global scale near infrared variability on mars analysis of 2003 mars opposition observations from hst nicmos abstract we have used hst nicmos to observe approximately 57 of the martian surface in 7 narrow band filters 0 97 1 08 1 13 1 66 1 90 2 12 and 2 15 m during the 2003 opposition l s 250 and at a resolution of 12 km pixel principal components analysis pca of the dataset has identified regional variability on scales of hundreds of kilometers associated with differences in the near infrared spectrum of mars visualization of the data in principal component space has allowed us to identify spectral endmembers associated with the south polar cap the classic bright terrains northern syrtis major southern syrtis major tyrrhena terra and acidalia planitia the two syrtis major endmembers and the tyrrhena terra endmember differ in their absolute reflectivities but have the same spectral shape at wavelengths longer than 1 6 m the acidalia endmember is distinct from the other dark terrain endmembers because it exhibits a strong negative near ir spectral slope comparisons with spectral library measurements cannot provide unique constraints on the surface mineralogy for these sparsely sampled spectral data however the observed spectral variations between tyrrhena terra and syrtis major are consistent with variations in iron and sulfur bearing minerals and the relatively strong negative spectral slope in the spectrum of acidalia is consistent with the presence of hydrated alteration products additional comparison with previous nicmos observations taken in 1997 at l s 150 indicate that the average near ir spectral slope of the acidalia region is more negative during the late northern fall than during the mid northern summer this may indicate seasonal variations in the presence of either adsorbed water or re hydrated minerals in the regolith of acidalia

visible albedo of mars south polar cap 2003 hst observations abstract the martian south polar cap was observed with the high resolution camera on hubble space telescope near the very favorable 2003 opposition well calibrated images taken at a number of wavelengths in visible and uv were used to measure the apparent lambert albedos of two bright polar areas these were corrected for the effects of atmospheric dust to obtain wavelength dependent surface albedos which are diagnostic for the purity and grain size of the co 2 deposits the bolometric albedo estimated from these data may be sufficiently large to be consistent with stability of the perennial co 2 in the residual cap

textured dust storm activity in northeast amazonis southwest arcadia mars phenomenology and dynamical interpretation abstractdust storms are mars s most notable meteorological phenomenon but many aspects of their structure and dynamics remain mysterious the cloud top appearance of dust storms in visible imagery varies on a continuum between diffuse hazy and textured textured storms contain cellular structure and or banding which is thought to indicate active lifting within the storm some textured dust storms may contain the deep convection that generates the detached dust layers observed high in mars s atmosphere this study focuses on textured local dust storms in a limited area within northeast ne amazonis and southwest sw arcadia planitiae 25 40 n 155 165 w using collocated observations by instruments on board the mars global surveyor mgs and mars reconnaissance orbiter mro satellites in northern fall and winter this area frequently experiences dust storms with a previously unreported ruffled texture that resembles wide mixed layer rolls in earth s atmosphere a resemblance that is supported by h

temperature inversions thermal tides and water ice clouds in the martian tropics 1 we report new results on the structure and dynamics of the tropical atmosphere of mars derived from a combination of radio occultation measurements by mars global surveyor and simulations by a mars general circulation model mgcm radio occultation experiments sounded the equatorial atmosphere at latitudes of 36 n to 30 s during midsummer of the northern hemisphere ls 134 162 sampling the predawn thermal structure at a local time of 0412 elevated temperature inversions are a conspicuous feature of these observations they appear at pressures between 30 and 200 pa well above the surface and their magnitude exceeds 6 k in 34 of the temperature profiles in this latitude band the properties and spatial distribution of these elevated inversions are organized across the tropics on planetary scales inversions are strongest and occur most frequently above elevated terrain achieving a peak magnitude of 30 k near tharsis and their altitude generally increases toward the south according to mgcm simulations which closely resemble the observations these temperature inversions arise from zonally modulated thermal tides the best simulation includes an interactive hydrologic cycle which results in strong coupling between the thermal tides and radiatively active water ice clouds prominent clouds form in response to wave induced adiabatic cooling and evolve in a pattern closely correlated with the thermal structure of the tides the tides in turn are intensified by radiative forcing from the clouds this tide cloud coupling imposes strong diurnal modulation on the properties of clouds in the tropics

thermophysical properties along curiosity s traverse in gale crater mars derived from the rems ground temperature sensor abstract the rems instrument onboard the mars science laboratory rover curiosity has measured ground temperature nearly continuously at hourly intervals for two mars years coverage of the entire diurnal cycle at 1 hz is available every few martian days we compare these measurements with predictions of surface atmosphere thermal models to derive the apparent thermal inertia and thermally derived albedo along the rover s traverse after accounting for the radiative effects of atmospheric water ice during fall and winter as is necessary to match the measured seasonal trend the rems measurements can distinguish between active sand other loose materials mudstone and sandstone based on their thermophysical properties however the apparent thermal inertias of bedrock dominated surfaces 350 550 j m 2 k 1 s are lower than expected we use rover imagery and the detailed shape of the diurnal ground temperature curve to explore whether lateral or vertical heterogeneity in the surface materials within the sensor footprint might explain the low inertias we find that the bedrock component of the surface can have a thermal inertia as high as 650 1700 j m 2 k 1 s for mudstone sites and 700 j m 2 k 1 s for sandstone sites in models runs that include lateral and vertical mixing although the results of our forward modeling approach may be non unique they demonstrate the potential to extract information about lateral and vertical variations in thermophysical properties from temporally resolved measurements of ground temperature

the water cycle and regolith atmosphere interaction at gale crater mars abstract we perform mesoscale simulations of the water cycle in a region around gale crater including the diffusion of water vapour in and out of the regolith and compare our results with measurements from the rems instrument on board the curiosity rover simulations are performed at three times of year and show that diffusion in and out of the regolith and adsorption desorption needs to be taken into account in order to match the diurnal variation of relative humidity measured by rems during the evening and night local downslope flows transport water vapour down the walls of gale crater when including regolith atmosphere interaction the amount of vapour reaching the crater floor is reduced by factors of 2 3 depending on season due to vapour diffusing into the regolith along the crater walls the transport of vapour into gale crater is also affected by the regional katabatic flow over the dichotomy boundary with the largest flux of vapour into the regolith initially occurring on the northern crater wall and moving to the southern wall by early morning upslope winds during the day transport vapour desorbing and mixing out of the regolith up crater walls where it can then be transported a few hundred metres into the atmosphere at convergence boundaries regolith atmosphere interaction limits the formation of surface ice by reducing water vapour abundances in the lower atmosphere though in some seasons ice can still form in the early morning on eastern crater walls subsurface ice amounts are small in all seasons with ice only existing in the upper few millimetres of regolith during the night the results at gale crater are representative of the behaviour at other craters in the mesoscale domain

absorption and scattering properties of the martian dust in the solar wavelengths a new wavelength dependent model of the single scattering properties of the martian dust is presented the model encompasses the solar wavelengths 0 3 to 4 3 m at 0 02 m resolution and does not assume a particular mineralogical composition of the particles we use the particle size distribution shape and single scattering properties at viking lander wavelengths presented by pollack et al 1995 we expand the wavelength range of the aerosol model by assuming that the atmospheric dust complex index of refraction is the same as that of dust particles in the bright surface geologic units the new wavelength dependent model is compared to observations taken by the viking orbiter infrared thermal mapper solar channel instrument during two dust storms the model accurately matches afternoon observations and some morning observations some of the early morning observations are much brighter than the model results the increased reflectance can be ascribed to the formation of a water ice shell around the dust particles thus creating the water ice clouds which colburn et al 1989 among others have predicted

results from the mars global surveyor thermal emission spectrometer the thermal emission spectrometer spectra of low albedo surface materials suggests that a four to one mixture of pyroxene to plagioclase together with about a 35 percent dust component provides the best fit to the spectrum qualitative upper limits can be placed on the concentration of carbonates 10 percent olivine 10 percent clay minerals 20 percent and quartz 5 percent in the limited regions observed limb observations in the northern hemisphere reveal low lying dust hazes and detached water ice clouds at altitudes up to 55 kilometers at an aerocentric longitude of 224 degrees a major dust storm developed in the noachis terra region the south polar cap retreat was similar to that observed by viking

chromaticity of the martian sky as observed by the mars exploration rover pancam instruments 1 we have derived quantitative color estimates of the martian sky from data acquired by the panoramic cameras pancams on the mars exploration rovers spirit and opportunity we calculate the perceptual color of the sky directly from the absolute radiometric calibration of the cameras following similar approaches to those used in previous studies with viking lander and mars pathfinder data we further use these measurements to study changes in sky color throughout the mer missions and to compare these to changes in atmospheric opacity determined from direct solar imaging by the pancams we have derived a functional relationship between sky color and optical depth and discuss its possible uses and limitations finally we simulate changes in sky color as suspended dust is removed and present visual representations of these based on modeling results past studies and observed mer sky brightnesses the color of the martian sky as opacity decreases from 1 0 to 0 0 is estimated to change from dark yellowish brown at high opacity to bluish black or black if dust free

spectral imaging of martian water ice clouds and their diurnal behavior during the 1999 aphelion season ls 130 abstract we report high spectral resolution 800 2300 near infrared mapping observations of mars at ls 130 april 1999 which were obtained by drift scanning the cryogenic long slit spectrometer at the kpno 2 2 m telescope across the disk data were reformatted into calibrated spectral image cubes x y spanning 2 19 to 4 12 m which distinguish atmospheric co2 features solar lines and surface and aerosol features maps of relative band depth between 3 0 and 3 5 m trace water ice clouds and show the diurnal evolution of features in the persistent northern summer aphelion cloud belt which was mapped contemporaneously but at fixed local time by the mars global surveyor thermal emission spectrometer mgs tes cloud optical depth particle sizes and ice aerosol content were estimated using a two stream single layer scattering model with mie coefficients derived from recently published ice optical constants followed by a linear spectral deconvolution process a comparison of data and model spectra shows evaporating nighttime clouds in the morning followed by afternoon growth of a prominent orographic cloud feature on the west flank of elysium mons cloud optical depth at 3 2 m evolved to 0 28 0 13 and ice aerosol column abundance to 0 9 0 3 pr m in the afternoon column abundances as large as 0 17 pr m were retrieved in nonorographic clouds within the aphelion cloud band around midday these clouds exhibit a modest decline in optical depth during the afternoon results show that ice particle radii from 4 m exist in both cloud types however large particles dominate the spectra consistent with recent mgs tes emission phase function measurements of aphelion cloud aerosol properties

mars aerosol studies with the mgs tes emission phase function observations optical depths particle sizes and ice cloud types versus latitude and solar longitude 1 emission phase function epf observations taken in 1999 2001 by mars global surveyor thermal emission spectrometer mgs tes support the broadest study of martian aerosol properties to date tes solar band and infrared ir spectral epf sequences are analyzed to obtain first time seasonal latitudinal distributions of visible optical depths particle sizes and single scattering phase functions this combined angular and wavelength coverage enables identification of two distinct ice cloud types over 45 s 45 n type 1 ice clouds exhibit small particle sizes reff 1 2 m and a distinctive backscattering increase they are most prevalent in the southern hemisphere during aphelion but also appear more widely distributed in season and latitude as topographic and high altitude 20 km ice hazes type 2 ice clouds exhibit larger particle sizes reff 3 4 m a distinct side scattering minimum at 90 100 phase angles characteristic of a change in particle shape relative to the type 1 and appear most prominently in the northern subtropical aphelion cloud belt the majority of retrieved dust visible to ir optical depth ratios are indicative of reff 1 5 0 1 m consistent with pathfinder and viking mariner 9 reanalyses however increased ratios 2 7 versus 1 7 appear frequently in the northern hemisphere over ls 50 200 indicating substantially smaller dust particles sizes reff 1 0 0 2 m at this time in addition larger reff 1 8 2 5 m dust particles were observed locally in the southern hemisphere during the peak of the 2001 global dust storm detailed spectral modeling of the tes visible band pass indicates agreement of epf derived dust single scattering albedos 0 92 0 94 with the spectrally resolved results from pathfinder observations

mars atmospheric opacity effects observed in the northern hemisphere by viking orbiter imaging observations of changing mars contrasts by viking orbiter television cameras have provided a description of changing atmospheric opacity in the southern hemisphere paper 1 this report extends those measurements into the northern hemisphere over a greater time period and provides a detailed description of photometric changes at the lander sites as seen from orbit reflectivity changes compared with optical depth increases produced by four dust storms indicate mean particle scattering changes with storm evolution as well as substantial opacity in the northern hemisphere for the duration of nearly a martian year

mars south polar hood as observed by the mars climate sounder 1 we have used observations from the mars climate sounder to investigate south polar hood water ice clouds at 12 m including the first systematic examination of the vertical 5 km resolution and nighttime structure we find that the structure and evolution of the polar hood is controlled more strongly by atmospheric temperature variations than by intrinsic fluctuations in water vapor abundance the clouds form as a belt during ls 10 70 phase 1 and ls 100 200 phase 2 during phase 1 the cloud belt extends over a wide latitude range between 30 s and 75 s with a visible column optical depth between 0 075 and 0 15 the cloud belt then evaporates as temperatures warm during phase 2 the cloud belt reappears due to an increase in water vapor as a partial band of low opacity clouds south of the tharsis region and eventually becomes continuous in longitude with a visible column opacity between 0 125 and 0 25 as the southern spring equinox approaches the cloud belt shifts southward following the seasonal cap edge from ls 140 to ls 200 the daytime belt lies about 15 farther south than the nighttime belt due to tidally driven diurnal temperature differences the vertical structure of the cloud belt is consistent within and between the two seasonal phases and is characterized by a thick lower cloud deck and an upper layer whose altitude shifts between the nighttime and daytime because of thermal tidal control of the condensation altitudes overall the southern polar hood is observed to rapidly form and dissipate as the temperature crosses the saturation point of water vapor

the distribution composition and particle properties of mars mesospheric aerosols an analysis of crism visible near ir limb spectra with context from near coincident mcs and marci observations the compact reconnaissance imaging spectral mapper crism onboard the mars reconnaissance orbiter mro obtains pole to pole observations i e full mro orbits of vertical profiles for visible near ir spectra 0 4 4 0 m which are ideally suited to identifying the composition and particle sizes of mars ice and dust aerosols over 50 100 km altitudes in the mars mesosphere within the coverage limitations of the crism limb data set a distinct compositional dichotomy is found in mars mesospheric ice aerosols co2 ice clouds appear during the aphelion period of mars orbit solar longitudes ls 0 160 at low latitudes 20s 10n over specific longitude regions meridiani valles marineris and at typical altitudes of 55 75 km apart from faint water ice hazes below 55 km mesospheric h2o ice clouds are primarily restricted to the perihelion orbital range ls 160 350 at northern and southern mid to low latitudes with less apparent longitudinal dependences mars mesospheric co2 clouds are presented in crism spectra with a surprisingly large range of particle sizes cross section weighted radii reff 0 3 to 2 2 m the smaller particle sizes reff 1 m appear concentrated near the spatial latitude and altitude boundaries of their global occurrences crism spectra of mesospheric co2 clouds also show evidence of iridescence indicating very narrow particle size distributions effective variance veff 0 03 and so very abrupt co2 cloud nucleation furthermore these clouds are sometimes accompanied by altitude coincident peaks in 1 27 m o2 dayglow which indicates very dry cold regions of formation mesospheric water ice clouds generally exhibit small particle sizes reff 0 1 0 3 m although larger particle sizes reff 0 4 0 7 m appear infrequently on average water ice cloud particle sizes decrease with altitude over 50 80 km in the perihelion mesosphere water ice mass appears similar in clouds over a large range of observed cloud particle sizes with particle number densities increasing to 10 cm 3 for reff 0 2 m near coincident mars climate sounder mcs temperature and aerosol profile measurements for a subset of crism mesospheric aerosol measurements indicate near saturation h2o and co2 conditions for ice clouds and distinct mesospheric temperature increases associated with mesospheric dust loading dayside 3 pm mesospheric co2 clouds with larger particle sizes reff 0 5 m scatter surface infrared emission in mcs limb infrared radiances as well as solar irradiance in the mcs solar band channel scattering of surface infrared emission is most strikingly presented in nighttime 3 am mcs observations at 55 60 km altitudes indicating extensive mesospheric nighttime co2 clouds with considerably larger particle sizes reff 7 m mesospheric co2 ice clouds present cirrus like waveforms over extensive latitude and longitude regions 10 10 as revealed in coincident mars color imager marci nadir imaging solar tides gravity waves and the large orbital variation of the extended thermal structure of the mars atmosphere influence all of these behaviors mesospheric dust aerosols appear infrequently over the non global planet encircling dust storm era of the crism limb data set 2009 2016 and exhibit smaller particle sizes reff 0 2 0 7 m relative to dust in the lower atmosphere one isolated case of an aphelion ls 96 mesospheric dust layer with large dust particle sizes reff 2 m over syria planum may reflect high altitude non local transport of dust over elevated regions

a global mars dust composition refined by the alpha particle x ray spectrometer in gale crater modern martian dust is similar in composition to the global soil unit and bulk basaltic mars crust but it is enriched in s and cl the alpha particle x ray spectrometer apxs on the mars science laboratory curiosity rover analyzed air fall dust on the science observation tray o tray in gale crater to determine dust oxide compositions the o tray dust has the highest concentrations of so3 and cl measured in mars dust so3 8 3 cl 1 1 wt the molar s cl in the dust 3 35 0 34 is consistent with previous studies of martian dust and soils s cl 3 7 0 7 fe is also elevated 25 over average mars soils and the bulk crust these enrichments link air fall dust with the s cl and fe rich x ray amorphous component of gale crater soil dust and soil have the same s cl constraining the surface concentrations of s and cl on a global scale

dust haze in valles marineris observed by hrsc and omega on board mars express 1 we present analysis of a bright haze observed inside valles marineris which formed in mid northern spring the data were collected by the high resolution stereo camera hrsc and the imaging spectrometer observatoire pour la mineralogie l eau les glaces et l activite omega aboard mars express this study provides a case example of the power of simultaneous multiple emission angle and hyperspectral imaging for study of aerosols and clouds in the martian atmosphere the haze appeared thinner after three days and disappeared in nine days it was limited to a 2 km layer at the bottom of the canyon the color was redder than the underlying surface the analysis of the omega spectra indicates that this haze was composed of dust particles the dust layer appeared brighter with the hrsc stereo channels than the nadir channel due to longer scattering paths we have estimated the optical depth of the haze by fitting both hrsc and omega data with radiative transfer calculations the retrieval of the optical depth is very sensitive to the aerosol scattering model used and the reflectance of the surface applying an aerosol scattering model derived from sky surveys at a constant elevation by the imager for mars pathfinder the optical depth of the haze is estimated from hrsc data to be within 1 7 to 2 3 at the wavelength of 0 675 m the wavelength dependence is obtained from omega spectrum it increases to 2 2 2 6 at 1 35 m and moderately decreases to 1 2 1 8 at 2 4 m

mro crism retrieval of surface lambert albedos for multispectral mapping of mars with disort based radiative transfer modeling phase 1 using historical climatology for temperatures aerosol optical depths and atmospheric pressures we discuss the disort based radiative transfer pipeline ldquocrism lambertalbrdquo for atmospheric and thermal correction of mro crism data acquired in multispectral mapping mode 200 m pixel 72 spectral channels currently in this phase one version of the system we use aerosol optical depths surface temperatures and lower atmospheric temperatures all from climatology derived from mars global surveyor thermal emission spectrometer mgs tes data and from surface altimetry derived from mgs mars orbiter laser altimeter mola the disort based model takes the dust and ice aerosol optical depths scaled to the crism wavelength range the surface pressures computed from mola altimetry mgs tes lower atmospheric thermometry and viking based pressure climatology the surface temperatures the reconstructed instrumental photometric angles and the measured i f spectrum as inputs and then a lambertian albedo spectrum is computed as the output the lambertian albedo spectrum is valuable geologically because it allows the mineralogical composition to be estimated here i f is defined as the ratio of the radiance measured by crism to the solar irradiance at mars divided by pi if there was no martian atmosphere i f divided by the cosine of the incidence angle would be equal to the lambert albedo for a lambertian surface after discussing the capabilities and limitations of the pipeline software system we demonstrate its application on several multispectral data cubes particularly the outer reaches of the northern ice cap of mars the tyrrhena terra area that is northeast of the hellas basin and an area near the landing site for the phoenix mission in the northern plains for the icy spectra near the northern polar cap aerosols need to be included in order to properly correct for the co2 absorption in the h2o ice bands at wavelengths near 2 0 mum in future phases of software development we intend to use crism data directly in order to retrieve the spatiotemporal maps of aerosol optical depths surface pressure and surface temperature this will allow a second level of refinement in the atmospheric and thermal correction of crism multispectral data

observations of the south seasonal cap of mars during recession in 2004 2006 by the omega visible near infrared imaging spectrometer on board mars express 1 the omega visible near infrared imaging spectrometer on board mars express has observed the southern seasonal cap in late 2004 and 2005 and then in the summer of 2006 these observations extended from the period of maximum extension close to the southern winter solstice to the end of the recession at ls 325 the spectral range and spectral resolution of omega make it possible to monitor the extent and effective grain size of co2 ice and h2o ice on the ground the level of contamination of co2 ice and h2o ice by dust and the column density of m sized ice grains in the atmosphere the co2 seasonal cap is very clean and clear in early southern winter contamination by h2o ice spreads eastward from the hellas basin until the southern spring equinox during southern spring and summer there is a very complex evolution in terms of effective grain size of co2 ice and contamination by dust or h2o ice h2o ice does not play a significant role close to the southern summer solstice contamination of co2 ice by h2o ice is only observed close to the end of the recession as well as the few h2o ice patches already reported by bibring et al 2004a these observations have been compared to the results of a general circulation model with good qualitative agreement on the distribution of h2o ice on the surface and in the atmosphere resolving the remaining discrepancies will improve our understanding of the water cycle on mars

seasonal slumps in juventae chasma mars dark topographic slumps several meters wide tens of meters in length and up to a meter in depth are observed on the slopes of juventae chasma jc valles marineris vm mars these slumps usually originate near the terminal points of recurring slope lineae rsl near their initiation points the slumps have topographic depressions due to the removal of materials near their lowermost reaches new materials are deposited in lobes over the course of three mars years ten active slumps have been observed in jc all of which formed in or near the same season areocentric longitude ls 0 120 mars color imager marci observations show low altitude atmospheric obscurations confined within the topography of the vm and jc in the seasons when the slumps form in one instance data from the compact reconnaissance imaging spectrometer for mars crism and marci show evidence of h2o ice in the atmospheric obscuration likely due to the formation of a low level afternoon cloud above a dust storm or mixing of condensate clouds with a diffuse dust cloud the presence of atmospheric obscurations with h2o ice near times when the slumps form is intriguing but no direct evidence currently exists to support that they aid in slump formation further monitoring of this site will help establish if rsl and or atmospheric events play a role in the creation of contemporary slumps

surface reflectance of mars observed by crism mro 1 multi angle approach for retrieval of surface reflectance from crism observations mars reco 1 this article addresses the correction for aerosol effects in near simultaneous multi angle observations acquired by the compact reconnaissance imaging spectrometer for mars crism aboard the mars reconnaissance orbiter in the targeted mode crism senses the surface of mars using 11 viewing angles which allow it to provide unique information on the scattering properties of surface materials in order to retrieve these data however appropriate strategies must be used to compensate the signal sensed by crism for aerosol contribution this correction is particularly challenging as the photometric curve of these suspended particles is often correlated with the also anisotropic photometric curve of materials at the surface this article puts forward an innovative radiative transfer based method named multi angle approach for retrieval of surface reflectance from crism observations mars reco the proposed method retrieves photometric curves of surface materials in reflectance units after removing aerosol contribution mars reco represents a substantial improvement regarding previous techniques as it takes into consideration the anisotropy of the surface thus providing more realistic surface products furthermore mars reco is fast and provides error bars on the retrieved surface reflectance the validity and accuracy of mars reco is explored in a sensitivity analysis based on realistic synthetic data according to experiments mars reco provides accurate results up to 10 reflectance error under favorable acquisition conditions in the companion article photometric properties of martian materials are retrieved using mars reco and validated using in situ measurements acquired during the mars exploration rovers mission

martian water ice clouds a view from mars global surveyor thermal emission spectrometer 1 we have used the mars global surveyor thermal emission spectrometer mgs tes data to map water ice clouds in the martian atmosphere in the latitude range 60 to 60 over a period of three martian years we have used the same method we have previously used on viking infrared thermal mapper data in order to allow direct comparison of the cloud behavior in the viking and mgs eras and confirmed the validity of this method by comparing it to mgs tes standard retrievals we note that the large scale behavior of water ice clouds is remarkably consistent both between the viking and the mgs eras as well as between years observed by mgs we also compare our results to water ice absorption only optical depths derived from tes data and show that correlation is best for type 2 water ice clouds

the spatial and seasonal distribution of martian clouds and some meteorological implications the spatial and seasonal distributions of martian atmospheric clouds organized according to simple morphologic criteria exhibit distinct patterns when interpreted self consistently using analogies to terrestrial cloud forms and martian temperature wind direction and water vapor measurements patterns of cloud occurrence provide some loose constraints on global scale near surface wind speed static stability and humidity we have examined all mariner 9 and viking orbiter images for this study we concentrate primarily on the larger viking data set whenever observations are possible relatively high near surface winds appear to follow the seasonal cap edges during early fall late winter and spring moderate to high winds are also inferred in mid latitudes for mid southern winter and in low latitudes mainly in the steeply sloping areas of tharsis near the solstices at other times lower winds are suspected hemispheric asymmetries are traced to differences in atmospheric hydration state and to global dust storm related effects on the atmospheric temperature structure and the north polar cap recession schedule cloud occurrence data suggest that the near surface daytime static stability is low in the northern hemisphere during summer and at low latitudes during mid northern spring relatively high static stability is deduced near the winter poles and globally during the dust storm season in spite of low atmospheric temperatures the correspondingly low absolute humidity apparently precludes the formation of thick water ice clouds at high latitudes in mid to late autumn and winter in both hemispheres and in southern mid latitudes during early winter during northern spring and summer saturation conditions seem to be easily achieved at mid latitudes and condensate clouds are abundant the situation is complicated by atmospheric dust in southern spring and summer low latitudes generally appear to be farther from saturation than mid latitudes and clouds generally form more easily in the northern hemisphere than in the south during corresponding seasons

radio occultation measurements and mgcm simulations of kelvin waves on mars we have derived new results concerning thermal tides on mars from a combination of radio occultation measurements and numerical simulations by a mars general circulation model mgcm this investigation exploits a set of concurrent observations by mars express mex and mars global surveyor mgs in mid 2004 when the season on mars was midspring in the northern hemisphere the mex occultations sampled the atmosphere near the evening terminator at latitudes ranging from 54 n to 15 s the mgs occultations provided complementary coverage near the morning terminator at latitudes of 35 n and 71 s the geopotential field derived from these measurements contains distinctive modulation caused by solar asynchronous thermal tides through careful analysis of the combined observations we characterized two prominent wave modes obtaining direct solutions for some properties such as the amplitude and phase as well as constraints on others such as the period zonal wave number and meridional structure we supplemented these observations with mgcm simulations after evaluating the performance of the mgcm against the measurements we used the validated simulation to deduce the identity of the two tidal modes and to explore their behavior one mode is a semidiurnal kelvin wave with a zonal wave number of 2 sk2 while the other is a diurnal kelvin wave with a zonal wave number of 1 dk1 both modes are known to be close to resonance in the martian atmosphere our observations of the sk2 are more complete and less ambiguous than any previous measurement the well known dk1 is the dominant solar asynchronous tide in the martian atmosphere and our results confirm and extend previous observations by diverse instruments

seasonal h2o and co2 ice cycles at the mars phoenix landing site 1 prelanding crism and hirise observations 1 the condensation evolution and sublimation of seasonal water and carbon dioxide ices were characterized at the mars phoenix landing site from martian northern midsummer to midspring ls 142 ls 60 for the year prior to the phoenix landing on 25 may 2008 ice relative abundances and grain sizes were estimated using data from the compact reconnaissance imaging spectrometer for mars and high resolution imaging science experiment aboard mars reconnaissance orbiter and a nonlinear mixing model water ice first appeared at the phoenix landing site during the afternoon in late summer ls 167 as an optically thin layer on top of soil co2 ice appeared after the fall equinox by late winter ls 344 the site was covered by relatively pure co2 ice 30 cm thick with a small amount of 100 m diameter water ice and soil as spring progressed co2 ice grain sizes gradually decreased a change interpreted to result from granulation during sublimation losses the combined effect of co2 sublimation and decreasing h2o ice grain sizes allowed h2o ice to dominate spectra during the spring and significantly brightened the surface co2 ice disappeared by early spring ls 34 and h2o ice by midspring ls 59 spring defrosting was not uniform and occurred more rapidly over the centers of polygons and geomorphic units with relatively higher thermal inertia values

coordinated analyses of orbital and spirit rover data to characterize surface materials on the cratered plains of gusev crater mars 1 comparison of the mars exploration rover spirit s pancam 0 4 to 1 0 m and mars express observatoire pour la mineralogie l eau les glaces et l activite omega 0 4 to 2 5 m spectral reflectance data over spirit s traverses shows that gusev cratered plains are dominated by nanophase ferric oxide rich dust covering weakly altered basaltic sands this interpretation is also consistent with both observations from omega data covering plains beyond the traverse region and interpretations of data from the other payload instruments on the spirit rover omega observations of relatively low albedo regions where dust has presumably been stripped by dust devils show negative spectral reflectance slopes from 1 5 to 2 5 m and moderately masked spectral features which are indicative of olivine or pyroxene high albedo regions north and south of the spirit landing site have flat spectral reflectance slopes and few spectral features although all spectra have a nanophase ferric oxide absorption edge between 0 4 and 0 75 m comparison of themis derived thermal inertia values with omega derived spectral parameters shows that although the dust cover can be optically thick 0 4 to 2 5 m wavelength region in some areas it is not thick enough 1 cm to mask the thermal inertia of the underlying substrate for areas included in this study

mars w cloud evidence of nighttime ice depositions 1 water clouds on mars their current and past connections with other forms of water along with surface features that suggest the early existence of flowing water continue to be intriguing aspects of the red planet discrete afternoon mountain clouds were one of the earliest atmospheric features to be observed on mars their exclusive formation near the high mountains led to the common belief that air lifting associated with local circulation induced by the mountains underlies their formation we demonstrate that an additional local source of water vapor is needed for the formation of opaque discrete afternoon clouds on the mountains of mars including the so called w formation we suggest that the possible deposition of ice from the thick aphelion cloud belt during the night is capable of providing this additional source this direct cloud water deposition on mountains on mars bears many similarities with the well known interception of water by mountains frequently immersed in fogs on earth

thermal constraints on the emplacement rate of a large intrusive complex the manaslu leucogranite nepal himalaya the emplacement of the manaslu leucogranite body nepal himalaya has been modelled as the accretion of successive sills the leucogranite is characterized by isotopic heterogeneities suggesting limited magma convection and by a thin 100 m upper thermal aureole these characteristics were used to constrain the maximum magma emplacement rate models were tested with sills injected regularly over the whole duration of emplacement and with two emplacement sequences separated by a repose period additionally the hypothesis of a tectonic top contact with unroofing limiting heat transfer during magma emplacement was evaluated in this latter case the upper limit for the emplacement rate was estimated at 3 4 mm year or 1 5 myr for 5 km of granite geological and thermobarometric data however argue against a major role of fault activity in magma cooling during the leucogranite emplacement the best model in agreement with available geochronological data suggests an emplacement rate of 1 mm year for a relatively shallow level of emplacement granite top at 10 km uninterrupted by a long repose period the thermal aureole temperature and thickness and the isotopic heterogeneities within the leucogranite can be explained by the accretion of 20 60 m thick sills intruded every 20 000 60 000 years over a period of 5 myr under such conditions the thermal effects of granite intrusion on the underlying rocks appear limited and cannot be invoked as a cause for the formation of migmatites

new insights into martian dust distribution and water ice cloud microphysics 1 in this paper we use a direct method which combines microphysics and photometric simulations of the martian atmosphere this approach allows us to reproduce vertical profiles of the light scattered by the haze at the limb of mars subsequent results are compared to a multiple color image provided by the viking orbiter camera the free parameters of our study are related to vertical transport and dust size distribution a sensitivity study has been conducted encompassing a relevant range of parameters in order to obtain the most satisfying multispectral modeled profile with respect to the one inferred from data except for an unlikely distribution of submicron particles reff 0 2 m no consistent fit can be obtained this implies that size distributions of dust suggested by previous studies are not in agreement with the present analysis this apparent discrepancy can be resolved by adding a separate peak of submicron particles to the size distribution previously extracted from viking lander images only in that case can spectral and vertical structures of haze be successfully matched while a bimodal distribution would change the current picture of martian dust such distribution is a common representation of soil derived aerosol size function in earth deserts we also attempted to derive information from the cloud shown in the viking limb image our estimates suggest that cloud particle effective radius is around 1 2 1 8 m while the cloud visible opacity is 0 02

atmospheric imaging results from the mars exploration rovers spirit and opportunity a visible atmospheric optical depth of 0 9 was measured by the spirit rover at gusev crater and by the opportunity rover at meridiani planum optical depth decreased by about 0 6 to 0 7 per sol through both 90 sol primary missions the vertical distribution of atmospheric dust at gusev crater was consistent with uniform mixing with a measured scale height of 11 56 0 62 kilometers the dust s cross section weighted mean radius was 1 47 0 21 micrometers mm at gusev and 1 52 0 18 mm at meridiani comparison of visible optical depths with 9 mm optical depths shows a visible to infrared optical depth ratio of 2 0 0 2 for comparison with previous monitoring of infrared optical depths

numerical simulations of the formation and evolution of water ice clouds in the martian atmosphere abstract a one dimensional aerosol model was used to study the microphysics of water ice cloud formation and evolution on mars the time dependent nature of the model permits realistic simulations of diurnal cycles the results are sensitive to the choice of the temperature profile the eddy diffusion coefficient the efficiency of nucleation of the condensation nuclei and the condensation history of the cloud simulations having a large diurnal temperature variation yield condensed water total optical depths of a few tenths in good agreement with the viking lander opacity data ice clouds are typically simulated at 25 30 km altitude with mean particle radii of 0 2 5 0 m we also obtain good agreement with the particle extinction observed in the viking orbiter limb data for a temperature profile constrained by the infrared thermal mapper data in order for repeated cloud formation to occur each day we need to include a vertical and or horizontal resupply of water and dust to the higher altitudes where the condensation occurs because of loss by sedimentation this can take the form of a micrometeoritic influx of particles at the top of the atmosphere or a latitudinal transport of material the efficiency of the nucleation process is determined by the contact angle changing this angle from 0 945 to 0 999 can have the effect of doubling the total ice optical depth of the cloud the time evolution of the cloud is important for comparison with the observations if a diurnal temperature change exists under these conditions the optical thickness of the cloud is dependent on the number of condensation cycles having previously occurred and the time of day this time dependence and the need for a resupply of material into the condensing region show that the cloud formation process cannot be considered a steady state phenomenon we have shown that the eddy diffusion coefficient and particle radii cannot be constrained by the available data even if a detailed model is used for the interpretation of the observations in our simulations there is an extensive vertical redistribution of water by clouds however water is only lost to the surface when the temperature is at the frost point near the ground precipitation across subsaturated layers is not significant

the vertical distribution of martian aerosol particle size using approximately 410 limb viewing observations from the compact reconnaissance imaging spectrometer for mars crism we retrieve the vertical distribution of martian dust and water ice aerosol particle sizes we find that dust particles have an effective radius of 1 0 m over much of the atmospheric column below 40 km throughout the martian year this includes the detached tropical dust layers detected in previous studies little to no variation with height is seen in dust particle size water ice clouds within the aphelion cloud belt exhibit a strong sorting of particle size with height however and the effective radii range from 3 m below 20 km to near 1 0 m at 40 km altitude conversely water ice clouds in the seasonal polar hoods show a near uniform particle size with an effective radius of approximately 1 5 m throughout the atmospheric column

candidates source regions of martian meteorites as identified by omega mex abstract the objective of this study is to identify and map spectral analogues of some key martian meteorites basaltic shergottites los angeles shergotty que 94201 lherzolitic shergottite alh a77005 nakhla chassigny and the orthopyroxenite alh 84001 in order to localize terrain candidates for their source regions we develop a best fit procedure to reproduce the near infrared nir spectral properties of the martian surface as seen by the hyperspectral imaging spectrometer omega mex from the nir spectra of the martian meteorites the fitting process is tested and validated and root mean square rms global maps for each meteorite are obtained it is found that basaltic shergottites have nir spectral properties the most representative of the martian surface with the best spectral analogues found in early hesperian volcanic provinces sites with spectral properties similar to those of alh a77005 are scarce they are mainly localized in olivine bearing regions such as nili fossae and small noachian early hesperian terrains the only plausible source region candidate for chassigny is the nili patera caldera dated to 1 6 ga widespread spectral analogues for the alh 84001 meteorite are found northeast of syrtis major and northwest of the hellas basin while this distribution is in agreement with the low calcium pyroxene rich composition and old age 4 1 ga of this meteorite the modal mineralogy of these candidates is not consistent with that of this meteorite no convincing spectral analogue is found for the amazonian aged nakhla meteorite suggesting that its olivine high calcium pyroxene rich composition could be representative of the amazonian terrains buried under dust finally some young rayed craters are proposed as possible candidates for source craters of the studied martian meteorites

geomorphologic and mineralogic characterization of the northern plains of mars at the phoenix mission candidate landing sites 1 a suite of remote sensing data is used to evaluate both geomorphology and mineralogy of the candidate landing sites for the 2007 phoenix mission three candidate landing site boxes are situated in the northern plains of mars on the distal flank of alba patera in the region from 67 n to 72 n and from 230 e to 260 e geomorphology is mapped at subkilometer spatial scales using thermal emission imaging system themis visible and mars orbiter laser altimeter mola topographic data supplemented by images from the high resolution imaging science experiment hirise and context imager ctx mineralogy and spectral properties are examined using compact reconnaissance imaging spectrometer for mars crism visible and near infrared multispectral mapping and targeted hyperspectral data at 200 and 20 m pixel respectively geomorphic mapping supports the idea that terrains along the boundary between the amazonian scandia region and vastitas borealis marginal geologic units have undergone extensive modification intercrater plains are disrupted to form mesas and interlocking blocks while irregular depressions and knobby terrain are consistent with erosion subsidence and local deposition despite the varied morphology the present day surface is nearly homogeneous with spectral signatures dominated by nanophase iron oxides and basaltic sand and rocks similar to that of the gusev crater plains at the mars exploration rover mer landing site the compilation of geomorphic and spectral information for the candidate phoenix landing sites provides a framework for the mission s in situ observations to be extrapolated to the northern plains as a whole

cold jets in the martian polar caps 1 mars seasonal polar caps display dark ice local darker spots aligned elongate patches and radially dendritic forms that reverse albedo contrast the unexpected variety and sequence of these features are explained on the basis of processes involving co2 dust sand and h2o these processes are largely related to the atmosphere being near its saturation temperature and they have few terrestrial analogies in the simplest case the 1 m thick seasonal cap initially dusty cleans itself and becomes translucent after sunrise and is impermeable over extensive regions except for local vents the slab ice sublimates at the base and is levitated on high pressure gas causing humidity exchange with deeper layers subslab gas converging toward the vents erodes channels in the soil and ejects this material in high velocity jets recent spectral observations indicate great variety in the details

martian phase function modeling the visible to near infrared surface photometric function using hst wfpc2 data abstract images of mars in the visible to near infrared acquired from 1996 to 2005 using the hubble space telescope wfpc2 have been used to model the martian surface photometric function at 502 673 953 and 1042 nm these data range in spatial resolution from 12 to 70 km pixel at the sub earth point and in phase angle coverage from 0 34 to 40 5 the wfpc2 images have been calibrated to radiance factor or i f and projected to a cylindrical map for coregistration and comparison to similarly mapped spacecraft data sets of albedo topography thermal inertia composition and geology we modeled the observed i f as a function of phase angle using minnaert lambert lunar lambert and hapke photometric functions for numerous regions of interest binned into albedo units defined by viking and tes albedo maps and thermal inertia units defined by tes thermal inertia maps visibly opaque water ice clouds and data acquired under high dust opacity conditions were excluded from the analysis our modeling suggests that under average to low atmospheric dust opacity conditions and over this range of phase angles the photometric properties of the martian surface at 502 673 953 and 1042 nm are best modeled by lunar lambert functions with parameters derived for three surface units defined by low moderate and high tes bolometric albedos

thermal emission imaging system themis infrared observations of atmospheric dust and water ice cloud optical depth 1 the mars odyssey spacecraft entered into martian orbit in october 2001 and after successful aerobraking began mapping in february 2002 thermal infrared images taken by the thermal emission imaging system themis on board the odyssey spacecraft allow for the quantitative retrieval of atmospheric dust and water ice aerosol optical depth data collected so far cover late northern winter spring and summer ls 330 160 during this period themis observed the decay of a regional dust storm a number of local dust storms along the edge of the retreating north polar cap and the growth of the low latitude aphelion water ice cloud belt data from themis complements the concurrent mars global surveyor thermal emission spectrometer tes data by sampling a later local time 1400 lt for tes versus 1600 1730 lt for themis and by observing at much higher spatial resolution comparison of water ice optical depth in the aphelion cloud belt from themis and tes shows a significantly higher optical depth in the late afternoon themis than in the early afternoon tes

light toned layered deposits in juventae chasma mars abstract we examine hypotheses for the formation of light toned layered deposits in juventae chasma using a combination of data from mars global surveyor s mars orbiter camera moc mars orbiter laser altimeter mola and thermal emission spectrometer tes as well as mars odyssey s thermal emission imaging system themis we divide juventae chasma into geomorphic units of i chasm wall rock ii heavily cratered hummocky terrain iii a mobile and largely crater free sand sheet on the chasm floor iv light toned layered outcrop llo material and v chaotic terrain using surface temperatures derived from themis infrared data and slopes from mola we derive maps of thermal inertia which are consistent with the geomorphic units that we identify llo thermal inertias range from 400 to 850 j m 2 k 1 s 1 2 light toned layered outcrops are distributed over a remarkably wide elevation range 5 8 km from the chasm floor to the adjacent plateau surface geomorphic features the absence of small craters and high thermal inertia show that the llos are composed of sedimentary rock that is eroding relatively rapidly in the present epoch we also present evidence for exhumation of llo material from the west wall of the chasm within chaotic and hummocky terrains and within a small depression in the adjacent plateau the data imply that at least some of the llo material was deposited long before the adjacent hesperian plateau basalts and that juventae chasma underwent and may still be undergoing enlargement along its west wall due to wall rock collapse chaotic terrain evolution and exposure and removal of llo material the new data allow us to reassess possible origins of the llos gypsum one of the minerals reported elsewhere as found in juventae chasma llo material forms only at low temperatures 60 c and thus excludes a volcanic origin instead the data are consistent with either multiple occurrences of lacustrine or airfall deposition over an extended period of time prior to emplacement of hesperian lava flows on the plateau above the chasm

evidence for enhanced hydration on the northern flank of olympus mons mars in this paper we report about a small region on the northern scarp of olympus mons showing an increase of the 3 m hydration band in the omega spectra together with low superficial temperatures although water ice clouds can occurs on the flank of big martian volcanoes radiative transfer modeling indicates that atmospheric water ice alone cannot justify the shape of the observed band a fit of the 1 9 3 m absorption features is obtained by hypothesizing that the study region consists of a mixture of dust and water ice covered by an optically thin 0 08 at 3 m layer of dust thermal modeling also suggests that water ice in this region may be stable during most of the martian year due to the saturation of the atmosphere if water ice is responsible for the observed spectral behavior it might consist of a number of ice or snow patches possibly deposited in small depressions

opacity of the martian atmosphere from the mars orbiter laser altimeter mola observations in this paper we present an analysis of the mars orbiter laser altimeter mola reflectivity measurements from the mars global surveyor mgs spacecraft during period of solar longitudes ls 198 212 reflectivity can be interpreted as a product of the surface geometrical albedo and the two way atmospheric transmission relative surface albedos were obtained from the red filter of viking color mars digital mosaics mdim to derive opacities at the mola wavelength 1 064 m opacity measurements are interpreted in terms of atmospheric aerosol loading in the canyons we also observed sudden increase of opacity in the northern regions 65 n which we interpret as condensing ice clouds

constraints on unroofing rates in the high himalaya eastern nepal thermobarometric data for samples across the main central thrust zone in eastern nepal show an inversion in temperature but not in pressure these data have been interpreted to represent a portion of the paleogeotherm at the time of main central thrust deformation a 40ar 39ar age on hornblende closure temperature tc 500 50 c constrains the timing of this deformation to be 21 0 2 ma the 40ar 39ar ages of other minerals muscovite tc 350 c age t 12 0 0 2 ma k feldspar tc 220 c t 8 0 0 2 ma from the same location further constrain the cooling history of this region together the geochronologic and thermobarometric data yield an average unroofing rate of 1 2 0 6 mm yr for the high himalaya of eastern nepal simple thermal models show that these geochronologic and thermobarometric data are consistent with a wide range of different initial geotherms applied boundary conditions and magnitude of radiogenic heat production the variation through time of the unroofing rates can only be poorly constrained however the unroofing histories were found to be largely insensitive to the details of the assumed initial geotherm fairly sensitive to the magnitude of radiogenic heat production and extremely sensitive to the nature of the boundary conditions applied below the fault zone this study underscores the difficulty in constraining uplift histories on the basis of cooling rates even when thermobarometric data are available to supplement geochronologic constraints on the cooling history of the region

the role of the wind transported dust in slope streaks activity evidence from the hrsc data abstract slope streaks are gravity driven albedo features observed on martian slopes since the viking missions the debated mechanism of formation could involve alternatively dry granular flow or wet mass wasting a systematic mapping of slope streaks from the high resolution stereo camera is presented in this paper two regions known for their slope streaks activity have been studied the first one is located close to cerberus lava flow and the second one is inside the olympus mons aureole the statistics of slope streaks shapes measured from orthorectified images confirm previous results from mars orbiter camera surveys preferential orientations of slope streaks are reported slope streaks occur preferentially on west facing slopes at latitudes lower than 30 n for olympus and on south west facing slopes for cerberus wind directions derived from a general circulation model during the dusty season correlate with these orientations furthermore west facing slopes at olympus have a thicker dust cover these observations indicate that slope streaks are dust avalanches controlled by the preferential accumulation of dust in the downstream side of the wind flow the paucity of slope streaks at high latitudes and their preferential orientation on south facing slopes have been presented as an evidence for a potential role of h 2 o phase transition in triggering or flow the potential role of h 2 o cannot be ruled out from our observations but the dust avalanche model together with the atmospheric circulation could potentially explain all observations the role of h 2 o might be limited to a stabilizing effect of dust deposits on northward facing slopes at intermediate latitudes 30 n 33 n and on all slopes further north

tes spectroscopic identification of a region of persistent water ice clouds on the flanks of arsia mons volcano mars 1 as part of a search for small scale spectrally anomalous regions within the mars global surveyor thermal emission spectrometer mgs tes data set we have identified a region 100 km in diameter on the southwest flanks of the volcano arsia mons that exhibits remarkable and persistent water ice cloud cover high opacity clouds by martian standards occur in this region in all of the 400 tes spectra covering this area regardless of season as well as in all of the mgs wide angle camera images of this same region we have also found evidence for similar persistent cloudiness at other local solar times of day in this region based on hubble space telescope uv imaging modeling of the tes spectra identifies the clouds as water ice and reveals average ir cloud optical depths near 0 5 and typical cloud particle sizes of 3 m the presence of persistent cloudiness in this area even during the relatively warm and cloud free season near perihelion may indicate unique local circulation processes perhaps related to orographic effects or the interaction between the global circulation and the tharsis region in general our analysis also demonstrates that through careful modeling it is possible to extend the search for unique spectral features in the tes data far into the wings of the strong 15 m co2 band

the effects of accretion erosion and radiogenic heat on the metamorphic evolution of collisional orogens petrological and thermochronological data provide our best record of the thermal structure of deeply eroded orogens and in principle might be used to relate the metamorphic structure of an orogen to its deformational history in this paper we present a two dimensional thermal model of collisional orogens that includes the processes of accretion and erosion to examine the p t evolution of rocks advected through the orogen calculated metamorphic patterns are similar to those observed in the field metamor phic temperatures depths and ages generally increase with distance from the toe of the orogen p t paths are anti clockwise with rocks heating during burial and early stages of unroofing followed by cooling during late stage unroofing the results indicate that peak metamorphic temperatures within the core of a collisional orogen and the distance from the toe of an orogen to the metamorphic core can be related to the relative rates of accretion erosion and plate convergence model orogens displaying high metamorphic temperatures 600 c are associated with low ratios of accretion rate to plate convergence velocity and with high heat flow through the foreland model orogens with metamorphic cores far from the toe of the orogen are associated with high ratios of accretion rate to erosion rate calculated metamor phic gradients mimic steady state geotherms and inverted thermal gradients can be preserved in the metamorphic record suggesting reconsideration of the concept that the metamorphic record does not closely reflect geothermal gradients within an orogen

no signature of clear co2 ice from the cryptic regions in mars south seasonal polar cap the seasonal polar ice caps of mars are composed mainly of co2 ice a region of low 30 albedo has been observed within the south seasonal cap during early to mid spring the low temperature of this cryptic region has been attributed to a clear slab of nearly pure co2 ice with the low albedo resulting from absorption by the underlying surface here we report near infrared imaging spectroscopy of the south seasonal cap the deep and broad co2 absorption bands that are expected in the near infrared with a thick transparent slab of co2 ice are not observed models of the observed spectra indicate that the low albedo results from extensive dust contamination close to the surface of a co2 ice layer which could be linked to atmospheric circulation patterns the strength of the co2 absorption increases after mid spring so part of the dust is either carried away or buried more deeply in the ice layer during the co2 ice sublimation process

vertical distribution of dust and water ice aerosols from crism limb geometry observations 1 near infrared spectra taken in a limb viewing geometry by the compact reconnaissance imaging spectrometer for mars crism on board the mars reconnaissance orbiter provide a useful tool for probing atmospheric structure specifically the observed radiance as a function of wavelength and height above the limb enables the vertical distribution of both dust and water ice aerosols to be retrieved more than a dozen sets of crism limb observations have been taken so far providing pole to pole cross sections spanning more than a full martian year radiative transfer modeling is used to model the observations taking into account multiple scattering from aerosols and the spherical geometry of the limb observations both dust and water ice vertical profiles often show a significant vertical structure for nearly all seasons and latitudes that is not consistent with the well mixed or conrath v assumptions that have often been used in the past for describing aerosol vertical profiles for retrieval and modeling purposes significant variations are seen in the retrieved vertical profiles of dust and water ice aerosol as a function of season dust typically extends to higher altitudes 40 50 km during the perihelion season than during the aphelion season 20 km and the hellas region consistently shows more dust mixed to higher altitudes than other locations detached water ice clouds are common and water ice aerosols are observed to cap the dust layer in all seasons

saltation under martian gravity and its influence on the global dust distribution abstract dust and sand motion are a common sight on mars understanding the interaction of atmosphere and martian soil is fundamental to describe the planet s weather climate and surface morphology we set up a wind tunnel to study the lift of a mixture between very fine sand and dust in a mars simulant soil the experiments were carried out under martian gravity in a parabolic flight the reduced gravity was provided by a centrifuge under external microgravity the onset of saltation was measured for a fluid threshold shear velocity of 0 82 0 04 m s this is considerably lower than found under earth gravity in addition to a reduction in weight this low threshold can be attributed to gravity dependent cohesive forces within the sand bed which drop by 2 3 under martian gravity the new threshold for saltation leads to a simulation of the annual dust cycle with a mars gcm that is in agreement with observations

the reflectivity of mars at 1064 nm derivation from mars orbiter laser altimeter data and application to climatology and meteorology abstract the mars orbiter laser altimeter mola on board mars global surveyor mgs made 10 8 measurements of the reflectivity of mars at 1064 nm r 1064 by both active sounding and passive radiometry past studies of r 1064 neglected the effects of atmospheric opacity and viewing geometry on both active and passive measurements and also identified a potential calibration issue with passive radiometry therefore as yet there exists no acceptable reference r 1064 to derive a column opacity product for atmospheric studies and planning future orbital lidar observations here such a reference r 1064 is derived by seeking r 1064 m n a minnaert corrected normal albedo under clear conditions and assuming minimal phase angle dependence over darker surfaces r 1064 m n and the absolute level of atmospheric opacity were estimated from active sounding over all surfaces the opacity derived from active sounding was used to exclude passive radiometry measurements made under opaque conditions and estimate r 1064 m n these latter estimates then were re calibrated by comparison with r m n derived from hubble space telescope hst observations over areas of approximately uniform reflectivity estimates of r 1064 m n from re calibrated passive radiometry typically agree with hst observations within 10 the resulting r 1064 m n is then used to derive and quantify the uncertainties of a column opacity product which can be applied to meteorological and climatological studies of mars particularly to detect and measure mesoscale cloud aerosol structures

thermobarometric constraints on the thermal history of the main central thrust zone and tibetan slab eastern nepal himalaya the main central thrust mct south of mt everest in eastern nepal is a 3 to 5km thick shear zone separating chlorite bearing schist in the lower plate from sillimanite bearing migmatitic gneiss in the overlying tibetan slab the metamorphic grade increases through the mct zone toward structurally higher levels previous workers have suggested that either post or synmetamorphic thrust movement has caused this inversion of metamorphic isograds in an effort to quantify the increase in grade and to constrain proposed structural relations between metamorphism and slip on the fault four well calibrated thermobarometers were applied to pelitic samples collected along two cross strike transects through the mct zone and tibetan slab results show an increase in apparent temperature up section in the mct zone from 778 k to 990 k and a decrease in temperature to 850 k in the lower tibetan slab which is consistent with synmetamorphic thrust movement a trend in calculated pressures across this section is less well defined but on average decreases up section with a gradient of 28mpa km resembling a lithostatic gradient pressure temperature paths for zoned garnets from samples within the mct zone modelled using the gibbs method show a significant decrease in temperature and a slight decrease in pressure from core to rim which might be expected for upper plate rocks during synmetamorphic thrust movement samples from the uppermost tibetan slab yield higher temperatures and pressures than those from the lower tibetan slab which may be evidence for later resetting of thermobarometers by intrusion of the large amounts of leucogranite at that structural level

formation and erosion of layered materials geologic and dust cycle history of eastern arabia terra mars 1 eastern arabia terra is mantled in a layer of dust a few centimeters to a meter thick yet contains morphologic features that suggest a history of multiple events of deposition and consolidation of fine grained material and a significant amount of erosion early in martian history this region was affected by volcanic and fluvial activity but has since been dominated by aeolian processes five craters in this region contain interior mound material that ranges in height from 1600 to 2100 m above the crater floor the fluted erosional pattern and the thermal inertia are suggestive of a weakly indurated material and the extensive layering implies that these mounds were formed by a repeated process or processes although these materials primarily occur within craters there are materials outside craters that have similar erosional features and fine laminations suggesting a more extensive deposit the most likely process to form this material is the deposition and cementation of air fall dust and is potentially related to martian obliquity changes the significant amount of erosion of the intracrater mounds unit indicates a dramatic change from a depositional environment to an erosional regime over the past 106 108 years currently dust is accumulating in this region in years with planet encircling dust events but global circulation model results indicate that dust devils may be removing slight amounts of dust from arabia terra these observations suggest that the thickness of the dust mantle may not be currently increasing and may instead be in equilibrium

the vertical structure of limb hazes in the martian atmosphere abstract profiles of scattered light above the planetary limb from over 100 viking orbiter images are used to constrain the temporal and spatial behavior of earosols suspended in the martian atmosphere the data cover a wide range of seasons locations and viewing geometry providing information about the aerosol optical properties and vertical distribution the vertical resolution of the data is about 1 5 km with an absolute elevation accuracy of 1 to 4 km viking orbiter camera colibration algorithms provided reflectance accuracies to 7 absolute allowing meaningful radiometric analysis the typical atmospheric column contains one or more discrete optically thin ice like haze layers between 30 and 90 km elevation depending on season whose composition is inferred to be water ice below the detached hazes there is a continuous haze extending to the surface the continuous haze is rarely observed above 50 km and is much redder in color than the detached hazes above implying a composition that has a strong dust component the aerosol distribution exhibits a strong seasonal control inferred to be driven by the variable solar flux around the orbit of mars

mars equatorial mesospheric clouds global occurrence and physical properties from mars global surveyor thermal emission spectrometer and mars orbiter camera limb observations 1 we report the occurrence of a new type of cloud in the mars dayside 1300 1400 local time atmosphere apparent as high altitude 60 to 80 km vertically discrete aerosol scattering layers mars global surveyor mgs limb observations from the thermal emission spectrometer tes visible channel indicate peak frequencies at the beginning and end of the aphelion northern summer season ls 30 and 150 where they are confined to equatorial 15 s 15 n latitudes and two longitude ranges 40 e 2 w and 50 w 120 w limb images from the mgs mars orbiter camera moc indicate significant horizontal variations in these mars equatorial mesospheric mem clouds on 20 50 km scales on the basis of the distribution of projected limb heights mem clouds exhibit peak optical depths over 70 75 km altitudes that are substantial nadir vis of order 0 01 for the low pressure region of formation 1 bar averaged tes limb infrared spectral 5 40 m and solarband radiance profiles corresponding to mem occurrence indicate dust aerosols reff 1 5 2 0 m vis 0 4 at 0 25 km altitudes capped by water ice clouds reff 1 5 2 0 m vis 0 2 at 20 45 km altitudes the lack of detectable infrared radiances at mem cloud heights precludes distinction of water versus co2 ice but indicates 1 m particle sizes for water or 1 5 m for co2 ice compositions more recent mars express observations point toward mars mesospheric co2 clouds although current dynamical and radiative models do not indicate sufficiently cold temperatures at mem cloud locations to produce daytime co2 saturation conditions

aphelion water ice cloud mapping and property retrieval using the omega imaging spectrometer onboard mars express mapping of the aphelion clouds over tharsis and retrieval of their particle size and visible opacity are made possible by the omega imaging spectrometer aboard mars express observations cover the period from my26 ls 330 degree sign to my29 ls 180 degree sign and are acquired at various local times ranging from 8am to 6pm cloud maps of the tharsis region constructed using the 3 1 m ice absorption band reveal the seasonal and diurnal evolution of aphelion clouds four distinct types of clouds are identified morning hazes topographically controlled hazes cumulus clouds and thick hazes the location and time of occurrence of these clouds are analyzed and their respective formation process is discussed an inverse method for retrieving cloud particle size and opacity is then developed and can only be applied to thick hazes the relative error of these measurements is less than 30 for cloud particle size and 20 for opacity two groups of particles can be distinguished the first group is found over flat plains and is composed of relatively small particles ranging in size from 2 to 3 5 m the second group is characterized by particle sizes of 5 m which appear to be quite constant over ls and local time it is found west of ascraeus and pavonis mons and near lunae planum these regions are preferentially exposed to anabatic winds which may control the formation of these particles and explain their distinct properties the water ice column is equal to 2 9pr m on average and can reach 5 2pr m in the thickest clouds of tharsis

the origin evolution and trajectory of large dust storms on mars during mars years 24 30 1999 2011 abstract mars daily global maps mdgm derived from the mars global surveyor mgs mars orbiter camera moc and mars reconnaissance orbiter mro mars color imager marci are used to study the distribution and evolution of large dust storms over the period from mars years 24 30 1999 2001 large storms are defined here as discrete dust events visible in image sequences extending over at least 5 sols mars days and where the dust covers areas beyond the origination region a total of 65 large dust storms meeting these criteria are identified during the observational period and all are observed during the l s 135 30 seasonal window dust storms originating in the northern and southern hemispheres appear to form two distinct families all but two of the storms originating in the northern hemisphere are observed in two seasonal windows at l s 180 240 and l s 305 350 while all but two of those originating in the southern hemisphere are observed during l s 135 245 none of the large dust storms originating in the northern hemisphere are observed to develop to global scale but some of them develop into large regional storms with peak area 1 10 7 km 2 and duration on the order of several weeks in comparison large dust storms originating in the southern hemisphere are typically much smaller except notably in the two cases that expanded to global scale the 2001 and 2007 global storms distinct locations of preferred storm origination emerge from the dust storm image sequences including acidalia utopia arcadia and hellas a route trajectory graph for the observed sequences is provided the routes are highly asymmetric between the two hemispheres in the south for non global dust storms the main routes are primarily oriented eastwest whereas in the north the routes are primarily north south and zonally concentrated into meridional channels in a few impressive cases storms originating in the northern hemisphere are observed to flush through acidalia and utopia across the equator and then branch in the low and mid southern latitudes the origin of the 2007 global dust storm is ambiguous from the imaging data immediately prior to the global storm a dust storm sequence from chryse is identified this storm s connection to the explosive expansion observed to start from noachis west hellas is unclear due to image coverage this paper further identifies and describes three different styles of dust storm development which we refer to as consecutive dust storms sequential activation and merging the evolution of a given dust storm sequence can exhibit different combinations of these growth styles at different stages of development dust storm sequences can overlap in time which makes them good candidate to grow into larger scale

the seasonal behavior of water ice clouds in the tharsis and valles marineris regions of mars mars orbiter camera observations abstract the mars global surveyor mars orbiter camera was used to obtain global maps of the martian surface with equatorial resolution of 7 5 km pixel in two wavelength ranges blue 400 450 nm and red 575 625 nm the maps used were acquired between march 15 1999 ls 110 and july 31 2001 ls 205 corresponding to approximately one and a quarter martian years using the global maps cloud area in km2 has been measured daily for water ice clouds topographically corresponding to olympus mons ascraeus mons pavonis mons arsia mons alba patera the western valles marineris canyon system and for other small surface features in the region seasonal trends in cloud activity have been established for the three tharsis volcanoes olympus mons and alba patera olympus ascraeus and pavonis mons show cloud activity from about ls 0 220 with a peak in cloud area near ls 100 one of our most interesting observational results is that alba patera shows a double peaked feature in the cloud area with peaks at ls 60 and 140 and a minimum near ls 100 arsia mons shows nearly continuous cloud activity the altitudes of several of these clouds have been determined from the locations of the visual cloud tops and optical depths were measured for a number of them using the disort code of stamnes et al 1988 appl opt 27 2502 2509 several aspects of the observations e g cloud heights effects of increased dust on cloud activity are similar to simulations in richardson et al 2002 j geophys res 107 5064 a search for short period variations in the cloud areas revealed only indirect evidence for the diurnal cloud variability in the afternoon hours unambiguous evidence for other periodicities was not found

wind driven particle mobility on mars insights from mars exploration rover observations at el dorado and surroundings at gusev crater 1 the ripple field known as el dorado was a unique stop on spirit s traverse where dust raising active mafic sand ripples and larger inactive coarse grained ripples interact illuminating several long standing issues of martian dust mobility sand mobility and the origin of transverse aeolian ridges strong regional wind events endured by spirit caused perceptible migration of ripple crests in deposits sse of el dorado erasure of tracks in sandy areas and changes to dust mantling the site localized thermal vortices swept across el dorado leaving paths of reduced dust but without perceptibly damaging nearly cohesionless sandy ripple crests from orbit winds responsible for frequently raising clay sized dust into the atmosphere do not seem to significantly affect dunes composed of more easily entrained sand sized particles a long standing paradox this disparity between dust mobilization and sand mobilization on mars is due largely to two factors 1 dust occurs on the surface as fragile low density sand sized aggregates that are easily entrained and disrupted compared with clay sized air fall particles and 2 induration of regolith is pervasive light toned bed forms investigated at gusev are coarse grained ripples an interpretation we propose for many of the smallest linear light toned bed forms of uncertain origin seen in high resolution orbital images across mars on earth wind can organize bimodal or poorly sorted loose sediment into coarse grained ripples coarse grained ripples could be relatively common on mars because development of durable well sorted sediments analogous to terrestrial aeolian quartz sand deposits is restricted by the lack of free quartz and limited hydraulic sediment processing

properties of a martian local dust storm in atlantis chaos from omega mex data abstract in this study we present the analysis of the dust properties of a local storm imaged in the atlantis chaos region on mars by the omega imaging spectrometer on march 2nd 2005 we use the radiative transfer model mitra to study the dust properties at solar wavelengths between 0 5 m and 2 5 m and infer the connection between the local storm dynamics and the topography we retrieve maps of effective grain radius reff optical depth at 9 3 m 9 3 and top altitude ta of the dust layer our results show that large particles reff 1 6 m are gathered in the centre of the storm lat 33 5 s lon 183 5 w where the optical depth is maximum 9 3 7 0 and the top altitude exceeds 18 km outside the storm we obtain 9 3 we speculate that a low thermal inertia region at the western border of atlantis chaos is a possible source of the dust storm moreover we find evidence that topography plays a role in confining the local storm in atlantis chaos the vertical wind component from the gcm does not provide any hint for the triggering of dust lifting on the other hand the combination of the horizontal and vertical wind profiles suggests that the dust once lifted is pushed eastward and then downward and gets confined within the north east ridge of atlantis chaos from our results the thickness of the dust layer collapsed on the surface ranges from about 1 m at the storm boundaries up to more than 100 m at its centre we verify that a layer of dust thicker than 1 m deposited on the surface can prevent the detection of mafic absorption features however such features are still present in omega data of atlantis chaos registered after the storm hence we deduce that once the storm is over the dust deposited on an area larger than the one where it has been observed

observations of martian ice clouds by the mars global surveyor thermal emission spectrometer the first martian year successful operation of the mars global surveyor spacecraft beginning in september 1997 ls 184 has permitted extensive observations over more than a martian year initially thin normal optical depth 0 06 at 825 cm 1 ice clouds and hazes were widespread showing a distinct latitudinal gradient with the onset of a regional dust storm at ls 224 ice clouds vanished in the southern hemisphere to reappear gradually after the decay of the storm the zonally averaged cloud opacities show little difference between the beginning and end of the first martian year a broad low latitude cloud belt with considerable longitudinal structure was present in early northern summer apparently characteristic of the northern summer season it vanished between ls 140 and 150 the latitudinal extent of this feature is apparently controlled by the ascending branch of the hadley circulation the most opaque clouds optical depth 0 6 were found above the summits of major volcanic features these showed spatial structure possibly associated with wave activity variety among low lying late morning clouds suggests localized differences in circulation and microclimates limb observations showed extensive optically thin optical depth 0 04 stratiform clouds at altitudes up to 55 km considerable latitude and altitude variations were evident in ice clouds in early northern spring ls 25 near 30 km thin clouds extended from just north of the equator to 45 n nearly to the north polar vortex a water ice haze was present in the north polar night ls 30 at altitudes up to 40 km because little dust was present this probably provided heterogeneous nucleation sites for the formation of co2 clouds and snowfall at altitudes below 20 km where atmospheric temperatures dropped to the co2 condensation point the relatively invariant spectral shape of the water ice cloud feature over space and time indicates that ice particle radii are generally between 1 and 4 m

martian dust storms 1999 mars orbiter camera observations the mars orbiter camera on board the mars global surveyor from march 9 1999 ls 107 where ls is the areocentric longitude of the sun measured in degrees from mars northern spring equinox to december 31 1999 ls 274 has obtained 7 5 km pixel 1 daily global maps of the martian surface in two wavelength bands blue 400 450 nm and red 575 625 nm visual inspection of these maps during the 1999 dust storm season has resulted in the detection of 783 dust storms ranging in size from local 102 km2 to regional 1 6 106 km2 no global storms were observed the difference in the numbers of dust storms occurring in the two hemispheres north 343 south 440 was not statistically significant fifty percent of the regional size dust storms formed as a result of the merger of two or more smaller local storms the regional storms from ls 207 to ls 223 were observed to move from the northern hemisphere into the southern hemisphere between 30 w and 50 w longitude this cross equatorial transport of dust suggests the location of the low lying southward flowing branch of the hadley circulation observations show that dust storms occur in several regions on mars at the two polar cap edges at the base of high elevation regions in the northern hemisphere near the polar hood during northern fall and at mid latitudes in both hemispheres specific regions such as solis planum and hesperia which were regions of significant dust activity in the past showed almost no dust storm activity in 1999 suggesting that regional dust sources are variable over a 20 year time frame one region of exceptional activity not noted previously was the arcadia amazonis border however other regions such as near elysium mons acidalia chryse hellas noachis argyre cimmeria and sirenum again were active dust storm regions relative dust opacities were modeled for 117 red wavelength events and ranged from 0 54 diffuse haze to 2 13 concentrated local events from the dust opacities we estimated the north polar sedimentation rate to be 6 0 10 10 4 g cm 2 yr 1 a factor of 40 smaller than previous estimates from the two 1977 global dust storms pollack et al 1979 along with the global dust mass loading 2 6 4 0 10 4 g cm 2 and cross equatorial dust mass loading 3 6 10 4 g cm 2 the 1999 cross equatorial mass dust loading suggests that the southern hemisphere subtropical latitudes require at least 2 3 martian years to replenish their dust sources before global storms can form

kwangsian crustal anatexis within the eastern south china block geochemical zircon u pb geochronological and hf isotopic fingerprints from the gneissoid granites of wugong and wuyi yunkai domains abstract gneissoid granites were traditionally thought to be the components of the precambrian basement in the eastern south china block but twenty four gneissoid granite samples from the wugong northern wuyi southern wuyi and yunkai domains gave zircon u pb ages of 424 456 ma 410 457 ma 426 438 ma and 415 450 ma respectively the existence of the abundant kwangsian gneissoid granites which have incorrectly been assigned to the precambrian basement indicates that the so called precambrian stratigraphic sequence of the cathaysia block should be termed complex rather than group these gneissoid granites are peraluminous granites with relatively high al 2 o 3 mgo tio 2 feot and cao na 2 o but low cao al 2 o 3 mgo feot and rb sr ratios they exhibit strongly negative ba sr nb p and ti and positive pb anomalies in primitive mantle normalized diagrams and have initial 87 sr 86 sr ratios ranging from 0 70924 to 0 72935 and negative end t values from 6 4 to 11 4 similar to those of paragneissic enclaves and precambrian sedimentary rocks in the eastern south china block the zircons crystallized in the kwangsian gneissoid granites gave ehf t values ranging from 2 4 to 19 4 with the peak at 4 almost all grains clustering at 1 to 12 and hf model ages of 1 1 2 1 ga the synthesis of these geochemical and in situ zircon hf isotopic data indicates that the kwangsian gneissoid granites dominantly originated from proterozoic metapelitic and meta igneous components with insignificant input of juvenile mantle derived magmas a model of two stage crustal anatexis is proposed for the kwangsian granitic magma in the eastern south china block with 1 the formation of 460 430 ma granite through the breakdown of hydrous minerals under the condition of the doubly thickened crust and 2 the generation of the 430 400 ma granite accompanying promoted melting along a path of isothermal decompression due to the increasing thermal weakening for the collapse of the thickened crust the crustal anatexis has probably occurred in an intracontinental tectonic regime that was geodynamically linked to the far field response to the assembly of the australian indian plate with the cathaysia block during middle paleozoic kwangsian time

topographic control of hydrogen deposits at low latitudes to midlatitudes of mars 1 correlations between the longitudinal wave number two distribution of water equivalent hydrogen weh at low latitudes to midlatitudes of mars with variations in topography surface albedo thermal inertia regional dust storms and atmospheric water vapor are explored to provide guidance in determining the mechanisms that recharge or maintain these weh reservoirs the closest match is with low thermal inertia coupled with orographic control of the present day atmospheric circulation dynamics the engine for the simulated longitudinal two wave pattern maxima in arabia and tharsis is relatively cold nighttime surface temperatures and large amplitude temperature inversions that concentrate water ice over these regions geologically recent precipitated water ice by itself is insufficient to account for the observed distribution of weh retention of precipitate by hydratable minerals is necessary while current research cannot presently identify the hydration mechanism for the weh distribution whether it be from a past obliquity present climate conditions or some convolution of both this research suggests that current climatic conditions can sustain if not emplace the observed longitudinally constrained distribution of equatorial weh

biofabrics as dynamic indicators in nummulite accumulations biofabric interpretation of skeletal accumulations consisting of biologically standardized nummulite tests larger foraminifera is based upon 1 the ratio of small bodied a forms megalospheric and large bodied b forms microspheric and 2 on their packing and imbrication features in the eocene mokattam formation of egypt nummulites gizehensis occurs in limestones with four basic biofabrics in wackestones the nummulites float throughout the matrix and a forms strongly dominate over b forms approximating the ratio reported for undisturbed assemblages packstones however reflect various degrees of sedimentary reworking and winnowing of the original substratum by physical processes for packstones with edge wise imbrication and a forms strongly dominating over b forms in situ winnowing of fine grained matrix by waves can be inferred in contrast packstones composed of imbricated b forms suggest hydraulic sorting and selective removal of a forms by currents packstones composed almost entirely of a forms represent transport sorted allochthonous deposits biofabric analysis thus allows us to understand better the dynamics of skeletal accumulations such as nummulite banks whose commonly complex and extensive buildups can form hydrocarbon reservoirs

gps measurements of present day convergence across the nepal himalaya the high elevations of the himalaya and tibet result from the continuing collision between india and asia which started more than 60 million years ago1 4 from geological and seismic studies of the slip rate of faults in asia5 it is believed that approximately one third of the present day convergence rate between india and asia 58 4mmyr 1 is responsible for the shortening uplift and moderate seismicity of the himalaya great earthquakes also occur infrequently in this region releasing in minutes the elastic strain accumulated near the boundary zone over several centuries and accounting for most of the advance of the himalaya over the plains of india the recurrence time for these great earthquakes is determined by the rate of slip of india beneath tibet which has hitherto been estimated indirectly from global plate motions6 from the slip rates of faults in asia7 8 from seismic productivity9 and from the advance of sediments on the northern ganges plain10 here we report geodetic measurements using the global positioning system gps of the rate of contraction across the himalaya which we find to be 17 52 2 mm yr 1 from the form of the deformation field we estimate the rate of slip of india beneath tibet to be 20 5 2 mmyr 1 strain sufficient to drive one or more great himalayan earthquakes with slip similar to that accompanying the magnitude 8 1 bihar nepal 1934 earthquake may currently be available in western nepal

characterization of artifacts introduced by the empirical volcano scan atmospheric correction commonly applied to crism and omega near infrared spectra abstract the empirical volcano scan atmospheric correction is widely applied to martian near infrared crism and omega spectra between 1000 and 2600 nm to remove prominent atmospheric gas absorptions with minimal computational investment this correction method employs division by a scaled empirically derived atmospheric transmission spectrum that is generated from observations of the martian surface in which different path lengths through the atmosphere were measured and transmission calculated using the beer lambert law identifying and characterizing both artifacts and residual atmospheric features left by the volcano scan correction is important for robust interpretation of crism and omega volcano scan corrected spectra in order to identify and determine the cause of spectral artifacts introduced by the volcano scan correction we simulated this correction using a multiple scattering radiative transfer algorithm disort simulated transmission spectra that are similar to actual crism and omega derived transmission spectra were generated from modeled olympus mons base and summit spectra results from the simulations were used to investigate the validity of assumptions inherent in the volcano scan correction and to identify artifacts introduced by this method of atmospheric correction we found that the most prominent artifact a bowl shaped feature centered near 2000 nm is caused by the inaccurate assumption that absorption coefficients of co2 in the martian atmosphere are independent of column density in addition spectral albedo and slope are modified by atmospheric aerosols residual atmospheric contributions that are caused by variable amounts of dust aerosols ice aerosols and water vapor are characterized by the analysis of crism volcano scan corrected spectra from the same location acquired at different times under variable atmospheric conditions

brittle frictional mountain building 1 deformation and mechanical energy budget an active fold and thrust belt is analogous to a wedge of soil or snow that forms in front of a moving bulldozer such wedges exhibit a critical taper and a regional state of stress that is everywhere on the verge of coulomb failure the width of such a critically tapered fold and thrust belt does not depend on its brittle strength or frictional properties but rather on the accretionary influx rate of fresh material at its toe and on the rate of erosion a steady state fold and thrust belt is one in which the accretionary influx is balanced by the erosive efflux rocks are accreted at the toe and then horizontally shortened as they are transported toward the rear those that enter lower in the accreted section are more deeply buried before being uplifted by erosion mass balance and isotropy constrain the kinematics of this large scale deformation enabling us to infer the trajectories residence times and stress strain histories of rocks incorporated into eroding fold and thrust belts a typical rock resides in the steady state taiwan wedge for 2 3 m y before it is uplifted and eroded during its motion through the wedge it experiences strain rates in the range 10 13 to 10 14 s 1 the mechanical energy budget of brittle frictional mountain building is described by the equation where is the rate of work performed on the base and front of the fold and thrust belt by the subducting plate is the rate at which energy is dissipated against friction on the decollement fault is the rate at which energy is dissipated by internal frictional processes within the deforming brittle wedge and is the rate of work performed against gravitational body forces in a reference frame attached to the overriding plate the total mechanical power being supplied by the subducting eurasian plate to the active fold and thrust belt in taiwan is slightly over 3 gw approximately 60 of this work of steady state mountain building is being dissipated against friction on the decollement fault and about another 25 is being dissipated against internal friction this leaves only 15 or roughly half a gigawatt available to do useful work against gravity in general fold and thrust belts with moderate pore fluid pressures are dominated by work done against friction on the decollement fault however those with nearly lithostatic pore fluid pressures may be dominated by work done against gravity internal frictional dissipation is always less than basal frictional dissipation as it is in taiwan an alternative and equivalent description of the mechanical energy balance of a steady state fold and thrust belt is provided by the equation in this version the quantity on the left is the rate at which work is performed on the back of the wedge by the overriding plate and is the rate of work performed against gravity in a reference frame attached to the subducting plate the latter quantity is always positive for any critically tapered fold and thrust belt whose decollement fault dips toward its rear in contradiction to the central premise of the gravity spreading theory of fold and thrust tectonics

msl apxs titanium observation tray measurements laboratory experiments and results for the rocknest fines at the curiosity field site in gale crater mars the mars science laboratory msl rover curiosity has a titanium science observation tray o tray upon which portions from drilled and scooped martian samples can be delivered for analyses by the alpha particle x ray spectrometer apxs the standard apxs calibration approach to derive elemental concentrations cannot be applied to samples on the o tray because they 1 have a nonuniform three dimensional distribution within the apxs field of view and 2 are thin 90 m to develop techniques for interpreting msl apxs o tray measurements we conducted laboratory measurements of thin particulate basalt samples on ti metal with the flight equivalent apxs unit the experiments demonstrate that relative to an infinitely thick sample increasing areal coverage of particulates on a ti metal substrate results in a proportional decrease in the ti signal and increase in the sample signal count rates for heavier elements mn and fe drop with decreasing sample thickness because the mean thickness is smaller than the apxs information depth similar effects were seen in the msl apxs o tray measurement of rocknest fines on martian solar day 95 an aliquot of material delivered to sample analysis at mars and chemistry and mineralogy the thin layer effect caused a drop in mn and fe signals which cannot be quantitatively compared to the in situ rocknest target portage because sample thickness was unknown otherwise rocknest fines on the o tray had no significant compositional differences from portage except for slight increases in s and cl

seasonal ice cycle at the mars phoenix landing site 2 postlanding crism and ground observations 1 the combination of ground observations from the mars phoenix lander and orbital data from the compact reconnaissance imaging spectrometer for mars crism provided a detailed view of the formation of late summer surface water ice at the landing site and surrounding regions crism observations of the landing site during and immediately after phoenix operations were analyzed to track the seasonal and diurnal ice cycles during the late spring to late summer and a nonlinear mixing model was used to estimate grain sizes and relative abundances of water ice and dust the surface around the phoenix landing site was ice free from late spring through midsummer although transient patches of mobile ices were observed in an 85 m diameter crater to the northeast of the landing site at the 10 km diameter heimdal crater located 10 km east of the landing site permanent patches of water ice were observed to brighten during the late spring and darken during the summer possibly as fine grained water ice that was cold trapped onto the ice during late spring sintered into larger grains or finally sublimated exposing larger grained ice crism spectra first show evidence of widespread ice during the night at solar longitude ls 109 9 sols before phoenix s surface stereo imager detected it crism spectra first show evidence of afternoon surface ice and water ice clouds after ls 155 after phoenix operations ended

photometric properties of mars soils analogs we have measured the bidirectional reflectance of analogs of dry wet and frozen martian soils over a wide range of phase angles in the visible spectral range all samples were produced from two geologic samples the standard jsc mars 1 soil simulant and hawaiian basaltic sand in a first step experiments were conducted with the dry samples to investigate the effects of surface texture comparisons with results independently obtained by different teams with similar samples showed a satisfying reproducibility of the photometric measurements as well as a noticeable influence of surface textures resulting from different sample preparation procedures in a second step water was introduced to produce wet and frozen samples and their photometry investigated optical microscope images of the samples provided information about their microtexture liquid water even in relatively low amount resulted in the disappearance of the backscattering peak and the appearance of a forward scattering peak whose intensity increases with the amount of water specular reflections only appeared when water was present in an amount large enough to allow water to form a film at the surface of the sample icy samples showed a wide variability of photometric properties depending on the physical properties of the water ice we discuss the implications of these measurements in terms of the expected photometric behavior of the martian surface from equatorial to circum polar regions in particular we propose some simple photometric criteria to improve the identification of wet and or icy soils from multiple observations under different geometries

viking era water ice clouds we have spatially and temporally mapped water ice clouds on mars for 1 25 martian years using the viking infrared thermal mapper irtm data our technique compares brightness temperatures in the 11 and 20 m irtm channels utilizing the 11 m water ice absorption feature a complication arises because of the surface nonunit and wavelength dependent emissivities we developed a technique for removal of this effect using a surface thermal model we calculated brightness temperatures and their differences for the irtm channels resulting from the surface emissivity effect alone these were then subtracted from the measured brightness temperatures yielding brightness temperature differences dominated by atmospheric effects the ability to identify water ice clouds in the infrared provides potential new information about particle size and physical processes by comparing these clouds to those seen in visible wavelengths we found that water ice clouds were more widespread and frequent during the viking period than had been previously recognized with the northern spring and summer being the cloudiest periods on mars we interpret some of the identified cloudy zones as the southern and northern solstice season upwelling branches of the hadley cell although these were shifted 15 20 southward from model predictions additionally the transition between the two branches occurred later in time than in the model predictions we observed the extension of the north polar hood below 60 n in longitudes 120 200 we did not find evidence for a south polar hood north of 60 s nor any evidence for interannual variability within our limited data set

analysis of a spectrally unique deposit in the dissected noachian terrain of mars 1 we have analyzed a spectrally anomalous dark intracrater deposit and an adjacent lighter toned fan shaped deposit in the dissected noachian terrain of mars using a combination of high spatial and spectral resolution remote sensing data sets the spatial proximity of these two deposits and their dust free spectral character make these prime targets for 1 determining whether the dark toned deposit is derived from the fan shaped deposit and 2 constraining the nature and mineralogy of the fan shaped deposit stereo observations and derived digital elevation models of the of the fan shaped deposit show a set of three flows lobes calculations of the yield strength based on morphometry of the lobes indicate yield strengths consistent with those of other volcanic flows on mars although an aqueous origin cannot be discounted the dark deposit consists of a mantle that forms dunes at its thickest portions and extends as a thinner veneer we find no obvious morphologic association between the dark deposit and adjacent fan multispectral imaging from the themis vis and ir instruments show that the two deposits have different spectral characteristics probably caused by differences in their mineralogy rather than their physical properties finally modeling of mgs tes spectra of the combined deposits indicates a feldspar rich composition that is possibly complemented by smaller quantities of alteration products such as carbonates and possibly sulfates and clays these results indicate that 1 there is no association between these deposits and 2 the combined deposits have a primarily igneous mineralogy although some aqueous alteration may have occurred

derivation of martian surface slope characteristics from directional thermal infrared radiometry abstract directional thermal infrared measurements of the martian surface is one of a variety of methods that may be used to characterize surface roughness and slopes at scales smaller than can be obtained by orbital imagery thermal emission spectrometer tes emission phase function epf observations show distinct apparent temperature variations with azimuth and emission angle that are consistent with the presence of warm sunlit and cool shaded slopes at typically 0 1 m scales a surface model of a gaussian distribution of azimuth independent slopes described by bar is combined with a thermal model to predict surface temperature from each viewing angle and azimuth of the tes epf observation the models can be used to predict surface slopes using the difference in measured apparent temperature from 2 separate 60 70 emission angle observations taken 180 in azimuth relative to each other most martian surfaces are consistent with low to moderate slope distributions the slope distributions display distinct correlations with latitude longitude and albedo exceptionally smooth surfaces are located at lower latitudes in both the southern highlands as well as in high albedo dusty terrains high slopes are associated with southern high latitude patterned ground and north polar sand dunes there is little apparent correlation between high resolution imagery and the derived bar with exceptions such as duneforms this method can be used to characterize potential landing sites by assuming fractal scaling behavior to meter scales more precisely targeted thermal infrared observations from other spacecraft instruments are capable of significantly reducing uncertainty as well as reducing measurement spot size from 10s of kilometers to sub kilometer scales

geochemical investigations of the origin of the manaslu leucogranite himalaya nepal the himalayan orogeny is characterized by an intraplate subduction zone the thrusting of the tibetan slab over the foreland is probably responsible for the origin of the manaslu type leucogranites this geochemical study tries to examine the crustal origin of the granite to verify whether the paragneisses of the tibetan slab are the most probable parent material and to determine the subsequent petrogenetic processes the rb sr systematics suggest that 1 1 the scatter of data points in the 87sr86srvs 87rb86sr diagram may be due to the heterogeneity of the initial 87sr86sr ratios 2 2 the initial isotopic ratios are very high 0 730 0 760 and are in agreement with those of the gneisses of the tibetan slab at the time of the melting pb isotopic ratios are homogeneous they are also consistent with a crustal prehistory the ree and th contents are unexpectedly low in comparison with the much higher contents of the parent material monazite left in the residue of melting or more probably extracted in an early stage of the magmatic history may explain the observed ree and th abundances alternatively field observations show that the emplacement of the granite has been accompanied by a very strong hydrothermal activity in consequence the low ree and th contents of the granite could also be due to the loss by solution during prolonged fluid circulation throughout the granitic melt and the sr and pb isotope distribution to the effect of late to post magmatic fluids the isotopic character of which was determined by the underlying tibetan slab

valles marineris cloud trails 1 distinctive cloud trails are identified in mars reconnaissance orbiter mars color imager marci images over specific locations associated with valles marineris and noctis labyrinthus and at perihelion solar longitudes l s 230 260 high contrast surface shadows are well defined as cast from their eastern margins supporting altitude and optical depth determinations these relatively high altitude clouds 40 50 km exhibit narrow latitudinal widths 25 75 km in comparison to extended longitudinal dimensions 400 1000 km marci multispectral imaging of cloud surface shadows in five wavelength channels 260 320 437 546 and 653 nm yields the wavelength dependence of cloud extinction optical depth revealing a range of small cloud particle sizes r eff 0 2 0 5 m and moderate cloud optical depths 0 03 0 10 visible and 0 1 0 2 ultraviolet local time and temporal sampling characteristics of marci cloud images indicate that these clouds develop very rapidly in afternoon hours 1300 1500 lt reach their full longitudinal extents within 2 h time scales and often reoccur on successive afternoons mars global surveyor mars orbital camera imaging in previous mars years indicates these clouds are annually repeating these observed characteristics suggest a cloud formation mechanism that is specific to 50 km horizontal and vertical scales transports water vapor and dust upward from lower levels exists during the afternoon and is likely associated with the mesoscale atmospheric circulations induced by the near equatorial canyons of mars cloud particles formed in such updrafts would then be rapidly transported westward in the strong retrograde zonal circulation of the subsolar middle atmosphere in this season

surface reflectance of mars observed by crism mro 2 estimation of surface photometric properties in gusev crater and meridiani planum the present article proposes an approach to analyze the photometric properties of the surface materials from multi angle observations acquired by the compact reconnaissance imaging spectrometer for mars crism on board the mars reconnaissance orbiter we estimate photometric parameters using hapke s model in a bayesian inversion framework this work also represents a validation of the atmospheric correction provided by the multi angle approach for retrieval of surface reflectance from crism observations mars reco proposed in the companion article the latter algorithm retrieves photometric curves of surface materials in reflectance units after removing the aerosol contribution this validation is done by comparing the estimated photometric parameters to those obtained from in situ measurements by panoramic camera instrument at the mars exploration rover mer spirit and mer opportunity landing sites consistent photometric parameters with those from in situ measurements are found demonstrating that mars reco gives access to accurate surface reflectance moreover the assumption of a non lambertian surface as included in mars reco is shown to be significantly more precise to estimate surface photometric properties from space in comparison to methods based on a lambertian surface assumption in the future the presented method will allow us to map from orbit the surface bidirectional reflectance and the related photometric parameters in order to characterize the martian surface

gusev photometric variability as seen from orbit by hrsc mars express minnaert and two term phase function hapke models are used to describe the photometric properties of the martian surface using hrsc high resolution stereo camera multi angular observations acquired along the ongoing mars express mission these observations can be pieced together to derive integrated phase functions over a wide range of phase angles the photometric diversity at 675 nm as seen from orbit of the martian surface properties across gusev is depicted with seven units three photometric units widespread across the flanks of apollinaris patera flank and the floor of gusev crater are identified as having high single scattering albedo with rather forward scattering properties low to intermediate macroscopic roughness and porous or not compacted powdered surface state as indicated by the opposition parameters another unit has the highest single scattering albedo the smoothest surface in terms of macroscopic roughness associated with an extremely forward scattering behavior the opposition parameters are consistent with the presence of transparent particles in the surface powder layer the distribution of this unit appears quite intermittent across the crater and does not seem to indicate any relationship with a given morphological structure it may correspond to sparse areas where the structure of the surface dust layer is the most preserved the most pronounced photometric changes are observed in three units associated with the low albedo features corresponding to dark wind streaks these units have a low single scattering albedo are the most backscattering surfaces across gusev have a high surface roughness and present variable surface states as shown by the opposition parameters estimates consistent with the occurrence of large grains organized in more or less packed layers clear differences are seen among these units in terms of opposition effect while one exhibits typical characteristics for the opposition effect another appears more unusual in terms of lobe width and the third suggests the occurrence of a packed compressed narrow size distribution powder surface the opposition effect thus appears to play a significant role suggesting that the surface state optical properties across gusev are strongly influenced by the porosity and packing characteristics or grain size distribution of the upper layer of the martian soil the mapping aspect of the investigation is quite useful to get a better sense of the meaning of the observed photometric variations indeed the hapke modeling suggests that surface organization surface roughness packing state is more important than the simple physical characterization of the intrinsic optical properties of the constitutive particles given the overall spatial patterns derived from the photometric analysis the variations at least for the western and central part of gusev crater are likely partly driven by the prevailing wind regimes considered to be oriented north northwest south southeast and disturbing the very upper surface layer the present photometric results agree with independent investigations based on thermal inertia reflectance spectroscopy in situ photometric and microscopic imaging and support the idea of a thin layer of fine grained dust being stripped off in the low albedo units to reveal a dark basaltic substrate comprising coarse grained materials

pressure temperature time paths of regional metamorphism i heat transfer during the evolution of regions of thickened continental crust the development of regional metamorphism in areas of thickened continental crust is investigated in terms of the major controls on regional scale thermal regimes these are the total radiogenic heat supply within the thickened crust the supply of heat from the mantle the thermal conductivity of the medium and the length and time scales of erosion of the continental crust the orogenic episode is regarded as consisting of a relatively rapid phase of crustal thickening during which little temperature change occurs in individual rocks followed by a lengthier phase of erosion at the end of which the crust is at its original thickness the principal features of pressure temperature time ptt paths followed by rocks in this environment are a period of thermal relaxation during which the temperature rises towards the higher geotherm that would be supported by the thickened crust followed by a period of cooling as the rock approaches the cold land surface the temperature increase that occurs is governed by the degree of thickening of the crust its conductivity and the time that elapses before the rock is exhumed sufficiently to be affected by the proximity of the cold upper boundary for much of the parameter range considered the heating phase encompasses a considerable portion of the exhumation decompression part of the ptt path in addition to the detailed calculation of ptt paths we present an idealized model of the thickening and exhumation process which may be used to make simple calculations of the amount of heating to be expected during a given thickening and exhumation episode and of the depth at which a rock will start to cool on its ascent path an important feature of these ptt paths is that most of them lie within 50 c of the maximum temperature attained for one third or more of the total duration of their burial and uplift and for a geologically plausible range of erosion rates the rocks do not begin to cool until they have completed 20 to 40 per cent of the total uplift they experience considerable melting of the continental crust is a likely consequence of thickening of crust with an average continental geotherm a companion paper discusses these results in the context of attempts to use metamorphic petrology data to give information on tectonic processes 1984 oxford university press

global patterns in cloud forms on mars abstract mariner 9 images and all viking orbiter images through july 1979 were searched for cloud forms a computer accessible catalog was assembled consisting of a classification of cloud type lee wav wave for example and properties directionality wavelength for example lee wave directionality shows a pattern and seasonal variation at high latitudes which is consistent with predictions of theoretical modeling fog and haze occurrence shows no obvious correlation with water abundance or any other simple causal factor lee waves are rare at equatorial latitudes plumes probably dust occur preferentially at locations where strong boundary layer convection is expected