correlation scales objective mapping and absolute geostrophic flow in the california current the spatial covariances of the time dependent density and geostrophic velocity fields off southern california are determined from a unique set of repeated hydrographic observations 44 cruises made by the california cooperative oceanic fisheries investigations from 1984 to 1994 the covariances and objective analysis are used to combine direct velocity observations from shipboard acoustic doppler current profiler adcp measurements made on a recent survey october 1993 with hydrographic observations the analysis reduces ageostrophic noise in the adcp velocities by smoothing and enforcing horizontal nondivergence additionally the velocities are mapped over scales that are dynamically consistent with the hydrography maximum surface geostrophic flow in the california current in october 1993 is about 35 cm s 1 50 larger than that estimated assuming a 500 m level of no motion absolute flow at 500 m is o 10 cm s 1 and indicates that the surface eddy field penetrates through the thermocline uncertainty in the geostrophic reference calculated from the adcp measurements is of o 4 cm s 1 the velocity residual objectively analyzed minus raw adcp estimates exhibits smaller correlation scales than the geostrophic flow

origin and composition of three heterolithic boulder and cobble bearing deposits overlying the murray and stimson formations gale crater mars heterolithic boulder containing pebble strewn surfaces occur along the lower slopes of aeolis mons mt sharp in gale crater mars they were observed in hirise images acquired from orbit prior to the landing of the curiosity rover the rover was used to investigate three of these units named blackfoot brandberg and bimbe between sols 1099 and 1410 these unconsolidated units overlie the lower murray formation that forms the base of mt sharp and consist of pebbles cobbles and boulders blackfoot also overlies portions of the stimson formation which consists of eolian sandstone that is understood to significantly postdate the dominantly lacustrine deposition of the murray formation blackfoot is elliptical in shape 62 26 m while brandberg is nearly circular 50 55 m and bimbe is irregular in shape covering about ten times the area of the other two the largest boulders are 1 5 2 5 m in size and are interpreted to be sandstones as seen from orbit some boulders are light toned and others are dark toned rover based observations show that both have the same gray appearance from the ground and their apparently different albedos in orbital observations result from relatively flat sky facing surfaces chemical observations show that two clasts of fine sandstone at bimbe have similar compositions and morphologies to nine chemcam targets observed early in the mission near yellowknife bay including the bathurst inlet outcrop and to at least one target pyramid hills sol 692 and possibly a cap rock unit just north of hidden valley locations that are several kilometers apart in distance and tens of meters in elevation these findings may suggest the earlier existence of draping strata like the stimson formation that would have overlain the current surface from bimbe to yellowknife bay compositionally these extinct strata could be related to the siccar point group to which the stimson formation belongs dark massive sandstone blocks at bimbe are chemically distinct from blocks of similar morphology at bradbury rise except for a single float block oscar sol 516 conglomerates observed along a low sinuous ridge at bimbe consist of matrix and clasts with compositions similar to the stimson formation suggesting that stream beds likely existed nearly contemporaneously with the dunes that eventually formed the stimson formation or that they had the same source material in either case they represent a later pulse of fluvial activity relative to the lakes associated with the murray formation these three units may be local remnants of infilled impact craters especially circular shaped brandberg decayed buttes patches of unconsolidated fluvial deposits or residual mass movement debris their incorporation of stimson and murray rocks the lack of lithification and appearance of being erosional remnants suggest that they record erosion and deposition events that post date the exposure of the stimson formation

mapping the u s west coast surface circulation a multiyear analysis of high frequency radar observations signals with phase speeds of o 10 and o 100 to 300 km day 1 and time scales of 2 to 3 weeks the signals with slow phase speed are only observed in southern california it is hypothesized that they are scattered and reflected by shoreline curvature and bathymetry change and do not penetrate north of point conception the seasonal transition of alongshore surfacecirculationforcedbyupwelling favorablewindsandtheirrelaxationiscapturedinfine detail submesoscaleeddies identifiedusingflowgeometry haverossbynumbersof0 1to3 diameters in the range of 10 to 60 km and persistence for 2 to 12 days the hfr surface currents resolve coastal surface ocean variability continuously across scales from

possible evidence for variation in magnitude for marsquakes from fallen boulder populations grjota valles mars following observations of mobilized boulder trail populations from cerberus fossae mars that have been interpreted as possible evidence of large magnitude marsquakes rupturing for distances of 207 km along exposed active faults additional boulder trail populations were measured along shorter faults within the region of grjota valles 50 150 km length to test the hypotheses that 1 these faults are also candidate locations for marsquakes and 2 that marsquake magnitude might be smaller limited by fault dimensions available for rupture for a region containing two en echelon graben boulder trail data define two anomalies with maxima in a boulder trails per kilometer and b maximum width of boulder trails one that is 116 km in length along strike and the other 70 km in length along strike values for the maxima are 45 trails per km and 5 m mean trail width for the 70 km long anomaly and 115 trails per km with 5 3 m mean trail width for the 116 km long anomaly above background values measured elsewhere along these faults of zero trails per kilometer with zero boulder trail widths if combined with published data from cerberus fossae with a 207 km long anomaly in boulder trails per km 125 trails per km maxima and maximum mean boulder trail width 8 5 m maximum trail width the 3 datasets suggest correlations between the a along strike length of boulder trail anomalies b boulder trails per km and c maximum boulder trail width if interpreted as due to single marsquakes and if the dimensions of these anomalies are a proxy for rupture length when combined one interpretation of this is that boulders have been mobilized by marsquakes and that the marsquake magnitude is proportional to the along strike length of the anomalies in other words the data suggest that marsquake magnitude if that is the cause of the anomalies is limited by fault length as expected for terrestrial seismically active faults such findings suggest that the martian surface may have been shaken in the very recent past by large magnitude marsquakes we discuss this in terms of the seismicity of mars

static and dynamic angles of repose in loose granular materials under reduced gravity granular materials avalanche when a static angle of repose is exceeded and freeze at a dynamic angle of repose such avalanches occur subaerially on steep hillslopes and wind dunes and subaqueously at the lee side of deltas until now it has been assumed that the angles of repose are independent of gravitational acceleration the objective of this work is to experimentally determine whether the angles of repose depend on gravity in 33 parabolic flights in a well controlled research aircraft we recorded avalanching granular materials in rotating drums at effective gravitational accelerations of 0 1 0 38 and 1 0 times the terrestrial value the granular materials varied in particle size and rounding and had air or water as interstitial fluid materials with angular grains had time averaged angles of about 40 and with rounded grains about 25 for all effective gravitational accelerations except the finest glass beads in air which was explained by static electricity for all materials the static angle of repose increases about 5 with reduced gravity whereas the dynamic angle decreases with about 10 consequently the avalanche size increases with reduced gravity the experimental results suggest that relatively low slopes of granular material on mars may have formed by dry flows without a lubricating fluid on asteroids even lower slopes are expected the dependence on gravity of angle of repose may require reanalysis of models for many phenomena involving sediment also at much lower slope angles

evidence for thermal stress induced rockfalls on mars impact crater slopes abstract here we study rocks falling from exposed outcrops of bedrock which have left tracks on the slope over which they have bounced and or rolled in fresh impact craters 1 10 km in diameter on mars the presence of these tracks shows that these rocks have fallen relatively recently because aeolian processes are known to infill topographic lows over time mapping of rockfall tracks indicate trends in frequency with orientation which in turn depend on the latitudinal position of the crater craters in the equatorial belt between 15 n and 15 s exhibit higher frequencies of rockfall on their north south oriented slopes compared to their east west ones craters 15 n s have notably higher frequencies on their equator facing slopes as opposed to the other orientations we computed solar radiation on the surface of crater slopes to compare insolation patterns with the spatial distribution of rockfalls and found statistically significant correlations between maximum diurnal insolation and rockfall frequency our results indicate that solar induced thermal stress plays a more important role under relatively recent climate conditions in rock breakdown and preconditioning slopes for rockfalls than phase transitions of h2o or co2 at mid and equatorial latitudes thermal stress should thus be considered as an important factor in promoting mass wasting process on impact crater walls and other steep slopes on mars

distribution and characteristics of adirondack class basalt as observed by mini tes in gusev crater mars and its possible volcanic source abstract we identified 104 unique rock targets belonging to the olivine rich adirondack class using mini tes data rare rocks on the west spur of the columbia hills and on the plains east of the hills also belong to this class we present evidence that adirondack class basaltic lavas may have had their origin at apollinaris tholus linear modeling of adirondack class rock spectra shows only minor variations in mineralogy and the primary phases identified are consistent with olivine basalt having an average olivine composition of fo 45 we used factor analysis and target transformation to identify variability within a single class of rocks for the first time and we find that olivine abundance varies independently of a basaltic matrix a spectral component previously attributed to downwelling radiance is proposed here to be attributable to optically thin dust on rocks which has a greater effect on mini tes spectra than previously recognized but can explain the sloping continuum observed in adirondack class rock spectra as well as the apparent distortion of an olivine absorption spectral mixing is not completely linear leading to the overestimation of sulfate and olivine fractions and the underestimation of plagioclase feldspar although linear mixing appears to successfully replicate the majority of the observed signal published tes spectra of low albedo low dust cover olivine bearing materials do not exhibit the spectral telltales of non linear behavior probably because orbital spectra represent mostly mobile regolith that has not accumulated a sufficient dust cover over 3 6 km areas

the levantine intermediate water experiment liwex group levantine basin a laboratory for multiple water mass formation processes 1 in winter 1995 the last major field work of the physical oceanography of the eastern mediterranean poem program was carried out the levantine intermediate water experiment liwex in this study a thorough analysis is presented of the data set collected during three successive surveys in january february and march april 1995 the major overall result is that the levantine basin is shown to be the site for multiple and different water mass formation processes levantine deep water ldw was formed in the rhodes gyre with the preconditioning phase starting in december 1994 in late january the chimney was ventilating to the atmosphere in february the strong mixing phase is documented by the convective cell vertically homogeneous to 900 m depth in march april recapping has occurred in the upper 200 m ldw remained confined inside the rhodes gyre cyclonic circulation levantine intermediate water liw is instead deeply affected by the upper thermocline circulation shallow ventilating chimneys with the liw thermostads were found in the january survey inside the cyclonic region of the northern levantine the formation process of liw does not involve deep penetrative convection winter surface cooling and evaporation are sufficient to produce a surface mixed layer 100 m deep with liw characteristics at the mixed layer basis liw subducts and spreads along isopycnal surfaces along pathways determined by the cyclonic anticyclonic structures of the upper thermocline circulation

anisotropic response of surface currents to the wind in a coastal region analysis of coastal surface currents measured off the coast of san diego for two years suggests an anisotropic and asymmetric response to the wind probably as a result of bottom coastline boundary effects including pressure gradients in a linear regression the statistically estimated anisotropic response explains approximately 20 more surface current variance than an isotropic wind ocean response model after steady wind forcing for three days the isotropic surface current response veers 42 86 28 to the right of the wind regardless of wind direction whereas the anisotropic analysis suggests that the upcoast onshore wind stress generates surface currents with 10 86 48 71 86 38 to the right of the wind direction the anisotropic response thus reflects the dominance of alongshore currents in this coastal region both analyses yield winddriven currents with 3 5 of the wind speed as expected in addition nonlinear isotropic and anisotropic response functions are considered and the asymmetric current responses to the wind are examined these results provide a comprehensive statistical model of the wind driven currents in the coastal region which has not been well identified in previous field studies but is qualitatively consistent with descriptions of the current response in coastal ocean models

a summary of viking sample trench analyses for angles of internal friction and cohesions analyses of sample trenches excavated on mars using a theory for plowing by narrow blades provide estimates of the angles of internal friction and the cohesions of the martian surface materials angles of internal friction appear to be the same as those of many terrestrial soils because they are generally between 27 and 39 drift material at the lander 1 site has a low angle of internal friction near 18 all the materials excavated have low cohesions generally between 0 2 and 10 kpa the occurrence of cross bedding layers of crusts and blocky slabs shows that these materials are heterogeneous and that they contain planes of weakness the results reported here have significant implications for future landed missions martian eolian processes and interpretation of infrared temperatures

size frequency distributions of rocks on the northern plains of mars with special reference to phoenix landing surfaces 1 the size frequency distributions of rocks 1 5 m diameter fully resolvable in high resolution imaging science experiment hirise images of the northern plains follow exponential models developed from lander measurements of smaller rocks and are continuous with rock distributions measured at the landing sites dark pixels at the resolution limit of mars orbiter camera thought to be boulders are shown to be mostly dark shadows of clustered smaller rocks in hirise images an automated rock detector algorithm that fits ellipses to shadows and cylinders to the rocks accurately measured within 1 2 pixels rock diameter and height by comparison to spacecraft of known size of 10 million rocks over 1500 km2 of the northern plains rock distributions in these counts parallel models for cumulative fractional area covered by 30 90 rocks in dense rock fields around craters 10 30 rock coverage in less dense rock fields and 0 10 rock coverage in background terrain away from craters above 1 5 m diameter hirise resolves the same population of rocks seen in lander images and thus size frequency distributions can be extrapolated along model curves to estimate the number of rocks at smaller diameters extrapolating sparse rock distributions in the phoenix landing ellipse indicate 1 chance of encountering a potentially hazardous rock during landing or that could impede the opening of the solar arrays extrapolations further suggest rocks large enough to depress the ground ice table and small enough to be picked up or pushed by the robotic arm should be present within reach for study after landing

current variability on a narrow shelf with large ambient vorticity signals respectively and with corresponding phase speeds of 0 85 and 1 7 m s 1 the phase trend in east west direction of the 10 hour signal is consistent with unstable growing waves the 10 and 27 hour signals appear dominantly barotropic near the coast out to depths of at least 50 m but the 10 hour signal displayed a 180 phase change between surface and bottom farther away from the shelf break at 160 m depth the two dominant signals cannot be attributed to barotropic instability index terms 4219 oceanography general continental shelf processes 4520 oceanography physical eddies and mesoscale processes 4572 oceanography physical upper ocean processes keywords shelf circulation florida current vorticity flow instability surface doppler radar

sedimentological evidence for a deltaic origin of the western fan deposit in jezero crater mars and implications for future exploration abstract we examine the stratigraphic architecture and mineralogy of the western fan deposit in the jezero crater paleolake on mars to reassess whether this fan formed as a delta in a standing body of water as opposed to by alluvial or debris flow processes analysis of topography and images reveals that the stratigraphically lowest layers within the fan have shallow dips

recent shallow moonquake and impact triggered boulder falls on the moon new insights from the schrodinger basin shallow moonquakes are thought to be of tectonic origin however the geologic structures responsible for these moonquakes are unknown here we report sites where moonquakes possibly occurred along young lobate scarps in the schrodinger basin our analysis of lunar reconnaissance orbiter and chandrayaan 1 images revealed four lobate scarps in different parts of the schrodinger basin the scarps crosscut small fresh impact craters 1500 boulders associated with trails and bouncing marks their origins are largely controlled by recent impact events ejecta rays and secondary crater chains from a 14 km diameter impact crater traversed schrodinger and triggered significant boulder falls about 17 ma therefore a combination of recent shallow moonquakes and impact events triggered the boulder falls in the schrodinger basin

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

spume drops produced by the wind tearing of wave crests the wind tearing of breaking wave crests produces spume drops the authors report preliminary laboratory data from direct and unambiguous observation of this process under various wind conditions using a video imaging technique results include the size distribution and production rates of these drops the curves for production rates at different wind speeds merge effectively when normalized by the number of breaking events this confirms that wave breaking occurrence not the wind speed is a dominant factor in spume production

avalanche slope angles in low gravity environments from active martian sand dunes 1 the properties of granular material have an important effect on surface landforms and processes recently it has been suggested that material properties called dynamic and static angle of repose vary with gravitational acceleration which would have a significant effect on many planetary surface processes such as crater collapse and gully formation in order to test that hypothesis we measured lee slopes of active aeolian sand dunes on mars using the high resolution imaging experiment hirise dtms digital terrain model we examined dune fields in nili patera herschel crater and gale crater our measurements showed that the dynamic angles of repose for the sands in these areas are 33 34 in the first region and 30 31 in the other two these results fall within the 30 to 35 window for the dynamic angles of repose for terrestrial dunes with similar flow depths and grain properties and thus show that this angle does not significantly vary with decreasing gravity

boulder fall activity in the jezero crater mars jezero crater is the landing site for the mars 2020 perseverance rover we report 63 boulder fall tracks within the crater using high resolution imaging science experiment hirise images the boulder tracks have both fresh and faded morphologies similar to those reported elsewhere on mars but reported for the first time in jezero crater we combine observations from 16 boulder tracks on the western delta deposit with 47 in the surrounding regions to infer possible process es of boulder destabilization which can be tested with rover observations this newly found hazard should be taken into account for rover operations boulders associated with tracks are geologically recent falls so it is possible that the surfaces of these boulders may provide an opportunity to sample material less exposed to radiation than other rocks at the martian surface and could be ideal targets to analyze for organics

poleward propagating subinertial alongshore surface currents off the u s west coast 1 the network comprising 61 high frequency radar systems along the u s west coast uswc provides a unique high resolution and broad scale view of ocean surface circulation subinertial alongshore surface currents show poleward propagating signals with phase speeds of o 10 and o 100 300 km d 1 that are consistent with historical in situ observations off the uswc and that can be possibly interpreted as coastally trapped waves ctws the propagating signals in the slow mode are partly observed in southern california which may result from scattering and reflection of higher mode ctws due to curvature of shoreline and bathymetry near point conception california on the other hand considering the order of the phase speed in the slow mode the poleward propagating signals may be attributed to alongshore advection or pressure driven flows a statistical regression of coastal winds at national data buoy center buoys on the observed surface currents partitions locally and remotely wind forced components isolates footprints of the equatorward propagating storm events in winter off the uswc and shows the poleward propagating signals year round

methodology for a regional tidal model evaluation with application to central california abstract observations from disparate observational assets including tide gauges moorings and high frequency hf radars were used to depict the tidal variability and to evaluate model tidal simulations for a region off central california including the monterey bay for this study the hydrodynamic model was forced only with tides derived from a large scale model for the northeast pacific ocean homogeneous density and initially horizontally uniform density stratification cases were considered the model successfully reproduced tidal sea surface height variations within the model domain as determined by comparisons with sea level or bottom pressure measured at six locations to achieve tidal currents with realistic amplitudes as determined from hf radar and moored measurements it was found that barotropic velocity as well as sea level from the large scale regional tidal model must be included in specifying the open boundary condition however even with such forcing the model with homogeneous density field under predicted the semidiurnal and diurnal barotropic currents as estimated from depth averaged currents measured at 11 locations in the diurnal frequency band the observed surface and nearshore depth averaged currents are likely influenced by meteorological forcing which was not included in the model the hf radar measured surface tidal currents both semidiurnal and diurnal are consistent from year to year and between the winter season and the entire year semidiurnal surface tidal currents derived from year long hf radar measurements do not resemble either the modeled or measured barotropic current fields rather they exhibit amplitudes and small scale spatial variability indicative of the presence of internal tides thus indicating that model derived barotropic tidal currents cannot be validated over large spatial extents using long time series of hf radar derived surface currents with initially horizontally uniform vertical density stratification the model produced surface currents with spatial variability and amplitude range comparable to what was derived from hf radar surface current measurements but the point by point comparisons are not impressive for this region of complex topography likewise the subsurface current comparisons performed at four deepwater locations show considerable model data differences possible reasons for these disparities include the effects of atmospheric forcing spatially and temporally varying stratification remotely generated coastally trapped waves and remotely generated internal tides

decomposing observations of high frequency radar derived surface currents by their forcing mechanisms decomposition techniques and spatial structures of decomposed surface currents 1 surface current observations from a high frequency radar network deployed in southern san diego are decomposed according to their driving forces pure tides and their neighboring off band energy local winds and low frequency several superposed ocean responses are present as a result of the complicated bottom topography and relatively weak winds off southern san diego as opposed to coastal regions where circulation can be explained by a dominant forcing mechanism this necessitates an application of a statistical decomposition approach surface currents coherent with pure tides are calculated using harmonic analysis locally wind driven surface currents are estimated by regression of observed winds on observed surface currents the dewinded and detided surface currents are filtered by weighted least squares fitting assuming white noise and three colored signal bands low frequency band less than 0 4 cycles per day and near tidal peaks at the diurnal k1 and semidiurnal m2 frequencies the spatial and temporal variability of each part of the decomposed surface currents is investigated in terms of ocean response to the driving forces in addition the spatial correlations of individual components exhibit gaussian and exponential shapes with varying decorrelation length scales

on the effect of sea drops on the atmospheric boundary layer 1 one of the possible mechanisms responsible for the reduction of the sea surface drag at high winds is explored the mechanism is based on the direct effect of sea drops as heavy particles on the turbulent mixing if assumed that sea drops are ejected upward from the sea surface no significant effect can be found a more realistic picture presumes that the spume drops resulting from a mechanical tearing of wave crests are ejected horizontally at altitudes of breaking crests a model of the spume drops generation is proposed the spume drops being torn off from breaking crests and sprayed inside the airflow significantly affect the surface drag at highest model wind speeds 60 80 m s the model actually predicts an effect of the slippery surface when the drag coefficient is reduced in about 10 times a comparison with available observations is given

the assessment of rockfall hazard at the base of talus slopes fragmental rockfall is characterized by the independent movement of individual rock fragments after detachment from a rock face the continued operation of the process leads to the accumulation of talus slopes on talus slopes the rockfall shadow extends beyond the base of the talus and consists of scattered boulders that have run out beyond the base of the slope the landing probability of boulders in the shadow is examined return periods of the order of 1000 years relative to a house site are typical rockfall behaviour particularly with respect to run out into the shadow can be assessed using geological evidence empirical methods physical modelling and computer based analytical models an empirical minimum shadow angle of 27 5 i e the angle between the distal limit of the shadow and the top of the talus slope is suggested and would be useful in rockfall vulnerability studies at the base of talus slopes as a first approximation to shadow limits it is preferable to the use of the rockfall fahrb

recent seismicity in valles marineris mars insights from young faults landslides boulder falls and possible mud volcanoes abstract current seismicity of mars is poorly known geodynamic models and analysis of surface faults indicate that mars could be seismically active globally particularly within the tharsis region however published geologic constraints on such activity are sparse in this study we use geomorphologic observations and crater size frequency age determinations gleaned from high resolution orbiter data to demonstrate that the valles marineris region is recently seismo tectonically active the chasmata shows evidence of reactivated dip slip faults that cross cut the chasmata walls and floors and indicates up to 1 2 km total vertical displacement along the trough bounding faults more than 16000 boulder fall occurrences with pristine trails are observed throughout the chasmata wall with an average slope of 25 degrees the boulder falls are interpreted to have been triggered by recent seismic shaking from the shallow marsquakes occurring along the chasmata faults possibly in the last thousands of years synthetic ground motion models indicate several m w 4 6 marsquakes at shallow depths 1 6 km are required to produce these canyon wide boulder falls in addition the presence of many young landslides 22 790 ma proximal to the reactivated trough bounding faults and formation of thousands of possible mud volcanic cones throughout the chasmata floor all suggest marsquake triggered shaking in the past tens to hundreds of million years corresponding to late to middle amazonian epochs we estimate formation of 20 m to 1 3 km diameter fresh impact craters around the chasmata had negligible contribution to the recent seismicity therefore valles marineris tectonism is an important source of marsquakes that may be readily detectable by the upcoming insight seismometers

impact of swell on the marine atmospheric boundary layer a model that describes the impact of swell on the marine atmospheric boundary layer is proposed the model is based on the two layer approximation of the boundary layer the near surface inner region and the outer region above the swell induced momentum and energy fluxes are confined within the inner region swell loses energy to the atmosphere and enhances the turbulent kinetic energy in the inner region the transfer of momentum results in acceleration or deceleration of the airflow near the surface following wind swell accelerates the flow which for a very low wind results in a swell driven wind opposite wind swell decelerates the airflow which for a steep swell could cause the reverse airflow the sea drag in the case of opposite wind swell is considerably enhanced as compared with the following wind swell case cross wind swell causes the rotation of the wind velocity vector with height which leads to the deviation of the turbulent stress vector from the wind velocity vector the impact of swell becomes more pronounced when the wind speed decreases or when the swell phase velocity increases in fact it is the wave age of the swell that characterizes the swell impact because the dimensionless wave induced fluxes of energy and momentum are proportional to the wave age parameter both fluxes are also proportional to the swell slope so that the swell impact is stronger for a steeper swell the model reproduces qualitatively and quantitatively the main experimental findings for the ocean swell the impact of swell on the sea drag is very pronounced for opposite wind swell is less pronounced for cross wind swell and is only at low wind speeds

the large scale inflow layer structure of hurricane frederic 1979 abstract aircraft rawinsonde satellite ship and buoy data collected over a 40 h period were composited to analyze the inflow layer structure of hurricane frederic 1979 within a radius of 10 latitude of the storm center to improve the quality of the composite analyses the low level cloud motion winds cmws employed in this study were assigned a level of best fit lbf an lbf was assigned to each cmw by determining the level at which the closest agreement existed between cmw and ground truth wind data e g rawinsonde aircraft ship and buoy the cmws were then adjusted vertically to uniform analysis levels combined with ground truth wind data and objectively analyzed these objectively analyzed wind fields were used to obtain kinematically derived fields of vorticity divergence and vertical velocity an angular momentum budget was also computed to obtain estimates of surface drag coefficients the low level cmws in this study were found to have lbfs ranging from 300 to 4000 m it was sho

periodic wind driven circulation in an elongated and rotating basin abstract an idealized model is developed for the three dimensional response of a coastal basin e g lagoon bay or estuary to time periodic wind stress this model handles basins that are deeper and or shallower than an ekman depth with wind forcing frequencies ranging from subinertial to superinertial here the model is used to describe how the response current and sea level of a basin deeper than one ekman depth depends on the wind forcing frequency at low subinertial frequencies the response is similar to the steady wind case and is hence called quasi steady there is a near surface ekman transport to the right of the wind balanced by a return flow at depth lateral bathymetric variations introduce an along basin circulation that decays with increasing frequency and sets the extent of the quasi steady response in the frequency domain at the inertial frequency the wind forces a damped resonant response with large vertical shear and weak depth integrated flow this result is potentially impor

small scale polygonal features on mars seasonal thermal contraction cracks in permafrost a time dependent viscoelastic model of thermal stress in martian ice rich permafrost is developed to test the hypothesis that small scale polygonal features observed from orbit and by the viking lander 2 are the result of thermal contraction cracking as commonly occurs in terrestrial permafrost results indicate that significant tensile stress occurs in martian ice rich permafrost as a result of seasonal cycles in the ground temperature using conservative rheological parameters appropriate for ice at low temperatures tensile stresses poleward of about 20 to 30 latitude easily exceed the tensile strength assumed to be 2 to 3 mpa and fractures should readily form in the equatorial regions special conditions may allow tensile stresses to approach the tensile strength these results support a thermal contraction origin of observed small scale polygonal features and emphasize the utility of these features as valuable morphological indicators of ground ice

bottom friction and wind drag for wave models abstract waves propagating in shallow water dissipate energy in a thin turbulent boundary layer near the bottom this friction can be estimated with a simple quadratic friction law scaled with an empirical coefficient two values of this coefficient have been recommended by previous studies for sandy bottoms a high value for waves in a storm and a low value for swell we show here that in contrast to current practise the lower value should be used for both applications the reason is that the high value dating from the early 1980s was inferred from observations in a severe storm using a relatively high wind drag our review of a large number of more recent observations gives a new wind drag parameterization with lower values with this new parameterization we infer from the same storm the lower value of the bottom friction coefficient using this lower value also improves the estimates of wave growth in shallow water and of low frequency wave decay in a tidal inlet independent of the wind drag

fluvial sedimentary deposits on mars ancient deltas in a crater lake in the nili fossae region 1 new spacecraft observations in the nili fossae region of mars reveal two valley networks 80 and 200 km long that each formed distributary fans as they entered an ancient 40 km diameter impact crater an outlet channel on the eastern crater rim lying at an elevation above the fans suggests these fans formed as subaqueous deltas in a crater lake water flowing in the valley networks entered the crater and deposited the fans and ponded to a maximum depth of about 450 m the lake then overtopped and breached the crater rim incising it and dropping the lake level by 100 m geological evidence combined with the volume of water necessary to fill the crater suggests the duration of flow through this system was prolonged the existence of the deposits described here implies that the early martian environment supported overland flow and ponding of water for an extended period of time

combining altimeter and subsurface float data to estimate the time averaged circulation in the upper ocean 1 a new technique is presented for estimating time averaged upper ocean geostrophic velocity from a combination of altimeter data and subsurface float data the technique makes uses of the strong relationship between sea surface height anomaly and anomalous velocity at depth to reduce mesoscale eddy variability in subsurface float displacements the technique is demonstrated on a region in the north atlantic that was well sampled by argo floats the 2004 through 2006 time averaged density field was estimated from the surface to 2000 db by combining altimeter and hydrographic data from the floats in addition a reference velocity field was estimated at 1000 db based on a combination of altimeter data and subsurface float displacements the reference velocity field was combined with geostrophic shear based on the density field to produce a three dimensional estimate of geostrophic velocity from the surface to 2000 db the gulf stream transport in the upper 2000 db is estimated to be 76 sv at 73 w in addition an estimate of the 3 year average dynamic height at the surface was computed by combining the 1000 db reference dynamic height and the time averaged density field

aspects of the tidal variability observed on the southern california continental shelf abstract observations of the current and temperature field from the southern california continental shelf are analyzed in a frequency band 0 6 6 cpd dominated by tidal fluctuations the seasonal variability of the temperature and horizontal velocity component fields for this frequency band is characterized both in terms of mean variance statistics and change in the power spectra the most striking seasonally varying feature is the o 102 increase in tidal band temperature variance observed from winter to summer on the inner shelf energetic cuspate peaks are observed centered at 1 2 3 and 4 cpd the bandwidth of the peaks is approximately 0 2 cpd giving a decorrelation time of 5 days for tidally induced current and velocity component fluctuations a complex empirical eigenfunction analysis indicates that the amplitude and phase of coherent structures in the velocity component and temperature fields vary over vertical and horizontal spatial scales comparable to the local depth and shelf width respectiv

water ice at low to midlatitudes on mars 1 in this paper we analyze water ice occurrences at the surface of mars using near infrared observations and we study their distribution with a climate model latitudes between 45 s and 50 n are considered data from the observatoire pour la mineralogie l eau les glaces et l actitite and the compact reconnaissance imaging spectrometer for mars are used to assess the presence of surface water ice as a function of location and season a modeling approach combining the 1 d and 3 d versions of the general circulation model of the laboratoire de meteorologie dynamique de jussieu is developed and successfully compared to observations ice deposits 2 200 m thick are observed during the day on pole facing slopes in local fall winter and early spring ice extends down to 13 latitude in the southern hemisphere but is restricted to latitudes higher than 32 in the north on a given slope the pattern of ice observations at the surface is mainly controlled by the global variability of atmospheric water precipitation and vapor with local ground properties playing a lower role only seasonal surface ice is observed no exposed patches of perennial ground ice have been detected surface seasonal ice is however sensitive to subsurface properties the results presented in this study are consistent with the recent discovery of low latitude subsurface ice obtained through the analysis of co 2 frost

tidal currents on the central oregon shelf models data and assimilation 1 measurements of tidal currents on the central oregon shelf are available from several sources including recent high frequency hf coastal radar and acoustic doppler profiler adp deployments and historical current moorings in this paper we use a generalized inverse gi approach to compare these data to and then assimilate them into numerical models for the barotropic tides harmonic analysis of the data in short time windows using a modified admittance approach reveals that tidal currents on the oregon shelf are highly variable in time and can contain significant baroclinic components data from the winter months when waters on the shelf are only weakly stratified are found to be most nearly barotropic and thus most reasonable for assimilation into the shallow water equations model the various data sources are used in several different combinations for assimilation and validation forcing the prior forward model with normal flow open boundary conditions obtained from a regional barotropic inverse model results in semidiurnal barotropic currents that are consistent within estimated error limits with all available data in contrast diurnal currents on the shelf are very sensitive to details of the model configuration and are significantly improved by data assimilation very similar solutions result from assimilation of either the hf radar or adp data sets the high sensitivity of the diurnal band currents can be understood dynamically in terms of trapped shelf waves a short 85 km long section of shelf off the central oregon coast is wide enough to allow first mode barotropic shelf waves at the subinertial diurnal frequencies this results in locally resonant large amplitude diurnal tidal currents that are very sensitive to details in the local forcing and hence quite variable in time

the fine structure of nearshore tidal and residual circulations revealed by h f radar surface current measurements abstract using the ocean surface current radar oscr developed by the rutherford appleton laboratory uk 30 days of synoptic hourly surface current vectors were obtained for 84 locations within a nearshore region some 18 kms square tidal analyses of these data show that the currents associated with the predominant m2 constituent sweep smoothly and regularly through the area unaffected by the finer topographic features moreover contours of the amplitude of the m2 semi major axis are mutually consistent to a precision of better than 0 5 cm s 1 statistical analyses of these data indicate that the standard error of oscr current measurements is less than 4 cm s 1 by contrast the major higher harmonic constituent m4 shows pronounced but ordered spatial variability relating the observed distributions for m4 and m2 is foreseen as an instructive modeling problem that should advance our knowledge of shallow water tidal interaction processes standard relationships between residual surface currents and

hf radar data assimilation in the monterey bay area 1 the utility of high frequency hf radar data for improving numerical circulation model predictions is evaluated comparisons of the statistical properties of the codar type hf radar data and the observed wind indicate a strong correlation between the dominant alongshore upwelling favoring wind forcing and hf radar derived surface currents along the central california coastline because inadequate knowledge of the wind stress is probably a significant source of error in the model solutions the idea of using hf radar data to provide corrections to the model wind forcing is promising different hf radar data assimilation schemes are compared and judged based on the correlations observed between model currents and independent observations from two mooring sites analysis of correlation maps between model predicted and observed currents indicates a spatial and temporal shift between modeled and observed features however the impact of hf radar data assimilation reduces these spatial and temporal shifts a significant improvement in the correlation between the model and observed subsurface currents is achieved when an ekman layer projection of the corrections is included in this approach assimilation of hf radar data produces additional ekman pumping vertical velocity based on the horizontal pattern of model observed velocity mismatch at the surface

production of spume drops by the wind tearing of wave crests the search for quantification much attention has been attracted recently to spume drops produced by the wind tearing of wave crests two models of their generation were proposed monahan et al 1986 andreas 1992 on the basis of our general observations on spray one in a wind wave tank wu 1973 and the other in the field wu et al 1984 these models are critically reviewed all relevant measurements of spray droplets in tanks and the field are analyzed to deduce the production spectrum of spume drops while the present generation function appears to adhere closely with physical conditions and experimental evidence of spume drop production wide discrepancies existing among models demand direct observations of this production by tearing

mechanisms of mid to outer shelf transport of shoreline released tracers abstracttransport of shoreline released tracer from the surfzone across the shelf can be affected by a variety of physical processes from wind driven to submesoscale with implications for shorelin

mapping ocean outfall plumes and their mixing using autonomous underwater vehicles this paper reports on our experiences developing methods to survey an ocean outfall discharge plume using an autonomous underwater vehicle auv the mobility of an auv provides a significant advantage in surveying discharge plumes over traditional boat based methods and when combined with optical and oceanographic sensors provides a capability for both detecting plumes and assessing their mixing in both the near and far fields unique to this study is the optical sensing of of the presence of colored dissolved organic matter cdom in the discharge plume for quantitatively assessing the dilution ratio of the plume water this capability is demonstrated for two publicly operated treatment works potws located offshore san diego california that have significantly different environmental settings and operating parameters the first is the south bay ocean outfall sboo operated by the international boundary water commission ibwc whose discharge is located in approximately 30m deep water at a flow rate of 28 million gallons per day mgd the second discharge is the point loma ocean outfall ploo which discharges at approximately 90m with a nominal volume flow rate of 250 mgd the methodologies for planning the auv missions to sample the discharge plume characterizing the plume using the signals measured by the onboard oceanographic and optical sensors and use of those data in predictive models is outline the results suggest that even in variable oceanic conditions properly planned missions for auvs equipped with appropriate sensors can accurately characterize and track ocean outfall plumes with high spatial resolution more effectively than traditional methods

temperature and currents on the southern california shelf a description of the variability abstract temperature and horizontal current observations at three water depths 15 30 and 60 m over the southern california shelf are reported for four discrete periods during 1978 79 roughly corresponding to each of the principal seasons the vertical structure of temperature changes markedly during the year the water over the shelf is weakly stratified in the winter n 50 cpd but stratification is stronger in the summer n 250 cpd seasonal changes in vertically averaged temperature are comparatively unimportant long term averages of the longshore currents are to the south near the surface in all seasons with amplitudes ranging up to 10 cm s 1 in the winter during spring and summer the stratification is accompanied by shear in the vertical structure of these long term current averages with surface currents sweeping to the south but with deeper colder water flowing in the opposite direction currents fluctuating at subtidal frequencies are predominantly alongshore and are strongest durin

seasonally active slipface avalanches in the north polar sand sea of mars evidence for a wind related origin 1 meter scale mro hirise camera images of dune slipfaces in the north polar sand sea of mars reveal the presence of deep alcoves above depositional fans these features are apparently active under current climatic conditions because they form between observations taken in subsequent mars years recently other workers have hypothesized that the alcoves form due to destabilization and mass wasting during sublimation of co2 frost in the spring while there is evidence for springtime modification of these features our analysis of early springtime images reveals that over 80 of the new alcoves are visible underneath the co2 frost thus we present an alternative hypothesis that formation of new alcoves and fans occurs prior to co2deposition we propose that fans and alcoves form primarily by aeolian processes in the mid to late summer through a sequence of aeolian deposition on the slipface over steepening failure and dry granular flow an aeolian origin is supported by the orientations of the alcoves which are consistent with recent wind directions furthermore morphologically similar but much smaller alcoves form on terrestrial dune slipfaces and the size differences between the terrestrial and martian features may reflect cohesion in the near subsurface of the martian features the size and preservation of the largest alcoves on the martian slipfaces also support the presence of an indurated surface layer thus new alcoves might be sites of early spring co2sublimation and secondary mass wasting because they act as a window to looser less indurated materials that warm up more quickly in the spring

wind driven erosion and exposure potential at mars 2020 rover candidate landing sites aeolian processes have likely been the predominant geomorphic agent for most of mars history and have the potential to produce relatively young exposure ages for geologic units thus identifying local evidence for aeolian erosion is highly relevant to the selection of landing sites for future missions such as the mars 2020 rover mission that aims to explore astrobiologically relevant ancient environments here we investigate wind driven activity at eight mars 2020 candidate landing sites to constrain erosion potential at these locations to demonstrate our methods we found that contemporary dune derived abrasion rates were in agreement with rover derived exhumation rates at gale crater and could be employed elsewhere the holden crater candidate site was interpreted to have low contemporary erosion rates based on the presence of a thick sand coverage of static ripples active ripples at the eberswalde and southwest melas sites may account for local erosion and the dearth of small craters moderate flux regional dunes near mawrth vallis were deemed unrepresentative of the candidate site which is interpreted to currently be experiencing low levels of erosion the nili fossae site displayed the most unambiguous evidence for local sand transport and erosion likely yielding relatively young exposure ages the downselected jezero crater and northeast syrtis sites had high flux neighboring dunes and exhibited substantial evidence for sediment pathways across their ellipses both sites had relatively high estimated abrasion rates which would yield young exposure ages the downselected columbia hills site lacked evidence for sand movement and contemporary local erosion rates are estimated to be relatively low

near tropical subsurface ice on mars near surface perennial water ice on mars has been previously inferred down to latitudes of about 45 and could result from either water vapor diffusion through the regolith under current conditions or previous ice ages precipitations in this paper we show that at latitudes as low as 25 in the southern hemisphere buried water ice in the shallow 1 m subsurface is required to explain the observed surface distribution of seasonal co2 frost on pole facing slopes this result shows that possible remnants of the last ice age as well as water that will be needed for the future exploration of mars are accessible significantly closer to the equator than previously thought where mild conditions for both robotic and human exploration lie copyright 2010 by the american geophysical union

size frequency distributions of rocks on mars and earth analog sites implications for future landed missions the size frequency distribution of rocks at the viking landing sites and a variety of rocky locations on the earth that formed from a number of geologic processes all have the general shape of simple exponential curves which have been combined with remote sensing data and models on rock abundance to predict the frequency of boulders potentially hazardous to future mars landers and rovers rock data from the near field of the viking landers where dimensions can be measured accurately in stereo images and estimates from the far field of viking 1 have convex up curved shapes on log log graphs of cumulative frequency per square meter or cumulative fractional area versus diameter the rock data show a sharp drop off at large diameters and a progressive approach to a plateau with decreasing diameter approaching the total rock coverage which can be fit well with simple exponential functions similar shaped size frequency distributions of rocks are found at a wide variety of rocky surfaces on the earth and can be fit well with simple exponential functions this distribution is compatible with fracture and fragmentation theory which provides a physical basis for its wide application a combined fit to rock area data at both viking sites was made with a general exponential function in which the pre exponential is the total area covered by rocks simple linear height versus diameter relationships were also derived from height diameter ratios at the viking sites which suggest that rockier areas on mars have higher standing rocks than less rocky areas height was then substituted into the general exponential function derived for diameter yielding the cumulative fractional area of rocks versus height for any given total rock coverage on mars results indicate that most of mars is rather benign with regard to hazards from landing on large rocks for total rock coverage of 8 equivalent to modal rock coverage on mars and the viking 1 site without the outcrops about 1 of the surface is covered by 20 cm or higher rocks a lander designed to accommodate landing on 0 5 m high boulders such as the mars pathfinder airbag system could land on a surface covered by about 20 rocks similar to the viking 2 site which is rockier than 95 of the planet with 1 of the surface covered by rocks of 0 5 m or higher

overview of the opportunity mars exploration rover mission to meridiani planum eagle crater to purgatory ripple the mars exploration rover opportunity touched down at meridiani planum in january 2004 and since then has been conducting observations with the athena science payload the rover has traversed more than 5 km carrying out the first outcrop scale investigation of sedimentary rocks on mars the rocks of meridiani planum are sandstones formed by eolian and aqueous reworking of sand grains that are composed of mixed fine grained siliciclastics and sulfates the siliciclastic fraction was produced by chemical alteration of a precursor basalt the sulfates are dominantly mg sulfates and also include ca sulfates and jarosite the stratigraphic section observed to date is dominated by eolian bedforms with subaqueous current ripples exposed near the top of the section after deposition interaction with groundwater produced a range of diagenetic features notably the hematite rich concretions known as blueberries the bedrock at meridiani is highly friable and has undergone substantial erosion by wind transported basaltic sand this sand along with concretions and concretion fragments eroded from the rock makes up a soil cover that thinly and discontinuously buries the bedrock the soil surface exhibits both ancient and active wind ripples that record past and present wind directions loose rocks on the soil surface are rare and include both impact ejecta and meteorites while opportunity s results show that liquid water was once present at meridiani planum below and occasionally at the surface the environmental conditions recorded were dominantly arid acidic and oxidizing and would have posed some significant challenges to the origin of life copyright 2006 by the american geophysical union

ultrahigh resolution topographic mapping of mars with mro hirise stereo images meter scale slopes of candidate phoenix landing sites 1 the objectives of this paper are twofold first to report our estimates of the meter to decameter scale topography and slopes of candidate landing sites for the phoenix mission based on analysis of mars global surveyor mgs mars orbiter camera moc images with a typical pixel scale of 3 m and mars reconnaissance orbiter mro high resolution imaging science experiment hirise images at 0 3 m pixel 1 and second to document in detail the geometric calibration software and procedures on which the photogrammetric analysis of hirise data is based a combination of optical design modeling laboratory observations star images and mars images form the basis for software in the u s geological survey integrated software for imagers and spectrometers isis 3 system that corrects the images for a variety of distortions with single pixel or subpixel accuracy corrected images are analyzed in the commercial photogrammetric software socet set bae systems yielding digital topographic models dtms with a grid spacing of 1 m 3 4 pixels that require minimal interactive editing photoclinometry yields dtms with single pixel grid spacing slopes from moc and hirise are comparable throughout the latitude zone of interest and compare favorably with those where past missions have landed successfully only the mars exploration rover mer b site in meridiani planum is smoother moc results at multiple locations have root mean square rms bidirectional slopes of 0 8 4 5 at baselines of 3 10 m hirise stereopairs one per final candidate site and one in the former site yield 1 8 2 8 slopes at 1 m baseline slopes at 1 m from photoclinometry are also in the range 2 3 after correction for image blur slopes exceeding the 16 phoenix safety limit are extremely rare

hf radar observations of surface circulation off bodega bay northern california usa 1 two high frequency radar stations codar were installed along the northern california coast in may 2001 comparisons of radar data with acoustic doppler current profiler adcp current data and near surface drifter tracks indicate considerable agreement with minimum rms differences of order 0 05 0 15 m s and average drifter hf radar track separation rates of 5 3 km d radar data resolve the three main sources of intraseasonal current variability in the area 1 upwelling relaxation dynamics 2 tidal and diurnal forcing and 3 inertial currents subtidal fluctuations are the largest component of variability accounting for 45 75 of the variance wind driven dynamics are the dominant source of this subtidal variability 67 of subtidal variability both upwelling and relaxation periods exhibit consistent patterns of surface velocity with nearshore currents being slower and more poleward than offshore currents which are strongly equatorward analysis of tidal and inertial variability indicate that current fluctuations are polarized toward clockwise rotation and are generally weaker and more linearly polarized near the coast m2 tidal current ellipses switch direction of rotation at the shelf break suggesting the presence of internal tidal waves currents in all frequency bands are deflected and accelerated around pt reyes and there are indications of increased current variability and changes in flow direction near cordell bank the presence of considerable cross shore and alongshore gradients in the strength and direction of surface flow patterns and in particular weak poleward currents over the inner shelf could have important consequences for plankton retention in the area

mineralogy composition and alteration of mars pathfinder rocks and soils evidence from multispectral elemental and magnetic data on terrestrial analogue snc meteorite and pathfinder samples major element multispectral and magnetic properties data were obtained at ares vallis during the mars pathfinder mission to understand the compositional mineralogical and process implications of these data we obtained major element mineralogical and magnetic data for well crystalline and nanophase ferric minerals terrestrial analogue samples with known geologic context and snc meteorites analogue samples include unaltered palagonitic and sulfatetic tephra from mauna kea volcano hydrolytic and acid sulfate alteration steam vent material from kilauea volcano hydrolytic alteration and impactites from meteor crater relithification salient results for mars pathfinder include 1 band depths bd530b and bd600 and the reflectivity ratio r800 r750 are consistent with the dominant ferric mineral being nanophase ferric oxide associated with an unknown amount of h2o and occurring in composite particles along with subordinate amounts of other ferric minerals hematite and hematite plus nanophase goethite are most consistent with the data but maghemite akaganeite schwertmannite and nanophase lepidocrocite are also possible interpretations ferric oxides that are consistently not favored by the data as sole alteration products are jarosites and well crystalline goethite and lepidocrocite 2 the strength of the ferric adsorption edge r750 r445 implies the fe3 fe2 values for pathfinder rock and soil are within the ranges 0 7 3 and 3 20 respectively 3 ferrous silicates are indicated for subsets of pathfinder rocks and soils one subset has a band minimum near 930 nm that can attributed to low ca pyroxene alternatively the band could be a second manifestation of certain ferric oxides including nanophase goethite maghemite akaganeite and schwertmannite another subset has a negative spectral slope from 800 to 1005 nm which could result from the high energy wing of a high ca pyroxene and or olivine band a mixture of bright and dark materials and for rocks thin coatings of bright dust on dark rocks 4 chemical data on pathfinder rocks and soils are consistent with two component mixtures between an andesitic rock with low mgo and so3 concentrations soil free rock and a global basaltic soil with high mgo and so3 concentrations rock free soil pathfinder rock free soil can be modeled as a chemical mixture of snc meteorites and the pathfinder soil free rock 5 pathfinder soil cannot be obtained by chemical alteration of pathfinder rocks by any of the hydrolytic and acid sulfate alteration processes we studied presumably global mixing has obscured and possibly erased the elemental signatures of chemical alteration 6 the strongly magnetic phase in palagonitic and sulfatetic tephra is titanomagnetite and possibly its oxidation product titanomaghemite fe ti spinels the saturation magnetization of the tephra samples 0 5 2 0 am2 kg is at or below the low end of the range inferred for martian dust 4 2 am2 kg implying that lithogenic fe ti spinels are a possible candidate for the martian strongly magnetic phase 7 the predominantly palagonitic spectral signature and magnetic nature of martian soil and dust are consistent with glassy precursors with imbedded fe ti spinel particles comparison with lunar glass production rates suggests that production of sufficient quantities of glassy materials on mars by volcanic and impact processes is sufficient to account for these observations

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

present day mass wasting in sulfate rich sediments in the equatorial regions of mars abstract present day topographic changes are observed on steep slopes in equatorial regions of mars that are associated with sulfate rich sediments hydrated sulfates are known to be present in many sedimentary deposits on mars we document volume changes in the form of mass movements and gullies over these regions we have estimated erosion rates of 12 mm yr or 1 2 120 mm yr with uncertainties over steep slopes on sulfate rich mounds in ganges chasma much higher than mars average erosion rate near a few m yr at this rate the mounds would have shrunk in diameter by 18 000 km over 3 b y which greatly exceeds the width of the canyon supporting suggestions that these sediments once filled the canyons due to the soft nature of typical sulfate rich sediment it is susceptible to mass wasting and active eolian processes may remove loose material to maintain steep slopes the water in hydrated sulfates could potentially be extracted and used as a resource for future humans on mars and our results suggest that such deposits would be mechanically weak

an analysis of hf radar measured surface currents to determine tidal wind forced and seasonal circulation in the gulf of the farallones california united states 1 a complete year of hourly 3 km resolution high frequency radar measured surface currents covering the gulf of the farallones were analyzed with the following three primary objectives 1 describe the seasonal surface circulation 2 identify tidal currents and 3 determine the influence of wind forcing three predominant seasonal circulation regimes were identified relaxation storm and upwelling the relaxation period exhibited mean poleward flow over the slope variable equatorward flow over the shelf and cyclonic and anticyclonic eddies south of pt reyes the storm period mean flow was variable and exhibited evidence of coastally trapped buoyancy flow from the mouth of the san francisco bay the upwelling period exhibited equatorward flow throughout the gulf with regions of intensified flow at the northern and southern regions over the slope the tidal variance ranged from 4 to 60 was highest around the mouth of the bay decreased past the shelf and its spatial pattern reflected the combined influence of the k1 and m2 tidal current amplitudes k1 ellipses typically rotated clockwise throughout the gulf and decreased in amplitude past the shelf m2 ellipses were comparably more variable in orientation and magnitude harmonic tidal analyses of buoy wind data over 4 month time periods showed significant k1 amplitudes which did not appear when the analysis was done for the entire year this indicates that harmonic tidal analyses on surface currents are probably more effective at disassociating diurnal sea breeze driven currents when performed over long periods of time such as a year

effects of wind trend and gustiness on the sea drag lake george study 1 the air sea coupling is usually parameterized in terms of the drag coefficient cd but the scatter of experimental data around such dependences is very significant and has not improved noticeably over some 30 years in the paper which is meant to be the first in a series a complex approach to the problem is suggested multiple mechanisms contributing into the sea drag are to be singled out studied separately evaluated and then reunited in a joint parameterization for cd dependences of the drag coefficient on the wind speed and sea state and effects of wind trends and gustiness are investigated in detail gustiness is found to be responsible for the most distant outliers our approach also combines an experimental lake george study with theoretical investigations conducted by means of the wowc wind over waves coupling model overall agreement of the model with measured wind stresses is quite good within 20 for the bulk of the data lower envelopes of the drag dependences are an important result of the paper they provide some lake george ideal relationships for the sea drag almost any deviation from such conditions causes the drag to increase it is suggested that decrease of the drag with respect to the ideal conditions which exhibits itself in a number of known open ocean data sets would be caused by a momentum flux back from the waves to the wind due to long waves outrunning the wind behavior of the charnock parameter in terms of wave age is also considered

decomposing observations of high frequency radar derived surface currents by their forcing mechanisms locally wind driven surface currents 1 the wind impulse response function and transfer function for high frequency radar derived surface currents off southern san diego are calculated using several local wind observations the spatial map of the transfer function reflects the influence of the coast on wind current dynamics near the coast within 20 km from the shoreline the amplitudes of the transfer function at inertial and diurnal frequencies are reduced due to effects of coastline and bottom bathymetry meanwhile the amplitude of low frequency currents increases near the coast which is attributed to the local geostrophic balance between cross shore pressure gradients against the coast and currents locally wind driven surface currents are estimated from the data derived response function and their power spectrum shows a strong diurnal peak superposed on a red spectrum similar to the spectra of observed winds current magnitudes and veering angles to a quasi steady wind are typically 2 5 of the wind speed and vary 50 90 to the right of the wind respectively a wind skill map is introduced to present the fractional variance of surface currents explained by local winds as a verification tool for wind data quality and relevance moreover the transfer functions in summer and winter are presented to examine the seasonal variation in ocean surface current response to the wind associated with stratification change

the global s1 tide the small s1 ocean tide is caused primarily by diurnal atmospheric pressure loading its excitation is therefore unlike any other diurnal tide in particular pressure loading is maximum near the equator where the diurnal gravitational potential is zero the global character of the s 1 tide is here determined by numerical modeling and by analysis of ocean topography experiment topex poseidon satellite altimeter data the two approaches yield reasonably consistent results amplitudes exceeding 1 cm in several regions are further confirmed by comparison with coastal tide gauges notwithstanding their excitation differences s 1 and other diurnal tides are found to share several common features such as relatively large amplitudes in the arabian sea the labrador sea the sea of okhotsk and the gulf of alaska the most noticeable difference is the lack of an s 1 antarctic kelvin wave these similarities and differences can be explained in terms of the coherences between neardiurnal oceanic normal modes and the underlying tidal forcings whereas gravitational diurnal tidal forces excite primarily a 28 h antarctic pacific mode the s 1 air tide excites several other near diurnal modes none of which has large amplitudes near antarctica