on the wave number spectrum of oceanic mesoscale variability observed by the seasat altimeter variations of sea surface height measured by the seasat altimeter in nearly repeat orbits during the last 24 days of the mission are used to compute the wave number spectrum of mesoscale variability in various parts of the oceans the instrument noise level 150 cm2 cycles km has limited the resulting oceanic spectrum to wavelengths longer than 100 km we found that the characteristics of the oceanic spectrum are dependent on the energy level of the mesoscale variability in the high energy areas close to major current systems most of the energy is contained at wavelengths longer than 250 km at wavelengths shorter than 250 km the spectrum basically follows a k 5 k is wave number dependence in the low energy areas remote from major current systems the spectrum follows a k 1 dependence at wave lengths from 100 to 1000 km based on the assumption of horizontal isotropy of mesoscale variability scalar wave number spectra of sea surface height and geostrophic kinetic energy are also presented dynamical implications of these spectra are discussed the effects of residual geoid and atmospheric water vapor on the computed oceanic spectra have been rigorously examined it was found that the general characteristics of the oceanic spectra were not significantly affected by them

shallow and deep water global ocean tides from altimetry and numerical modeling we present here a 1 4 resolution near global barotropic tidal model designed specifically to provide more accurate tides in shallow water the model assimilates tides derived from 4 years of topex poseidon t p altimetric data procedures are used that tend to preserve the small spatial scales in the tidal structure in shallow water data from coastal tide gauges are also assimilated into the model the result is a tidal model that is useful in most of the shallow and deep areas of the global oceans some problems exist in regions where no data are available for assimilation such as the southern ocean pelagic tide gauge comparisons show that in deep water the new model is comparable in accuracy to the best of the existing t p based global tidal models comparisons to crossover differences in shallow water suggest improved performance we found that more accurate accounting of the load tides in the ocean tide model using an iterative technique based on the green s function formalism does not yield ocean tides that are significantly different from the simpler approaches used thus far by ocean tide modelers when data are assimilated it is our hope that this tidal model will not only help advance our understanding of shallow water tidal processes around the globe but also extend the utility of altimetry to waters shallower than 1000 m

surface eddy momentum flux and velocity variances in the southern ocean from geosat altimetry abstract satellite altimetry has previously been used to map the magnitude of the surface eddy variability of the global oceans but the direction of the time variable velocities have been more difficult to determine here a technique is presented for resolving both magnitude and direction of residual surface geostrophic velocities at geosat altimeter crossover points providing a two year time series with a temporal resolution of 17 days and horizontal resolution of around 100 km the time series of residual velocity components are then used to determine surface eddy statistics in the southern ocean and to investigate the role of transient eddies in the southern ocean momentum balance the surface eddy statistics from geosat crossover points show a complex spatial distribution in the surface reynolds stresses u 2 v 2 u v in contrast to the assumptions of isotropic variability in previous analyses of altimeter data velocity variance ellipses are found to be distinctly anisotropic in many regions

seasonal activity and morphological changes in martian gullies abstract recent studies of martian dune and non dune gullies have suggested a seasonal control on present day gully activity the timing of current gully activity especially activity involving the formation or modification of channels which commonly have been taken as evidence of fluvial processes has important implications regarding likely gully formation processes and necessary environmental conditions in this study we describe the results of frequent meter scale monitoring of several active gully sites by the high resolution imaging science experiment hirise on the mars reconnaissance orbiter mro the aim is to better assess the scope and nature of current morphological changes and to provide improved constraints on timing of gully activity on both dune and non dune slopes our observations indicate that 1 gully formation on mars is ongoing today and 2 the most significant morphological changes are strongly associated with seasonal frost and defrosting activity observed changes include formation of all major components of typical gully landforms although we have not observed alcove formation in coherent bedrock these results reduce the need to invoke recent climate change or present day groundwater seepage to explain the many martian gullies with pristine appearance

dynamics in the deep canada basin arctic ocean inferred by thermistor chain time series abstract a 50 day time series of high resolution temperature in the deepest layers of the canada basin in the arctic ocean indicates that the deep canada basin is a dynamically active environment not the quiet stable basin often assumed vertical motions at the near inertial tidal frequency have amplitudes of 10 20 m these vertical displacements are surprisingly large considering the downward near inertial internal wave energy flux typically observed in the canada basin in addition to motion in the internal wave frequency band the measurements indicate distinctive subinertial temperature fluctuations possibly due to intrusions of new water masses

eulerian and lagrangian statistics in the bluelink numerical model and aviso altimetry validation of model eddy kinetics 1 we compare eulerian and lagrangian timescales velocity autocorrelations and spectra from 14 years of hindcast ocean model and satellite velocities with direct observations our main aim is to determine how well the model bluelink version bran 2 1 and satellite derived currents archiving validation and interpretation of satellite oceanographic data aviso simulate mesoscale eddy variability which is important in mixing heat salinity and momentum and in controlling dispersion ocean eulerian observations are from topex poseidon t p crossover velocities and lagrangian observations are from global drifter program gdp surface drifters eulerian spectra from bluelink are similar to eulerian spectra from crossover velocities over the range of common frequencies the 10 day sampling from t p limits the comparison to low frequencies and eulerian timescales from bluelink are slightly shorter than from the observations part of this difference may be an effect of the t p sampling rate in contrast lagrangian spectra from bluelink are considerably steeper than spectra from gdp drifters and consequently lagrangian timescales from bluelink are longer than from the observations both eulerian and lagrangian spectra from aviso are steeper than from observations so that both eulerian and lagrangian aviso timescales are longer than observed the real ocean is an ocean where the eulerian lagrangian relationship described by middleton 1985 is followed the tasman sea averaged ratio of lagrangian to eulerian timescales is about 0 1 zonally and 0 15 meridionally however the eulerian lagrangian relationship described by middleton 1985 is not obeyed by bluelink and we believe that this behavior in bluelink reflects a loss of short wavelength eddies in the model

the delay doppler radar altimeter the key innovation in the delay doppler radar altimeter is delay compensation analogous to range curvature correction in a burst mode synthetic aperture radar sar following delay compensation height estimates are sorted by doppler frequency and integrated in parallel more equivalent looks are accumulated than in a conventional altimeter the relatively small along track footprint size is a constant of the system typically on the order of 250 m for a ku band altimeter the flat surface response is an impulse rather than the more familiar step function produced by conventional satellite radar altimeters the radar equation for the delay doppler radar altimeter has an h sup 5 2 ct sup 1 2 dependence on height h and compressed pulse length spl tau which is more efficient than the corresponding h sup 3 ct factor for a pulse limited altimeter the radiometric response obtained by the new approach would be 10 db stronger than that of the topex poseidon altimeter for example if the same hardware were used in the delay doppler altimeter mode this new technique leads to a smaller instrument that requires less power yet performs better than a conventional radar altimeter the concept represents a new generation of altimeter for earth observation with particular suitability for coastal ocean regions and polar ice sheets as well as open oceans

uncertainties in altimetry based velocity estimates 1 three methods to estimate ocean geostrophic surface currents from satellite altimetry measurements are evaluated for several single and multiple satellite configurations with specific emphasis on resulting uncertainties altimetric sea surface height measurements are simulated by sampling along satellite ground tracks the surface pressure output from the 1 10 north atlantic run of the los alamos parallel ocean program model and by subsequently adding realistic instrument and orbit errors the effects of both sampling and data errors on the velocity estimates are discussed the satellite orbit configurations considered represent current missions or candidates for future coordinated tandem missions data error budgets are based on those of existing missions and on estimates for new altimetric technology currently under development in midlatitude regions characterized by strong variability such as the gulf stream region velocities estimated at crossovers of interleaved tracks and along a virtual ground track between two parallel tracks with a 0 75 zonal offset are found to be comparable in accuracy and more accurate than velocities estimated from optimally interpolated sea surface height maps error variances as low as 15 25 of the local signal variance can be obtained from all three methods near the gulf stream core larger relative errors are found almost everywhere else with the exact details of the error in the two velocity components depending on data error orbit configuration latitude estimation method and smoothing several scientific applications of the configurations and methods are discussed including the estimation of reynolds stresses momentum fluxes velocity spectra and covariance functions accuracy and applicability suggest that the newly proposed parallel track configuration is a viable option for future tandem missions

evolution of the deep water in the canadian basin in the arctic ocean abstract an overflow of magnitude 0 25 sv sv 106 m 3 s 1 has been predicted to enter the makarov basin part of the canadian basin in the arctic ocean from the eurasian basin via a deep gap in the dividing lomonosov ridge the authors argue that this overflow does not ventilate the deep makarov basin below 2400 m where the water is too warm and salty to be compatible with such a large cold fresh inflow however complete isolation of the homogeneous bottom layer of the makarov basin must be ruled out because changes there are too small to arise from more than a small fraction of the measured geothermal heat flux into the basin a small cold fresh inflow of about 0 01 sv from the amundsen basin seems to be required this could occur if the gap in the dividing lomonosov ridge is shallower than previously thought it could also occur if there is active mixing and dilution of the predicted overflow in the gap leaving only a small fraction to descend into the deep makarov basin hydraulic theory and hy

the arctic ocean warms from below 1 the old 450 year isolation age and near homogenous deep waters of the canada basin cbdw that are found below 2700 m warmed at a rate of 0 0004 c yr 1 between 1993 and 2010 this rate is slightly less than expected from the reported geothermal heat flux fg 50 mw m 2 a deep temperature minimum tmin layer overlies cbdw within the basin and is also warming at approximately the same rate suggesting that some geothermal heat escapes vertically through a multi stepped 300 m thick deep transitional layer double diffusive convection and thermobaric instabilities are identified as possible mechanisms governing this vertical heat transfer the cbdw found above the lower continental slope of the deep basin maintains higher temperatures than those in the basin interior consistent with geothermal heat being distributed through a shallower water column and suggests that heat from the basin interior does not diffuse laterally and escape at the edges

a barotropic inverse tidal model for the arctic ocean 1 we describe high resolution 5 km grid linear dynamics and inverse models of arctic ocean barotropic tides obtained with the osu tidal inversion software otis package the 8 constituent dynamics based model uses the latest ibcao bathymetry and open boundary forcing from the recent tpxo 6 2 global barotropic tidal solution this model performs significantly better than the present benchmark arctic tidal model 14 km grid by z kowalik and a proshutinsky as judged by comparisons with 300 coastal tide gauges the greatest improvements are found in the canadian arctic archipelago nares strait and the baffin bay and labrador sea and can be explained by the higher resolution of the new model in these topographically complex regions the new arctic inverse model assimilates coastal and benthic tide gauges and topex poseidon and ers altimetry for further improvements of the 4 dominant constituents m2 s2 k1 and o1

global statistical space time scales of oceanic variability estimated from the topex poseidon altimeter data four years of the topex poseidon altimeter data are used to produce estimates of statistical space time scales of ocean variabilities for the sea surface height a three dimensional space time correlation function with an anisotropic directional dependence is assumed the function has gaussian distributions in radial directions in the space time coordinates and ellipsoidal contour surfaces the function can reveal the space time scales and propagations of the variabilities and statistical errors in the altimeter data we evaluated the space time scales using the best fit correlation function to the altimeter data the scales show geographical differences this means that dominant variabilities depend on regions we show an optimum interpolation oi method as an example of the application of the fitted correlation function the oi is applied to the altimeter data in the space time domain to make grid point data with higher accuracy than those obtained from a usual spatial two dimensional oi 2 d oi the values of the correlation function are used for the correlation coefficients of the first guess error in the oi a propagation diagram obtained from the space time oi 3 d oi shows clear propagations of planetary disturbances with larger amplitude the grid point values from the 3 d oi show better correspondences with sea levels from tide gauges than those from the 2 d oi the advantage is due to the data of the different cycles being additionally adopted and the correlation function reflecting propagation of the ocean variabilities

the seasat altimeter data and its accuracy assessment the seasat satellite launched on june 27 1978 carried a radar altimeter designed to measure the altitude of the satellite above the ocean surface the surface wave height and the ocean surface backscatter coefficient from which wind speed can be inferred postlaunch engineering assessment indicated that the seasat altimeter met the performance specification for 10 cm precision noise in the altitude measurements however to determine the accuracy of this measurement as well as the accuracy of the wave height and wind speed measurements a significant calibration validation and model development effort was required this summary describes the instrument atmospheric and geophysical effects which influence the radar altimeter measurement accuracies and the attendant correction models adopted for the altimeter geophysical data record also summarized are the activities of the seasat altimeter precision orbit determination experiment team directed towards the validation and improvement of these models as well as the investigations required to assess the accuracy of the altimeter measurement and the computed satellite altitude ephemeris finally an accuracy assessment is made for the various altimeter measurement corrections which are included on the altimeter geophysical data record

numerical modeling of martian gully sediment transport testing the fluvial hypothesis 1 using a stereo pair of hirise images of a pole facing crater slope at 38 s 218 e we measure topographic profiles along nine gullies typical slopes of the interior channel region above the depositional apron are 20 we test the hypothesis that sediment transport on gully slopes occurs via fluvial transport processes by developing a numerical sediment transport model based on steep flume experiments performed by smart 1984 at 20 slopes channels 1 m deep by 8 m wide and 0 1 m deep by 3 m wide transport a sediment volume equal to the alcove volume of 6 105 m3 in 10 h and 40 days respectively under constant flow conditions snowpack melting cannot produce the water discharge rates necessary for fluvial sediment transport unless long term kyr storage of the resulting meltwater occurs if these volumes of water are discharged as groundwater the required aquifer thicknesses and aquifer drawdown lengths would be unrealistically large for a single discharge event more plausibly the water volume required by the fluvial transport model could be discharged in 10 episodes for an aquifer 30 m thick with a recurrence interval similar to that of martian obliquity cycles 0 1 myr

long term monitoring of martian gully formation and evolution with mro hirise abstract gully landforms are commonly taken as evidence for surface liquid water in the recent geological history of mars repeat observations with the high resolution imaging science experiment hirise instrument on the mars reconnaissance orbiter demonstrate widespread activity in gullies in the southern hemisphere particularly in those with the freshest morphologies this activity includes substantial channel incision and large scale mass movements and constitutes ongoing gully formation rather than degradation of older landforms new apron deposits that are bright dark and neutrally toned have all been observed the timing of gully activity is seasonally controlled and occurs during the period when seasonal frost is present and defrosting these observations support a model in which currently active gully formation is driven mainly by seasonal co 2 frost gullies in the northern hemisphere are far less active than those in the south this may be due to the current timing of perihelion near the northern winter solstice integrated over time activity like that observed within the past few years appears capable of forming all of the martian gully landforms on timescales of millions of years additionally the current style and rate of activity is able to erase meter to decameter scale surface features that might have been uniquely produced by other processes during the last obliquity high 0 4 ma although it is impossible to rule out a past role for water in the formation of martian gullies a model in which gullies form only through currently active processes with little or no liquid water is consistent with our observations

on the choice of orbits for an altimetric satellite to study ocean circulation and tides the choice of an orbit for satellite altimetric studies of the ocean s circulation and tides requires an understanding of the orbital characteristics that influence the accuracy of the satellite s measurements of sea level and the temporal and spatial distribution of the measurements three orbital parameters determine the temporal and spatial sampling characteristics of the satellite the orbital altitude the inclination of the orbit and the repetition period the eccentricity of the chosen orbit should be less than 0 001 to minimize altimeter errors caused by uncertainty in determining the time of each altimeter measurement and to maintain the rate of height variation over the oceans within the limits of the altimeter tracker the choice of the satellite s orbital altitude is constrained by the influences of atmospheric drag and errors in models of the gravity field which decrease with height and the required complexity of the altimeter e g the power and or antenna size required and the effect on satellite systems of radiation from earth s radiation belts which increase with height the choice of inclination is constrained by a desire to measure sea level over all the ocean by the requirement that the acute angle between intersections of the subsatellite track be as large as possible and by the time phasing of the repeat of the satellite s ground track as a function of inclination which determines the aliased frequencies of the measurements of the oceanic tides the choice of repetition period is constrained by tradeoffs between temporal and spatial coverage and by the aliasing of tidal constituents combining the above constraints leads to a set of orbits in a narrow range of altitude and inclination called here the topex poseidon window this window extends from 1100 to 1500 km altitude and 62 to 66 inclination for a 10 day repeat period and consists of three subwindows following lines of equal orbit plane precession there are four choices of orbits within these subwindows that overfly the planned calibration sites at bermuda and dakar these are at 64 80 and 1335 km 62 01 and 1252 km 65 84 and 1255 km and 62 69 and 1173 km these choices have a minimum separation between the aliased frequencies of the eight largest diurnal and semidiurnal tides of one cycle per 4 71 years one cycle per 4 86 years one cycle per 4 87 years and one cycle per 4 27 years respectively thus there will be less than one cycle separation over the nominal 3 years mission of these four choices the first at 64 8 and 1335 km is preferable because it is less sensitive to error in estimating the upcoming solar cycle which will be a maximum during the mission and because it is more nearly centered in terms of inclination than the other choices for other calibration sites other choices would have to be made additional work beyond the scope of this paper will also be necessary to determine if the topex poseidon mission requires a frozen orbit i e an orbit for which there are no long term variations in the eccentricity and argument of perigee of the orbit if a frozen orbit is required then the first and third choices listed above have frozen orbits with an eccentricity that is acceptable for topex poseidon

seafloor tectonic fabric from satellite altimetry abstract ocean floor structures with horizontal scales of 10 to a few hundred kilometers and vertical scales of 100 m or more generate sea surface gravity anomalies observable with satellite altimetry prior to 1990 altimeter data resolved only tectonic lineaments some seamounts and some aspects of mid ocean ridge structure new altimeter data available since mid 1995 resolve 10 km scale structures over nearly all the world s oceans these data are the basis of new global bathymetric maps and have been interpreted as exhibiting complexities in the sea floor spreading process including ridge jumps propagating rifts and variations in magma supply this chapter reviews the satellite altimetry technique and its resolution of tectonic structures gives examples of intriguing tectonic phenomena and shows that structures as small as abyssal hills are partially resolved a new result obtained here is that the amplitude of the fine scale 10 80 km roughness of old ocean floor is spreading rate dependent i

martian hillside gullies and icelandic analogs abstract we report observations of icelandic hillside gully systems that are near duplicates of gullies observed on high latitude martian hillsides the best icelandic analogs involve basaltic talus slopes at the angle of repose with gully formation by debris flows initiated by ground water saturation and or by drainage of water from upslope cliffs we report not only the existence of mars analog gullies but also an erosional sequence of morphologic forms found both on mars and in iceland the observations support hypotheses calling for creation of martian gullies by aqueous processes issues remain whether the water in each case comes only from surficial sources such as melting of ground ice or snow or from underground sources such as aquifers that gain surface access in hillsides iceland has many examples of the former but the latter mechanism is not ruled out our observations are consistent with the martian debris flow mechanism of f costard et al 2001c science 295 110 113 except that classic debris flows begin at midslope more frequently than on mars from morphologic observations we suggest that some martian hillside gully systems not only involve significant evolution by extended erosive activity but gully formation may occur in episodes and the time interval since the last episode is considerably less than the time interval needed to erase the gully through normal martian obliteration processes

internal wave variability in the beaufort sea during the winter of 1993 1994 1 acoustic doppler current profiler observations were obtained at the sea ice mechanics initiative ice camp as it drifted through the beaufort sea over the winter of 1993 1994 in this paper the variability of the internal wave field is examined initially december 1993 january 1994 the camp drifted westward through the central canada basin 75 n 139 153 w numerous anticyclonic baroclinic eddies were encountered internal wave energy levels averaged 1 25 of the garrett munk gm standard shear variance averaged 1 17 gm during february march 1994 the camp drifted meridionally along 156 w near the northwind ridge reversing direction several times large baroclinic vortices were not detected internal wave energy levels were significantly greater during this period peaking at 1 6 gm shear variance peaked at 1 3 gm the waves were predominantly near inertial resulting from three distinct surface generation events downward vertical energy fluxes ranged from typical values of 0 02 mw m2 to a peak value of 0 15 mw m2 two thirds of the downward flux was associated with waves of vertical scale greater than 55 m the remainder with smaller scale waves upward energy fluxes ranged from 0 02 mw m2 typical to 0 10 mw m2 peak supported almost entirely by the larger scale waves high ice water relative velocities atmospheric storms accompanied by ice deformation appear to be necessary but not sufficient to assure a downward propagating wave generation event the highly variable mesoscale has a significant effect on the near inertial wave field propagation the data suggest that the vertical propagation of near inertial waves is strongly affected by the depth variation of the vertical component of mesoscale vorticity the large beaufort sea vortices appear to have a dual effect on the wave field enhanced vertical propagation speed and decreased energy density is found in the negative vorticity cores propagation into the positive vorticity regions surrounding the cores is inhibited the increase in wave energy experienced as the ice camp left the central beaufort sea is jointly associated with the passage of storms and the absence of large baroclinic vortices over the northwind ridge

evaporation effects on the formation of martian gullies abstract in order to investigate the formation of martian gullies and the stability of fluids on mars we examined about 120 gully images twelve hirise images contained a sufficient number of transverse aeolian ridges tars associated with the gullies to make the following measurements overall gully length length of the alcove channel and apron and we also measured the frequency of nearby tars six of the 12 images examined showed a statistically significant negative correlation between overall gully length alcove channel and apron length and tar frequency previous experimental work from our group has shown that at temperatures below 200 k evaporation rate increases by about an order of magnitude as wind speed increases from 0 to 15 m s thus the negative correlations we observe between gully length and dune frequency can be explained by formation at temperatures below 200 k where wind speed evaporation is a factor governing gully length in these cases evaporation of the fluid carving the gully was a constraint on their dimensions cases where there is no correlation between gully length and tar frequency can be explained by formation at temperatures 200 k the temperatures are consistent with global circulation model and thermal emission spectrometer tes data for these latitudes the temperatures suggested by these trends are consistent with the fluid responsible for gully formation being a strong brine such as fe 2 so 4 3 which has a eutectic temperature of 200 k we also find that formation timescales for gullies are 10 5 10 6 years

formation of recent martian gullies through melting of extensive water rich snow deposits the observation of gullies on mars indicates the presence of liquid water near the surface in recent times1 2 which is difficult to reconcile with the current cold climate gullies have been proposed to form through surface runoff from subsurface aquifers1 3 or through melting of near surface ice under warmer conditions4 but these gullies are observed to occur preferentially in cold mid latitudes2 where the presence of liquid water is less likely and on isolated surfaces where groundwater seepage would not be expected making both potential explanations unsatisfactory here i show that gullies can form by the melting of water rich snow that has been transported from the poles to mid latitudes during periods of high obliquity within the past 105 to 106 years refs 5 6 melting within this snow7 can generate sufficient water to erode gullies in about 5 000 years my proposed model for gully formation is consistent with the age and location of the gullies and it explains the occurrence of liquid water in the cold mid latitudes as well as on isolated surfaces remnants of the snowpacks are still present on mid latitude pole facing slopes and the recent or current occurrence of liquid water within them provides a potential abode for life

laboratory simulation of debris flows over sand dunes insights into gully formation mars gully morphology often summarized as comprising an alcove channel and debris apron is one of the key elements used to support the argument for liquid water in the recent past on mars nevertheless the processes that create different gully morphologies on both mars and earth are not fully understood one of the puzzling morphologic attributes of martian dune gullies is their apparent lack of an apron or terminal deposit which has caused debate about their formation process several physical processes such as runoff debris flows granular flows and sliding blocks falling downslope could explain the formation of these gullies in this work we focus on the role of liquid in the substrate as well as in the flow and choose to experimentally test the plausibility of this hypothesis we performed a series of analogue experiments to investigate the formation of gullies on sand dune like substrates we used controlled flows of water over an inclined sand box to produce gully like forms ice rich sedimentary substrates were used including substrates that included a thin liquid water saturated thawed layer an active layer above the ice saturated zone to give an analogue for a periglacial environment we quantitatively demonstrate that debris flow processes in periglacial experiments are conducive to the formation of narrow and long channels with small terminal deposits with perched channels by re analysis of martian elevation data for dune gullies on mars we have found good evidence that such terminal deposits could exist our experiments revealed that increased water content in the thawed layer above the frozen bed increases flow length due to the subsequent reduction in infiltration capacity water is incorporated into the flow by erosion of the wet thawed layer sand plus water and by drainage of the thawed layer using a mars environment simulation chamber we found that atmospheric pressure conditions seem to have a limited influence on the morphology of the flows our experimental investigation allowed the reproduction of terrestrial debris flow and martian gully morphologies suggesting that a substrate that is resistant to infiltration could be present beneath the dune gullies on mars we suggest that like in our laboratory experiments the presence of ice at shallow depth is a possible explanation for the formation of these morphologies and that a wet thawed layer is a possible explanation for the long flow length

martian gullies a comprehensive review of observations mechanisms and insights from earth analogues upon their discovery in 2000 martian gullies were hailed as the first proof of recent i e less than a few million years flowing liquid water on the surface of a dry desert planet many processes have been proposed to have formed martian gullies ranging from liquid water seepage from aquifers melting of snow ice and frost to dry granular flows potentially lubricated by co2 terrestrial analogues have played a pivotal role in the conception and validation of gully formation mechanisms comparison with the terrestrial landscape argues for gully formation by liquid water debris flows originating from surface melting however limited knowledge of sediment transport by sublimation is a critical factor in impeding progress on the co2 sublimation hypothesis we propose avenues towards resolving the debate a laboratory simulations targeting variables that can be measured from orbit b applications of landscape evolution models c incorporation of the concept of sediment connectivity d using 3d fluid dynamic models to link deposit morphology and flow rheology and e a more intense exchange of techniques between terrestrial and planetary geomorphology including quantitative and temporal approaches finally we emphasize that the present may not accurately represent the past and that martian gullies likely formed by a combination of processes

sinuous gullies on mars frequency distribution and implications for flow properties recent gullies on mars are suspected to be the result of liquid water bearing flows a formation from wet flows has been challenged by studies invoking granular dry flows our study focuses on the sinuous shapes observed for some of the recent martian gullies sinuous gullies are found in locations and slopes of 10 15 similar to straight gullies and they are therefore related to the same formation processes numerical simulations of granular flows are performed here by introducing topographic variations such as obstacles roughness or slope changes that could possibly generate flow sinuosity none of these simulations was able to reproduce sinuous shapes on a slope lower than 18 with friction angles typical of dry granular material the only way to simulate sinuous shapes is to create small amplitude periodic variations of the topography of the deposit an origin not supported by current martian imagery given the presence of sinuosity in natural terrestrial debris flows we have concluded that sinuous martian gullies are better reproduced by liquid water bearing debris flows sinuous shapes in leveed flows are used to derive mechanical parameters from several martian gullies using photoclinometry values in yield strength of 100 2200 pa velocities of 1 1 3 3 m s 1 and viscosities from 40 to 1040 pa s are found which are all within the range of values for terrestrial debris flows with various proportions of liquid water 20 40

statistical parameters of the geostrophic ocean flow field estimated from the jason 1 topex poseidon tandem mission 1 frequency and along track wave number spectra of zonal u and meridional v geostrophic surface velocity anomalies retrieved from the jason 1 topex poseidon jtp tandem mission are presented as global basin latitudinal and regional averages over the entire extratropical ocean frequency spectra show slightly higher energy levels for the v component in the frequency range below 100 days relative to the u component a lower energy for periods longer than 180 days furthermore quasi universal frequency slopes of close to f 2 are found for the high frequency part of all extratropical spectra representing regions with various different eddy energy levels differences in wave number spectra between u and v velocity components both computed along the satellite track result primarily from the sampling of the flow field on the jtp track with a meridionally changing track orientation taking this into account nearly similar spectral shapes are found for the wave number spectra of both velocity components over extratropical regions

asymmetries between wavenumber spectra of along and across track velocity from tandem mission altimetry satellite altimetry has proven to be one of the most useful oceanographic datasets providing a continuous near global record of surface geostrophic currents among other uses one limitation of observations from a single satellite is the difficulty of estimating the full geostrophic velocity field the 3 yr jason 1 ocean topography experiment topex poseidon tandem mission with two satellites flying parallel tracks promised to overcome this limitation however the wide track separation severely limits the tandem mission s resolution and reduces the observed velocity variance in this paper the effective filter imposed by the track separation is discussed and two important consequences for any application of the tandem mission velocities are explained first while across track velocity is simply low pass filtered along track velocity is attenuated also at wavelengths much longer than the track separation second velocity wavenumber spectral slopes are artificially steepened by a factor of k 22 at wavelengths smaller than the track separation knowledge of the effective filter has several applications including reconstruction of the full velocity spectrum from the heavily filtered observations here the hypothesis that the tandem mission flow field is horizontally nondivergent and isotropic is tested the effective filter is also used to predict the fraction of the eddy kinetic energy eke that is captured for a given track separation the ekecaptured falls off rapidly for track separations greater than about 20 km

eulerian and lagrangian eddy statistics of the tasman sea and southwest pacific ocean 1 ocean eddy variability dominates many important processes in the ocean at a range of length and timescales we describe the eddy statistics in the tasman sea new zealand region using drifter data from the global drifter program gdp to derive lagrangian statistics and topex poseidon t p satellite data to derive eulerian statistics the ratio of the lagrangian to eulerian timescales is also a measure of length scales in the ocean when is high lagrangian length scales are short compared with eulerian length scales and vice versa we compute both in the time domain from temporal autocorrelations of drifter and satellite data and in the frequency domain from drifter and satellite velocity spectra the zonal component of this ratio appears to be constant in the tasman sea whereas the meridional component shows a latitudinal dependence we argue that if is known all eulerian and lagrangian timescales can be determined from relatively easy measurements of the eulerian timescale and eddy kinetic velocity

evidence of gully formation by regional groundwater flow in the gorgonum newton region mars abstract the discovery of gullies on mars suggests liquid water activity near the surface of the planet in recent times since liquid water is unstable under the present day p t martian conditions the formation mechanisms of the gullies and the source of the putative water have been a matter of debate for the last years to provide new insights into these matters we have approached the problem studying the gullies in relation to their regional setting a major point in our study relates to the geographic orientation of gullies an aspect that has been previously regarded as a crucial matter in different models and has profound implications regarding their origin we present a comprehensive and detailed survey of the gorgonum newton region and a study of the dao and nirgal vallis regions the survey was carried out with the aid of 965 high resolution moc images 752 for gorgonum newton 102 for nirgal vallis and 111 for dao vallis regions and mola derived dems we found that gullies display a clear regional pattern geographically and topographically consistent with a decreasing regional slope we interpret the results in terms of the existence of several groundwater flow systems operating at different scales which ultimately may have led to gully formation by seepage at the slopes of craters and canyons we suggest that aquifers discharging at gully systems may have recharged from the surface in response to the melting of young partially eroded ice rich deposits

dynamics of unusual debris flows on martian sand dunes 1 gullies that dissect sand dunes in russell impact crater often display debris flow like deposits in their distal reaches the possible range of both the rheological properties and the flow rates are estimated using a numerical simulation code of a bingham plastic flow to help explain the formation of these features our simulated results are best explained by a rapid debris flow for example a debris flow with the viscosity of 102 pa s and the yield strength of 102 pa can form the observed deposits with a flow rate of 0 5 m3 s sustained over several minutes and total discharged water volume on the order of hundreds of cubic meters which may be produced by melting a surface layer of interstitial ice within the dune deposits to several centimeters depth

a new dry hypothesis for the formation of martian linear gullies long narrow grooves found on the slopes of martian sand dunes have been cited as evidence of liquid water via the hypothesis that melt water initiated debris flows eroded channels and deposited lateral levees however this theory has several short comings for explaining the observed morphology and activity of these linear gullies we present an alternative hypothesis that is consistent with the observed morphology location and current activity that blocks of co2 ice break from over steepened cornices as sublimation processes destabilize the surface in the spring and these blocks move downslope carving out leveed grooves of relatively uniform width and forming terminal pits to test this hypothesis we describe experiments involving water and co2 blocks on terrestrial dunes and then compare results with the martian features furthermore we present a theoretical model of the initiation of block motion due to sublimation and use this to quantitatively compare the expected behavior of blocks on the earth and mars the model demonstrates that co2 blocks can be expected to move via our proposed mechanism on the earth and mars and the experiments show that the motion of these blocks will naturally create the main morphological features of linear gullies seen on mars

near inertial wave propagation in the western arctic abstract from october 1997 through october 1998 the surface heat budget of the arctic sheba ice camp drifted across the western arctic ocean from the central canada basin over the northwind ridge and across the chukchi cap during much of this period the velocity and shear fields in the upper ocean were monitored by doppler sonar near inertial internal waves are found to be the dominant contributors to the superinertial motion field typical rms velocities are 1 2 cm s 1 in this work the velocity and shear variances associated with upward and downward propagating wave groups are quantified patterns are detected in these variances that correlate with underlying seafloor depth these are explored with the objective of assessing the role that these extremely low energy near inertial waves play in the larger scale evolution of the canada basin the specific focus is the energy flux delivered to the slopes and shelves of the basin available for driving mixing at the ocean boundaries the energy and

detection of large scale ocean circulation and tides as emphasized recently by munk wunsch the traditional methods of monitoring the ocean circulation give data too hopelessly aliased in space and time to permit a proper assessment of basin wide dynamics and heat flux on climatic timescales the prospect of nearly continuous recording of ocean surface topography by satellite altimetry with suitable supporting measurements might make such assessments possible the associated identification of the geocentric oceanic tidal signal in the data would be an additional bonus the few weeks of altimetry recorded by seasat gave a glimpse of the possibilities but also clarified the areas where better precision and knowledge are needed further experience will be gained from currently projected multi purpose satellites carrying altimeters but serious knowledge of ocean circulation will result only from missions that are entirely dedicated to the precise measurement of ocean topography

estimates of sea surface height and near surface alongshore coastal currents from combinations of altimeters and tide gauges 1 present methods used to retrieve altimeter data do not provide reliable estimates of sea surface height ssh in the nearshore region resulting in a measurement gap of 25 50 km next to the coast in the present work gridded ssh fields produced by archiving validation and interpretation of satellite oceanographic data aviso in the offshore region are combined with coastal tide gauge time series of ssh to improve estimation in that gap along the west coast of the united states in the northern california current system between 40 and 45n and 123 8 and 126w to assess the increase in skill provided by this procedure the geostrophic alongshore currents calculated from the new ssh fields in the gap region are compared to three in situ nearshore current measurements resulting in correlation coefficients of 0 73 0 83 and standard deviations of the differences of 11 6 12 6 cm s substantially improved from the aviso only results when the ekman current components are estimated and added to the geostrophic currents comparisons to the 10 m deep acoustic doppler current profiler velocities are only slightly improved the ekman components make a more significant contribution when compared to hf radar surface current measurements providing correlations of 0 94 and standard deviations of the differences of 6 4 9 5 cm s these results represent a dramatic improvement in the quality of the ssh fields and estimated alongshore currents when additional realistic ssh data from the coastal region are added here we use coastal tide gauges to provide the additional ssh data but also discuss more general approaches for altimeter ssh retrievals in coastal regions where tide gauge data are not available

debris flows over sand dunes on mars evidence for liquid water 1 this study focuses on the formation and physical properties of the gullies observed over large martian dunes especially those of the russell crater 54 s 347 w geomorphic features like sinuosities and connections of the channels show that gullies over dunes involve flows with a significant proportion of liquid the occurrence of levees implies that these flows are debris flows with a yield strength characteristics of bingham plastic materials we apply terrestrial methods to estimate viscosity and velocity of these flows from levee size and sinuosities we obtain average velocities in the range of 1 to 7 m s 1 and apparent viscosities of 2 8 to 46 000 pa s with an average at 740 pa s compared with the 0 001 pa s of pure water these viscosities and velocities are in the range of terrestrial debris flows with a proportion of 10 to 40 of h2o these properties are typical of water holding debris flows but not of pure water surface runoff or co2 driven flows the debris flows over dunes are oriented on south facing slopes like other recent gullies meltwater from ground ice formed during a recent period of high obliquity is the more likely explanation for the formation of such flows over dunes

recent progress in the application of satellite altimetry to observing the mesoscale variability and general circulation of the oceans recent progress in the application of satellite altimetry from seasat and geos 3 to the observation of the oceanic mesoscale variability and general circulation is reviewed the lack of accurate geoid models has been the major obstacle in the study of the general ocean circulation from altimetry the use of geoid independent methods that utilize the temporal differences in altimetric measurements taken at fixed locations however has made significant contributions to our knowledge of the mesoscale variability of the ocean the mesoscale energies of the sea surface height and geostrophic current have been mapped on a global basis their distributions in wave number space have also been analyzed because of many of the deficiencies of existing altimeter data short duration inadequate orbit poor accuracy etc most of these results describe only a small portion of the frequency wave number spectrum of the variability but they have nonetheless demonstrated the great value of an optimally designed altimetric mission in advancing our knowledge of the global mesoscale variability the current technology allows satellite altimetry to detect oceanic variability at periods from a few days to 3 5 years and wavelengths from 50 to 10 000 km determining the time averaged general ocean circulation from altimetry is more problematic because an accurate geoid is indispensable the currently available global geoid models have useful accuracies only at wavelengths greater than about 7000 km there have been several attempts at mapping the global ocean circulation at those scales using existing altimeter data and geoids when these results are compared with hydrographic surveys some qualitative agreement can be observed but the quantitative differences are mostly inconclusive because of the geoid and orbit errors it has been suggested however that an altimetric mission that is optimally designed with the current technology when complemented by a state of the art gravimetric mission to map the earth s gravity field is able to determine the ocean circulation quantitatively at scales from the ocean basin to about 200 km

de aliasing of global high frequency barotropic motions in altimeter observations theexistenceofhighfrequency periodsshorter than 10 days energetic barotropic motions in the ocean is shown to lead to a large aliasing error in satellite altimetric observations this error is most easily seen in the tracki ness of 10 day altimetric maps and commonly attributed to orbit error fortunately existing ocean general circula tion models when driven with twice daily windstresselds have considerable skill in predicting these motions with improved forcing and models we can expect that in the fu ture the alias can be largely suppressed by subtracting the model generated high frequency elds

role of aquicludes in formation of martian gullies liquid water is not currently stable on the surface of mars but images provided by the mars orbiter camera aboard the mars global surveyor spacecraft reveal erosional landforms previously interpreted to be geologically young gullies formed by groundwater seepage we test the basic hypothesis that as on earth the location of these gullies is controlled in part by the presence of an impermeable rock layer aquiclude and that the depths of the gully heads below the surface should thus be correlated to subsurface geology we show that 1 gullies emanate from a specific cliff forming layer even if the layer is faulted and 2 the depth of gullies below the local surface ranges from 70 to 800 m and 3 is positively correlated to mapped geologic units gully formation is therefore dependent upon both favorable climatic conditions to produce and sustain liquid water and the presence of impermeable subsurface layers to collect the groundwater gullies may mark the distribution of subsurface impermeable layers globally and are prime targets for the search for present water and life on mars

surface manifestation of internal tides generated near hawaii analysis of topex poseidon satellite altimetry reveals short wavelength fluctuations in the ocean surface tide that are attributable to internal tides a significant fraction of the semidiurnal internal tide generated at the hawaiian ridge is evidently phase locked to the astronomical potential and can modulate the amplitude of the surface tide by 5 cm the internal tide is thus easily mapped along satellite groundtracks and it is found to be spatially coherent over great distances with waves propagating well over 1000 km from the hawaiian ridge before decaying below noise level both first and second baroclinic modes are observed in both the m 2 lunar and s 2 solar tides the high space time coherence is in sharp contrast to what is often inferred from current meter observations but it confirms recent speculations from an acoustic experiment north of hawaii

enhanced diapycnal mixing by salt fingers in the thermocline of the tropical atlantic diapycnal mixing plays a significant role in the ocean s circulation and uptake of heat and carbon dioxide but has not been quantified in salt finger driven thermohaline staircases we recently performed a tracer release experiment in the western tropical atlantic staircase at approximately 400 m depth the observed dispersion implies an effective diapycnal diffusivity for tracer and salt of 0 8 to 0 9 x 10 4 m2 s temperature microstructure data interpreted in terms of a vertical production dissipation balance yields a smaller effective diffusivity for heat of 0 45 0 2 x 10 4 m2 s consistent with salt fingers and well above the mixing ascribable to mechanical turbulence

cold springs in permafrost on earth and mars 1 perennial springs located on west central axel heiberg island in the canadian high arctic occur in a region with a mean annual air temperature of 15 c and flow through continuous permafrost 600 m thick the spring water is a low temperature up to 6 c brine that maintains constant discharge temperatures and flow rates throughout the year here we report on observations of temperature and discharge rate of these springs and develop a combined flow and thermal model of the subsurface flow using the measured geothermal gradient we also consider the implications these springs have for the search for similar environments past or present on mars

evidence for present day gully activity on the russell crater dune field mars 1 on the basis of high resolution imaging science experiment hirise images of two successive years we observed changes of a gully on the russell crater dune field within the first year the length of a 2 m wide incised gully channel grew about 50 m downslope and 120 m within in the second year gully activity occurred in early spring between ls 198 and 218 in the first year and between ls 192 and 221 in the second year based on the channel morphology spectral data and modeled surface temperatures the changes can be best explained with transient melting of small amounts of h2o ice triggering slurry flows consisting of sand mixed with liquid water

downslope sediment transport by boiling liquid water under mars like conditions experiments and potential implications for martian gullies gullies are widespread morphological features on mars for which current changes have been observed liquid water has been one of the potential mechanisms to explain their formation and activity however under present day martian conditions liquid water is unstable and should only be transiently present in small amounts at the surface yet little attention has been paid to the mechanisms by which unstable water transports sediment under low atmospheric pressure here we present the results of laboratory experiments studying the interaction between liquid water owing over a sand bed under mars like atmospheric pressure c 9 mbar the experiments were performed in a mars simulation chamber at the open university uk in which we placed a test bed of ne sand at a 25 slope we chose to investigate the in uence of two parameters the temperature of the water and the temperature of the sand we performed 27 experiments with nine different combinations of water and sand temperatures ranging from 278 to 297 k under all experimental conditions the water was boiling we investigated and compared the types and timing of sediment transport events and the shapes characteristics and volumes of the resulting morphologies in agreement with previous laboratory studies we found that more intense boiling increased the volume of sediment transported for a given volume of water we found four main types of sediment transport entrainment by overland ow grain ejection grain avalanches and levitation of saturated sand pellets our results showed that increasing sand temperature was the main driving parameter in increasing the sand transport and in modifying the dominant sediment transport mechanism the temperature of the water played a negligible or minor role apart from the duration of sand ejection and avalanches which lasted longer at low water temperature at low sand temperature the majority of the sand was transported by overland ow of the liquid water at higher sand temperatures the transport was dominated by processes triggered by the boiling behaviour of the water at the highest temperatures sediment transport was dominated by the formation of levitating pellets dry avalanches and ejection of the sand grains this resulted in a transport volume about nine times greater at a sand temperature of 297 k compared with 278 k our heat transfer scaling shows that the boiling behaviour will be enhanced under martian low gravity resulting in more ef cient transport of sediment by levitating sand pellets even at temperatures close to the triple point our results showed that the boiling intensity played an important role in the physics of sediment transport by liquid water this implied that the amount of water required to produce morphological changes at the surface of mars could be lower than previously estimated by assuming stable liquid water boiling is a critical process to be considered when assessing gully formation and modi cation mechanisms mobilized by liquid water our work could have similar implications for any water formed landform on mars which could include recurring slope lineae dark dune ows and slope streaks

measuring gravity field variability the geoid ocean bottom pressure fluctuations and their dynamical implications 1 to obtain insight into bottom pressure variability and requirements for assimilating gravity data into an ocean general circulation model we use recent results from a constrained global model bottom pressure variability as contrasted to surface elevation variability is examined at the annual semiannual chandler wobble and 4 month periods surface elevation and bottom pressure variability occurs on all spatial and temporal scales resolvable by our analysis and patterns can be quite different a barotropic index developed to quantify variability character suggests the importance of steric effects at longer periods variability decomposition into standing eastward and westward traveling waves indicates a strong zonal component for both surface elevation and bottom pressure with bottom pressure showing a greater overall tendency toward eastward propagation and surface elevation showing a greater overall tendency toward westward propagation bottom pressure variability signals are estimated to be recoverable from space to spherical harmonic degree 27 for the annual cycle and 14 for the semiannual and chandler wobble cycles mass exchange arising from model approximations is detectable to about degree 7 polar motion excitation by ocean seafloor loading is found to be quantitatively important spurious oscillations encountered in using spherical harmonics to represent oceanic fields are suppressed using lanczos factors

seasonal variations of the large scale geostrophic flow field and eddy kinetic energy inferred from the topex poseidon and jason 1 tandem mission data 1 geostrophic surface velocity anomalies are used to analyze the annual variations of the large scale geostrophic currents and of the eddy kinetic energy eke field of the ocean circulation the underlying geostrophic currents were estimated from the jason 1 topex poseidon jtp tandem altimetric sea surface height data using the parallel track approach with a 10 km along track resolution however because of the given separation of the tracks of the two satellites only large mesoscale eddies are resolved by the tandem measurements the analysis covers the entire 3 year period of the tandem mission 109 repeat cycles from september 2002 to september 2005 the analysis of the seasonal flow changes reveals annual changes of all major current systems but especially of the zonal flow field in low latitudes leading to zonal jets on the annual cycle in the southern pacific atlantic and indian oceans in middle and high latitudes indications of a seasonally modulated strength of the sverdrup circulation emerge from the analysis the eke field also shows changes in its amplitude on the annual period in low latitudes those can be rationalized as resulting from seasonally modulated currents in middle and high latitudes changes in the wind driven barotropic circulation loom large which are not represented in other altimetric velocity products results shown suggest that velocity time series of the jtp tandem mission should be continued through similar constellations e g of jason 1 and jason 2

identification of mars gully activity types associated with ice composition the detection of geologically recent channels at the end of the 20th century rapidly suggested that liquid water could have been present on mars up to recent times a mechanism involving melting of water ice during ice ages in the last several million years progressively emerged during years following the first observations of these gullies however the recent discovery of current activity within gullies now suggests a paradigm shift where a contemporary co2 ice based and liquid water free mechanism may form all gullies here we perform a survey of near infrared observations and construct time sequences of water and co2 ice formation and sublimation at active gully sites we observe that all major new erosive features such as channel development or lengthening systematically occur where and if applicable when co2 ice is observed or probable co2 ice layers are however estimated to be only 1 mm to 1 cm thick for low latitude sites which may have implication for potential formation mechanisms we also observe that part of current gully activity notably the formation of some new deposits is poorly compatible with the presence of co2 ice in particular all new bright deposits reported in the literature have a low co2 ice probability while water ice should be present at most sites our results confirm that co2 ice is a key factor controlling present day channel development on mars and show that other mechanisms potentially involving sublimation or melting of water ice are also contributing to current gully activity

debris flows on the great kobuk sand dunes alaska implications for analogous processes on mars abstract we observed niveo aeolian deposits denivation features and small meltwater induced debris flows that had formed at the great kobuk sand dunes northwestern interior alaska in late march 2010 this high latitude cold climate dune field is being studied as a planetary analog to improve our understanding of factors that may trigger debris flows on the lee slopes of martian aeolian dunes debris flows consisted of a sand and liquid water mixture that cascaded down the lee slopes of two barchanoid dunes on days when measured ground surface temperatures were below freezing we hypothesize that relatively dark sand on snow caused local hot spots where solar radiation could be absorbed by the sand and conducted into the underlying snow enabling meltwater to form and sand to be mobilized this investigation provides insights into the interactions between niveo aeolian deposition slope aspect and insolation thawing and initiation of alluvial processes these debris flows are morphologically similar to those associated with seasonal gullies or erosion tracks visible on the slopes of mid to high latitude dune fields in both martian hemispheres localized heating and thawing at scales too small for orbital sensors to identify may yield martian debris flows at current climate conditions

satellite altimetry the marine geoid and the oceanic general circulation for technical reasons the general circulation of the ocean has historically been treated as a steady laminar flow field the recent availability of extremely highaccuracy and high precision satellite altimetry has provided a graphic demonstration that the ocean is actually a rapidly time evolving turbulent flow field to render the observations quantitatively useful for oceanographic purposes has required order of magnitude improvements in a number of fields including orbit dynamics gravity field estimation and atmospheric variability with five years of very high quality data now available the nature of oceanic variability on all space and time scales is emerging including new findings about such diverse and important phenomena as mixing coefficients the frequency wavenumber spectrum and turbulent cascades because the surface elevation is both a cause and consequence of motions deep within the water column oceanographers soon will be able to provide general circulation numerical models tested against and then combined with the altimeter data these will be complete three dimensional timeevolving estimates of the ocean circulation permitting greatly improved estimates of oceanic heat carbon and other property fluxes

a preliminary tidal analysis of topex poseidon altimetry approximately 12 months of data from the topex poseidon satellite altimeter mission are analyzed for the major short period oceanic tides a harmonic analysis is performed on data captured within bins defined on a deep ocean grid which owing to tidal aliasing considerations must have a relatively coarse spatial resolution our analysis is in terms of corrections to the schwiderski and cartwright ray models and it confirms many of the schwiderski differences previously reported by cartwright and ray our differences with respect to the geosat based cartwright and ray model form a sectorial pattern in m2 with high low differences separated roughly 180 in longitude we suggest that these sectorial errors were most likely induced by geosat s relatively large orbit error comparisons to independent data validate the improved topex poseidon solutions in situ ground truth shows m2 rms differences of 4 10cm schwiderski 3 86cm cartwright and ray 2 63cm this paper global rates of energy dissipation confirm earlier estimates for m2 and show improved agreement with satellite tracking studies for k1 and s2 these preliminary exercises confirm that topex poseidon should result in a new generation of improved global tidal models

improving the quality of satellite altimetry data over continental shelves 1 satellite altimetry has proven to be a useful tool to study oceanic processes in the deep ocean over continental shelves however the aliasing of unresolved high frequency signals of tidal and wind induced origin is the source of long wavelength errors that corrupt altimetry measurements and limit their use in shallow waters in 2005 ssalto duacs performed a complete reanalysis of altimeter data to accommodate the latest tidal model got2000 and a correction for the aliased high frequency signals using a hydrodynamic model mog2d g this paper examines the quality and the performance of the newly released altimetry data over the northwest european shelf this region is known for complex tides and for frequent storm surges the newly corrected maps of sea level anomalies were compared with a previous altimetry product residual tidal aliasing was analyzed and the impact of mog2d g and got2000 models was assessed altimeter records were compared with tide gauge measurements this research showed a significant reduction in the contamination of data by high frequency aliasing achieved through the use of the aforementioned models however aliased shallow water tidal constituents pose a serious problem and it is obvious that future tidal corrections should feature local tides nonaliased physical sea level variability was also studied focusing on interannual seasonal and intra annual periods from 20 days to 1 year modes the magnitudes and the contributions of each mode to the total variance were estimated it was demonstrated that the newly corrected data can successfully be used to study the variability of sea level over continental shelves

formation of recent martian debris flows by melting of near surface ground ice at high obliquity the observation of small gullies associated with recent surface runoff on mars has renewed the question of liquid water stability at the surface of mars the gullies could be formed by groundwater seepage from underground aquifers however observations of gullies originating from isolated peaks and dune crests question this scenario we show that these landforms may result from the melting of water ice in the top few meters of the martian subsurface at high obliquity our conclusions are based on the analogy between the martian gullies and terrestrial debris flows observed in greenland and numerical simulations that show that above freezing temperatures can occur at high obliquities in the near surface of mars and that such temperatures are only predicted at latitudes and for slope orientations corresponding to where the gullies have been observed on mars

tidal corrections for topex altimetry in the coral sea and great barrier reef lagoon comparisons with long term tide gauge records 1 the well known capability of topex poseidon altimetry to map sea levels precisely in the deep oceans motivates its application to the topographically complex coral sea and ne australian continental margin we assess several global tidal models for correcting topex altimetry in the coral sea and find csr3 0 offers good overall performance based on comparisons of model predicted and tide gauge harmonic constituents using csr3 0 tidal corrections we evaluate residual sea surface height ssh root mean square rms variability and residual m2 tidal alias errors away from large reefs and islands csr3 0 amplitude and phase errors for m2 are typically less than 5 cm and 8 deg respectively with rms tidal errors of 5 cm or less and rms ssh residuals approximating 10 cm since model deficiencies appear in the macro tidal region of the southern great barrier reef lagoon near broad sound we employ a high resolution hydrodynamic model in this area to compute the tidal corrections predicted m2 amplitude and phase in this region are within 3 cm and 5 deg of observations rms errors are mostly under 4 cm and coastal rms ssh residuals are as low as 15 cm in spite of coastal trapped waves and submesocale eddies in the lagoon daily and monthly smoothed ssh residual time series respectively yield optimal lagged correlations with in situ sea level data in the range 0 3 0 9 and 0 6 0 9 for locations spanning the coral sea and in the lagoon lag correlations of monthly smoothed geostrophic current anomalies derived from topex ssh gradients with long term currents from the continental slope yield optimal correlations of 0 5 and 0 8 respectively near jewell lat 14 deg s and myrmidon reef 19 deg s our results demonstrate that low frequency sea level and geostrophic current variations can be reliably observed using altimetry over the coral sea and ne australian continental slope and for selected locations on the continental shelf if appropriate tide correction models are employed

physical modelling of fault scarp degradation under freeze thaw cycles physical modelling has been developed in order to simulate the effects of periglacial erosion processes on the degradation of slopes and scarps data from 41 experimental freeze thaw cycles are presented they attest to the efficiency of periglacial processes that control both erosion and changes in scarp morphology i cryoexpulsion leads to an increase of scarp surface roughness and modifies significantly the internal structure of the active layer ii combined effects of frost creep and gelifluction lead to slow and gradual downslope displacements of the active layer 0 3 cm cycle iii debris flows are associated with the most significant changes in scarp morphology and are responsible for the highest rate of scarp erosion iv quantification of the erosion rate gives values close to 1 cm3 cm 2 for 41 freeze thaw cycles these experimental results are consistent with field data acquired along the la hague fault scarp normandy france where an erosion rate of 4 6 1 m3 m 2 per glacial stage has been computed from the volume of natural slope deposits stored during the weichselian glacial stage these results show that moist periglacial erosion processes could lead to an underestimation of plio quaternary deformation in the mid latitudes copyright 2006 john wiley sons ltd

a comparison of surface eddy kinetic energy and reynolds stresses in the gulf stream and the kuroshio current systems from merged topex poseidon and ers 1 2 altimetric data analyses of surface eddy kinetic energy eke inferred from 5 years of merged topex poseidon and ers 1 2 altimetric data are presented in the gulf stream gs and the kuroshio ks current systems focusing on anisotropy and eke seasonal interannual and long term variations as well as reynolds stresses for both gs and ks a descriptive analysis of the eke field shows that it is anisotropic along the path of the currents and assesses the close relationship between the spatial distribution of eke high levels and bottom topography a striking ocean feature is found in the gs shaped as a zonal double blade structure in the eke field centered at 37 n 71 5 w that likely corresponds to a regular and permanent lateral displacement of the mean path of the current at this geographical location maps of eke seasonal means for years 1993 1996 and 1997 provide a detailed description of the surface variability meanders pinched off eddies etc and show strong interannual variations in the ks eke monthly mean changes in the ks reveal a well marked seasonal cycle during the first 3 years 1993 1995 with eke peaking in july august this is followed by a constant increase of its level from the beginning of year 1996 till the beginning of 1997 during this increase the zonal velocity variance u 2 is up to 30 higher than its meridional counterpart suggesting a zonal acceleration of the eastward flow eke seasonal changes are also found in the ks current 30 35 n 130 140 e and also show a regular annual cycle during the first 3 years which precedes by 2 months the eke seasonal cycle in the ks extension maximum in may june the maximum in eke in both regions precedes by 2 months the maximum surface transport found by qiu et al 1991 and zlotnicki 1991 occurring in july and late september respectively no such annual cycle is found in the gs region during the first 3 years year 1996 is anomalous in both current systems with mean eke level that increases by more than 20 compared to the other years also eke monthly mean changes in the ks reveal a well marked positive tendency in the eastern part of the current of more than 300 cm2 s 2 yr 1 and a negative tendency both in its eastern part and in the ks current this feature is absent from the gs at last eddy mean flow interaction is presented both the spatial averaging of turbulent quantities and the relative contribution of the different terms of the horizontal momentum fluxes are discussed a tentative explanation is given for the anomalously large u 2 at the end of 1996 in the ks extension

space borne gravimetric satellite constellations and ocean tides aliasing effects summary ocean tides redistribute mass at high temporal frequencies satellite missions that aim to observe medium to low frequency mass variations need to take into account this rapidly varying mass signal correcting for the effects of ocean tides by means of imperfect models might hamper the observation of other temporal gravity field signals of interest this paper explores different methods for mitigating aliasing errors for the specific example of observing mass variations due to land hydrology including temporal filtering of time series of gravity solutions spatial smoothing and the use of satellite constellations for this purpose an earth system model esm was constructed which included state of the art time varying components for ocean atmosphere solid earth hydrology ice sheets and ocean tides using the esm we simulated the retrieval of the hydrologically driven gravity field changes using a number of different satellite constellations we find that 1 the ocean tide aliasing strongly depends on the satellite constellation the choice of orbital parameters and the length of the data span 2 the aliasing effect manifests itself differently for different geographical regions 3 the aliasing causes a peculiar striping pattern along the ground track of the satellite orbits 4 optimizing the choice of orbital parameters of a single grace type tandem can be more effective at reducing the aliasing of ocean tide model errors than flying more tandems finally we corroborate the experiences with grace data analysis that appropriate post processing techniques can significantly improve the quality of the retrieved gravity changes

liquid co2 breakout and the formation of recent small gullies on mars we show that the action of a co2 suspended flow could have produced the recent small gullies on mars and hence that liquid water is not required the model involves the build up of a liquid co2 aquifer behind and below a dry ice barrier dam cap rock in the pore spaces a few meters into the rock from the cliff face and on order of a hundred meters below the top of the cliff brink surface seasonal or obliquity cycle seasonal heating causes pinching out of the dry ice barrier and rapid release of the liquid co2 erosion of the gullies occurs as the rapid vaporization of the liquid co2 with entrainment of rock and clathrate hydrate ice produces a density flow analogous to a terrestrial nue ardente

laboratory simulations of martian gullies on sand dunes 1 small gullies observed on mars could be formed by groundwater seepage from an underground aquifer or may result from the melting of near surface ground ice at high obliquity to test these different hypotheses a cold room based laboratory simulation has been performed the experimental slope was designed to simulate debris flows on sand dune slopes at a range of angles different granulometry and permafrost characteristics preliminary results suggest that the typical morphology of gullies observed on mars can best be reproduced by the formation of linear debris flows related to the melting of a near surface ground ice with silty materials this physical modelling highlights the role of the periglacial conditions especially the active layer thickness during debris flow formation

the formation and evolution of youthful gullies on mars gullies as the late stage phase of mars most recent ice age gullies are extremely young erosional depositional systems on mars that have been carved by an agent that was likely to have been comprised in part by liquid water malin m c edgett k s 2000 evidence for recent groundwater seepage and surface runoff on mars science 288 2330 2335 mcewen a s et al 2007 a closer look at water related geologic activity on mars science 317 1706 1709 the strong latitude and orientation dependencies that have been documented for gullies require 1 a volatile near the surface and 2 that insolation is an important factor for forming gullies these constraints have led to two categories of interpretations for the source of the volatiles 1 liquid water at depth beneath the melting isotherm that erupts suddenly groundwater and 2 ice at the surface or within the uppermost layer of soil that melts during optimal insolation conditions surface near surface melting in this contribution we synthesize global hemispheric regional and local studies of gullies across mars and outline the criteria that must be met by any successful explanation for the formation of gullies we further document trends in both hemispheres that emphasize the importance of top down melting of recent ice rich deposits and the cold trapping of atmospherically derived h 2o frost snow as important components in the formation of gullies this provides context for the incorporation of high resolution multi spectral and hyper spectral data from the mars reconnaissance orbiter that show that 1 cold trapping of seasonal h 2o frost occurs at the alcove channel level on contemporary mars 2 gullies are episodically active systems 3 gullies preferentially form in the presence of deposits plausibly interpreted as remnants of the late amazonian emplacement of ice rich material and 4 gully channels frequently emanate from the crest of alcoves instead of the base showing that alcove generation is not necessarily a product of undermining and collapse at these locations a prediction of the groundwater model we interpret these various lines of evidence to mean that the majority of gullies on mars are explained by the episodic melting of atmospherically emplaced snow ice under spin axis orbital conditions characteristic of the last several myr

comparison of small lunar landslides and martian gullies some lunar crater wall landslides strongly resemble martian gullies despite the lack of geologically active water on the moon today or in the past the lunar features indicate that alcove channel apron morphology attributed on mars to seepage of liquid water can also form via a dry landslide mechanism therefore a more stringent test than just an alcove channel apron morphology is necessary to differentiate dry landslides from water carved gullies

enhanced diapycnal mixing due to near inertial internal waves propagating through an anticyclonic eddy in the ice free chukchi plateau abstractthe arctic ocean is known to be quiescent in terms of turbulent kinetic energy tke associated with internal waves to investigate the current state of tke in the seasonally ice free chukchi plateau arctic ocean this study performed a 3 week fixed point observation fpo using repeated microstructure hydrographic and current measurements in september 2014 during the fpo program the microstructure observation detected noticeable peaks of tke dissipation rate e during the transect of an anticyclonic eddy moving across the fpo station particularly e had a significant elevation in the lower halocline layer near the critical level reaching the order of 10 8 w kg 1 the adcp measured current displayed energetic near inertial internal waves niws propagating via the stratification at the top and bottom of the anticyclone according to spectral analyses of horizontal velocity the waves had almost downward energy propagation and its current amplitude reached 10 cm s 1 the wkb scaling inco

on the use of satellite altimetry to detect ocean circulation s magnetic signals oceanic magnetic signals are sensitive to ocean velocity salinity and heat content the detection of respective signals with global satellite magnetometers would pose a very valuable source of information while tidal magnetic fields are already detected electromagnetic signals of the ocean circulation still remain unobserved from space we propose to use satellite altimetry to construct proxy magnetic signals of the ocean circulation these proxy time series could subsequently be fitted to satellite magnetometer data the fitted data could be removed from the observations or the fitting constants could be analyzed for physical properties of the ocean e g the heat budget to test and evaluate this approach synthetic true and proxy magnetic signals are derived from a global circulation model of the ocean both data sets are compared in dependence of location and time scale we study and report when and where the proxy data describe the true signal sufficiently well correlations above 0 6 and explained variances of above 80 can be reported for large parts of the antarctic ocean thus explaining the major part of the global sub seasonal magnetic signal

an investigation of ocean tides derived from along track altimetry with the availability of a long data record of accurate sea surface height measurements it is now possible to estimate the ocean tide along the ground track of topex poseidon t p this has been done from over 4 5 years of data using both response and harmonic analyses these estimates agree well with each other and with other gridded models over both long and short wavelengths in deep water for those tidal components whose alias frequencies are separable by the rayleigh criterion comparisons of along track at estimates to current tide models show shorter wavelength features not present in dynamical and empirical global models at estimates follow the general trends of empirical models far from sharp topographical changes but near sharp changes they tend to follow dynamical model results error estimates show that the t p data are not significantly worse in shallow water than in deep water suggesting that there is accurate information about tides in shallow water in the t p data tides at crossover locations are improved by computing estimates with both ascending and descending track data possible techniques to improve at tidal estimates between crossover points are discussed at tidal estimation can be useful for studying local regions where resolution is more important than regular spacing for studying tidal interactions over sharp topography and for extending tidal models from deep to shallow waters through assimilation into a dynamical model

present day formation and seasonal evolution of linear dune gullies on mars linear dune gullies are a sub type of martian gullies as their name suggests they only occur on sandy substrates and comprise very long compared to their width straight or sinuous channels with relatively small source areas and almost non existent visible deposits linear dune gullies have never been observed on terrestrial dunes and their formation process on mars is unclear here we present the results of the first systematic survey of these features in mars southern hemisphere and an in depth study of six dunefields where repeat imaging allows us to monitor the changes in these gullies over time this study was undertaken with hirise images at 25 30 cm pix and 1 m pix elevation data derived from hirise stereo images we find the latitudinal distribution and orientation of linear dune gullies broadly consistent with the general population of martian gullies they occur predominantly between 36 3 s and 54 3 s and occasionally between 64 6 s and 70 4 s they are generally oriented toward ssw at bearings between 150 and 260 we find that these gullies are extremely active over the most recent 5 martian years of images activity comprises 1 appearance of new channels 2 lengthening of existing channels 3 complete or partial reactivation and 4 disappearance of gullies we find that gully channels lengthen by 100 m per year the intense activity and the progressive disappearance of linear dune gullies argues against the hypothesis that these are remnant morphologies left over from previous periods of high obliquity millions of years ago the activity of linear dune gullies reoccurs every year between the end of winter and the beginning of spring ls 167 4 216 6 and coincides with the final stages of the sublimation of annual co ice deposit this activity often coincides spatially and temporally with the appearance of recurrent diffusing flows rdfs digitate shaped dark patches with low relative albedo up to 48 lower than the adjacent dune that encompass the active site south and ssw facing dune slopes are those which preferentially host co2 frost deposits however it is only those with angles of 20 just below the crest which possess linear dune gullies suggesting a slope limited formation process these observations provide a wealth of temporal and morphometric data that can be used to undertake numerical modeling to direct future image monitoring and guide laboratory experiments that can be used to better constrain the formation process of these features

evidence of a 4 6 day barotropic planetary oscillation of the pacific ocean abstract spectral analysis of scattered island and coastal tide gage records from the pacific ocean reveals the presence of a coherent sea level fluctuation at 4 6 days period the oscillation is distinct from baroclinic inertia gravity wave fluctuations of sea level at the same periods that are trapped to the central pacific equatorial zone concomitant spectral analysis of island surface weather data demonstrates that sea level is forced by surface atmospheric pressure but does not respond statically like an inverted barometer the basinwide character and uniform westward propagation of the oscillation suggest the presence of a barotropic planetary wave s however the oscillation is strongly attenuated with an estimated energy e folding time of less than three days

present day development of gully channel sinuosity by carbon dioxide gas supported flows on mars martian gullies have been widely studied but their formation mechanism is still under debate their channels generally trend straight downslope but some display sinuosity seasonally active gullies are common on sand dunes and their channels have been reported to develop sinuosity here we perform a detailed analysis of a gully on a dune within matara crater 49 5 s 34 9 e where development of channel sinuosity has taken place over 5 martian years my29 33 of observation this study was performed using hirise images hirise elevation data spectroscopic crism data and a 1d gcm for surface temperature modelling the morphological evolution of the gully suggests a significant seasonal contribution of fluid each year we observed material collapse and accumulation in the alcove followed by transport events during which lateral migration and extension of the channel occur together with growth of the debris apron over one martian year the debris apron propagated by almost 140 m from an initial length of 800 m these transport events occur in the middle of winter when co2 frost is still present and are contemporaneous with the beginning of the defrosting we propose that the activity and the sinuosity development in the gully could be explained by 1 a flow composed of sand and co2 gas producing morphologies similar to those in hyper concentrated flows on earth and 2 contribution of material from alternating of the alcove source location

temporal changes in ocean eddy transports abstract new estimates from 11 yr of altimetric data are made of the global time average variability kinetic energy and its decadal scale variability making the approximation that the variability reflects primarily eddy motions a time mean but spatially varying eddy mixing coefficient is then estimated along with its changes over the last decade with a record length more than 2 times that previously available the time mean variability kinetic energy ke is statistically more reliable and smoother in its spatial pattern minimum values of ke are present in the subpolar north pacific ocean and in the eastern south pacific both less than 100 cm2 s 2 in contrast to the north pacific the subpolar north atlantic ocean shows relatively enhanced ke eddy kinetic energy and eddy mixing appear to have declined during the last decade over large parts of the western pacific ocean in some regions by as much as 50 of the time mean value increased eddy variability can be found in the kuroshio and gulf stream

recent debris flows on mars seasonal observations of the russell crater dune field 1 debris flows occur on slopes in the russell crater dune field the morphology of the erosion features resembles terrestrial viscous slurry flows mudflows and suggests that a flow of fine grained material mixed with liquid water might have been responsible for their formation seasonal mgs tes and moc imagery based observations of the dune field show 1 an annual frosting and defrosting cycle and 2 that liquid h2o could be stable within a limited time period in the summer of the southern hemisphere these observations lead to the conclusion that debris flows in the russell crater dune field may form under current climatic conditions by episodic or seasonal melting of small amounts of autumn winter condensed water ice

verification of geosat sea surface topography in the gulf stream extension with surface drifting buoys and hydrographic measurements altimeter data from geosat have been analyzed in the gulf stream extension area horizontal maps of the sea surface height anomaly relative to an annual mean for various 17 day intervals were constructed using an objective mapping procedure the mean sea level was approximated by the dynamic topography from climatological hydrographic data geostrophic surface velocities derived from the composite maps mean plus anomaly are significantly correlated with surface drifter velocities observed during an oceanographie experiment in the spring of 1987 the drifter velocities contain much energy on scales less than 100 km which are not resolved in the altimetric maps it is shown that the composite sea surface height also agrees well with ground verification from hydrographic data along sections in a triangle between the azores newfoundland and bermuda except in regions of high mean gradients

altimeter derived variability of surface velocities in the california current system 1 evaluation of topex altimeter velocity resolution in this paper we evaluate the temporal and horizontal resolution of geostrophic surface velocities calculated from topex satellite altimeter heights moored velocities from vector averaging current meters and an acoustic doppler current profiler at depths below the ekman layer are used to estimate the temporal evolution and accuracy of altimeter geostrophic surface velocities at a point surface temperature gradients from satellite fields are used to determine the altimeter s horizontal resolution of features in the velocity field the results indicate that the altimeter resolves horizontal scales of 50 80 km in the along track direction the rms differences between the altimeter and current meters are 7 8 cm s 1 much of which comes from small scale variability in the oceanic currents we estimate the error in the altimeter velocities to have an rms magnitude of 3 5 cm s 1 or less uncertainties in the eddy momentum fluxes at crossovers are more difficult to evaluate and may be affected by aliasing of fluctuations with frequencies higher than the altimeter s nyquist frequency of 0 05 cycles d 1 as indicated by spectra from subsampled current meter data the eddy statistics that are in best agreement are the velocity variances eddy kinetic energy and the major axis of the variance ellipses spatial averaging of the current meter velocities produces greater agreement with all altimeter statistics and increases our confidence that the altimeter s momentum fluxes and the orientation of its variance ellipses the statistics differing the most with single moorings represent well the statistics of spatially averaged currents scales of 50 100 km in the ocean besides evaluating altimeter performance the study reveals several properties of the circulation in the california current system 1 velocity components are not isotropic but are polarized strongly so at some locations 2 there are instances of strong and persistent small scale variability in the velocity and 3 the energetic region of the california current is isolated and surrounded by a region of lower energy starting 500 700 km offshore this suggests that the source of the high eddy energy within 500 km of the coast is the seasonal jet that develops each spring and moves offshore to the central region of the california current rather than a deep ocean eddy field approaching the coast from farther offshore

oceanic tides from geosat altimetry direct tidal analysis of the altimetry from the geosat exact repeat mission s first year is used to derive estimates of the diurnal and semidiurnal oceanic tides the geoid is removed by collinear differences at 34 1 day separation and the orbit error is reduced by subtracting a slowly modulated 1 cycle revolution term a sequence of independent analyses at grid areas of 1 latitude 1 5 longitude using orthotide functions ensures complete definition of the diurnal and semidiurnal species global admittance maps for m2 and s2 within the latitudes 58 n and 59 s compare well with ground truth at 66 open ocean sites maps of differences between geosat and the naval surface weapons center model show important areas of the order of 10 15 cm the integral for the global power input from the moon gives 2 51 tw m2 0 44 tw s2 lower than many previous estimates but in agreement with figures deduced from a recent analysis of satellite orbits

are different martian gully morphologies due to different processes on the kaiser dune field we describe and compare the morphology and activity of two types of gullies with different orientations collocated on the kaiser dune field in the southern hemisphere of mars large apron gullies and linear dune gullies the activity of large apron gullies follows an annual cycle i material collapse into the alcove mid autumn late winter as co2 condenses ii remobilization by mass flows late winter and iii continuous appearance of hundreds of digitate flows on the fan autumn winter we find that large apron gullies could form in hundreds of martian years in contrast linear dune gullies are active briefly in late winter when the co2 frost disappears their activity is characterized by the extension of channels the creation of pits and the darkening of the surface linear dune gullies are likely to form within one to tens of martian years we infer that insolation which influences the depth to ground ice and the amount of volatile deposited may be the factor differentiating large apron gullies and linear dune gullies sediment transport by co2 sublimation is a good candidate for the activity observed in all of these features however linear gullies could also be formed by brine release when the temperature rises abruptly after the removal of the co2 ice

altimetry ship gravimetry and the general circulation of the north atlantic gravity accelerations estimated from satellite altimetric mean sea surfaces seasat and geos 3 are compared to ship gravity measurements ship gravity are closer to an estimate based on least squares collocation orbit perturbations altimetry and terrestrial gravity than to an estimate based on fourier transforms orbit perturbations and altimetry only both altimetric estimates yield a smoothed picture of the geostrophic component of sea surface currents in the north atlantic when gravity acceleration data from only nine cruises are subtracted from the altimetric gravity

preservation of late amazonian mars ice and water related deposits in a unique crater environment in noachis terra age relationships between lobate debris tongues and gullies abstract the amazonian period of mars has been described as static cold and dry recent analysis of high resolution imagery of equatorial and mid latitude regions has revealed an array of young landforms produced in association with ice and liquid water because near surface ice in these regions is currently unstable these ice and water related landforms suggest one or more episodes of martian climate change during the amazonian here we report on the origin and evolution of valley systems within a degraded crater in noachis terra asimov crater the valleys have produced a unique environment in which to study the geomorphic signals of amazonian climate change new high resolution images reveal hesperian aged layered basalt with distinctive columnar jointing capping interior crater fill and providing debris via mass wasting for the surrounding annular valleys the occurrence of steep slopes 20 relatively narrow sheltered valleys and a source of debris have provided favorable conditions for the preservation of shallow ice deposits detailed mapping reveals morphological evidence for viscous ice flow in the form of several lobate debris tongues ldt superimposed on ldt are a series of fresh appearing gullies with typical alcove channel and fan morphologies the shift from ice rich viscous flow formation to gully erosion is best explained as a shift in martian climate from one compatible with excess snowfall and flow of ice rich deposits to one consistent with minor snow and gully formation available dating suggests that the climate transition occurred 8 ma prior to the formation of other small scale ice rich flow features identified elsewhere on mars that have been interpreted to have formed during the most recent phases of high obliquity taken together these older deposits suggest that multiple climatic shifts have occurred over the last tens of millions of years of martian history

quantitative analysis of the morphology of martian gullies and insights into their formation the process of formation of observed geologically recent gully features on mars has remained a topic of intense debate since their discovery in this study we performed quantitative morphological analysis on certain parameters of gullies from different settings such as crater walls terraces and sand dunes on the martian surface in addition to the meteor and xiuyan craters on the earth the morphometric parameters were measured for cross profiles which were extracted along each gully at certain intervals some interesting relationships among the parameters were determined which could provide us a comprehensive understanding of the morphologies of the gullies the results show that strong correlations exist among those parameters and the gullies are morphometrically similar except for a scale difference in different geologic settings the morphometric similarity implies that they were probably formed by some common processes on the other hand the morphometric differences indicate that the processes may have played different roles in the formation of the gullies the formation of gullies on the earth crater walls was heavily affected by surface flow and slippage and pre existing fractures and faults were also very influential in their formation we propose that gullies in martian crater walls and terraces should have a similar formation mechanism and they can probably account for most of gullies appearing on crater walls the morphometric differences between the gullies in sand dunes and other gully types are probably a result of the disparity in lithological settings which have significant influence on erosion ability even for the same agents

geologic settings of martian gullies implications for their origins 1 martian gullies are found on steep slopes of all origins on all sorts of terrains of all ages scattered across nearly all of mars gullies are observed on all manner of substrates layered massive shattered rubble with or without nearby mantling deposits gullies are most common in the southern midlatitudes but also occur in the northern hemisphere in near polar terrain on equatorial volcanoes and on northern plains most gullies in the southern hemisphere are on south facing slopes but they occur on slopes of all orientations gullies are among the youngest features on mars but locally are overlain by eolian deposits and cut by faults old or eroded gullies are rare and those found have been partially stripped from slopes leaving no rock debris behind most gully deposits contain no detectable rocks these data are inconsistent with published hypotheses of gully formation including seeps and breakouts of water or brine hydrothermal activity cryovolcanism and breakouts from liquid carbon dioxide the data are consistent with gullies being dry flows of eolian material dust and silt comparable to climax snow avalanches on earth eolian sedimentation should be correlated little with underlying geology cause of slope age of terrain type of terrain or the nature of the rocks eolian sedimentation should be correlated with wind deceleration which will cause suspended sediment to drop and areas with common gullies are those with strong wind deceleration predicted by global circulation model in such areas sediment will be deposited preferentially in the lee of obstacles for the gully rich areas of the southern midlatitudes winds blow from the nnw so that sediment is deposited on sse facing slopes i e poleward these predictions are in accord with observations