origin of giant wave ripples in snowball earth cap carbonate the most extreme climate transitions in earth history are recorded by the juxtaposition of neoproterozoic glacial deposits with overlying cap carbonate beds some of the most remarkable sedimentary structures within these beds are sharp crested trochoidal bedforms with regular spacing of as much as several meters that are often interpreted as giant wave ripples formed under extreme wave conditions in a nonuniform postglacial climate here we evaluate this hypothesis using a new bedform stability diagram for symmetric oscillatory fl ows that indicates that the fi rst order control on the formation of trochoidal rather than hummocky bedforms is sediment size not wave climate new measurements of bedform wavelengths and particle sizes from the ca 635 ma nuccaleena formation australia indicate that the giant ripples are generally composed of coarse to very coarse sand most are within the trochoidal bedform stability phase space for normal wave climates moreover numerical simulations of flover fi xed bedforms show that symmetric trochoidal ripples with a nearly vertical angle of climb may be produced over long time periods with variable wave climates in conjunction with rapid seabed cementation these data reveal that rather than extreme wave conditions the giant wave ripples are a consequence of the unusual mode of carbonate precipitation during a global carbon cycle perturbation unprecedented in earth history

measurement of eolian sand ripple cross sectional shapes assuming that the profiles of eolian sand ripples remain constant over a short distance it is possible to measure their shapes by casting a shadow perpendicular to the ripple crests we describe a method whereby this can be done accurately and easily tests of the method demonstrate that accuracies on the order of one sand grain diameter can be achieved

evaluation and interpretation of thirteen official van telegrams for the period september 10 1986 to april 28 1988 abstract all the thirteen official earthquake prediction telegrams sent by van researchers during september 10th 1985 to april 28th 1988 based on seismic electric signals ses observations were examined against seismic data the first four telegrams pertaining to the m s 6 0 kalamata earthquake and its aftershocks were all failures of the remaining nine telegrams five were complete failures because there was no earthquakes with m 4 in the candidate areas within 11 d after the telegram even when some events occured after the telegram correlation with prediction was either non unique or the error in magnitude was too large in seven cases earthquakes with a magnitude comparable to that of predicted events took place in the candidate areas just before the related telegrams without any ses contrary to van s assertion of one to one correspondence between ses and earthquakes

orbital observations of contemporary dune activity in endeavor crater meridiani planum mars 1 although aeolian landforms are pervasive on mars evidence for contemporary activity has been limited the next major campaign for the mars exploration rover opportunity is the investigation of the 20 km diameter endeavor crater 6 km to southeast of the rover s position as of december 2010 we present evidence from orbital imagery that eight aeolian bed forms 14 000 m2 in endeavor crater have been active within the past decade 2001 2009 at a spatial scale that should be directly observable by opportunity from the crater rim two dunes appear to show translational migration 10 20 m but all dunes indicate erosion to be the dominant process with up to 100 sediment removal thermophysical properties of these dunes are consistent with very fine to fine sand sizes the particle sizes most easily moved by the martian atmosphere the dunes that show the most surface change have a rippled appearance without well defined slip faces based on their morphology elliptical shape we classify them as dome dunes mesoscale atmospheric modeling is employed to provide insight into the atmospheric forcing of this aeolian system the major wind regimes from modeling are consistent with observations of wind streaks sand streamers ripples and slip faces of regional dune fields although modeled wind speeds are insufficient to move sand the translation and erosion of these dunes constitutes the largest contemporary movement of sand sized sediment reported on mars to date and demonstrates that endeavor crater has been subject to wind profiles exceeding the threshold velocity at the surface daily seasonally and or episodically in the recent past

surface elevation contours of greenland and antarctic ice sheets surface elevations of the ice sheets are contoured at 50 m intervals for the region of greenland covered by seasat radar altimetry south of 72 n and at 100 m intervals for a region of east antarctica north of 72 s the surface elevations were obtained from computer retracking of the radar altimeter waveforms which were recorded at 0 1 s intervals corresponding to 662 m spacings on the surface the precision of the elevation measurements before adjustment for radial orbit errors is 1 9 m as shown by analysis of elevation differences at orbital crossover points this precision is partly determined by radial errors of approximately 1 0 m in orbit determination and partly by noise due to ice surface irregularities adjustment of the radial components of the orbits to minimize the differences in elevations at crossovers over a small relatively flat region reduces the rms difference to 0 25 m which is indicative of the optimum precision obtainable over the ice sheets however the precision degrades as the slope of the surface or amplitude of the undulations increases yielding an overall precision of 1 6 m the preliminary contour maps are not corrected for slope induced displacements a 2 m contour map in a region of highest data density illustrates the three dimensional characteristics of some surface undulations

the confluence zone of the intense katabatic winds at terra nova bay antarctica as derived from airborne sastrugi surveys and mesoscale numerical modeling the surface wind field inland of the intense coastal kataba c wind regime at terra nova bay antarctica has been studied both observationally and numerically airborne surveys of windinduced features on the snow surface have been used to construct the time averaged winter surface airflow pattern the surface motion field has also been simulated by a mesoscale primitive equation model using terrain slopes with a horizontal resolution of 32 km both methods of analys s demonstrate that the intense katabatic airstream at terra nova bay is forced by converging air currents in the continental interior the broadscale confluence zone becomes organized into two regions within about 180 km of the coast the primary route for katabatic mass transport into the terra nova bay area is reeves glacier valley but an important secondary source is provided by airflow down david glacier the former is generated by the coriolis induced concentration of mass transport on the left side looking downwind of the broadscale confluence zone as well as by the near coastal mountain deflection of airflow into the valley head the confluence zone feeding into david glacier valley stretches over 100 km into the interior and is forced by the broadscale terrain configuration of the ice sheet source areas for the two airstreams differ with reeves glacier valley being fed by cold air formed well into the interior whereas the airflow down david glacier is sustained by radiative cooling over lower parts of the ice sheet which are much closer to the ross sea evaluation of the observational and modeling results reveals both the strengths and weaknesses of each approach airborne surveys of sastrugi orientations are a highly successful method for establishing the detailed pattern of surface airflow however a systematic examination of sastrugi dimensions suggests that such work could also be carried out using spot type satellite observations which is a more cost effective approach than aircraft surveying the double jet structure of katabatic airflow into the terra nova bay area is well represented by the primitive equation modeling but much finer grids are needed to resolve the near coastal drainage details

large wind ripples on mars a record of atmospheric evolution wind blowing over sand on earth produces decimeter wavelength ripples and hundred meter to kilometer wavelength dunes bedforms of two distinct size modes observations from the mars science laboratory curiosity rover and the mars reconnaissance orbiter reveal that mars hosts a third stable wind driven bedform with meter scale wavelengths these bedforms are spatially uniform in size and typically have asymmetric profiles with angle of repose lee slopes and sinuous crest lines making them unlike terrestrial wind ripples rather these structures resemble fluid drag ripples which on earth include water worked current ripples but on mars instead form by wind because of the higher kinematic viscosity of the low density atmosphere a reevaluation of the wind deposited strata in the burns formation about 3 7 billion years old or younger identifies potential wind drag ripple stratification formed under a thin atmosphere

visible near infrared spectral diversity from in situ observations of the bagnold dune field sands in gale crater mars as part of the bagnold dune campaign conducted by mars science laboratory rover curiosity visible near infrared reflectance spectra of dune sands were acquired using mast camera mastcam multispectral imaging 445 1013 nm and chemistry and camera chemcam passive point spectroscopy 400 840 nm by comparing spectra from pristine and rover disturbed ripple crests and troughs within the dune field and through analysis of sieved grain size fractions constraints on mineral segregation from grain sorting could be determined in general the dune areas exhibited low relative reflectance a weak 530 nm absorption band an absorption band near 620 nm and a spectral downturn after 685 nm consistent with olivine bearing sands the finest grain size fractions occurred within ripple troughs and in the subsurface and typically exhibited the strongest 530 nm bands highest relative reflectances and weakest red near infrared ratios consistent with a combination of crystalline and amorphous ferric materials coarser grained samples were the darkest and bluest and exhibited weaker 530 nm bands lower relative reflectances and stronger downturns in the near infrared consistent with greater proportions of mafic minerals such as olivine and pyroxene these grains were typically segregated along ripple crests and among the upper surfaces of grain flows in disturbed sands sieved dune sands exhibited progressive decreases in reflectance with increasing grain size as observed in laboratory spectra of olivine size separates the continuum of spectral features observed between the coarse and fine grained dune sands suggests that mafic grains ferric materials and air fall dust mix in variable proportions depending on aeolian activity and grain sorting

chemistry mineralogy and grain properties at namib and high dunes bagnold dune field gale crater mars a synthesis of curiosity rover observations the mars science laboratory curiosity rover performed coordinated measurements to examine the textures and compositions of aeolian sands in the active bagnold dune field the bagnold sands are rounded to subrounded very fine to medium sized 45 500 m with 6 distinct grain colors in contrast to sands examined by curiosity in a dust covered inactive bedform called rocknest and soils at other landing sites bagnold sands are darker less red better sorted have fewer silt sized or smaller grains and show no evidence for cohesion nevertheless bagnold mineralogy and rocknest mineralogy are similar with plagioclase olivine and pyroxenes in similar proportions comprising 90 of crystalline phases along with a substantial amorphous component 35 15 yet bagnold and rocknest bulk chemistry differ bagnold sands are si enriched relative to other soils at gale crater and h 2o s and cl are lower relative to all previously measured martian soils and most gale crater rocks mg ni fe and mn are enriched in the coarse sieved fraction of bagnold sands corroborated by visible near infrared spectra that suggest enrichment of olivine collectively patterns in major element chemistry and volatile release data indicate two distinctive volatile reservoirs in martian soils 1 amorphous components in the sand sized fraction represented by bagnold that are si enriched hydroxylated alteration products and or h 2o or oh bearing impact or volcanic glasses and 2 amorphous components in the fine fraction 40 m represented by rocknest and other bright soils that are fe s and cl enriched with low si and adsorbed and structural h 2o

windy mars a dynamic planet as seen by the hirise camera 1 with a dynamic atmosphere and a large supply of particulate material the surface of mars is heavily influenced by wind driven or aeolian processes the high resolution imaging science experiment hirise camera on the mars reconnaissance orbiter mro provides a new view of martian geology with the ability to see decimeter size features current sand movement and evidence for recent bedform development is observed dunes and ripples generally exhibit complex surfaces down to the limits of resolution yardangs have diverse textures with some being massive at hirise scale others having horizontal and cross cutting layers of variable character and some exhibiting blocky and polygonal morphologies reticulate fine polygonal texture bedforms are ubiquitous in the thick mantle at the highest elevations

azimuth variation in microwave scatterometer and radiometer data over antarctica while designed for ocean observation scatterometer and radiometer data have proven very useful in a variety of cryosphere studies over large regions of antarctica ice sheet and bedrock topography and the snow deposition drift and erosional environment combine to produce roughness on various scales roughness ranges from broad basin scale ice sheet topography at spl sim 100 km wavelengths to large spatially coherent dune fields at spl sim 10 km wavelength to erosional features on the meter scale known as sastrugi these roughness scales influence the microwave backscattering and emission properties of the surface combining to introduce azimuth angle dependencies in the satellite observation data in this paper the authors explore the use of nasa scatterometer nscat data european remote sensing ers advanced microwave instrument ami scatterometer mode data and special sensor microwave imager ssm i data to study surface roughness effects in antarctica all three sensors provide strong evidence of azimuth modulation which is correlated with the surface slope environment and results in a katabatic wind flow regime due to its broad azimuth coverage nscat data appears to be the best suited for azimuth angle observations a simple empirical model for the azimuth variation in the radar backscatter is developed and an algorithm for computing the parameters of the model from nscat data at a fine scale is presented results indicate relationships exist between the azimuthal variation of the data and the orientation of the surface slope and small scale roughness relative to the sensor look direction

seismic electric signals ses and earthquakes a review of an updated van method and competing hypotheses for ses generation and earthquake triggering abstract electromagnetic phenomena are sometimes associated with seismic events but earthquake prediction using seismic electric signals ses has not been seriously considered since the early 1990s there are several causes 1 false alarms that have created panics in greece and 2 a strong critique of the varotsos alexopoulos nomicos van method used there an updated van method that includes time series analysis has made successful medium range predictions and short range predictions when coupled with seismic time series analysis four types of potential mechanisms to create precursory ses relying on deformation effects temperature effects ore mineral movement or groundwater variation are reviewed data relevant to each are insufficient to favor a single mechanism records of the number of false positive and missed events for an updated van method have not been well maintained false positives appear to be abundant and render the method unusable co seismic groundwater fluctuations are addressed and two novel hypotheses of earthquake trigger mechanism are also presented ionospherically induced electric and resultant magnetic fields to weaken rock thereby causing failure and volatiles liberated from minerals additionally promoting rock failure recommendations for further study are included

what sets the size of current ripples water flowing over sand in fluvial and marine settings often results in the formation of current ripples found in modern and ancient deposits on earth and mars ripple stratification records flow directions and fluid properties that are crucial to interpreting sedimentary records despite decades of observations of current ripples there is no universal scaling relation to predict their size or to distinguish them from dunes here we use dimensional analysis and a new data compilation to develop a scaling relation that collapses data for equilibrium wavelengths of ripples forming under unidirectional flows results show that ripples are larger with more viscous fluids coarser grains smaller bed shear stresses and smaller specific gravity of sediment the scaling relation also segregates ripples from dunes highlighting a narrow regime of transitional bedforms that have morphologic properties and sediment transport conditions that overlap with both ripples and dunes our analysis shows that previous absolute size based definitions of ripples and dunes only hold for certain conditions such as water flows transporting siliciclastic grains on earth the new theory allows estimates of ripple sizes in foreign fluids and on other planets including meter scale ripples in methane flows on titan or in viscous brines on mars

the application of the magnetotelluric impedance tensor to earthquake prediction research in greece continuous short period 0 1 3600 s measurements of the magnetotelluric field components were conducted simultaneously at two sites in greece for a period of 5 weeks the estimation of the impedance tensor elements from 8 hr windows of recorded data at each station is found to describe the local electromagnetic induction with great accuracy the computation of the residual electric field obtained as the difference between the observed and estimated inductive part of the electric fields clearly improves the detection of any local electric field anomaly this method was used in an attempt to detect precursory sci smic electrical signals ses that have been reported to precede earthquakes in greece the results indicate the success of this method in resolving ambiguities about the nature of the reported ses i e whether it has an external or internal source although during the recording period no large earthquake occurred five with a magnitude of between ml 4 0 and ml 4 3 occurred within a radius of 150 km from one of the stations the magnetotelluric recordings and the computed residual electric fields for the time intervals reported to contain the ses precursors to these events were analysed in some detail in two of the cases it was found that the sources could not be related to earthquake processes in the other three cases the nature of the source of the suspected ses although electric could not be established with certainty these results indicate that for earthquakes of small magnitude ml 4 3 or of large epicentral distance r 100 km the detection of a ses is extremely difficult

observation and characterization of radar backscatter over greenland characterization of the microwave signature of the greenland snow surface enables delineation of the different snow facies and is a tool for tracking the effects of climate change a new empirical observation model is introduced that uses a limited number of parameters to characterize the snow surface based on the dependence of radar backscatter on incidence angle azimuth angle spatial gradient and temporal rate of change the individual model parameters are discussed in depth with examples using data from the nasa scatterometer nscat and from the c band european remote sensing ers satellite advanced microwave instrument in scatterometer mode the contribution of each model term to the overall accuracy of the model is evaluated the relative contributions of the modeled dependencies vary by region two studies illustrating applications of the model are included first interannual changes over the greenland ice sheet are investigated using nine years of ers data surface changes are observed as anomalies in the spl sigma spl deg model parameters second intraannual variations of the surface are investigated these changes are observed in the average backscatter normalized to a given observation geometry the results indicate that the model can be used to obtain a more complete understanding of multiyear change and to obtain low variance high temporal resolution observations of intraannual changes the model may be applied for increased accuracy in scatterometer synthetic aperture radar sar and wide angle sar studies

mapping of the topography of continental ice by inversion of satellite altimeter data satellite altimeter data over ice sheets provide the best tool for mapping their topography and its possible climatic variations however these data are affected by measurement errors orbit errors and slope errors we develop here a three step inversion technique which accommodates the a priori information on the expected topography and correctly handles and propagates the data errors it estimates first a large scale reference surface then maps the residuals related to undulations and finally iteratively corrects the slope error the method is tested on overlapping small fragments of the antarctic ice sheet using a sub set of seasat data finally a topographic map of terre adelie is produced over areas of small slopes the a posteriori error should be of the order of 0 4 m using ers i data it is therefore expected that climatic variations in the ice sheet topography since the introduction of seasat will be observable

altimetric observations of surface characteristics of the antarctic ice sheet the aim of this paper is to investigate the geophysical characteristics of the antarctic ice sheet using radar altimetric observations to do this we use an altimetric waveform simulator in situ observations ers 1 european remote sensing satellite data and spot satellite pour l observation de la terre images the small scale study takes place at dome c terre adelie which is a relatively flat region with gentle undulations and low wind speed despite this the altimetric waveform parameters height energy leading edge and trailing edge are highly noisy the effect of undulations on the waveform parameters is found to be dominant the combination of a subsurface signal and a rough surface produces a linear effect on the altimetric backscattering or on the trailing edge of the waveform but a strongly non linear effect on the leading edge of the waveform or height estimation as a consequence the height measurement is very sensitive to the altimeter technical or orbital characteristics and is not reproducible from one mission to another observations show sastrugi fields that enhance the leading edge and affect the whole waveform observed local backscattering changes probably due to local variations in surface microroughness enhance the backscattered energy and may artificially create a topographic signal the continental scale study shows coherent patterns even if both surface and subsurface components affect the altimetric observation the large scale signal is mostly controlled by surface backscattering variations the surface or near subsurface characteristics of the snowpack may then be reached by altimetric observations

physical properties of the variations of the electric field of the earth preceding earthquakes ii determination of epicenter and magnitude abstract as reported in the preceding paper a transient change of the electric field of the earth seismic electric signal hereafter called ses appears many hours before an earthquake eq by measuring this change in a given direction and dividing it with a suitable relative effective resistivity one obtains a quantity that reflects the current density in this direction measurements in two directions e w and n s give the relative signal intensity jrel at the station under consideration by measuring jrel at a number of stations and considering that it attenuates according to a 1 r law the epicenter can be determined with an accuracy usually around 100 km once the epicenter has been determined the product jrel r can be evaluated so that the magnitude m can be estimated by resorting to an empirical log jrel r versus m plot the uncertainty of m is around 0 5 units following sobolev 1975 and for the statistics to be beyond any doubt predictions were officially documented before the eq occurrence for 23 earthquakes with a magnitude equal or greater than ms 5 0 two events were missed the present method is compared to other electrical methods used in china japan and soviet union a number of problems concerning the origin of the effect its directivity and the attenuation with distance remain open for further studies

different ers altimeter measurements between ascending and descending tracks caused by wind induced features over ice sheets the ers1 satellite provides a high resolution radar altimeter measurement up to 81 5 latitude for polar cap studies here we examine one particular effect of the interaction between the radar wave and the snowpack surface on height measurements measurements from ascending and descending tracks show systematic differences as large as 1 m such an artifact to be removed if it can be estimated the difference appears to be related to the way the altimeter perceives wind induced sculpting of the snowpack differences in the volume echo weight between ascending and descending passes appear to be the explanation seasat scatterometer allowed us to estimate independently the signal that could be inferred by wind features our results yield a map of the effect of wind on radar altimetric measurement finally we consider the possibility of long term variations in altimeter measurements caused by climatic changes

flume experiments on the alignment of transverse oblique and longitudinal dunes in directionally varying flows for more than a century geologists have wondered why some bedforms are orientated roughly transverse to flow whereas others are parallel or oblique to flow this problem of bedform alignment was studied experimentally using subaqueous dunes on a 3 6 m diameter sand covered turntable on the floor of a 4 m wide flume in each experiment two flow directions relative to the bed were produced by alternating the turntable between two orientations the turntable was held in each orientation for a short time relative to the reconstitution time of the bedforms the resulting bedforms were in equilibrium with the time averaged conditions of the bimodal flows dune alignment was studied for five divergence angles the angle between the two flow directions 45 67 5 90 112 5 and 135 the flow depth during all experiments was approximately 30 cm mean velocity was approximately 50 cm s 1 and mean grain diameter was 0 6 mm each experiment continued for 30 75 min during which time the flume flow was steady and the turntable position changed every 2 min at the end of each experiment water was slowly drained from the flume and dune alignment was measured transverse dunes defined relative to the resultant transport direction were created when the divergence angle was 45 and 67 5 and longitudinal dunes were created when the divergence angle was 135 at intermediate divergence angles dunes with both orientations were produced but transverse dunes were dominant at 90 and longitudinal dunes were dominant at 112 5 one experiment was conducted with a divergence angle of 135 and with unequal amounts of transport in the two flow directions this was achieved by changing the orientation of the turntable at unequal time intervals thereby causing the amount of transport to be unequal in the two directions the dunes formed during this experiment were oblique to the resultant transport direction these experimental dunes follow the same rule of alignment as wind ripples studied in previous turntable experiments in both sets of experiments the bedforms developed with the orientation having the maximum gross bedform normal transport the orientation at which the sum of the bedform normal components of the two transport vectors reaches its maximum value in other words the bedforms develop with an orientation that is as transverse as possible to the two flows in those cases where the two flows diverge by more than 90 and transport equal amounts of sand bedforms that are as transverse as possible to the two separate flows will be parallel to the resultant of the two flow vectors although such bedforms have been defined by previous work as longitudinal bedforms they are intrinsically the same kind of bedform as transverse bedforms

the surface windfield over the antarctic ice sheets the intense radiative cooling of air over the ice slopes of antarctica generates a surface wind regime that is strongly controlled by topography and plays a key role in determining the behaviour of the atmosphere and ocean in high southern latitudes1 7 resultant surface winds are intimately linked to the orientation of the ice terrain fig 1 and display the highest degree of persistence found on earth the close coupling between wind and topography allows estimation of the former if the latter is known with some precision here we report on time averaged near surface airflow over the antarctic continent during winter diagnosed from a recent accurate synthesis of terrain slopes and from estimates of the lower atmospheric temperature structure the simulated drainage pat tern exhibits strong spatial variability with the airflow concentrated into several zones near the coastal margin these confluence regions are responsible for strong persistent katabatic winds over downstream coastal stretches and are indicative of zones of greatest katabatic potential

latest aspects of earthquake prediction in greece based on seismic electric signals ii abstract since 1983 continuous monitoring of the electrotelluric field has been carried out using an array of measuring stations located at various sites in greece the basic physical properties of the transient changes seismic electric signals ses in the electrotelluric field that are forerunners of earthquakes were first described six years ago since then a large body of data has been collected resulting in new insight into various aspects of the method the present paper reviews the latest developments in ses based earthquake prediction and describes the current procedures used to predict the epicenter and magnitude of an impending earthquake a detailed list of the predictions officially issued in greece during the past 3 years january 1 1987 november 30 1989 is also given public warnings were issued well before the most destructive seismic activity

comparison of microwave backscatter anisotropy parameterizations of the antarctic ice sheet using ascat the c band eumetsat advanced scatterometer ascat was launched in 2007 and provides backscatter measurements with excellent azimuth and incidence angle diversity in polar regions c band backscatter measurements can be used to retrieve near surface snow firn properties such as grain size and accumulation rate however the antarctic ice sheet ais exhibits strong microwave backscatter anisotropy as a function of both incidence and azimuth angles and this anisotropy must be well understood before such physical parameter retrieval can be accurately performed this paper presents a detailed comparison of several different parameterizations of both the azimuth and the incidence anisotropy parameterizations used here result in residuals similar to the radiometric performance of ascat indicating accurate characterization of the anisotropy the analysis of these parameterizations provides an insight into the physical mechanisms taking place near the surface of the ais 30 day composite maps of several parameters are presented and discussed in the context of near surface glaciology this anisotropy characterization will form the basis of a technique for extraction of physical parameters of the ais

compositional variations in sands of the bagnold dunes gale crater mars from visible shortwave infrared spectroscopy and comparison with ground truth from the curiosity rover during its ascent up mount sharp the mars science laboratory curiosity rover traversed the bagnold dune field we model sand modal mineralogy and grain size at four locations near the rover traverse using orbital shortwave infrared single scattering albedo spectra and a markov chain monte carlo implementation of hapke s radiative transfer theory to fully constrain uncertainties and permitted solutions these predictions evaluated against in situ measurements at one site from the curiosity rover show that x ray diffraction measured mineralogy of the basaltic sands is within the 95 confidence interval of model predictions however predictions are relatively insensitive to grain size and are nonunique especially when modeling the composition of minerals with solid solutions we find an overall basaltic mineralogy and show subtle spatial variations in composition in and around the bagnold dunes consistent with a mafic enrichment of sands with cumulative aeolian transport distance by sorting of olivine pyroxene and plagioclase grains furthermore the large variations in fe and mg abundances 20 wt at the bagnold dunes suggest that compositional variability may be enhanced by local mixing of well sorted sand with proximal sand sources our estimates demonstrate a method for orbital quantification of composition with rigorous uncertainty determination and provide key constraints for interpreting in situ measurements of compositional variability within martian aeolian sandstones

intensity of satellite radar altimeter return power over continental ice a potential measurement of katabatic wind intensity au dessus de glace continentale antarctique des mesures d altimetrie radar par seasat commande automatique de gain ont ete effectuees les variations observees sont dues essentiellement a l intensite du vent catabatique

apxs derived chemistry of the bagnold dune sands comparisons with gale crater soils and the global martian average we present apxs data for the active bagnold dune field within the gale impact crater msl mission we derive an apxs based average basaltic soil abs composition for mars based on past and recent data from the msl and mer missions this represents an update to the taylor and mclennan 2009 average martian soil and facilitates comparison across martian datasets the active bagnold dune field is compositionally distinct from the abs with elevated mg ni and fe suggesting mafic mineral enrichment and uniformly low levels of s cl and zn indicating only a minimal dust component a relationship between decreasing grain size and increasing felsic content is revealed the bagnold sands possess the lowest s cl of all martian unconsolidated materials gale soils exhibit relatively uniform major element compositions similar to meridiani planum and gusev crater basaltic soils mer missions however they show minor enrichments in k cr mn and fe which may signify a local contribution the lithified eolian stimson formation within the gale impact crater is compositionally similar to the abs and bagnold sands which provide a modern analogue for these ancient eolian deposits compilation of apxs derived soil data reveals a generally homogenous global composition for martian soils but one that can be locally modified due to past or extant geologic processes that are limited in both space and time

do big and little earthquakes start differently can the occurrence of earthquakes be predicted this question has profound social and scientific implications but little is known about what triggers earthquakes or what precursor events might indicate one is about to happen in his perspective vidale reviews recent findings that attempt to resolve the question of whether large earthquakes are initiated by different mechanisms than smaller ones

cross sectional profiles of sand ripples megaripples and dunes a method for discriminating between formational mechanisms cross sectional profiles of sand ripples megaripples and sand dunes provide a useful tool for discriminating between formation by ripple and dune processes feature width defined as the basal break in slope along the profile to either side of the crest represents a good standard for comparison of profile attributes across more than three orders of magnitude aspect ratio height width as a function of log width separates measurements into clusters representing differing mechanisms of formation scaling both height and distance for individual profiles by feature width facilitates comparison of profile shapes across three orders of magnitude in width the data presented here should prove useful for evaluating possible mechanisms of origin for aeolian features observed remotely including on planetary bodies copyright 2012 john wiley sons ltd

a comparison between active and passive microwave measurements of the antarctic ice sheet and their association with the surface katabatic winds the intensity of the seasat altimeter return power over antarctica varies in strong correlation with the intensity of model katabatic winds it is also strongly correlated with the polarization of the passive microwave signal at 37 ghz of the nimbus 7 smmr data it is shown that this is most likely the result of the wind induced micro roughness of the ice surface

aeolian saltation on mars at low wind speeds laboratory experiments indicate that the fluid threshold friction speed u tf required to initiate fully developed aeolian saltation is much higher on mars than on earth a discrepancy exists between mars climate models that do not predict winds this strong and observations that sand sized particles are indeed moving this paper describes how wind friction speeds well below u tf but above the impact threshold u ti required to sustain saltation can initiate sustained saltation on mars but at relatively low flux numerical experiments indicate that a sand grain on mars mobilized sporadically between u ti and u tf will develop over fetch lengths longer than generally available within low pressure wind tunnels trajectories capable of splashing grains that propagate saltation and collectively form a cluster of saltating grains that migrate downwind together the passage of a saltation cluster should leave behind a narrow zone of affected surface grains the cumulative effect of many clusters represents a low flux phenomenon that should produce slow changes to aeolian bedforms over periods in which winds remain close to u ti and never or rarely reach u tf field evidence from small impact ripples along rover traverses is consistent with effects of saltation at these low friction speeds without obvious evidence for events u tf the potential utility of this grain mobility process is that it can operate entirely at more common winds well below u tf and so help explain widespread sand movements observed on mars wherever evidence might be mostly absent for u tf being exceeded

martian aeolian activity at the bagnold dunes gale crater the view from the surface and orbit the first in situ investigation of an active dune field on another planetary surface occurred in 2015 2016 when the msl curiosity rover investigated the bagnold dunes on mars hirise images show clear seasonal variations that are in good agreement with atmospheric model predictions of intra annual sand flux and migration directions that together indicate that the campaign occurred during a period of low wind activity curiosity surface images show that limited changes nevertheless occurred with movement of large grains particularly on freshly exposed surfaces two occurrences of secondary grain flow on the slip face of namib dune and a slump on a freshly exposed surface of a large ripple these changes are seen at sol to sol time scales grains on a rippled sand deposit and unconsolidated dump piles show limited movement of large grains over a few hours during which mean friction speeds are estimated at 0 3 0 4 m s 1 overall the correlation between changes and peak rems winds is moderate with high wind events associated with changes in some cases but not in others suggesting that other factors are also at work the distribution of rems 1 hz wind speeds show a tail up to the 20 m s 1 showing that even higher speed winds occur non aeolian triggering mechanisms are also possible the low activity period at the dunes documented by curiosity provides clues to processes that dominated in the martian past under conditions of lower obliquity

giant saltation on mars saltation the motion of sand grains in a sequence of ballistic trajectories close to the ground is a major factor for surface erosion dune formation and triggering of dust storms on mars although this mode of sand transport has been matter of research for decades through both simulations and wind tunnel experiments under earth and mars conditions it has not been possible to provide accurate measurements of particle trajectories in fully developed turbulent flow here we calculate the motion of saltating grains by directly solving the turbulent wind field and its interaction with the particles our calculations show that the minimal wind velocity required to sustain saltation on mars may be surprisingly lower than the aerodynamic minimal threshold measurable in wind tunnels indeed mars grains saltate in 100 times higher and longer trajectories and reach 5 10 times higher velocities than earth grains do on the basis of our results we arrive at general expressions that can be applied to calculate the length and height of saltation trajectories and the flux of grains in saltation under various physical conditions when the wind velocity is close to the minimal threshold for saltation

relating microwave backscatter azimuth modulation to surface properties of the greenland ice sheet azimuth dependence of a normalized radar cross section over the greenland ice sheet is modeled with a simple surface scattering model the model assumes that azimuth anisotropy in surface roughness at scales of 3 300 m is the primary mechanism driving the modulation to evaluate the contribution of azimuth anisotropy in surface roughness to the radar backscatter the model is compared to models based on isotropic surface roughness the models are inverted to estimate snow surface properties using measurements from the c band european remote sensing satellite advanced microwave instrument in scatterometer mode results indicate that the largest mesoscale rms surface slopes are found in the lower portions of the dry snow zone estimates of the preferential direction in surface roughness are highly correlated with katabatic wind fields over greenland which is consistent with wind formed sastrugi as the dominant mechanism causing azimuth modulation of the maximum improvement of the azimuth modulation surface model compared to its isotropic counterparts occurs in the lower regions of the dry snow zone where the azimuth variability of is the largest in regions with azimuth modulation over 1 db the mean root mean square error estimate of the azimuth dependent surface scattering model is 0 46 db compared with 0 70 db for similar models using isotropic roughness

a unifying model for planform straightness of ripples and dunes in air and water abstract geologists physicists and mathematicians have studied ripples and dunes for more than a century but despite considerable effort no general model has been proposed to explain perhaps the most fundamental property of their morphology why are some bedforms straight continuous parallel and uniform in planform geometry i e two dimensional whereas others are irregular three dimensional here we argue that physical coupling along the crest of a bedform is required to produce straight crests and that along crest flow and sand transport provide effective physical mechanisms for that coupling ripples and dunes with the straightest and most continuous crests include longitudinal and oblique dunes in unidirectional flows wave ripples dunes in reversing flows wind ripples and ripples migrating along a slope at first glance these bedforms appear quite different ripples and dunes air and water transverse oblique and longitudinal orientations relative to the net sand transport direction but they all have one property in common a process that increases the amount of along crest sand transport that lengthens and straightens their crests relative to the across crest transport that makes them migrate and take the more typical and more three dimensional planform geometry in unidirectional flows that produce straight bedforms along crest transport of sand is caused by along crest flow non transverse bedform orientation gravitational transport along an inclined crest or ballistic splash in air bedforms in reversing flows tend to be straighter than their unidirectional counterparts because reverse transport across the bedform crest reduces the net across crest transport that causes the more typical irregular geometry relative to the along crest transport that smoothes and straightens planform geometry

transverse instability of megaripples as a result of their inherent differences in stability sand ripples and megaripples exhibit variations in terms of their wavelengths and grain size distributions unimodal for sand ripples and bimodal for megaripples while sand ripples form almost straight lines megaripples have greater sinuosity due to their transverse instability a property that causes small megaripple undulations to grow with time the origin of the instability is due to variations in megaripple height variations that do not diminish over time and due to the inverse dependence of ripple drift velocity on the height thus the taller regions of ripples will move more slowly than the adjacent shorter portions an outcome that promotes further perturbation growth we show an example based on fi eld work of the transverse instability of megaripples the instability growth rate depends on the difference between the heights of the different segments of the megaripple in contrast to the underlying instability of megaripples normal sand ripples are essentially stable and are not affected by transverse perturbations instead reacting quickly to the wind which tends to smooth ripple height irregularities the transverse instability of megaripples derives from the composition of their crests which comprise coarse particles that allow initial perturbations in ripple height to grow further the results suggest a physical mechanism for the transverse instability of megaripples and new insight into the spatial patterns of sand ripples

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

windsat passive microwave polarimetric signatures of the greenland ice sheet windsat has systematically collected the first global fully polarimetric passive microwave data over both land and ocean as the first spaceborne polarimetric microwave radiometer it was designed to measure ocean surface wind speed and direction by including the third and fourth stokes parameters which are mostly related to the asymmetric structures of the ocean surface roughness although designed for wind vector retrieval windsat data are also collected over land and ice and this new data has revealed for the first time significant land signals in the third and fourth stokes parameter channels particularly over greenland and the antarctic ice sheets the third and fourth stokes parameters show well defined large azimuth modulations that appear to be correlated with geophysical variations particularly snow structure melting and metamorphism and have distinct seasonal variation the polarimetric signatures are relatively weak in the summer and are strongest around spring this corresponds well with the formation and erosion of the sastrugi in the dry snow zone and snowmelt in the soaked zone in this paper we present the full polarimetric signatures obtained from windsat over greenland and use a simple empirical observation model to quantify the azimuthal variations of the signatures in space and time

gravel mantled megaripples of the argentinean puna a model for their origin and growth with implications for mars gravel megaripples in the puna of argentina are the most extreme aeolian megaripples on earth and are useful analogs for aeolian processes on mars field observations supplemented by experimental and numerical constraints on wind characteristics and aeolian transport reveal their conditions of formation and growth to be an aeolian geomorphology perfect storm the bedforms are formed on a substrate of weakly indurated ignimbrite aeolian deflation of which yields a bimodal lag of lithics and pumice clasts onto an undulating surface under normal wind conditions in this region the lithics are organized into bedforms on local upslopes and highs through creep induced by the impact of saltating sand and pumice the gravel bedforms grow through shadowing and trap sand and silt that is gradually kinetically sieved down to lift the gravel mantle upwards to form the megaripples these observations connote that the largest features are not ripples in the sense of migrating bedforms but rather nucleation sites of wind transported sediment strong control by bedrock topography means that the largest bedform wavelengths are not a result of particle trajectories and this complicates their comparison with other ripples and may require a new classification of relevance to mars the puna megaripples are morphologically and contextually similar to small ripple like transverse aeolian ridges tars moreover the puna gravels have similar equivalent weight mg to those composing granule ripples at meridiani planum and their local origin may have implications for the origin of sediment in martian aeolian bedforms finally the stable yet dynamic character of the puna megaripples could help reconcile current models of tars with periodic bedrock ridges that may be produced by aeolian erosion

continental scale simulation of the antarctic katabatic wind regime abstract katabatic winds are a common feature of the lower antarctic atmosphere although these drainage flows are quite shallow there is increasing evidence that the low level circulations are an important component in establishing large scale tropospheric motions in the high southern latitudes three dimensional numerical simulations of the antarctic katabatic wind regime and attendant tropospheric circulations have been conducted over the entire continent to depict the topographically forced drainage patterns in the near surface layer of the atmosphere results of the simulation enable a mapping of katabatic wind potential and identification of coastal regions which may experience anomalously intense katabatic winds a large upper level cyclonic circulation forms rapidly in response to the evolving katabatic wind structure in the lower atmosphere suggesting that the drainage circulations are an important component in prescribing the resulting resulting circumpolar vortex these results imply that som

morphologic diversity of martian ripples implications for large ripple formation large ripples with meter scale wavelengths are ubiquitous across mars curiosity s traverse of the bagnold dune field revealed a morphologic diversity of large martian ripples that helps constrain their formative mechanism large ripples develop in isolated fields and on dunes they form transversely and obliquely to longitudinally to the net sand flux direction in unimodally and bimodally distributed very fine to very coarse sand they have either straight or sinuous crestlines inactive ripples are covered with dust whereas migrating ripples are dust free here we present a unifying view of ripples that form in near bed sediment transport conditions encompassing fluid drag and coarse grained ripples to explain the range of large martian ripple morphologies and expand the use of bedforms as environmental indicators

mars global digital dune database and initial science results 1 a new mars global digital dune database mgd3 constructed using thermal emission imaging system themis infrared ir images provides a comprehensive and quantitative view of the geographic distribution of moderate to large size dune fields area 1 km2 that will help researchers to understand global climatic and sedimentary processes that have shaped the surface of mars mgd3 extends from 65 n to 65 s latitude and includes 550 dune fields covering 70 000 km2 with an estimated total volume of 3 600 km3 this area when combined with polar dune estimates suggests moderate to large size dune field coverage on mars may total 800 000 km2 6 times less than the total areal estimate of 5 000 000 km2 for terrestrial dunes where availability and quality of themis visible vis or mars orbiter camera narrow angle moc na images allow we classify dunes and include dune slipface measurements which are derived from gross dune morphology and represent the prevailing wind direction at the last time of significant dune modification for dunes located within craters the azimuth from crater centroid to dune field centroid referred to as dune centroid azimuth is calculated and can provide an accurate method for tracking dune migration within smooth floored craters these indicators of wind direction are compared to output from a general circulation model gcm dune centroid azimuth values generally correlate to regional wind patterns slipface orientations are less well correlated suggesting that local topographic effects may play a larger role in dune orientation than regional winds

katabatic wind intensity and direction over antarctica derived from scatterometer data although satellite radar scatterometers are initially designed to measure ocean surface wind speed and direction they also provide important observations over continental ice sheets data from the seasat scatterometer analysed over a sector of antarctica show that the signal is strongly dependent on the incidence angle of observation but that it also depends on azimuth ledroit et al 1992 the minimum values of the backscatter coefficient the ratio of backscattered versus incident power are always observed in the direction of katabatic winds a theoretical analysis shows that the backscatter coefficient must be very sensitive to the sastrugi slopes and orientations which are streamlined features formed on the snow surface in the wind direction parish and bromwich 1987 satellite scatterometers can thus map the characteristics of sastrugis of importance for the interpretation of microwave measurements above ice sheets this indirectly provides the intensity and direction of these very persistent and strong winds which play a important role in the behaviour of the atmosphere and ocean in high southern latitudes

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

surface airflow over east antarctica abstract surface winds over the antarctic interior occur mainly due to the strong radiational cooling of the ice slopes as a consequence such winds exhibit a high degree of persistence with a predominant direction closely related to the terrain orientation using detailed contour maps of the interior ice topography and representative values of the mean wintertime strength of the temperature inversion it is possible to infer the terrain induced accelerations a simple diagnostic equation system is formulated from which a time averaged surface airflow pattern of east antarctica is generated the results appear consistent with observations the occurrence of localized anomalously strong katabatic winds is explained as a result of typographically forced patterns of cold air convergence depicted in the airflow analysis

surficial geologic surveys of gale crater and melas chasma mars integration of remote sensing data abstract remote sensing observations of gale crater and melas chasma are synthesized to better understand the present surface layer in these two scientifically interesting regions data sets analyzed include geologic maps mars orbiter laser altimeter mola elevation thermal emission spectrometer tes albedo tes thermal inertia mola residual pulse width tes rock abundance and viking and mars orbiter camera images using these data sets we constrain the properties of and processes acting on the present surface and create self consistent models for the surface layer surface properties within gale crater are variable and complex and interpreting the surface layer is not straightforward observations indicate that aeolian processes have shaped some of the intracrater surface but other areas do not comply with this model and have counterintuitive surface characteristics in contrast aeolian activity appears to have played a large role in shaping the present day physical structure of all surfaces in melas chasma and is reflected in the remote sensing data sets here we summarize our analysis and discuss the surface attributes as determined from these data sets

wind related processes detected by the spirit rover at gusev crater mars wind abraded rocks ripples drifts and other deposits of windblown sediments are seen at the columbia memorial station where the spirit rover landed orientations of these features suggest formative winds from the north northwest consistent with predictions from atmospheric models of afternoon winds in gusev crater cuttings from the rover rock abrasion tool are asymmetrically distributed toward the south southeast suggesting active winds from the north northwest at the time midday of the abrasion operations characteristics of some rocks such as a two toned appearance suggest that they were possibly buried and exhumed on the order of 5 to 60 centimeters by wind deflation depending on location

ripple migration and dune activity on mars evidence for dynamic wind processes 1 in this report we show evidence of widespread ripple migration over the stoss side of dark barchan dunes in nili patera on mars the measured average migration of 1 7 meters in less than 4 terrestrial months clearly indicates that active sand saltation is occurring in the study area in addition we document widespread changes in the dune base ground surface contact and in the slip face structures showing that not only the ripples but the whole dunes are actually migrating in the present day atmospheric setting these results provide unequivocal evidence of recent aeolian activity and suggest that other dunes and ripples on mars may also be active

physical properties of the variations of the electric field of the earth preceding earthquakes i abstract in an earlier paper we described the physical properties of the preseismic transient variations in the electrotelluric field the present letter clarifies a few points that were not properly emphasized in our previous publications furthermore recent results like that of the destructive kalamata earthquake on september 13 1986 indicate that the duration of a preseismic electric signal may reach considerably high values lasting up to several hours

the particle size of martian aeolian dunes the effective particle size of unconsolidated materials on the martian surface can be determined from thermal inertia due to a pore size dependence of thermal conductivity at martian atmospheric pressures because dunes consist of a narrow range of well sorted unconsolidated particles they provide for a test of the relationship between particle size and thermal inertia calculated from midinfrared emission data for the martian surface we use two independent approaches first thermal inertia data indicate that martian dunes have an average particle size of about 500 100 m or medium to coarse sand second we determine expected dune particle sizes from grain trajectory calculations and the particle size transition from suspension to saltation on earth the transition occurs for a grain when the ratio of the terminal fall velocity to the wind friction speed u t is near unity for grains at u t this occurs at about 52 m terrestrial dune sands have a mean of 250 m and are composed entirely of grains 52 m the corresponding martian transition grain size is about 210 m suggesting that martian dunes should be significantly coarser than terrestrial dunes grain saltation path length as a function of particle size also shows that under martian conditions larger grains than on earth will become suspended both approaches indicate that martian dune sand should be coarser than terrestrial dune sand thus while terrestrial dune grains are in the fine to medium sand range the average martian dune sediments are probably medium to coarse sands these results closely match the grain sizes determined from thermal inertia models providing the first direct test of the validity of these models for actual martian surface materials

identification and analysis of electromagnetic signals in greece the case of the kozani earthquake van prediction an electric station was installed in july 1993 4 5 km away from the van station of ioannina and recorded in the following two years a number of anomalous signals including those of april 18 and 19 1995 interpreted by the van group as seismic electric signals precursors to the may 13 kozani earthquake west macedonia a magnetic station was also installed and clearly recorded the magnetic components of the same events the amplitude shape characteristic pattern and duration magnetic characteristics and polarisation of the anomalous signals suggest that they are generated by artificial industrial sources

observations of the antarctic ice sheet with the seasat scatterometer relation to katabatic wind intensity and direction the seasat a satellite scatterometer radar initially designed to measure ocean wind intensity and direction also provided observations on the antarctic ice sheet the signal of the back scatter coefficient decreases strongly from 10 to 20 db when the incidence angle of the observations increases from 0 to 65 an additional 5 db signal is found which is correlated with the direction and intensity of katabatic winds independent of the incidence angle and polarization of the signal by using simplified models of the volume scattering within the snowpack which is mostly sensitive to snow grain size and surface scattering from the air snow interface which depends on roughness it is evident that the signal of the scatterometer could result from the effects of snow dunes at low incidence angle and of micro roughness and volume back scatter at incidence angles greater than 25 the instrument therefore provides a means of measuring the direction and intensity of katabatic winds

polarimetric decomposition over glacier ice using long wavelength airborne polsar in recent years there has been increased interest in using synthetic aperture radar sar to study and monitor glaciers and ice sheets for glaciological and climate change research however due to the medium s complexity sar backscattering from ice remains poorly understood including the relative importance of scattering from surface and volume layers and also dependences on frequency and glacier zone extreme weather conditions can result in quickly changing surface conditions influencing backscatter signatures while leaving the underlying volume of interest unchanged surface and volume components must thus be separated in order to infer information regarding the properties of the ice volume this paper describes a three component scattering model to decompose polarimetric sar polsar images of glacier ice total backscatter is modeled as the incoherent summation of surface volume and sastrugi wind induced feature components the proposed model adapts and extends the freeman and durden decomposition for an ice volume scenario in which the volume is a dielectric medium forms of the model for both random and oriented volumes are considered and a new oriented sastrugi component is introduced which is able to explain backscatter behavior between different winter scenes validation is performed with airborne polsar data at l and p band collected using the e sar system of the german aerospace center over the austfonna ice cap in svalbard norway as part of the icesar campaign

earth like sand fluxes on mars strong and sustained winds on mars have been considered rare on the basis of surface meteorology measurements and global circulation models raising the question of whether the abundant dunes and evidence for wind erosion seen on the planet are a current process recent studies showed sand activity but could not determine whether entire dunes were moving implying large sand fluxes or whether more localized and surficial changes had occurred here we present measurements of the migration rate of sand ripples and dune lee fronts at the nili patera dune field we show that the dunes are near steady state with their entire volumes composed of mobile sand the dunes have unexpectedly high sand fluxes similar for example to those in victoria valley antarctica implying that rates of landscape modification on mars and earth are similar

spatial grain size sorting in eolian ripples and estimation of wind conditions on planetary surfaces application to meridiani planum mars the landscape seen by the mars exploration rover mer opportunity at meridiani planum is dominated by eolian wind blown ripples with concentrated surface lags of hematitic spherules and fragments these ripples exhibit profound spatial grain size sorting with well sorted coarse grained crests and poorly sorted generally finer grained troughs these ripples were the most common bed form encountered by opportunity in its traverse from eagle crater to endurance crater field measurements from white sands national monument new mexico show that such coarse grained ripples form by the different transport modes of coarse and fine grain fractions on the basis of our field study and simple theoretical and experimental considerations we show how surface deposits of coarse grained ripples can be used to place tight constraints on formative wind conditions on planetary surfaces activation of meridiani planum coarse grained ripples requires a wind velocity of 70 m s at a reference elevation of 1 m above the bed from images by the mars orbiter camera moc of reversing dust streaks we estimate that modern surface winds reach a velocity of at least 40 m s and hence may occasionally activate these ripples the presence of hematite at meridiani planum is ultimately related to formation of concretions during aqueous diagenesis in groundwater environments however the eolian concentration of these durable particles may have led to the recognition from orbit of this environmentally significant landing site

ripple morphology under oscillatory flow 1 prediction 1 recent laboratory and field experiments have shown the inability of existing oscillatory flow ripple predictors to accurately predict both ripple size and ripple planform geometry however at this time only partial adaptations of these predictors have been proposed to account for the observed discrepancies with new experimental data the present work starts by presenting a comprehensive data set compiled from 27 literature studies and our own experimental data which are presented in a companion paper dimensional analysis is used both to clarify the importance of the different variables involved in the development of ripples and to generate the basic dimensionless framework for the study of ripple morphology under oscillatory flow several ripple size and planform geometry predictors are contrasted against the compiled data set afterward a new ripple wavelength and height predictor and a new planform geometry predictor are proposed which overcome several of the limitations found in the earlier formulations the new predictors emphasize the existence of local and global sediment transport mechanisms over a ripple bed each of them acting at different scales in particular sediment size is found to have an important effect on the size and geometry of bed forms that can be generated by oscillatory flows

persistent aeolian activity at endeavour crater meridiani planum mars new observations from orbit and the surface abstract aeolian driven bedform activity is now known to occur in many regions of mars based on surface and orbital observation of contemporary martian ripple and dune mobility events many of these sites have only been monitored with sufficient resolution data for the last few mars years when the high resolution imaging science experiment hirise began acquiring images of mars one exception is the well monitored endeavour crater in meridiani planum which was one of the first known sites of unambiguous dune activity migration and deflation however those early detections used lower resolution images over longer temporal baselines versus the hirise data now available leaving some measurements poorly constrained new orbital and surface observations of endeavour show multiple spatial cm m km and temporal seasons mars year scales of aeolian driven surface change which confirms earlier reports dome dunes in the eastern portion of the crater persistently deflate disseminating dark sand across lighter toned regolith and or eroded bright dust and likely contribute to the crater interior s episodic decreases in orbital albedo measurements other dome dunes are detected with the highest migration rates 4 12 m per mars year and volumetric sand fluxes reported yet for mars estimated dune construction times or turnover times here and elsewhere on mars are significantly shorter than martian obliquity cycles implying that it is not necessary to invoke paleoclimate wind regimes to explain current dune morphologies located on the crater rim the opportunity rover detected evidence for near and far field aeolian driven activity with observations of spherules sand movement in the rover workspace bedform albedo alteration and dust lifting events observations of intracrater dunes show periodic shifting dark streaks that significantly constrain local wind regimes directionality and seasonality constraints on wind directions from surface and orbital images show that aeolian bedforms can be extremely active in bi and possibly tri modal wind regimes and during periods without major dust storms

pervasive aeolian activity along rover curiosity s traverse in gale crater mars the nasa mars science laboratory msl rover curiosity has safely landed near a 35 km long dark dune field in gale crater on mars this dune field crosses the landing site from the northeast to the southwest and lies along curiosity s traverse to aeolis mons here we present the first evidence of recent aeolian activity in the form of ripple and dune migration and further estimate wind directions within the dune field through analysis of ripple and dune morphologies and the mars regional atmospheric modeling system mrams we measured a minimum ripple migration rate of 0 66 m per earth year and dune migration rate of 0 4 m per earth year in the southwest portion of the field a strongly bidirectional ripple crestline orientation nearly orthogonal dune slipfaces and linear seif or oblique dunes indicate a bidirectional wind regime with winds mainly coming from the ene and from the northwest however mrams results indicate primary winds from the ene our constraints on the wind regime provide the unique opportunity to use ground measurements from msl to test the accuracy of winds predicted from orbital data

the van method contradictory and misleading results since 1981 we reexamine the van telegrams available to us in terms of the seismological data observed in the candidate region before and after the relevant telegram for the time period 1981 1985 the correlations are random earthquakes of any magnitude from an extremely low threshold i e m 2 5 at very short distances i e a few kilometers to large magnitudes i e m 7 0 at very large distances i e 500 km or even teleseismic events i e the iran earthquake of 1981 at a distance of about 2000 km were correlated by van with apparent ses on the basis of the occurrence of an earthquake anywhere from italy to aegean sea and from albania to crete island and usually based on telegrams exchanged between the van researchers from 1986 onwards the van telegrams were restricted mostly to the area of western greece which has the highest seismicity in europe by analyzing all of the van telegrams available to us we conclude that in no case was a mainshock predicted whenever the reported van correlation seems to be satisfactory the correlated event was either an aftershock or the correlation was not unique meaning that any of several earthquakes in the same focal region could be arbitrarily correlated with the telegram