ventifacts at the pathfinder landing site about half of the rocks at the mars pathfinder ares vallis landing site appear to be ventifacts rocks abraded by windborne particles comparable resolution images taken by the imager for mars pathfinder imp camera and the viking landers show that ventifacts are more abundant at the pathfinder site the ventifacts occur in several forms including rocks with faceted edges finger like projections elongated pits flutes grooves and possible rills the trends of elongated pits flutes grooves and rills cluster at 280 330 clockwise from north and generally dip 10 30 away from their trend direction these orientations are indicative of southeast to northwest winds and differ from the trend of wind tails at the landing site the direction of local wind streaks and predictions of the global circulation model all of which indicate northeast to southwest winds the disparity between these data sets strongly suggests that local circulation patterns have changed since the abrasion of the ventifacted rocks the greater number of ventifacts at the pathfinder site compared to either of the viking sites is most easily explained as being due to a larger supply of abrading particles composed of either sand sized grains or indurated dust aggregates and higher surface roughness which should increase the momentum of saltating grains the pathfinder ventifacts may have formed shortly after the deposition of outflow channel sediments nearly 2 gry ago when a large local supply of abrading particles should have been abundant and atmospheric conditions may have been more conducive to rock abrasion from saltating grains based on how ventifacts form on earth the several ventifact forms seen at the pathfinder site and their presence on some rocks but not on others are probably due to local airflow conditions original rock shape exposure duration rock movement and to a lesser extent rock lithology the abundance of ventifacts at the pathfinder site together with other evidence of weathering indicates that unaltered rock surfaces are rare on mars

the equatorial response to higher latitude forcing abstract the classic view following charney and webster and holton is that significant midlatitude forcing of the tropics can be expected only in regions with westerly winds in the upper troposphere because it is only in these regions that stationary rossby waves will be able to propagate toward the equator here it is shown that higher latitude forcing can project directly onto equatorial waves and give a significant tropical response in both easterly and westerly tropical flow the equatorial response to higher latitude forcing is considered in the context of a dry atmosphere and a localized higher latitude forcing with eastward or westward phase speed previous ideas of the doppler shifting of equatorial waves by zonal flows are extended to include consideration of a forcing involving a range of zonal wavenumbers a gill type model suggests that there can be significant forcing of equatorial waves by either vorticity forcing or heating in higher latitudes in agreement with the theory the kelvin wav

erosion rates on mars and implications for climate change constraints from the pathfinder landing site the observation that the mars pathfinder landing site looks very similar to its appearance after it was deposited by catastrophic floods around 1 8 3 5 ga allows quantitative constraints to be placed on the rate of change of the site since that time the abundance of erosional features such as an exhumed former soil horizon sculpted wind tails ripplelike and other tag deposits and ventifacts fluted and grooved rocks all suggest the site has undergone net deflation or loss of 3 7 cm of material the presence of barchan dunes and ventifacts argues for erosion by saltating crystalline sand size particles entrained in the wind most ventifacts probably formed soon after the catastrophic flood which likely introduced a large fresh supply of sand size particles distributed across the rocky plain the strongest winds blew toward the northwest during this time resulting in the sculpting of ventifacts deflation of the surface collections of dunes within big crater and other lows and possibly preferentially eroding small crater rims the predominant wind direction changed to blow toward the southwest similar to today these winds further deflated the surface completed the deposition of sand size material in dunes and ultimately trapped these dunes in lows the erosional features observed by pathfinder indicate extremely low long term deflation rates of 0 01 0 04 nm yr since the end of the hesperian 1 8 3 5 ga similar to less precise rates of 1 nm yr based on the preservation of craters at the viking 1 and pathfinder landing sites short term redistribution rates deposition and removal of atmospheric dust at the pathfinder landing site and preexisting dust and sand at other locations on mars are up to 10 5 nm yr estimates of erosion rates on mars show a rapid decrease by 3 6 orders of magnitude from 10 2 10 4 nm yr in noachian terrains characterized by rimless flat floored craters and valley networks to the exceedingly slow rates 10 2 10 nm yr operating during the hesperian and amazonian noachian erosion rates comparable to low continental denudation rates on earth are consistent with erosion by running water and perhaps a more clement climate the rapid decrease in erosion rates is consistent with a major climatic change during the noachian at the tail end of heavy bombardment and a cold dry desiccating climate similar to today s since that time

degradation of the organic molecules in the shallow subsurface of mars due to irradiation by cosmic rays 1 detection of the organic matter on mars is one of the main goals of the future martian landing missions yet the degradation of organic molecules by cosmic ray irradiation on mars is often ignored we calculate the radiation dose accumulation rates from solar and galactic cosmic rays at various depths in the shallow martian subsurface we demonstrate that a 1 billion year outcrop on mars accumulates the dosage of 500 mgy in the top 0 2 cm and 50 mgy at 5 10 cm depths we show that the preservation of ancient complex organic molecules in the shallow 10 cm depth subsurface of rocks could be highly problematic if the exposure age of a geologic outcrop would exceed 300 myr we demonstrate that more simple organic molecules with masses 100 amu should have a good chance to survive in the shallow subsurface of rocks implications to the sampling strategy for the oncoming martian missions are discussed

transverse aeolian ridges tars on mars aeolian processes are probably the dominant ongoing surface modification process on mars as demonstrated by observations of dunes ripples yardangs ventifacts wind streaks dust devils and dust storms large dark dunes ldds are particularly common and were first recognized in the 1960 s from mariner data however another population of smaller often brighter ripple like aeolian bed forms that are morphologically distinct from ldds has been observed in recent higher resolution images calculations of saltation path length under martian conditions suggest these small bed forms could have formed as small barchanoid dunes or as mega ripples also known as granule ripples these features have therefore been called transverse aeolian ridges tars as this label has no genetic inference we have begun a study of tars that examines all high resolution mars orbiter camera data 1 5 to 8 m pixel resolution in a 45o longitude wide pole to pole swath we aim to determine the geographic distribution of tars assess whether they are active and to identify possible sediment sources we have already made some key observations first we present a new classification of tar deposits based on crest ridge morphology of individual forms and the size and degree of topographic control of the entire sediment mass second we present associations of tars with ldds slope streaks dust devils tracks and small impact craters that provide clues as to whether tars are currently active finally we present preliminary pole to pole survey results for the northern hemisphere that show clusters of tar deposits in the low latitudes suggesting possible unique sediment sources in these regions

rate of wind abrasion on mars estimation of the rate of aeolian abrasion of rocks on mars requires knowledge of 1 particle flux 2 susceptibilities to abrasion of various rocks and 3 wind frequencies on mars fluxes and susceptibilities for a wide range of conditions were obtained in the laboratory and combined with wind data from the viking meteorology experiment assuming an abundant supply of sand sized particles estimated rates range up to 2 1 10 2 cm of abrasion per year in the vicinity of viking lander 1 this rate is orders of magnitude too great to be in agreement with the inferred age of the surface based on models of impact crater flux the discrepancy in the estimated rate of abrasion and the presumed old age of the surface cannot be explained easily by changes in climate or exhumation of ancient surfaces we consider the primary reason to be related to the agents of abrasion either windblown grains are in very short supply or the grains are ineffective as agents of abrasion at least some sand sized 100 m grains appear to be present as inferred from both lander and orbiter observations high rates of abrasion occur for all experimental cases involving sands of quartz basalt or ash however previous studies have shown that sand is quickly comminuted to silt and clay sized grains in the martian aeolian regime experiments also show that these fine grains are electrostatically charged and bond together as sand sized aggregates laboratory simulations of wind abrasion involving aggregates show that at impact velocities capable of destroying sand aggregates form a protective veneer on the target surface and can give rise to extremely low abrasion rates

aeolian processes and dune morphology in gale crater abstract datasets at resolutions many times greater than previously available were used to study aeolian features within gale crater high resolution thermal inertia data allowed for detailed particle size estimation with the data sufficient to resolve dunefields a wide range of grain sizes have now been identified in the gale crater dunefields ranging from medium to very coarse sand high resolution imaging science experiment hirise and themis vis data allowed for detailed analysis of the dune morphology and slip faces which shows that the dunes have responded to topographic influences on prevailing wind directions under a present day wind regime this result was corroborated by a regional mesoscale model for the crater under dust storm conditions the central mound and smaller scale crater floor topography has altered the prevailing wind regime and dune patterns aeolian activity has thus played and continues to play an important role in shaping many of the present surface features of gale crater the arrival of a future lander mission such as the mars science laboratory would be able to sample these surface features directly and add a wealth of data to the understanding of gale crater

upper tropospheric waves in the tropics part ii association with clouds in the wavenumber frequency domain abstract the relationship between the large scale transient wave disturbances at the 200 mb level and the associated cloud field is studied in the latitude belt 20 s to 40 n based on wind and satellite measured brightness data for the period june august 1967 space time cross spectral analysis is used to examine the degree of association of the wind and cloud fields in the wavenumber frequency domain the total time variance of the brightness field has a well defined maximum near 10 n corresponding to a belt of sea surface temperature maximum the divergence and relative vorticity as well as the brightness have a pronounced spatial scale of zonal wavenumber s 10 at this latitude the major component contributing to this scale is westward moving disturbances with a period 5 days there is high coherence between the brightness and divergence fields at these scales in addition high coherence is found for s 3 6 and a period 5 days of westward moving disturbances corresponding to the wavenumber and p

assessing the mineralogy of the watershed and fan deposits of the jezero crater paleolake system mars we present results from geomorphic mapping and visible to near infrared spectral analyses of the jezero crater paleolake basin and its associated watershed the goal of this study is to understand the provenance of the sedimentary deposits within this open basin lake using a source to sink approach two fan deposits located within the basin have distinct visible to near infrared mineralogic signatures measured by the compact reconnaissance imaging spectrometer for mars crism the northern fan is spectrally characterized by a mixture of mg rich carbonate and olivine while the western fan is characterized by fe mg smectite e g saponite or nontronite with variable amounts of mg rich carbonate and olivine in isolated exposures the watersheds of these deposits contain a variety of geomorphic units that are likely to have supplied sediment to the jezero crater paleolake as the fluvial valleys that fed the basin incise these units the geomorphic units include exposures of fe mg smectite olivine and mg rich carbonate bearing terrain we show that the difference in fan deposit mineralogy is a function of the areal exposure of the major geomorphic units within their watersheds this indicates that the spectrally dominant aqueous alteration minerals in the fan deposits are primarily detrital or transported in nature and did not form in situ we conclude that the aqueous alteration of the units in the watershed occurred prior to the fluvial activity that carved the valleys of the jezero crater paleolake system and that the two periods of aqueous activity are not genetically related

horizontal and vertical structure of observed tropospheric equatorial rossby waves equatorial rossby er waves are identified in an 8 year data set of national meteorological center operational analyses the westward moving waves have symmetric circulations about the equator and eastward energy dispersion with maximum zonal wind perturbations along the equator and meridional wind maxima roughly 10 15 off the equator they have maximum amplitude in the lower troposphere and are associated with convective signals at roughly the mean latitude of the tropical convergence zones the circulations thus possess many of the features of the equatorially trapped n 1 rossby modes derived by matsuno 1966 they are generally around zonal planetary wavenumber 6 scale and have a deep nearly equivalent barotropic structure up to 100 mbar this is in contrast with the madden julian oscillation and mixed rossby gravity waves which generally have a first baroclinic mode vertical structure during the intensive observing period iop of the tropical ocean global atmosphere toga coupled ocean atmosphere response experiment coare and in other years westward propagating er disturbances along the equator are observed by using 6 to 30 day filtered circulation data at 850 mbar zonal wind anomalies at 850 mbar are preferentially associated with like signed anomalies in a deep layer at this frequency as was observed during coare the er waves are most common during northern winter in the central pacific although they can be detected sporadically over the other ocean basins and in other seasons as well one source for the equatorial rossby waves appears to be upper level extratropical rossby wave activity propagating into the eastern pacific although the equatorial waves are sometimes present during the northern summer when the extratropical source is absent we cite evidence that propagation of er wave activity from the central into the western pacific is related to occurrences of westerly wind bursts

observations of a convectively coupled kelvin wave in the eastern pacific itcz abstract a case study of a convectively coupled kelvin wave in the eastern pacific intertropical convergence zone itcz is presented as observed during the 1997 pan american climate studies pacs tropical eastern pacific process study tepps the large scale convective envelope associated with this disturbance with a zonal scale of approximately 1000 2000 km propagates eastward at 15 m s 1 along the mean convective axis of the itcz this envelope consists of many smaller scale westward moving convective elements with zonal scales on the order of 100 500 km as the convectively coupled kelvin wave disturbance propagates eastward it exerts a strong control on local convection radar and vertical profiler data collected aboard the noaa r v ronald h brown during the wave passage show that convection deepens rapidly as the kelvin wave approaches from the west progressing from isolated shallow cumuli to organized deep convective features within just 12 h initially rainfall in the vicinity of the s

frosted granular flow a new hypothesis for mass wasting in martian gullies abstract recent gully deposits on mars have been attributed to both wet and dry mass wasting processes in this paper frosted granular flow fgf is presented as a new hypothesis for recent mass wasting activity in martian gullies fgf is a rare type of granular flow observed on a talus slope in the province of quebec canada hetu b van steijn h vandelac p 1994 geogr phys quat 48 3 22 frost reduces dynamic inter particle friction enabling flows to mobilize onto relatively low slope gradients 25 30 compared to those involving dry granular flow of the same material 35 41 resulting erosional and depositional features include straight to sinuous channels levees and digitate to branching arrangements of terminal deposits similar features are commonly found in association with geologically young gully systems on mars based on terrestrial observations of fgf processes the minimum criteria required for their occurrence on mars include i readily mobilized unconsolidated sediment at the surface ii an upper slope gradient at or near the angle of repose iii frost accumulation at the surface and iv triggering by rock fall all four conditions appear to be met in many areas on present day mars though triggering mechanisms may vary compared to terrestrial fgfs which are lubricated by thin liquid films at inter particle contacts those occurring on mars are more likely lubricated by vaporization of co 2 and small amounts of h 2 o frost that becomes incorporated in the translating mass some recent mass wasting activity in martian gullies therefore could be interpreted as the product of fgf

the madden julian oscillation observed during the toga coare iop global view abstract during the toga coare intensive observing period november 1992 february 1993 two pronounced madden julian oscillation mjo events associated with super cloud clusters and westerly wind bursts were observed this paper presents a global view of the mjos including the origin of the super clusters in the indian ocean their migration into the maritime continent and the toga coare large scale soundings array lsa in the western equatorial pacific and their rapid decay over cold water of the eastern pacific the structure and evolution of the mjo are examined with emphasis on the coupling between large scale motion and convection because of differences in propagation speeds the positions of maximum zonal wind perturbations relative to deep convection undergo systematic changes during the travel of the mjo however the centers of deep convection always coincide with those of large scale ascent the super cloud cluster accompanies a wide area of warm air in the upper troposphere over the warm

mars global digital dune database mgd 3 global dune distribution and wind pattern observations abstract the mars global digital dune database mgd 3 is complete and now extends from 90 n to 90 s latitude the recently released south pole sp portion mc 30 of mgd 3 adds 60 000 km 2 of medium to large size dark dune fields and 15 000 km 2 of sand deposits and smaller dune fields to the previously released equatorial eq 70 000 km 2 and north pole np 845 000 km 2 portions of the database bringing the global total to 975 000 km 2 nearly all np dunes are part of large sand seas while the majority of eq and sp dune fields are individual dune fields located in craters despite the differences between mars and earth their dune and dune field morphologies are strikingly similar bullseye dune fields named for their concentric ring pattern are the exception possibly owing their distinctive appearance to winds that are unique to the crater environment ground based wind directions are derived from slipface sf orientation and dune centroid azimuth dca a measure of the relative location of a dune field inside a crater sf and dca often preserve evidence of different wind directions suggesting the importance of local topographically influenced winds in general however ground based wind directions are broadly consistent with expected global patterns such as polar easterlies intriguingly between 40 s and 80 s latitude both sf and dca preserve their strongest though different dominant wind direction with transport toward the west and east for sf derived winds and toward the north and west for dca derived winds

clay minerals in delta deposits and organic preservation potential on mars clay rich sedimentary deposits are often sites of organic matter preservation and have therefore been sought in mars exploration however regional deposits of hydrous minerals including phyllosilicates and sulphates are not typically associated with valley networks and layered sediments that provide geomorphic evidence of surface water transport on early mars the compact reconnaissance imaging spectrometer for mars crism has recently identified phyllosilicates within three lake basins with fans or deltas that indicate sustained sediment deposition eberswalde crater holden crater and jezero crater here we use high resolution data from the mars reconnaissance orbiter mro to identify clay rich fluvial lacustrine sediments within jezero crater which has a diameter of 45 km the crater is an open lake basin on mars with sedimentary deposits of hydrous minerals sourced from a smectite rich catchment in the nili fossae region we find that the two deltas and the lowest observed stratigraphic layer within the crater host iron magnesium smectite clay jezero crater holds sediments that record multiple episodes of aqueous activity on early mars we suggest that this depositional setting and the smectite mineralogy make these deltaic deposits well suited for the sequestration and preservation of organic material

a habitable fluvio lacustrine environment at yellowknife bay gale crater mars the curiosity rover discovered fine grained sedimentary rocks which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy this aqueous environment was characterized by neutral ph low salinity and variable redox states of both iron and sulfur species carbon hydrogen oxygen sulfur nitrogen and phosphorus were measured directly as key biogenic elements by inference phosphorus is assumed to have been available the environment probably had a minimum duration of hundreds to tens of thousands of years these results highlight the biological viability of fluvial lacustrine environments in the post noachian history of mars

the environmental significance of ventifacts a critical review abstract ventifacts wind abraded clasts or rock surfaces are common features of many terrestrial hot and cold deserts coastal periglacial and mountain environments as well as on mars and have a long history of investigation this review paper discusses some of the main themes in terrestrial ventifact research including their formation and geomorphic controls the varied morphological forms of ventifacts in terrestrial environments and their environmental significance as indicators of past and present wind direction and sediment mobility are critically evaluated future research directions are identified

convectively coupled equatorial waves 1 convectively coupled equatorial waves ccews control a substantial fraction of tropical rainfall variability their horizontal structures and dispersion characteristics correspond to matsuno s 1966 solutions of the shallow water equations on an equatorial beta plane namely kelvin equatorial rossby mixed rossby gravity and inertio gravity waves because of moist processes the tilted vertical structures of ccews are complex and their scales do not correspond to that expected from the linear theory of dry waves the dynamical structures and cloud morphology of ccews display a large degree of self similarity over a surprisingly wide range of scales with shallow convection at their leading edge followed by deep convection and then stratiform precipitation mirroring that of individual mesoscale convective complexes ccews have broad impacts within the tropics and their simulation in general circulation models is still problematic although progress has been made using simpler models a complete understanding of ccews remains a challenge in tropical meteorology

long term wind erosion on mars abstract wind erosion and deposition are powerful agents of surface change on mars erosion is sensitive to the atmospheric density so feedback between orbit variations and atmospheric density can enhance the sensitivity of erosion rates to orbital parameters we use statistics derived from a 1 gyr integration of the spin axis of mars coupled with runs of the nasa ames 3 d general circulation model gcm at a variety of orbital conditions and pressures to explore this feedback we find that wind erosion in the gcm is associated with two factors baroclinic zone winds and strong cross equator solstice flows both of these factors are influenced by topography producing an asymmetry in the erosion pattern between the north and the south the erosion model averaged over 1 gyr produces potential erosion rates of 1 7 10 5 m yr 1 in the north and 1 0 10 5 m yr 1 in the south which increase by an order of magnitude in an early 28 mbar atmosphere the stability of these potential erosion patterns over geological time indicates that the lowland regions of mars are continuously eroded and that wind is capable of revealing ancient sedimentary deposits or eroding substantial deposits that may have otherwise been preserved

a combined wave number frequency and time extended eof approach for tracking the progress of modes of large scale organized tropical convection an algorithm combining filtering in the wave number frequency domain with time extended empirical orthogonal function eeof analysis is developed and applied to diagnose and track signals associated with modes of organized moist deep convection in the tropics the wave number frequency spectrum of outgoing long wave radiation olr is broken down into five broad filter bands in order to concentrate signals associated with the madden julian oscillation convectively coupled equatorial rossby kelvin and mixed rossby gravity waves easterly waves and low frequency variations such as the el nino southern oscillation enso the eeof patterns are obtained from analysis of the filtered data and principal component pc time series are generated by projection of temporally smoothed but otherwise unfiltered data onto the eeof patterns filtered data are reconstructed by taking the product of the eeof patterns and the corresponding pcs these reconstructed data compare well with unfiltered olr anomalies and with olr anomalies filtered in the wave number frequency domain for the same modes the method is easily applied in real time since results are not influenced by the proximity to the end of the dataset copyright 2009 royal meteorological society

the suppression of inertinite reflectance abstract the suppression of reflectance of vitrinite with hydrogen rich composition compared to iso rank vitrinite of normal composition is widely recognized from a consideration of fluorescence alteration properties it is argued that inertinite macerals associated with hydrogen rich vitrinites in coal or dispersed organic matter will also show suppressed reflectance in dispersed organic matter in which vitrinite is rare or absent hydrogen rich unstructured inertinite may easily be misidentified as vitrinite if only reflectance data are available

ventifacts on earth and mars analytical field and laboratory studies supporting sand abrasion and windward feature development abstract terrestrial ventifacts rocks that have been abraded by windblown particles are found in desert periglacial and coastal environments on mars their abundance suggests that aeolian abrasion is one of the most significant erosional processes on the planet there are several conflicting viewpoints concerning the efficacy of potential abrasive agents principally sand and dust and the relationships between wind direction and ventifact form our research supported by a review of the literature shows that sand rather than dust or other materials is the principle abrasive agent on earth and mars relative to dust sand delivers about 1000 the energy onto rock surfaces on a per particle basis even multiple dust collisions will do little or no damage because the stress field from the impact is much smaller than the spacing of microflaws in the rock the abrasion profiles of terrestrial ventifacts are consistent with a kinetic energy flux due to saltating sand not airborne dust furthermore scanning electron microscope images reveal surfaces that are fractured and cleaved by sand grain impact with respect to their distribution ventifacts are found in regions that contain sand or did so in the past but are not found where only dust activity occurs contrary to some published reports our evidence from field studies analytical models and wind tunnel and other experiments indicates that windward not leeward abrasion is responsible for facet development and feature formation pits flutes and grooves leeward abrasion is confined to fluvial conditions in which the high viscosity and density of water are able to entrain sand size material in vortices therefore ventifacts and abraded terrain provide an unambiguous proxy for the direction of the highest velocity winds and can be used to reconstruct palaeowind flow

the rock abrasion record at gale crater mars science laboratory results from bradbury landing to rocknest ventifacts rocks abraded by wind borne particles are found in gale crater mars in the eastward drive from bradbury landing to rocknest they account for about half of the float and outcrop seen by curiosity s cameras many are faceted and exhibit abrasion textures found at a range of scales from submillimeter lineations to centimeter scale facets scallops flutes and grooves the drive path geometry in the first 100 sols of the mission emphasized the identification of abrasion facets and textures formed by westerly flow this upwind direction is inconsistent with predictions based on models and the orientation of regional dunes suggesting that these ventifact features formed from very rare high speed winds the absence of active sand and evidence for deflation in the area indicates that most of the ventifacts are fossil features experiencing little abrasion today

effects of convective processes on gcm simulations of the madden julian oscillation abstract weak temporal variability in tropical climates such as the madden julian oscillation mjo is one of major deficiencies in general circulation models gcms the uncertainties in the representation of convection and cloud processes are responsible for these deficiencies with the improvement made to the convection scheme the iowa state university isu gcm which is based on a version of the ncar community climate model is able to simulate many features of mjo as revealed by observations in this study four 10 yr 1979 88 isu gcm simulations with observed sea surface temperatures are analyzed and compared to examine the effects of the revised convection closure convection trigger condition and convective momentum transport cmt on the mjo simulations the modifications made in the convection scheme improve the simulations of amplitude spatial distribution eastward propagation and horizontal and vertical structures especially for the coherent feature of eastward propagating convection a

scarp orientation in regions of active aeolian erosion on mars abstract the morphologies of wind formed features on mars provide diagnostic information about ancient and modern surface winds aeolian erosional features include decimeter scale ventifacts and kilometer scale yardangs but intermediate scale erosional features are less well understood understanding aeolian erosion may be critical to identifying ancient martian biosignatures cosmogenic radiation destroys complex organic molecules during prolonged exposure at the martian surface but outcrops freshly re exposed by aeolian erosion provide potential sites where biosignatures could have been protected and made recently available for sampling wind driven scarp retreat has been cited as the cause for young exposure ages measured in gale crater upcoming exploration by the mars 2020 rover will focus on jezero crater another location of extensive aeolian erosion and meter scale scarps this work is motivated by the hypothesis that retreating scarps on mars may prefer orientations that reflect the direction of erosive winds we mapped scarps in jezero and gale craters and compared their orientation distributions with local wind regimes interpreted from other aeolian indicators no strong correlation between wind direction and scarp orientation was identified the near random distribution of scarp orientations suggests that in the locations studied the dominant processes controlling scarp orientation are either processes that do not prefer an orientation e g impact or thermal fracturing processes or that turbulent flow structures form at the scale of scarp topography and obscure the regional scale signals of erosion with scarp scale eddies and flow deflection

periodic bedrock ridges on mars 1 evidence for sediment transport and erosion by wind is widespread over the surface of mars today and was likely a major geomorphic process for much of its geological past although martian surface features resembling aeolian dunes and ripples have been recognized since the mariner and viking missions such features have been interpreted previously as active indurated or exhumed sedimentary forms here we report evidence based on high resolution imaging science experiment images that show some megaripple forms are eroded into cohesive substrate rather than being composed of loose granular material or fossilized dunes exposure of stratigraphic continuity within layered cohesive material extending crest to trough through features with mean wavelengths of 18 to 51 m demonstrates the primarily erosional formation of what we term periodic bedrock ridges pbrs hence some surfaces on mars previously considered to be covered by wind deposited material are actually wind carved exposures that offer windows into martian history pbrs lack the distinctive streamlining associated with wind parallel yardangs and comparison of pbr orientation to yardangs megayardangs and active sedimentary dunes in the same vicinity confirm that these pbrs formed transverse to prevailing winds observed wavelengths of pbrs are comparable to those predicted by a simple model for erosional wavelengths of periodic transverse bed forms owing to the spacing of flow separations within the flow recognition of these transverse aeolian erosional forms brings up the question of how widespread martian pbrs are and how many have been misinterpreted as active or indurated fossilized sedimentary dunes