P11A-0244
Evolution of Exospheric Suprathermal Oxygen over Martian History
As a part of a global effort, the dynamics of the flow of energetic particles through the Martian upper atmosphere has been studied. Being the most important reaction, the dissociative recombination (DR) of O2+ is responsible of most of the production of hot atomic oxygen deep in the thermosphere of Mars. To understand the Martian exosphere, it is then necessary to employ a global kinetic model which can include a self-consistent description of both thermosphere collisional region and exospheric collisionless domain. In this study, we have used our Direct Simulation Monte Carlo (DSMC) model in combination with the 3D Mars Thermosphere General Circulation Model (MTGCM) of Bougher et al. [2006, Geophys. Res. Lett., 33, doi:10.1029/2005GL024059.] to describe self-consistently the region of the upper thermosphere where the exosphere is generated, the entire exosphere, and its feedback into the thermosphere generally. Along with the effect of ionization, the DSMC method allows us to provide profiles of density and temperature, atmospheric loss rates and return fluxes as functions of the Solar Zenith Angle (SZA) for all cases considered. To present a complete description of this physical problem we examined several of the most limiting cases spanning spatial and temporal domains. The contribution of the different physical and chemical escape processes was studied and compared for the present but also earlier Mars epochs characterized by different solar inputs (1 EUV, 3 EUV and 6 EUV) for Equinox conditions [Zhang et al., 1993, JGR, 98].
P11A-0245
Ionopause Features of Mars as observed by the Radio Science Experiment MaRS on Mars Express
The ionopause of a planet is defined as the boundary between the ionosphere and the solar wind regime. It was first described for Venus when a sharp decrease in electron density towards very small values was found at certain altitudes. So far, the ionopause at Mars has not been well observed. One reason is that the noise of the Viking profiles was relatively high and did not drop below 500 el/cc. The MGS data base is inconclusive concerning the ionopause. The highly elliptical orbit of Mars Express allows us to investigate the electron density of Mars up to an altitude of about 1500 km. We want to define the ionopause feature at Mars as an electron density gradient starting well above the topside ionospheric main peak, tending to decrease the electron density towards noisy values around zero. The Radio Science Experiment MaRS on Mars Express sounded the Martian atmosphere and ionosphere during four occultation seasons starting from April 2004. So far, more than 400 vertical profiles of the ionospheric electron density could be derived covering both hemispheres and almost all local times. This presentation will show the high variability of the ionopause structures of Mars.
P11A-0246
Investigation of Gravity Wave Propagation in the Martian Atmosphere.
Periodic atmospheric variations with the characteristics of gravity waves have been detected in the Martian atmosphere since the early measurements from Viking and Mariner 9. More recent temperature and aerobraking data from Mars Global Surveyor (MGS), and Mars Odyssey (ODY) suggest the presence of lee waves in ice clouds near the Martian surface, and show fluctuations in the thermospheric density with periods and wavelengths typical of gravity waves. Gravity waves are believed to have important effects in the Earth's atmosphere, producing fluctuations in the density, temperature, winds, and airglow intensities in the mesosphere and lower thermosphere, and generating a reversal of the summer to winter temperature gradient, which produces winter warming near the mesopause. If gravity waves are regularly present in the Martian atmosphere, they may also have significant effects on the circulation and energy budget. The effects of sub-grid scale gravity wave processes are generally represented in atmospheric models through a number of parameterization schemes. However, in this work, we determine the propagation of realistic individual gravity waves in the Martian atmosphere, using a linearized one-dimensional full-wave model. Calculations have been performed using atmospheric parameters based on observations of apparent lee waves in high latitude clouds, measured by the MOLA instrument aboard MGS. The results show that some of the generated lee waves are capable of propagating up into the Martian thermosphere. Wave propagation is found to be sensitive to the properties of the background atmosphere, including the wind and temperature structure. Waves which reach the thermosphere produce fluctuations in density with characteristics consistent with those of the density variations detected in ODY aerobraking data. The presence of critical levels and the temperature profile of the Martian atmosphere are found to determine the wavelengths, periods, and direction of propagation of the waves that are able to propagate up to the thermosphere. Gravity waves of modest amplitude are found to deposit momentum and generate significant heating and cooling in the Martian atmosphere.
P11A-0247
The Neutral Atmosphere of Mars as Observed Through Radio Occultation Measurements With MEX and MGS
Radio occultation experiments conducted with Mars Express (MEX) and Mars Global Surveyor (MGS) yield atmospheric profiles with fine vertical resolution, typically about 1 km. We are exploiting this attribute of the occultation measurements to investigate the structure and dynamics within the lowest scale height of the Martian atmosphere. Radio occultation experiments were conducted concurrently by the two spacecraft during several intervals: May to August 2004, December 2004 to January 2005, August to September 2005, and November 2005 to April 2006. Owing to differences in orbital geometry, the MEX and MGS occultations generally sound the atmosphere at widely different combinations of latitude and local time [e.g., Hinson et al., Radio occultation measurements and MGCM simulations of Kelvin waves on Mars, Icarus, in press, 2007]. Our current analysis of these observations addresses two topics. The first concerns the temperature lapse rate in the lower atmosphere and its diurnal variations. As an example of initial results in this area, the convective boundary layer extends to a height of 4--9 km at local time 17:00 in a set of MEX occultations that sounded the tropics during northern spring of Mars Year (MY) 27. The depth of the boundary layer varies significantly among these profiles, possibly in response to spatial variations in surface thermal properties and local topography. This investigation can provide valuable constraints for Mesoscale Models and Large Eddy Simulations. We are also using these observations to characterize the meridional variations in temperature and geopotential height associated with the winter polar vortex and to estimate the near-surface zonal wind speeds implied by geostrophic balance. For example, the geopotential height at 400 Pa decreases by about 3 km from equator to pole in late northern winter of MY 27. The gradient of geopotential height near 60°N implies a zonal wind speed of about 40 m s-1.
P11A-0248
The Influence of Water Ice Clouds on Martian Tropical Thermal Structure
The Reanalysis derived from the UK Mars general circulation model (MGCM) assimilation of TES temperature retrievals provides the best current estimate of the evolving state of the martian atmosphere over the course of the Mars Global Surveyor (MGS) mapping mission. The assimilation uses the observed dust column opacity with a vertical distribution that is prescribed as a function of season and latitude. The TES temperature retrievals effectively serve as an external forcing that acts to supplement the model's radiative and dynamical forcing. A Control simulation has also been carried out using the same evolving dust distribution as the Reanalysis, but without the assimilation of temperature. Differences in zonal mean temperatures between these two simulations reflect biases in the representation of dynamical and radiative effects in the MGCM. Model bias is due to missing or incomplete physical processes, as well as errors in the specification of the vertical distribution and radiative properties of aerosols. We have identified a cold bias in the "Control" simulation of the tropical temperature that robustly develops in the northern hemisphere (NH) summer solstice season that we attribute to the absence of radiatively active water ice clouds in the model. We show that MGCM simulations with radiatively active clouds are able to account for the temperature bias in the Control simulation. An analysis of the thermal tides in the Reanalysis is also consistent with this interpretation. We conclude that cloud influences likely play a prominent role in shaping the vertical thermal structure of the tropical atmosphere during the NH summer season
P11A-0249
Temperature and dust profiles of Mars' atmosphere derived from Mars Climate Sounder (Mars Reconnaissance Orbiter)
Mars Climate Sounder (MCS) on board NASA's Mars Reconnaissance Orbiter (MRO) primarily operates as a limb sounding infrared radiometer. The small field of view and limb scanning mode allow retrieval of atmospheric temperature and dust properties from the surface up to approximately 80km with 5km vertical resolution. The polar orbit of MRO gives coverage of all latitudes at 3pm and 3am Mars local-time. The ability of MCS to sounds these altitudes at high spatial and temporal resolution gives a unique dataset with which to test our understanding of the Martian atmosphere. It also complements and extends upon previous climatalogical datasets (for example TES). Measured mid-infrared radiances from MCS were analysed using the correlated-k approximation with Oxford's NEMESIS retrieval software. The correlated-k approximation was compared with a line-by-line model to confirm its accuracy under Martian atmospheric conditions. Dust properties were taken from analysis of TES data by Wolff and Clancy (2003). We present profiles of temperature and dust for data covering September to December 2006. During this period Mars' north pole was experiencing summer and the south pole was in winter. Preliminary results show that high altitude warming over the southern winter pole is greater than that predicted by models. Our results will be compared to numerical models of the Martian atmosphere and the implications discussed.
P11A-0250 [WITHDRAWN]
Intergration of MGS observations of 2001 global dust storm on Mars
The monitoring of the 2001 global dust storm on Mars by Mars Global Surveyor has yielded an unprecedented wealth of data on the initiation and growth of a major dust event. The data include MOC daily global weather maps, MOC dust (visible) optical depth measurements, TES measurements of atmospheric temperature and 9- micron dust opacity, and MHSA measurements of middle atmosphere temperatures. Together these allow for the juxtaposition of temperature, and opacity fields with visual imagery to enable a more comprehensive assessment of the storm development. Known limitations of TES observations result in significant spatial gaps in data, especially at high latitudes and in regions with very high dust opacity. We supplement these opacity estimates with the MOC imagery to construct a detailed description of the initiation and growth of the dust event. Our goal is to produce the best possible description of the evolution of the column optical depth and regions of active dust lifting based on a synthesis of all available data. We are using these improved evolving opacity estimates as input into the NASA/NOAA Mars General Circulation Model (MGCM). We will present model results that relate the simulated circulation, atmospheric temperature and aerosol distribution to the available observations in an effort to better understand the underlying dynamics of the initiation and growth of the 2001 storm.
P11A-0251
Ensemble-Based Data Assimilation With a Martian GCM
Quantitative study of Mars weather and climate will ultimately stem from analysis of its dynamic and thermodynamic fields. Of all the observations of Mars available to date, such fields are most easily derived from mapping data (radiances) of the martian atmosphere as measured by orbiting infrared spectrometers and radiometers (e.g., MGS / TES and MRO / MCS). Such data-derived products are the solutions to inverse problems, and while individual profile retrievals have been the popular data-derived products in the planetary sciences, the terrestrial meteorological community has gained much ground over the last decade by employing techniques of data assimilation (DA) to analyze radiances. Ancillary information is required to close an inverse problem (i.e., to disambiguate the family of possibilities that are consistent with the observations), and DA practitioners inevitably rely on numerical models for this information (e.g., general circulation models (GCMs)). Data assimilation elicits maximal information content from available observations, and, by way of the physics encoded in the numerical model, spreads this information spatially, temporally, and across variables, thus allowing global extrapolation of limited and non-simultaneous observations. If the model is skillful, then a given, specific model integration can be corrected by the information spreading abilities of DA, and the resulting time sequence of "analysis" states are brought into agreement with the observations. These analysis states are complete, gridded estimates of all the fields one might wish to diagnose for scientific study of the martian atmosphere. Though a numerical model has been used to obtain these estimates, their fidelity rests in their simultaneous consistency with both the observations (to within their stated uncertainties) and the physics contained in the model. In this fashion, radiance observations can, say, be used to deduce the wind field. A new class of DA approaches based on Monte Carlo approximations, "ensemble-based methods," has matured enough to be both appropriate for use in planetary problems and exploitably within the reach of planetary scientists. Capitalizing on this new class of methods, the National Center for Atmospheric Research (NCAR) has developed a framework for ensemble-based DA that is flexible and modular in its use of various forecast models and data sets. The framework is called DART, the Data Assimilation Research Testbed, and it is freely available on-line. We have begun to take advantage of this rich software infrastructure, and are on our way toward performing state of the art DA in the martian atmosphere using Caltech's martian general circulation model, PlanetWRF. We have begun by testing and validating the model within DART under idealized scenarios, and we hope to address actual, available infrared remote sensing datasets from Mars orbiters in the coming year. We shall present the details of this approach and our progress to date.
P11A-0252
Dust storms originating in the northern hemisphere of Mars
Data from the first three Mars Global Surveyor (MGS) mapping years (MY 24, 25 and 26) are used to investigate dust storms originating in the northern hemisphere. Flushing dust storms, which originate as frontal dust storms at the northern polar vortex edge and propagate southward through topographic channels, are observed immediately before and after a quiescent period that occurs around the northern winter solstice (between Ls 240 and Ls 300). Both the pre- and post-solstice active periods in the third year (MY 26) can be further divided into two sub-periods. The most vigorous of these flushing storms occurred during Ls 210-220 and Ls 310-320. The lifted dust crossed the equator and accumulated in the southern hemisphere. These major dust storms enhanced the Hadley circulation and suppressed the lower-level baroclinic eddies in the northern mid and high latitudes. The 2- 3 sol wave number m=3 traveling waves show the best correlation with flushing dust storms and can combine with other wave modes to produce storm tracks and fronts within individual sub-periods.
P11A-0253
Climate-driven Erosion Patterns in Southern Hemisphere Dune Fields on Mars
Studies of recent climate change on Mars have sought to determine the magnitude and frequency of climate changes by studying their impact on geological and atmospheric processes. Sand dunes and other aeolian features are unique in the study of climate change in that they are geological features formed by atmospheric forces. In particular, cold-climate sand dunes are surface features that become more active under windy, nonicy conditions, but less active under nonwindy and/or icy conditions. Thus they are extremely sensitive to changes in temperature, humidity, and atmospheric dynamics that drive climate change. The presence of a well-defined shift in southern hemisphere dune morphology may shed new light on recent climate change on Mars. Poleward of roughly 60°S, dunes take on a rounded and eroded appearance consistent with inactivity, whereas dunes equatorward of this latitude appear largely indistinguishable from active dunes. All dune fields poleward of 55°S that are visible in Mars Odyssey THEMIS visible images and Mars Global Surveyor MOC images have been identified and categorized according to their level of degradation. Preliminary results suggest that the morphological shift occurs at approximately 60°S at all longitudes, generally corresponding well with the boundary of near-surface ground ice according to ground ice models, terrain morphological studies, and data from the Neutron Spectrometer on Mars Odyssey. In one meridional corridor (40°E-130°E, south and east of Hellas Planitia), Neutron Spectrometer data extend as far north as 50°S. This bulge is not reflected in dune morphology, suggesting that any link between ground ice and dune morphology is complex.
P11A-0254
Wind-Driven Particle Mobility on Mars: Insights from MER Observations
High-resolution images from MOC and HiRISE reveal numerous small, linear, light-toned bedforms in settings all across Mars. These features represent one of the most abundant aeolian feature types on the planet, yet their nature and origin remain uncertain. Larger, dark-toned features have been identified confidently as dunes from their morphologies; they presumably are relatively depleted of dust and some therefore could be currently active, but only minor surface changes to a small number of dunes have been reported. There have been no reports of changes to any of the numerous light-toned bedforms. It is problematic that winds responsible for frequently raising dust do not seem to significantly affect bedforms that very likely are composed of (more easily-entrained) sand-sized particles. Here we consider factors other than wind frequency that control bedform mobility across Mars, applying observations from MER traverses at Gusev and Meridiani Planum. (1) MI images show that surface dust at Gusev (and likely elsewhere across Mars) typically occurs as extended, fragile aggregates that should be far easier to entrain than mono-particle "dust"-sized grains. (2) Light-toned bedforms investigated at Gusev are coarse-grained ripples (i.e., bedforms with coarse grains mantling finer-grained, sandy interiors). Currently they are crusted and dust-covered. We suggest that the numerous small, linear, light-toned bedforms seen in high resolution orbital images are coarse-grained ripples also. Although such ripples are much less familiar on Earth compared with ripples and dunes having unimodal particle size-frequencies, we suggest this is partly due to the lack of free quartz on Mars available for contributing to an abundant, durable, very well-sorted sediment supply for saltation. Poorly-sorted debris is organized by wind into relatively slow-moving coarse- grained ripples, so in the absence of quartz, we speculate that coarse-grained ripples should be relatively more common on Mars than on Earth. The relatively slow rate of movement typical of coarse-grained ripples makes these features more vulnerable to immobilization by induration developing during extended periods of quiescence. (3) Spirit also visited a darker-toned unit ("El Dorado") potentially analogous to many similar dark features observed from orbit that have been interpreted as aeolian deposits. Spirit found very slightly crusted (nearly cohesionless), mafic, 200-300 micron sand overlying unconsolidated finer mafic sand. Induration within the dark-toned unit cannot proceed far between disruptions by frequent wind events strong enough to initiate movement of the fine-medium sand. (4) The same fine-medium sand composing El Dorado also is found in small, widely-scattered drifts and in scattered patches of small ripples. Perceptible crest migration of ripples composed of these grains occurred when high winds affected Spirit's site during recent global dust storm activity. (5) At Meridiani Planum, strong wind events associated with the same global dust storm activity--very likely the strongest wind events ever experienced by Opportunity--mobilized 100 micron mafic sand and a few coarser particles (in creep), but only within areas disturbed by the rover wheels. Most changes involved stripping of 100 micron sand from tracks where original cohesive induration of the surface had been destroyed by remolding under wheel movement.
P11A-0255
Formation of Silica Deposits on Mars by Acid Weathering: Physical-Chemical Constraints
Many chemical and mineralogical characteristics of martian surface materials are indicative of exposure to acidic solutions. Silica-rich outcrops and soils found in Gusev crater could also result from acid weathering. We used thermochemical equilibrium and coupled kinetic-thermodynamic models to investigate conditions under which abundant amorphous silica forms by low-temperature (273 K) H2SO4-HCl acid weathering of mafic/ultramafic rocks. We explored the effects of pH, solution/rock ratio (W/R) and rock composition on secondary mineralogy, solution chemistry, and timing of weathering. Modeling shows that silica-rich deposits form mainly under very acid conditions (pHs<~2-3) and at high W/R ratios (~102-103). High W/R ratios may represent solution discharge in spring environments, groundwater flow, or lake settings. If solution pH does not change much during high W/R alteration, silica-rich (>90 vol% silica) mineral assemblages form at pHs<~2. If acid solutions with original pH<~2 are neutralized as weathering proceeds, abundant silica precipitates at early stages of weathering (W/Rs >~102) below pH ~3. Calculated timing of silica deposition is consistent with these inferences. Kinetic models also demonstrate that silica can dissolve when the solution neutralizes. Silica precipitation conditions are similar for several potential martian protoliths, however, the volume precipitated increases with increasing rock SiO2 content (Shergotty basalt > Adirondack olivine basalt > Chassigny dunite). Low-pH deposition of amorphous silica is consistent with experimental Mars analog studies and theoretical models directed at understanding martian acid weathering. Observed Ti enrichment in some of the high silica deposits in Gusev crater is also consistent with a low-pH process. Rapid dissolution of mafic minerals and glass in cold, low-pH fluids could have been followed by the precipitation of silica and Ti-oxide owing to their low and comparable solubilities in these solutions. However, a high-temperature (e.g., hydrothermal) origin for the observed deposits remains a possibility.
P11A-0256
Plausible Forms of Carbon Dioxide Ice Clouds in the Lower Atmosphere of Mars
Observations supporting the suspected presence of clouds composed of carbon dioxide ice crystals in the lower atmosphere of Mars date to at least the early part of the Mars Global Surveyor (MGS) mission. Intriguing MOLA laser ranging results in the polar night indicate the nearly undeniable presence of populations of unidentified aerosol particles capable of reflecting or absorbing/scattering a significant portion of the near-infrared laser pulse. Furthermore, MGS radio science temperature retrievals in the polar night often exhibit regions aloft where the air temperature is significantly less than the carbon dioxide ice saturation temperature. Since observations able to concretely confirm or refute the existence of such clouds are still elusive, numerical models must be used to explore the hypothesis further. A microscale numerical model with detailed cloud microphysics capability should be able to provide valuable insight on the plausible form(s), environmental sensitivities, and climatic impacts of such carbon dioxide ice clouds. Results from investigations using such a model will be presented. This work is supported by a grant from the NASA Mars Fundamental Research Program.
P11A-0257
Physical Characterization of the South Seasonal Cap of Mars From OMEGA Observations
The time and space evolution of the South Seasonal Polar Cap (SSPC) is a major annual climatic signal. The composition, physical state and texture of the SSPC give clues about the exchange of CO2, H2O and dust with the atmosphere. The imaging spectrometer OMEGA on board Mars Express has acquired the most comprehensive set of observations to date in the near-infrared (0.93-5.1 microns) on the SSPC from winter solstice to the end of the recession at Ls=325o of the martian year 27 [1]. The time resolution is 3 days to one month and the spatial resolution ranges from 700m to 10 km/pixel. The spectral range covered by OMEGA is particularly relevant for our studies since it samples numerous absorption bands distinctive of CO2 and H2O in their solid state. Here we analyze with statistical techniques and a physical model a collection of OMEGA spectral images covering the SSPC at Ls ~223o, i.e. close to the maximum development of the cryptic region. Our goals are to (i) segment the SSPC into different CO2 ice terrains based on material composition and organization (ii) map the spatial variations of some of their physical properties: dust abundance, granularity, icy layer thickness, etc. In an earlier work [2] we introduced the "snowdrop time", i.e.: at a given location, the time necessary to decrease the areal coverage of CO2 from 98% to 2% during recession. We showed that it is mainly controlled by the dispersion of its local albedo distribution ~one martian month earlier. The physical characterization of the CO2 deposits allows to identify and understand the processes governing this albedo distribution variability: sub-pixel mixing, ice thickness, grain size, dust content, etc. [1] Langevin et al., JGR Vol. 112, 2007 [2] Schmidt et al., LPSC XXXVIII (2007), #1743.
P11A-0258
Basal sublimation and venting of the north seasonal cap of Mars
Spots, fans and dark polygonal patterns form during the spring on the southern seasonal cap of Mars as a consequence of 1) the basal sublimation of the translucent and impermeable slab of carbon dioxide and 2) the venting of the CO2 gas loaded with dust and sand size material scoured from the surface of the polar layered deposits. The dark polygons on the cap have a similar formation process as the spots but the dust and sand erupt from elongated vents rather than point sources. In the summer, spiders and etched polygons remain on the southern polar layered deposits. The spiders are shaped by the scouring action of confined CO2 gas flowing between the cap and the basement and converging toward point sources, whereas the etched polygons result form the forced migration of the CO2 gas over longer distances. Comparable observations during the spring near the north pole on the seasonal cap indicate that similar processes occur in both polar regions and that the venting model developed for the south seasonal cap also operates near the north pole. However, spider and etched polygonal features are extremely uncommon on the north substrate, indicating that the conditions for their formation (e.g. mechanical strength of the slab and the substrate, transparency of the seasonal cap) are not met. The continual erosion and re-sedimentation occurring at the surface of the polar layered deposits by the seasonal degassing is a major geomorphological agent shaping the polar regions. The polar layered deposits have been proposed to contain the stratigraphic record of climatic changes and catastrophic events of very high interest for future missions. Our observations suggest that both polar regions deposits may have been locally disrupted by the seasonal sub-ice gas flow and that the stratigraphic record may have been partially lost. The Phoenix landing site might have been affected in the past and the stratigraphic information associated with the original deposition of the polar material partially disrupted due to this surface reworking.
P11A-0259
A.M. High Albedo Events in Martian northern polar craters: An Investigation Using THEMIS Infrared Data
Following the work done on surveying High Albedo Events (HAEs) in Mars" northern polar craters (Armstrong et al., 2007), we use data from THEMIS (Thermal Emission Imaging System) on board the Mars Odyssey spacecraft to correlate the findings of the TES (Thermal Emission Spectroscopy) survey. In the TES survey, there were 9 craters (65°N to 71°N) with a diameter larger than 10km which displayed HAE's in a.m. hours (0140-0330 local time) during late spring to mid-summer, at temperatures well above the sublimation point of carbon dioxide frost. According to Armstrong et al., this implies that water ice forms overnight, sublimates during the day, and re-deposites in the following night. Using the THEMIS image database at http://themis.asu.edu, we found a total of 40 infrared images and several visible images which fell into our search criteria for the a.m. crater HAE's. These images were captured at a local time ranging from 0419-0511 during Ls 47° to 180°, with solar incidence angles ranging from 95.4° to 72.1°. An investigation of these images showed mixed results. Some craters (65.43°N/128.33°E, 66.35°N/163.44°E, 66.38°N/144.02°E, 70.04°N/352.05°E) exhibit what could be interpreted as signs of interior crater frost but none of them is definitive, while others (64.82°N/209.40°E, 64.90°N/350.77°E, 65.49°N/283.67°E, 69.87°N/285.01°E, 70.88°N/193.55°E) display no sign of interior crater frost at all. Additionally, there are a number of craters (64.90°N/350.77°E, 65.43°N/128.33°E, 66.35°N/163.44°E, 66.38°N/144.02°E, 70.04°N/352.05°E, 70.88°N/193.55°E) which show definite signs of water frost along the crater rim. These observations suggest one of the followings: (1) the interior crater frost sublimates before the THEMIS images were taken; (2) the THEMIS data cannot capture the diffuse, scattered, and thin frost deposits well enough to be used in any conclusive manner; or (3) there was simply no interior crater frost to begin with. Further investigations are in progress.
P11A-0260
Non-condensable gas in a Mars General Circulation Model
We model the variation of non-condensable trace gases that results from the seasonal cycle of CO2 on Mars. A simple condensation scheme has been incorporated into MarsWRF, a 3-dimensional numerical model for the atmospheres of Mars. Non-condensable trace gas (mostly N2 and Ar) mass mixing ratios are affected by the phase change of CO2 and by transport. The distribution of Ar abundance has been observed by the Gamma Ray Spectrometer on the Mars 2001 Odyssey spacecraft. We are able to qualitatively reproduce the Ar observations, including the seasonal evolving latitudinal distribution. However, the modeled magnitudes of maximum enrichment are lower than observed. Smoothing Ar enrichment in the vertical reduces susceptibility to transport by near-surface, off-cap circulation, therefore gives further enhancement of non-condensable tracer in the winter pole. We suggest that a missing process in the model may account for the underestimation. An extra buoyancy term in the dynamics should result from the vertical gradient in mean molecular mass as Ar mass mixing ratio increases.
P11A-0261
Comparison of bulk water ice clouds in GM3 with SPICAM ice cloud measurements
The Global Multiscale Mars Model (GM3) has an improved simulation of the water cycle on Mars which includes phase transitions between water vapour and bulk ice particles, eddy and molecular diffusion, gravitational sedimentation and transport between the polar caps, regolith and atmosphere. One year of nadir UV (200-310 nm) measurements from SPICAM have been used to retrieve cloud and dust optical thickness after allowing for Rayleigh and aerosol scattering and surface scattering. For the comparison with GM3 we focus on the tropical cloud belt (Ls 90-150).
P11A-0262
Integration of MGS Observations of the 2001 Global Dust Storm on Mars: Implications for Atmospheric Modeling
The monitoring of the 2001 global dust storm on Mars by Mars Global Surveyor has yielded an unprecedented wealth of data on the initiation and growth of a major dust event. The data include MOC daily global weather maps, MOC dust (visible) optical depth measurements, TES measurements of atmospheric temperature and 9- micron dust opacity, and MHSA measurements of middle atmosphere temperatures. Together these allow for the juxtaposition of temperature, and opacity fields with visual imagery to enable a more comprehensive assessment of the storm development. Known limitations of TES observations result in significant spatial gaps in data, especially at high latitudes and in regions with very high dust opacity. We supplement these opacity estimates with the MOC imagery to construct a detailed description of the initiation and growth of the dust event. Our goal is to produce the best possible description of the evolution of the column optical depth and regions of active dust lifting based on a synthesis of all available data. We are using these improved evolving opacity estimates as input into the NASA/NOAA Mars General Circulation Model (MGCM). We will present model results that relate the simulated circulation, atmospheric temperature and aerosol distribution to the available observations in an effort to better understand the underlying dynamics of the initiation and growth of the 2001 storm.