding of swirls, etc.
Hypervelocity microparticle impact studies using a novel cosmic dust mass spectrometer
Authors: Austin Daniel E. , Grimm Ronald L. , Manning Heidi L. K. , Bailey Carl L. , Farnsworth James E. , Ahrens Thomas J. , Beauchamp J. L.
Published: May 2003

Micron‐sized iron and copper particles accelerated to 2–20 km/s in a 2 MV van de Graaff electrostatic accelerator were used to test the performance of our recently developed cosmic dust mass spectrometer. This compact in situ dust analyzer, known as the Dustbuster, is designed to determine the elemental composition of cosmic dust particles through impact ionization and subsequent time‐of‐flight mass spectrometry. Results from 750 laboratory impacts show high mass resolution, typically 150–350 (m/Δm) for projectile components and 300–600 for the target material (tantalum). Peaks corresponding to H, C, O, Na, and K ions are also observed, consistent with previous microparticle impact experiments. Field‐induced emission of electrons immediately before impact is a possible cause of ion formation from species with high ionization potentials. The high mass resolution, large sensitive target area, and small size make the Dustbuster an ideal instrument for inclusion on a spacecraft payload.
Carbon dioxide on Ganymede
Authors: Hibbitts C. A. , Pappalardo R. T. , Hansen G. B. , McCord T. B.
Published: May 2003

CO2 is inferred on the surface of Ganymede by the presence of an absorption band at ∼4.26 μm in reflectance spectra returned by the Near Infrared Mapping Spectrometer (NIMS) aboard the Galileo spacecraft. Detailed studies of NIMS observations of Ganymede show that the CO2 absorption band on Ganymede is symmetric about 4.257 μm ± 0.004 μm and is negligibly different from the CO2 absorption band on Callisto. In general, bright terrains (sulci) contain less CO2 than dark terrains (regiones), little or no CO2 is detected at the poles, and, unlike for Callisto, there does not appear to be any leading/trailing hemisphere asymmetry in the distribution of CO2 nor do impact craters tend to be CO2 rich. High spatial resolution observations show that CO2 is occasionally enriched in terrain containing larger‐grained ice in comparison with adjacent terrain of similar morphology and ice abundance, that the dark ejecta of Kittu is depleted in CO2 with respect to adjacent terrain, and that only one observed impact crater (Mir) is enriched in CO2. The CO2 that is detected by NIMS is in the nonice material(s) present, not in the fraction that is ice. The ice in all terrain types where CO2 is detected is always sufficiently large‐grained that its low reflectance in the region of the CO2 band prevents discrimination of the CO2 absorption band from the continuum. Areas with relatively fine‐grained ice that are sufficiently bright at 4 μm for CO2 to be observed, such as the polar regions, do not contain detectable CO2.
Debris flows over sand dunes on Mars: Evidence for liquid water
Authors: Mangold N. , Costard F. , Forget F.
Published: May 2003

This study focuses on the formation and physical properties of the gullies observed over large Martian dunes, especially those of the Russell crater (54°S, 347°W). Geomorphic features like sinuosities and connections of the channels show that gullies over dunes involve flows with a significant proportion of liquid. The occurrence of levees implies that these flows are debris flows with a yield strength characteristics of Bingham plastic materials. We apply terrestrial methods to estimate viscosity and velocity of these flows from levee size and sinuosities. We obtain average velocities in the range of 1 to 7 m s−1 and apparent viscosities of 2.8 to 46,000 Pa s, with an average at 740 Pa s, compared with the 0.001 Pa s of pure water. These viscosities and velocities are in the range of terrestrial debris flows with a proportion of 10 to 40% of H2O. These properties are typical of water‐holding debris flows but not of pure water surface runoff or CO2 driven flows. The debris flows over dunes are oriented on south‐facing slopes like other recent gullies. Meltwater from ground ice formed during a recent period of high obliquity is the more likely explanation for the formation of such flows over dunes.
Flow field stratigraphy surrounding Sekmet Mons Volcano, Kawelu Planitia, Venus
Authors: Zimbelman James R.
Published: May 2003

Detailed mapping has revealed several stratigraphic components among lobate plains in the vicinity of Sekmet Mons volcano (44.5°N. lat., 240.5° long.), located on the northern lowland plains of Kawelu Planitia on Venus. Volcanic effusion events produced discrete lobate plains throughout the area. Superposition of flow margins between adjacent lobate plains components indicate that the effusive activity generally progressed from southwest to northeast across the Sekmet Mons area, leading to a cumulative total of 1.5 million km2 covered by adjacent lobate plains components. Source areas for the effusion responsible for the lobate plains components occur primarily along fracture zones or from concentrations of low volcanic domes (“shield fields”) instead of from single constructs. Magellan radar backscatter values from a mixture of both radar bright and radar dark flow components within the flow fields are well below values typical of clinkery a′a lava flows on Earth, but they are consistent with values from terrestrial pahoehoe flows. Detailed mapping of Strenia Fluctus (centered on 41.5° N. lat., 251.0° long.), one of the latest lobate plains units in the area, does not show a systematic trend among effusive centers that contributed to the generation of this flow field. Instead, the Strenia Fluctus flow field is a complex mixture of flows that emanated from a shield field along Mist Chasma and that flowed down a very gentle (>0.1°) regional slope to the east. A 4‐km‐diameter cone north of Strenia Fluctus was the source of a flow complex traceable for more than 200 km over a slope of only 0.03°. Individual flows within Strenia Fluctus are composed of intermixed lobes, similar to relationships observed on the distal portion of the 75‐km‐long Carrizozo basalt flow in New Mexico, which also displays abundant inflation features and a predominant pahoehoe surface texture. If the Venusian lobate plains consist of pahoehoe flows comparable to the Carrizozo flow, they were most likely emplaced at modest effusion rates (∼50 to 500 m3/s), and even with inflation the flows are likely ≤15 m in thickness. Under these conditions all of the lobate plains surrounding Sekmet Mons could have been emplaced in ∼14,000 to 1400 Earth years, assuming continuous effusion with only one source vent active at a time. At similar rates all of the lowland plains in the northern hemisphere of Venus could have been resurfaced by 15‐m‐thick flows through continuous single‐vent effusion in ∼1.4 million to ∼140 thousand Earth years.
Energy for biologic sulfate reduction in a hydrothermally formed ocean on Europa
Authors: Zolotov Mikhail Y. , Shock Everett L.
Published: May 2003

Formation of a sulfate‐bearing ocean on Jupiter's satellite Europa by quenched hydrothermal fluids provides a source of metabolic energy for low‐temperature sulfate‐reducing organisms that use dissolved H2 as an electron donor. Inhibition of thermodynamically favorable sulfate reduction in cooled hydrothermal fluids creates the potential for biologic reduction. Both high temperature and reduced conditions of ocean‐forming hydrothermal solutions favor sulfate reduction in quenched fluids. The maximum amount of energy available to support autotrophic sulfate reduction is on the order of a few kilojoules per kilogram of water and is limited by the low abundances of either H2 or sulfate in ocean‐forming fluids. Although this irreplaceable energy source might have supported early life on Europa, maintenance of biologic sulfate reduction throughout the ocean's history would require a supply of organic compounds from endogenic sources or from the satellite's surface.
Composition of the lunar surface as will be seen from SMART‐1: A simulation using Clementine data
Authors: Shkuratov Yuriy G. , Stankevich Dmitriy G. , Kaydash Vadim G. , Omelchenko Vitaliy V. , Pieters Carle M. , Pinet Patrick C. , Chevrel Serge D. , Daydou Yves H. , Foing Bernard H. , Sodnik Zoran , Josset Jean‐Luc , Taylor Lawrence A. , Shevchenko Vladislav V.
Published: May 2003

We present a new technique for remote sensing determination of lunar surface composition in the context of the SMART‐1 mission. The technique is based on spectral and composition data obtained by Lunar Soil Characterization Consortium for a few particle‐size separates of lunar soils. We map the abundance of TiO2 and FeO, pyroxene content, maturity degree (Is/FeO), and a characteristic size of particles. Comparison of the TiO2 and FeO abundance maps with proper distributions obtained by Lucey et al. [2000a] shows high correlation. We found also an inverse correlation between the Is/FeO distribution and Lucey et al.'s [2000b] parameter OM. Application of this approach shows that fresh mare crater regolith is characterized with a higher abundance of pyroxenes, coarse particles, and low maturity degree. The pyroxene abundance map can be used to identify pyroclastic regions. An excess of small particles is predicted for highland areas. We note appreciable variations of the characteristic size of particles in mare regions. Our preliminary results for the Reiner‐γ formation show that there is no composition anomaly for the TiO2 and FeO abundance, in agreement with previous analyses. Our maps also indicate that the formation contains a surface material characterized with low maturity and high degree of crystallinity, consistent with the occurrence of immature regolith possibly contaminated with dust.
Atmospheric rotational effects on Mars based on the NASA Ames general circulation model
Authors: Sanchez Braulio V. , Rowlands D. D. , Haberle Robert M. , Schaeffer James
Published: May 2003

Atmospheric rotational effects on Mars are computed and analyzed. Both axial (ΔLOD) and equatorial effects (polar motion) are evaluated. Surface values of stress and pressure from the NASA Ames general circulation model are used as inputs to compute the topographic, stress, and gravitational torques. Time series for the ice caps moments of inertia and the axial component of atmospheric angular momentum provide inputs for a separate computation of axial effects. Stress torque dominates the torque budget. This is different from the results obtained from Earth atmospheric models, in which pressure effects are paramount. Axial torque and ice caps yield annual and semiannual ΔLOD amplitudes of 0.747 and 0.121 ms, respectively. Torque‐induced polar motion reaches a maximum of 16.26 mm in the second half of the Martian northern hemisphere winter. Changes in LOD using the angular momentum approach are 0.187 and 0.136 ms for the annual and semiannual harmonics. The expected precision of the planned NetLander Ionospheric and Geodesic Experiment (NEIGE) should detect the main harmonics in the ΔLOD time series. Annual and semiannual polar motion harmonics induced by atmospheric torque are below the level of NEIGE detectability.