the formation of longitudinal fronts in a coastal plain estuary longitudinal estuarine fronts aligned parallel to the axis of the estuary are characteristic of the york river their time scale for genesis and decay is of the order of hours they are usually located at the inner edge of the shoals or over the main channel field measurements have shown marked intratidal differences in density and current speeds across this estuary these can be correlated with changes in depth and the strength of the advective processes differential advection between the channel and shoal regions when acting upon a constant longitudinal density gradient is shown to be of sufficient magnitude to generate strong lateral density gradients and thus fronts at particular times within the tidal cycle

hydration state of the martian coarse grained hematite exposures implications for their origin and evolution 1 the discovery of areas of bulk gray hematite on the surface of mars is among the most interesting of the results from mars global surveyor mgs the individual outcrops are concentrated in equatorial low albedo regions from the valles marineris to the meridiani planum region to the east while the thermal emission spectrometer tes team favored an aqueous process for the formation of this deposit recent geologic studies have interpreted deposits in the region to have a volcanic origin competing ideas for the method of formation of bulk hematite range from aqueous alteration burial diagenesis and metamorphism to igneous processes here we show that some of the spectra collected over meridiani planum and aram chaos from the mariner 6 and 7 spacecraft have a high 3 m band depth this feature is associated with hydrated minerals in the surface layer and the hydrated spectra coincide with the mapped hematite regions this supports an aqueous mode of hematite formation and as hematite itself is not hydrated suggests the presence of other hydrous mineral phases in these areas we discuss the implications of this association for origin and evolution of these deposits

tidal residual intertidal mudflat trim model and its applications to san francisco bay california abstract a numerical model using a semi implicit finite difference method for solving the two dimensional shallow water equations is presented the gradient of the water surface elevation in the momentum equations and the velocity divergence in the continuity equation are finite differenced implicitly the remaining terms are finite differenced explicitly the convective terms are treated using an eulerian lagrangian method the combination of the semi implicit finite difference solution for the gravity wave propagation and the eulerian lagrangian treatment of the convective terms renders the numerical model unconditionally stable when the baroclinic forcing is included a salt transport equation is coupled to the momentum equations and the numerical method is subject to a weak stability condition the method of solution and the properties of the numerical model are given this numerical model is particularly suitable for applications to coastal plain estuaries and tidal embayments in which tidal currents are dominant and tidally generated residual currents are important the model is applied to san francisco bay california where extensive historical tides and current meter data are available the model calibration is considered by comparing time series of the field data and of the model results alternatively and perhaps more meaningfully the model is calibrated by comparing the harmonic constants of tides and tidal currents derived from field data with those derived from the model the model is further verified by comparing the model results with an independent data set representing the wet season the strengths and the weaknesses of the model are assessed based on the results of model calibration and verification using the model results the properties of tides and tidal currents in san francisco bay are characterized and discussed furthermore using the numerical model estimates of san francisco bay s volume surface area mean water depth tidal prisms and tidal excursions at spring and neap tides are computed additional applications of the model reveal qualitatively the spatial distribution of residual variables

the tidally averaged momentum balance in a partially and periodically stratified estuary abstract observations of turbulent stresses and mean velocities over an entire spring neap cycle are used to evaluate the dynamics of tidally averaged flows in a partially stratified estuarine channel in a depth averaged sense the net flow in this channel is up estuary due to interaction of tidal forcing with the geometry of the larger basin the depth variable tidally averaged flow has the form of an estuarine exchange flow downstream at the surface upstream at depth and varies in response to the neap spring transition the weakening of the tidally averaged exchange during the spring tides appears to be a result of decreased stratification on the tidal time scale rather than changes in bed stress the dynamics of the estuarine exchange flow are defined by a balance between the vertical divergence of the tidally averaged turbulent stress and the tidally averaged pressure gradient in the lower water column in the upper water column tidal stresses are important contributors particularly during the n

wind driven subinertial circulation inside a semienclosed bay in the gulf of california abstractmoored current and pressure observations were obtained at bahia concepcion a semienclosed bay located on the eastern side of the baja california peninsula in mexico to describe the wind driven subinertial circulation in winter and early spring the bay is well mixed and forced by persistent winds toward the southeast aligned with the central axis the authors observations show that the sea surface rises downwind in response to wind stress and that there exists a crosswind drift at the surface that is consistent with ekman dynamics this feature is typical of a bay that is deeper than one ekman depth and hence affected by the rotation of the earth there is a persistent along bay circulation toward the end of the bay along its western side with return flow on the opposite side drifters released near the surface across a transect move westward and downwind toward the closed end where they recirculate cyclonically wind driven linear theoretical models successfully predict the observed cross b

variability of internal tides in the laurentian channel data from three sequential stations of thermistor chains and current meters along the main axis of the lower st lawrence estuary during the summer fall period in 1978 were analyzed to help understand generation and variability of the internal tide the lagrangian or direct tracing method has been developed to compute the displacements of internal tides which can overcome limitations of the eulerian method caused by the very small vertical temperature gradients internal tides of semidiurnal frequency were observed but diurnal tides were not in both the time domain and frequency band the surface diurnal tide behaves like a standing wave rather than a progressive one due to the nonlinear interaction of the internal tide generated locally near the sill with topography quarter diurnal and higher frequency oscillations were also generated the displacement of internal tides can reach 80 40 and 30 m during spring tides respectively at station 1 and at two downstream stations 3 and 5 the internal tides propagate seaward with attenuation downstream which mainly results from changing vertical stratification conditions but may also be partly attributed to wave breaking and turbulent mixing in the upper layer and bottom and lateral friction the amplitude ratio of s2 m2 is smaller 0 2 for the baroclinic current than for the barotropic current 0 24 at station 1 but becomes larger at stations 3 and 5 this implies the presence of the narrower response frequency band of the baroclinic tide to the barotropic forcing near the generation site the progressive semidiurnal and quarter diurnal internal tides were of the poincare type which implies a three dimensional structure the nutrient pumping due to the internal tides was confirmed to occur only near the generation region of the internal tide this convergence zone of higher primary productivity is considered to be equivalent to the rotor clouds in atmospheric mountain waves

chemistry and mineralogy of outcrops at meridiani planum analyses of outcrops created by the impact craters endurance fram and eagle reveal the broad lateral continuity of chemical sediments at the meridiani planum exploration site on mars approximately ten mineralogical components are implied in these salt rich silicic sediments from measurements by instruments on the opportunity rover compositional trends in an apparently intact vertical stratigraphic sequence at the karatepe west ingress point at endurance crater are consistent with non uniform deposition or with subsequent migration of mobile salt components dominated by sulfates of magnesium striking variations in cl and enrichments of br combined with diversity in sulfate species provide further evidence of episodes during which temperatures ph and water to rock ratios underwent significant change to first order the sedimentary sequence examined to date is consistent with a uniform reference composition modified by movement of major sulfates upward and of minor chlorides downward this reference composition has similarities to martian soils supplemented by sulfate anion and the alteration products of mafic igneous minerals lesser cementation in lower stratigraphic units is reflected in decreased energies for grinding with the rock abrasion tool survival of soluble salts in exposed outcrop is most easily explained by absence of episodes of liquid h2o in this region since the time of crater formation

on the nature of transverse variability in a coastal plain estuary even though estuarine processes are inherently three dimensional most of the previous studies have focused primarily on the axial longitudinal and vertical variabilities recent surveys in the lower delaware bay indicate the presence of significant transverse variability in the salinity distribution and residual circulation pattern conceptual models are developed to examine the mechanisms which might explain the observed transverse structure results indicate that both the gravitational effect and wind forcing are capable of generating substantial transverse structure in drowned river valley estuaries with triangular cross sections

reassessing the evidence for the earliest traces of life the isotopic composition of graphite is commonly used as a biomarker in the oldest 3 5 gyr ago highly metamorphosed terrestrial rocks earlier studies on isotopic characteristics of graphite occurring in rocks of the approximately 3 8 gyr old isua supracrustal belt isb in southern west greenland have suggested the presence of a vast microbial ecosystem in the early archean this interpretation however has to be approached with extreme care here we show that graphite occurs abundantly in secondary carbonate veins in the isb that are formed at depth in the crust by injection of hot fluids reacting with older crustal rocks metasomatism during these reactions graphite forms from the disproportionation of fe ii bearing carbonates at high temperature these metasomatic rocks which clearly lack biological relevance were earlier thought to be of sedimentary origin and their graphite association provided the basis for inferences about early life the new observations thus call for a reassessment of previously presented evidence for ancient traces of life in the highly metamorphosed early archaean rock record

effects of bathymetry friction and rotation on estuary ocean exchange an analytical model that includes pressure gradient friction and the earth s rotation in both components of the flow is used to study the transverse structure of estuarine exchange flows and the nature of transverse circulation in estuaries of arbitrary bathymetry analytical results are obtained for generic bathymetry and also over real depth distributions and are compared with observations this study extends previous efforts on the topic of transverse structure of density induced exchange flows in three main aspects 1 the analytical model explores any arbitrary bathymetry 2 the results reflect transverse asymmetries relative to a midchannel centerline associated with the effects of the earth s rotation and 3 the transverse circulation produced by the analytical model is examined in detail analytical results over generic bathymetry show in addition to the already reported dependence of exchange flow structure on the ekman number two new features first the transverse structure of along estuary flows shows the earth s rotation effects even in relatively narrow systems thus producing transverse asymmetries in these flows the asymmetries disappear under strongly frictional high ekman number conditions thus illustrating the previously documented pattern of inflow in channels and outflows over shoals for typical estuaries second transverse flows resemble a sideways gravitational circulation when frictional effects are apparent ekman number greater than 0 1 responding to a transverse balance between pressure gradient and friction these transverse flows reverse direction under very weak friction and reflect coriolis deflection of along estuary flows that is geostrophic dynamics all examples of observed flows are satisfactorily explained by the dynamics included in the analytical model

on the thermal regime of some tectonic units in a continental collision environment in romania an analysis of the evolution of the main tectonic units in romania shows that the thermal regime of the lithosphere should be derived according on the one hand to the particular tectonic interactions the various tectonic units have been involved in and on the other hand to the investigated depth interval a steady state conduction model of the crustal temperature field based on the heat flow distribution and information on the structure is presented for the romanian territory it shows large lateral thermal variations between tectonic units as a result of different geological and thermal histories within the frame of a complex modelling of the thermal evolution of the lithosphere in the east carpathians as proposed in this study the zero order thermal effects of the pre miocene oceanic subduction of the eurasian plate are evaluated the deep thermal structure of the subducted slab is derived and shown to be compatible with the velocity structure of the lithosphere and the intermediate depth seismicity of the vrancea area

planetary science on earth as it is on mars the small spheres of haematite nicknamed blueberries that litter the mars landing site of nasa s rover opportunity might have an analogue on earth formed from groundwater in southern utah

simulation of storm surge wave currents and inundation in the outer banks and chesapeake bay during hurricane isabel in 2003 the importance of waves 1 this paper investigates the effects of waves on storm surge currents and inundation in the outer banks and chesapeake bay during hurricane isabel in 2003 through detailed comparison between observed wind wave surge and inundation data and results from an integrated storm surge modeling system ch3d ssms ch3d ssms which includes coupled coastal and basin scale storm surge and wave models successfully simulated measured winds waves storm surge currents and inundation during isabel comprehensive modeling and data analysis revealed noticeable effects of waves on storm surge currents and inundation among the processes that represent wave effects radiation stress outside the estuaries and wave induced stress outside and inside the estuaries are more important than wave induced bottom stress in affecting the water level maximum surge was 3 m while maximum wave height was 20 m offshore and 2 5 m inside the chesapeake bay where the maximum wave induced water level reached 1 m significant waves reached 3 5 m and 16 s at duck pier north carolina and 1 6 m and 5 s at gloucester virginia at duck wave effects accounted for 36 cm or 20 of the peak surge elevation of 1 71 m inside the chesapeake bay wave effects account for 5 10 of observed peak surge level a two layer flow is found at kitty hawk north carolina during the peak of storm surge owing to the combined effects of wind and wave breaking higher surge elevations result when the 3 d surge model instead of the 2 d surge model is coupled with the 2 d wave model owing to its relatively lower bottom friction wave heights obtained with 3 and 2 d surge models show little difference

a three dimensional numerical simulation of hudson bay summer ocean circulation topographic gyres separations and coastal jets abstract the summer ocean circulation in hudson bay is studied numerically using the blumberg mellor model with a 27 5 km 27 5 km horizontal grid and a realistic bottom topography in the control run 1 monthly climatological forcing fields of wind stress oceanic inflow outflow and salt and heat fluxes are used in addition results are presented for a number ot sensitivity experiments 2 no topography otherwise conditions are identical to the control run 3 no wind forcing 4 no oceanic inflow outflow 5 no heat and salt fluxes 6 no temperature and salinity variations and 7 without the nonlinear terms while the overall simulated circulation in hudson bay is cyclonic the strong steering of the flow by the bathymetry is particularly noticeable mesoscale topographic gyres are simulated and the separation of the coastal current due to topographic bumps occurs in several locations the simulated circulation also has well developed vorticity features and narrow density driven coastal jets al

a further earthquake on the kerguelen plateau summary the search procedure of the international seismological centre for previously unreported earthquakes has located a further earthquake on the eastern edge of the kerguelen plateau about 1200 km sse of kerguelen island this event mb 4 7 occurred on 1981 april 6 and was about 65 km west of a larger event mb 5 2 that occurred in 1973 these two earthquakes are the only ones known to have occurred on the plateau apart from three events close to kerguelen island the position of the new event is about midslope on the steep eastern edge of the plateau and analysis of depth phases confirms that it occurred in a water depth of 2 2 km with a focal depth of 10 12 km beneath the seafloor similar analysis of the earlier event which is beneath the bottom of the slope places it at a depth of 20 25 km near the base of the crust and indicates that there is a likely thickness of about 1 km of unconsolidated sediment in this area kerguelen gaussberg plateau the broad area of shallow water extending sse from kerguelen island towards antarctica is variously known as the kerguelen or gaussberg plateau or ridge its structure and topography are described by houtz hayes mark1 1977 and more recently by schlich 1982 in its northern part it includes the islands of kerguelen and heard and is shallower than 1000 m for a length of about 800 km beyond a ne sw trending col between 55 and 58 s the southern part of the plateau continues towards antarctica near 85 e the plateau is generally classified as an aseismic ridge the northern part has a rather complex basement topography whereas the southern part is smoother with more uniform sedimentation schlich 1982 magnetic anomalies indicate a shallower basaltic basement and gravity measurements that the ridge is nearly compensated with a crustal thickness of about 20 km houtz et al 1977 such thicknesses are commonly found in other areas of similar depth such as the campbell plateau to the south of new zealand adams 1962 seismicity

tidal and tidally averaged circulation characteristics of suisun bay california availability of extensive field data permitted realistic calibration and validation of a hydrodynamic model of tidal circulation and salt transport for suisun bay california suisun bay is a partially mixed embayment of northern san francisco bay located just seaward of the sacramento san joaquin delta the model employs a variant of an alternating direction implicit finite difference method to solve the hydrodynamic equations and an eulerian lagrangian method to solve the salt transport equation an upwind formulation of the advective acceleration terms of the momentum equations was employed to avoid oscillations in the tidally averaged velocity field produced by central spatial differencing of these terms simulation results of tidal circulation and salt transport demonstrate that tides and the complex bathymetry determine the patterns of tidal velocities and that net changes in the salinity distribution over a few tidal cycles are small despite large changes during each tidal cycle computations of tidally averaged circulation suggest that baroclinic and wind effects are important influences on tidally averaged circulation during low freshwater inflow conditions exclusion of baroclinic effects would lead to overestimation of freshwater inflow by several hundred m3 s for a fixed set of model boundary conditions likewise exclusion of wind would cause an underestimation of flux rates between shoals and channels by 70 100

spectral characteristics of iron bearing phyllosilicates comparison to orgueil ci1 murchison and murray cm2 abstract phyllosilicate alteration minerals are commonly found in low petrologic types of carbonaceous chondrites previous spectral studies have examined mg bearing phyllosilicates with limited success in matching the spectral properties of cm and ci chondrites transmission electron microscope and other analytical techniques suggest that fe bearing clays are more abundant in ci and cm chondrites than magnesian varieties here we present the results of an examination of the reflectance spectra of fe phyllosilicates including serpentines and berthierines of which the latter were formerly known as septechlorites we have measured the diffuse reflectance spectra of powdered samples from 0 3 to 25 n we find that these minerals provide a better spectral match to many of the features seen in ci and cm chondrites and simple linear combinations of the spectra of both fe and mg phyllosilicates closely approximate the spectra of cm and ci chondrites

modeling of bathymetry locked residual eddies in well mixed tidal channels with arbitrary depth variations abstract the concept of the in out type exchange flow in estuaries only applies to situations with significant freshwater discharge and or elongated channels with relatively simple variations in depth and coastline along the channel in waterways with complex bottom topography the in out type exchange flows may be replaced by residual eddies that are locked to bathymetry this paper develops an analytic model for such tidally induced residual eddies the model allows arbitrary depth variations in both along and across channel directions the model produces residual eddies locked to bathymetry features similar to observations in wassaw sound using a ship mounted adcp analysis indicates that for problems in a short channel with standing wave characteristics the residual circulation is significantly influenced by advection the frictional effect however is dominant and the wave propagation effect cannot be uniformly neglected i e it sometimes can still compete or reinforce the effect of advection

internal waves in the gulf of california observations from a spaceborne radar pronounced signatures of internal waves were detected repeatedly in the gulf of california by the seasat synthetic aperture radar sar a series of nine images with exactly repeating ground coverage was used to study the temporal variability of the internal wave field in the area it was found that the number of observed wave groups was highly correlated with the strength of the local tides the maximum number occurred during spring tides and the minimum number occurred during neap tides indicating that the internal waves were tidally forced most of the wave activity was found to the north of 28 n where the tides were the strongest in the gulf the application of a simple nonlinear internal wave model to the observations indicated that the peak to peak amplitude of the observed waves was about 50 m with an uncertainty of a factor of 2 the estimated upper bound for the rate of the loss of tidal energy to internal waves was about 5 1015 erg s representing only 10 of the rate of the dissipation of the dominant m2 tide in the gulf

global mineral distributions on mars 1 determining the mineralogy of mars is an essential part of revealing the conditions of the surface and subsurface a deconvolution method was used to remove atmospheric components and determine surface mineralogy from thermal emission spectrometer data at 1 pixel per degree ppd minerals are grouped into categories on the basis of compositional and spectral similarity and global concentration maps are produced all binned pixels are fit well with rms errors of 0 005 in emissivity higher rms errors are attributed to short wavelength particle size effects on dust covered surfaces significant concentrations 0 10 of plagioclase high ca pyroxene sheet silicates high si glass and hematite are detected and display distributions consistent with previous studies elevated concentrations of plagioclase and high ca pyroxene are consistent with basaltic surfaces and are located in low albedo highlands regions north of 45 s significant concentrations of plagioclase and sheet silicates high si glass and low concentrations of high ca pyroxenes are consistent with andesitic surfaces and are concentrated in both southern and northern high latitude low albedo regions andesitic surfaces in the southern hemisphere have a lower spectral contrast than northern surfaces an isolated surface located in solis planum is spectrally distinct but compositionally similar to other surfaces interpreted to be andesitic in composition concentrations of olivine below the detection limit correctly identify its presence in two of three locations potassium feldspar low ca pyroxene basaltic glass olivine sulfate carbonate quartz and amphibole are not detected with confidence at 1 ppd the results presented here indicate a predominance of volcanic compositions within martian dust free surfaces

summer thermal structure and anticyclonic circulation of lake erie 1 in most thermally stratified lakes the summer thermocline has the shape of a dome with a shallower depth offshore than nearshore this configuration is accompanied by a lake wide cyclonic circulation lake wide observations of subsurface temperature in central lake erie revealed an atypical depressed or bowl shaped thermocline in late summer with a deeper thermocline in the middle of the lake and a shallower thermocline nearshore currents measured in the central basin when the bowl shaped thermocline was observed were anticyclonic forming a single basin wide gyre it is suggested that the unusual bowl shaped thermocline is the result of ekman pumping driven by anticyclonic vorticity in surface winds the bowl shaped thermocline can lead to greater hypoxia in bottom waters and negative effects on biota by reducing the hypolimnetic volume

tidal and residual circulations in coupled restricted and leaky lagoons abstract finite element numerical modelling based on field data is used to study the tidal and tidally induced residual circulation dynamics of a coupled restricted and leaky coastal lagoon system located in the magdalen islands gulf of saint lawrence havre aux maisons lagoon hml is of a restricted nature with a neutral inlet in terms of tidal asymmetry grande entree lagoon gel is of a leaky nature with a marked ebb dominance at the inlet due to direct interactions between the main astronomical tidal constituents the imbalance caused by the different tidal filtering characteristics of both inlets combines with the internal morphological asymmetries of the system to produce a residual throughflow from hml to gel the residual circulation is also characterized by strongest values at both inlets very weak residual currents in hml deep basin and a dipole of residual eddies over the deeper areas of gel further investigations including numerical tracer experiments will be necessary to achieve a full understanding of the long term circulation of this lagoonal system

on lagrangian residual currents with applications in south san francisco bay california the lagrangian residual circulation has often been introduced as the sum of the eulerian residual circulation and the stokes drift unfortunately this definition of the lagrangian residual circulation is conceptually incorrect because both the eulerian residual circulation and the stokes drift are eulerian variables in this paper a classification of various residual variables are reviewed and properly defined the lagrangian residual circulation is then studied by means of a two stage formulation of a computer model the tidal circulation is first computed in a conventional eulerian way and then the lagrangian residual circulation is determined by a method patterned after the method of markers and cells to demonstrate properties of the lagrangian residual circulation application of this approach in south san francisco bay california is considered with the aid of the model results properties of the eulerian and lagrangian residual circulation are examined it can be concluded that estimation of the lagrangian residual circulation from eulerian data may lead to unacceptable error particularly in a tidal estuary where the tidal excursion is of the same order of magnitude as the length scale of the basin a direction calculation of the lagrangian residual circulation must be made and has been shown to be feasible

a numerical model of stratified circulation in indian arm british columbia a laterally integrated numerical model has been developed for the study of stratified circulation in inlets the model is time dependent and includes advective terms horizontal and vertical turbulent diffusion of momentum and salt and variations in width and depth initial and boundary conditions based on winter measurements in burrard inlet and indian arm were used to study the inlet s response to tidal forcing the friction term was tuned to match calculated and observed dissipation rates evidence for a standing wave pattern in the response of the m2 and k1 tidal constituents is discussed a comparison of model results with cyclesonde current meter time series at two locations in indian arm is consistent with resonance a modal decomposition of the calculated response shows that most of the energy is contained in the barotropic and first baroclinic modes with the former dominating near the sill and the latter dominating in the deep basin second mode energy was significant for the k1 at some locations

tidal dissipation and stratification in the gulf of california the effect of tidal mixing upon the distribution of stratification and sea surface temperature sst in the gulf of california is studied by direct observation and by numerical modeling data from conductivity temperature depth surveys made in september and december of 1986 are used to describe the distribution of stratification and sst a vertically integrated finite differences numerical model was used to obtain the geographical distribution of available turbulent kinetic energy tke from the m2 tide the following three areas were found to be strongly affected by tidal mixing the shallow coastal area at the head of the gulf the shelf south of tiburon island and the area of the midgulf archipelago the first two are vertically well mixed and are therefore similar to other shelf sea frontal areas dissipation occurs all around the islands of the archipelago and the sills are foci of the most intense tidal dissipation stratification in this area was reduced with respect to the background but complete vertical mixing does not occur therefore the strong sst fronts that occur in this area do not mark the boundary between well mixed and stratified water the simpson hujiter criterion simpson and hunter 1974 for stratification and frontal position produced 2 75 crit 3 0 for the frontal position in the shallow northern gulf this value of crit is larger than in other shelf sea fronts which may be due to horizontal advection which is not included in the criterion we found that the effect of advection may be of the same order of magnitude as that of buoyancy flux in the area over the sills criti the available tke is not enough to produce complete mixing over the 400 m of water over the sills

modeling summer circulation and thermal structure of lake erie athree dimensionalprimitiveequationnumericalmodelwasappliedtolakeerieona2kmgridtostudyitssummercirculation andthermalstructure modelresultswerecomparedtolong termobservationsofcurrentsandtemperaturemadein2005at severallocations mostlyinitscentralbasin intheshallowandmostlyunstrati edwesternbasincirculationisdrivenbydetroitriverin ow modi edtosomeextentbywind andisfromwesttoeast inthecentralbasin which isofintermediate depthandhasarelatively atbottom themodeledcirculationisanticyclonic clockwise drivenbyanticyclonicvorticityinthesurfacewind andthethermocline isbowl shaped inlinewithobservations inthedeeppartoftheeastern basin the thermoclineisdome shapedandcirculationiscyclonic counter clockwise duetodensitygradients acon gurationtypicalforotherlargedeeplakes whileshallower areasareoccupiedbyanticyclonic circulationdrivenbyanticyclonic windvorticity inthe centralbasin modeledtemperatureandcirculationpatternsare quitesensitivetothespeci cationofthe wind eld anticyclonicwindvorticityleadstothinningofthehypolimnion inthecentralbasinandearlierdestrati cationinthefall

oblique subduction of a newtonian fluid slab a newtonian fluid model is proposed to describe the oblique subduction of a planar 2 d slab the slab is assumed to subduct in response to the ridge push force exerted along the trench the slab pull force at the downdip of the slab the gravitational body force within the slab and the frictional resistance force at the upper surface of the slab because the slab motion along strike is being resisted by the frictional resistance at the interplate coupling area while the slab motion along the trench normal is being maintained by the gravitational pulling the slab turns gradually toward the trench normal direction as it subducts this model offers an alternative explanation for earthquake slip partitioning the observation that the earthquake slip vectors deflect away from the relative plate motion direction toward the trench normal direction along most of the oblique subduction zones worldwide numerical models suggest that slip partitioning caused by slab deformation could be as much as 30 at 100 km downdip of the slab the slab viscosity the plate coupling width the interplate resistance coefficient the slab pull force and the gravitational body force are all important in determining the geometry of the slab subduction

mars remote sensing analog studies in the badwater basin death valley california 1 the search for evaporites on mars has important implications for the role that liquid water has played in shaping the planet s geologic climatic and potential biologic history orbital investigations of surface mineralogy are crucial to this exploration effort with the exception of coarse grained gray hematite at a restricted number of sites and trace amounts of carbonate in globally distributed dust deposits the thermal emission spectrometer tes and thermal emission imaging system themis instruments have yet to find widespread mineralogical evidence of aqueously formed minerals this may reflect the coarse spatial resolution of tes 3 5 km pixel and low spectral resolution of themis 10 bands between 6 5 and 14 5 m spectral mapping in the badwater basin death valley california was conducted to better understand the capabilities of tes and themis in detecting evaporite minerals high resolution modis aster airborne simulator master data degraded to tes and themis spatial resolutions were used to evaluate the detection limits of sulfates and carbonates to assess the validity of this spectral remote sensing a quantitative ground truth analysis of surface mineralogy in the badwater basin was performed the analysis was based on thin section petrography x ray diffraction electron microprobe and laboratory and field thermal emission spectrometer analyses taken together the results of all five methods provided enough constraints for a robust interpretation that was in general agreement with the spectral remote sensing mapping study for 90 of the surface samples examined

spectral reflectance and morphologic correlations in eastern terra meridiani mars the mars express observatoire pour la mineralogie l9eau les glaces et l9activite omega hyperspectral image data covering eastern terra meridiani indicate the ubiquitous presence of molecular water in etched terrain materials that disconformably overlie heavily cratered terrains and underlie the hematite bearing plains explored by the opportunity rover identification of crystalline water in kieserite mgso4 h2o is linked to materials exposed in a valley and plateau to the north of hematite bearing plains the mineralogical similarities between the etched terrain deposits examined with omega data and the layered rocks examined by opportunity imply that the ancient aqueous environments inferred from analyses of the rover data extend over regional scales

energy partitioning and horizontal dispersion in a stratified rotating lake abstract the response of a stratified rotating basin to the release of a linearly tilted interface is derived this case is compared with a uniformly forced basin in the two limits when the duration of the forcing is much greater than the period of the dominant internal waves and when it is much smaller energy partitioning is studied as a function of the burger number s relative importance of stratification versus rotation showing the dominance of a geostrophic component over the wave field for low s trajectories are integrated numerically revealing the stokes drift of the waves to be always cyclonic transport properties are classified in terms of s and the wedderburn number w relative importance of the disturbance versus stratification the geostrophic flow is the main source of advection but only the waves allow particles to break the barrier to transport between the two geostrophic gyres ultimately leading to stretching and folding for low values of w advection can become chaotic conserva

a simple model of estuarine subtidal fluctuations forced by local and remote wind stress observations of estuarine low subtidal sea level and current fluctuations have often shown domination by the remote effects of the wind acting on the adjacent coastal ocean over the local surface stress acting on the estuary itself the remote effects are transmitted to the estuary by impressment on its mouth of sea level change indtlced by the onshore component of coastal ekman transport and become increasingly dominant as the frequency decreases a simple barotropic model is developed to investigate the joint action of these two wind forcing mechanisms the relative shortness of most estuaries relative to low subtidal estuarine wavelengths explains the dominance of the remote effect for both sea level and barotropic current fluctuations in the estuary for the same reason however surface slope is dominated by local wind setup for an estuary with axis nearly parallel to the coast the two effects will operate either in concert or in opposition depending on hemisphere and orientation of the estuary axis relative to the coast for the geometries of both chesapeake bay and the delawm e estuary the model predicts opposition with the remote effect dominant at lower frequencies consistent with recent observations

three dimensional residual tidal circulation in an elongated rotating basin abstract the three dimensional residual circulation driven by tides in an elongated basin of arbitrary depth is described with a small amplitude constant density model on the f plane the inclusion of rotation fundamentally alters the residual flow with rotation fluid is drawn into the basin on the right side of an observer looking toward the closed end in the northern hemisphere and the return flow is on the opposite side a lateral circulation is superposed on the axial flow with upwelling over the deeper part of each section and downwelling near the sides the residual flow is driven by a combination of advective terms including the lateral advection of axial momentum associated with the coriolis acceleration and stokes forcing tidally averaged fluid parcel trajectories are determined by integrating the lagrangian mean velocities with or without rotation these trajectories vary considerably depending on small differences in initial position as well as on basin shape and other parameters of the

application of three dimensional lagrangian residual transport three dimensional lagrangian residual circulation computed from an intratidal hydrodynamic model is used to drive an intertidal water quality transport model the sum of the eulerian residual and stokes drift is used as a first order approximation for the lagrangian residual current the stokes drift approximates residual currents induced by the nonlinear interactions of the tidal currents computed residual velocities show close agreement with a two dimensional vertical longitudinal analytical result the methodology is applied to chesapeake bay for the entire year of 1985 salinity computed with the intertidal transport model i e with lagrangian residuals shows good agreement with observed salinity data and that computed with the intratidal hydrodynamic model the basic effect of the stokes drift is to transport water mass e g salinity up estuary the procedures provide a practical means of interfacing intratidal hydrodynamic model information to water quality models for making long term in

lagrangian surface circulation in the gulf of california from a 3d numerical model the surface circulation of the gulf of california was studied from a lagrangian point of view using the results of a 3d numerical model the advection of particles whose depth is fixed was carried out for annual and monthly periods with 710 particles homogeneously distributed over the gulf an anticyclonic circulation was found at the northern region from october to may and in the central and southern regions during may and from october to november cyclonic circulation was found in the entire gulf from july to august this circulation pattern agrees with direct measurements of drifters in the northern region during the cyclonic period the particles from the central and southern regions travel to the northern basin where they are trapped by a gyre for more than a month on the other hand during the anticyclonic period the particles flow to the southern part of the gulf some particles escape to the pacific ocean and others remain in the gulf and return to the northern part during the cyclonic period the principal gyre that appears on the center of the northern gulf in both cyclonic and anticyclonic periods traps particles for more than 30 days in a radius of 50 km in the central and southern regions a trapping zone was found in the peninsula side where the particles travel less than 100 km in 30 days on the other hand over the continental coast there is a rapid transit zone the particles escape only during the anticyclonic period

the response of the coastal boundary layer to wind and waves analysis of an experiment in lake erie wind waves currents and water levels were measured near lake erie s southeastern shore during fall 1981 data were recorded continuously at a wave research tower 6 km offshore at three waverider buoys deployed around the tower and at three current meter moorings along a transect between the tower and the shore during four storm episodes wave and current data were also recorded from a dense array of instruments along a transect across the surf zone a statistical analysis of the deep water data was performed and histograms of meteorological parameters wave parameters and water level slope were plotted as a function of wind direction the atmospheric boundary layer was usually unstable on the average the water was 2 3 c warmer than the air this was true for all wind directions at the tower the highest waves were associated with the greatest fetch distances to the wsw and wnw directions the longest period waves were also associated with these wind directions the mean water level slope was opposite the mean wind direction this discrepancy is most likely due to small leveling errors in the water level gages the variation of currents with wind direction was also examined the currents are strongest when the winds are from the west the quadrant with the strongest wind speeds however there are strong currents 5 10 cm s for all wind directions the deep water currents are basically shore parallel with the onshore offshore component averaging 39 of the root mean square longshore component analysis of the four storm episodes reveals the influence of the offshore currents on the flow regime within the surf zone quantitative estimates of the longshore momentum balance outside the surf zone show wind stress and pressure gradient to be the dominant dynamic terms inside the surf zone the radiation stress wind stress and bottom stress terms all have comparable effects and are usually larger than the acceleration and pressure gradient terms in between there is evidence of longshore flow reversals in the breaker zone and the effect of seiche induced offshore currents on the near shore flow regime

lagrangian trajectories residual currents and rectification process in the northern gulf of california abstract considering a semi implicit approximation of the coriolis terms a numerical solution of the vertically integrated equations of motion is proposed to test the two dimensional numerical model several experiments for the calculation of euler stokes and lagrange residual currents in the gulf of california were carried out to estimate the lagrangian residual current trajectories of particles were also simulated the applied tidal constituents were m2 s2 k2 n2 k1 p1 and o1 at spring tides strong tidal velocities occur in the northern half of the gulf in this region of complex geometry depths change from a few meter in the northern shelf zone to more than 3000 m in the southern part in the archipelago region the presence of islands alters amplitude and direction of tidal currents producing a rectification process which is reflected in a clockwise circulation around tiburon island in the lagrangian residual current the rectification process is explained by the superposition of the euler and stokes residual currents residual current patterns show several cyclonic and anticyclonic gyres in the northern gulf of california numerical experiments for individual and combinations of several tidal constituents revealed a large variability of lagrangian trajectories

a new view of near shore dynamics based on observations from hf radar abstract since 1984 the oscr hf radar system has been used in over 50 deployments to measure near shore surface currents for both scientific and engineering applications the enhanced scope resolution and accuracy of these measurements have yielded new insights into the tidal wind and density driven dynamics of the near shore zone tidal current ellipses obtained from these radar measurements have been shown to be in good aggrement with values calculated by numerical models both for the predominant constituents and also for higher harmonics coherent patterns of wind forced currents ahve been determined with strong evidence of a slab like surface response in one deployment with offshore winds blowing over relatively deep water this slab rotated clockwise at near inertial frequency strong up to 20cm s 1 persistent surface residual currents are commonly observed these are almost certainly generated by small horizontal density gradients these observed surface residuals provide ideal data for rigorous testing of 3 d numerical models with a threatened rise in sea level hf radar is well suited for observing the expected changes in the dynamics of near shore regions continuing development of these radar systems offers exciting prospects of remote sensing of both surface waves and currents future applications may extend beyond the near shore region to measurements along the shelf edge in oceanic gyres and for beach processes

estuarine salt conservation a lagrangian approach abstract understanding tidal and mean flow transport mechanisms that maintain the estuarine salt balance against seaward transport by river flow is one of the fundamental questions of estuarine oceanography previous salt transport studies have failed to resolve this problem for two principal methodological reasons in addition to the inherent variability of estuaries first salt transport expansions used to represent the salt balance have included a large number of terms that could not be related to any theory of estuarine circulation and whose physical meaning was thus unclear second it has proven difficult to measure small mean velocities in the presence of much larger tidal variations a new analysis method that expresses lagrangian scalar property transport in terms of time and space variations of eulerian variables is much simpler than expansions previously used and yields new insights into estuarine transport processes this approach like previous expansions is valid for narrow systems in which cross channel transport processes are weak and the ratio of tidal amplitude to mean depth is small a surface boundary condition is used to eliminate one class of troublesome terms the equivalence of the tidal cycle average transport of tidal variations in salinity and the stokes transport of mean salinity is then employed to show that the vertically integrated tidal flow plays no role in the overall salt balance that is seaward transport of salt caused by the river flow can only be balanced by landward transport resulting from correlations between shear and stratification in the mean tidal and overtide flows in a hypothetical inviscid estuary tide and overtide flows would be vertically uniform and outward fluvial salt transport could only be balanced by shear and stratification in the mean gravitational circulation in a more realistic example with strong friction the gravitational circulation would be severely damped and inward transport could only be accomplished by correlations of shear and stratification in the tide and overtide flows

effect of tropical cyclones on residual circulation and momentum balance in a subtropical estuary and inlet observation and simulation 1 a three dimensional 3 d hydrodynamic model curvilinear grid hydrodynamics in 3 d ch3d and observation data are used to investigate the effects of tropical storms fay and hanna in 2008 on the spatial structure of residual circulation and momentum balance inside the subtropical estuarine system of the northern coastal basin and st augustine inlet during a typical tidal cycle four residual eddies are formed two strong eddies inside of the inlet and two weaker eddies outside of the inlet during tropical storms fay and hanna the alongshore component of the northeasterly winds disrupted the ocean side eddies first and forced the alongshore southeasterly current owing to not so strong local winds residual flow at the mouth of the inlet never became complete inflow however following tropical storm fay s landfall flow inside the inlet became complete outflow owing to relaxing wind and the remote wind effect created by the alongshore component of the southeasterly wind the residual circulation returned to its prestorm condition in 4 days owing to relatively short storm duration model results revealed that the cross sectional residual flow pattern observed at the inlet mouth is highly variable with time and location of the cross section comparison of various terms in the horizontal momentum equations shows that the balance is primarily between the barotropic pressure gradient and nonlinear advection although the wind stress and bottom friction briefly become significant in the balance they are still at least an order of magnitude smaller baroclinic pressure gradient is weak despite the increase in precipitation and river discharge

transient tidal circulation and momentum balances at a shallow inlet an analysis of transient momentum balances is carried out to elucidate circulation dynamics and exchange mechanisms at shallow barotropic tidal inlets circulation is computed using a depth integrated fully nonlinear time stepping finite element model with variably spaced grids having horizontal resolution down to 50 m velocity and elevation fields from the model are used to directly evaluate the contribution of each term in the momentum equations to the overall momentum balance a transformation of the x y momentum terms into an s n coordinate system is used to simplify the interpretation of the dynamics and provide vivid illustrations of the forces and resulting accelerations in the flow the analysis is conducted for an idealized inlet and contrasted with a highly detailed model of beaufort inlet north carolina results show that momentum balances in the immediate vicinity of these inlets vary significantly in time and space and oscillate between two dynamical states near maximum ebb or flood the alongstream momentum balances are dominated by advective acceleration pressure gradient and bottom friction cross stream balances are dominated by centrifugal acceleration and pressure gradients near slack balances more closely follow linear wave dynamics with local accelerations balancing pressure gradients and to a lesser degree coriolis comparisons between the idealized inlet and beaufort inlet show broad similarities in these momentum balances however natural inlet geometry and bottom topography as well as the tidal transmission characteristics of the sounds behind beaufort inlet produce strong asymmetries moreover momentum balances are highly localized often with subkilometer length scales the dynamics are used to explain the physical mechanisms for inlet exchange in particular the results indicate that the cross stream dynamics generate a wall along the length of an inlet during the stronger phases of the tide the wall is established by opposing cross inlet pressure gradients and centrifugal forces and it poses a significant barrier to cross inlet exchange during the stronger phases of the tide but is absent near slack

analysis procedures at the international seismological centre abstract analysis at the international seismological centre isc falls into three main categories association location and quantification difficulties of association on a global scale are not always appreciated the isc currently analyses 40 50 events a day and as the first arrivals from any particular earthquake may span a time interval of up to 20 min readings from events occurring in different parts of the world may overlap considerably in time the present association algorithm depends on time only and results in many chance mis associations or even the synthesis of fictitious events at present these mis associations are rectified by seismologists intervention but full use of amplitude and period information could help to detect these errors automatically revision of locations follows standard least squares procedures based on jeffrey s method of uniform reduction and jeffreys bullen travel times locations are made from p phases only including crustal phases but other first arrivals and secondary phases are identified and residuals calculated if depth cannot be determined by geometric means a search is made for depth phases or failing this the depth is restrained to that given by another agency or to a conventional value no provision is made for local variations in travel time body wave magnitudes are allocated within the distance range 21 100 from reported readings of a and t or their ratio using gutenberg richter calibration curves surface wave magnitudes are calculated from the prague formula using reports of long period a and t in the distance range 5 160 but only values from stations at distances of 20 or more are used to determine an average ms for a particular event there is no provision for the determination of local magnitude other than to reproduce values assigned by local agencies improvements in these procedures could be made through the automatic association of station readings the introduction of local travel times and better determination of earthquake size particularly for local events

high resolution topomapping of candidate mer landing sites with mars orbiter camera narrow angle images 1 we analyzed narrow angle mars orbiter camera moc na images to produce high resolution digital elevation models dems in order to provide topographic and slope information needed to assess the safety of candidate landing sites for the mars exploration rovers mer and to assess the accuracy of our results by a variety of tests the mapping techniques developed also support geoscientific studies and can be used with all present and planned mars orbiting scanner cameras photogrammetric analysis of moc stereopairs yields dems with 3 pixel typically 10 m horizontal resolution vertical precision consistent with 0 22 pixel matching errors typically a few meters and slope errors of 1 3 these dems are controlled to the mars orbiter laser altimeter mola global data set and consistent with it at the limits of resolution photoclinometry yields dems with single pixel typically 3 m horizontal resolution and submeter vertical precision where the surface albedo is uniform the dominant error is 10 20 relative uncertainty in the amplitude of topography and slopes after calibrating photoclinometry against a stereo dem to account for the influence of atmospheric haze we mapped portions of seven candidate mer sites and the mars pathfinder site safety of the final four sites elysium gusev isidis and meridiani was assessed by mission engineers by simulating landings on our dems of hazard units mapped in the sites with results weighted by the probability of landing on those units summary slope statistics show that most hazard units are smooth with only small areas of etched terrain in gusev crater posing a slope hazard

a two channel laterally averaged estuarine circulation model laecim a two dimensional two channel laterally averaged estuarine circulation model laecim with a sigma coordinate in the vertical is developed for tides tidal currents and salinity in a two channel estuary with any arbitrary angle the model is forced by oceanic tides composed of 16 major constituents and freshwater discharge the two channels are governed by the same dynamic equations a control volume at the junction between the two channels is designed to conserve mass and volume transport and to guarantee the continuity of momentum in the finite difference schemes based on the physical principle in continuum medium of fluid an explicit leapfrog scheme in time and centered differencing in space are employed together with a time filter to remove the computational mode an euler backward scheme is periodically used to correct retard the phase frequency which is overestimated due to the explicit leapfrog scheme used the model is applied to the entire san francisco bay with its two channels the main north south channel and the golden gate channel which is perpendicular to the former i e with a right angle to the former the simulated time series of tides tidal currents and salinities compare favorably with the observed tidal gauge data and moored current and salinity time series during the summer 1980 the simulated along channel salinity section also compares well to the conductivity temperature depth sectional observations during the same period the model simulated eulerian residual current is consistent with two layer flow theory

water content of the martian soil laboratory simulations of reflectance spectra reflectance spectra from the surface of mars collected by instruments such as the imaging spectrometer ism onboard the 1988 soviet phobos 2 spacecraft exhibit strong 3 m absorption features that have long been attributed to hydrated materials on the martian surface this interpretation is consistent with a series of chemical weathering models suggesting an abundance of palagonites clays and other hydrated mineral phases in the martian fines little work however has been done to constrain the actual water content of the martian surface materials new laboratory data presented here show that the ism spectra are consistent with up to 4 water by weight and that the deep hydration features observed in the spacecraft data could be due to less than 0 5 water if the hydrated phases are present in the form of grain coatings these results are consistent with the somewhat uncertain in situ measurements obtained by the viking landers which yielded approximately 2 wt water from samples heated to 500 c on the basis of this work we expect the tega instrument on the mars 98 lander to find less than 4 adsorbed or bound water in the upper few centimeters of the martian soil

measuring surface currents in lakes with high spatial resolution thermal infrared imagery 1 high spatial resolution thermal infrared satellite images acquired 38 minutes apart from landsat etm and aster were used to measure the surface currents and circulation in lake tahoe california nevada usa mean currents of 5 10 cm s were measured with maximum currents approaching 35 cm s the eastward transport of an upwelling surface jet was clearly apparent with 15 30 cm s currents three gyres were evident in the vector fields the satellite image derived surface currents and circulation patterns are consistent with surface drifter measurements acquired during a different period these results modify the findings of an earlier study using 1 1 km avhrr imagery which concluded there were two counter rotating gyres in the opposite sense to the two dominant large gyres measured in this study the high spatial resolution and small time separation allow the surface currents and general circulation in lakes and coastal environments to be accurately quantified using the maximum cross correlation method

crustal phases in earthquake location for crustal earthquakes of moderate or large size the first reported phases at distant stations are usually the first predicted by the crustal model used for smaller events however or for stations at larger distances the first phase detected is often a later crustal phase of larger amplitude this may be eitherpg which travels entirely in the upper crustal layer with a velocity of about 5 6 km s orp with a path mainly in the lower crustal layer at a velocity of about 6 7 km s many earthquake location programs do not take account of these phases and treat their arrivals as if they were the earlier phasepn at the international seismological centre we re identify up to 200 crustal phases each month this often results in significant improvement in position the direct determination of depth or even the obtaining of a formal solution where none was possible before we find that these re identifications are needed in most continental areas of the world and that the original crustal model of jeffreys and bullen still remains a useful standard

small scale heterogeneities below the grafenberg array germany from seismic wavefield fluctuations of hindu kush events summary small scale elastic heterogeneities 5 km are found in the upper lithosphere under neath the grafenberg array southeast germany the results are based on the analysis of broadband recordings of 17 intermediate depth 201 272 km events from the hindu kush region the wavefront of the first p arrival and the following 40 s coda are separated into coherent and incoherent scattered parts in the frequency range from 0 05 to 5 hz the frequency dependent intensities of the mean and fluctuation wavefields are used to describe the scattering characteristics of the lithosphere underneath the receivers it is possible to discriminate a weak fluctuation regime of the wavefield in the frequency range below approximately 1 5 2 5 hz and a strong fluctuation regime starting at 2 0 2 5 hz and continuing to higher frequencies in order to explain the observed wavefield fluctuations an approach with seismic scattering at random media type structures is proposed the preferred model contains heterogeneities with 3 7 per cent perturbations in seismic velocity and correlation lengths of 0 6 4 8 km in the crust this is compatible with models from active seismic experiments scattering in the lithospheric mantle is not required but cannot be excluded at weak velocity contrasts 3 per cent

modeling circulation in lakes spatial and temporal variations the influence of spatial and temporal variations in wind forcing on the circulation in lakes is investigated using field data and the three dimensional estuary and lake computer model elcom applied to lake kinneret lake kinneret field data from six thermistor chains and eight wind anemometers deployed during july 2001 are presented internal wave motions are well reproduced by the numerical model when forced with a spatially uniform wind taken from a station near the lake center however simulated seiche amplitudes are too large especially vertical mode 2 and lead observations by 3 10 h for a 24 h period wave at different locations around the lake consideration of the spatial variation of the wind field improves simulated wave amplitude and phase error at all stations is reduced to less than 1 5 h this improvement is attributable to a better representation of the horizontally averaged wind stress and can be reproduced with a spatially uniform wind that has the same horizontally averaged wind stress as the spatially varying wind field however a spatially varying wind field is essential for simulating mean surface circulation which is shown to be predominantly directly forced by the surface layer averaged wind stress moment

hydrous carbonates on mars evidence from mariner 6 7 infrared spectrometer and ground based telescopic spectra absorption features at 2 28 and 5 4 m identified in mariner 6 7 infrared spectrometer and terrestrial telescopic spectra are consistent with the spectra of hydrous magnesium carbonates such as hydromagnesite and artinite spectral characteristics of these hydrous carbonates are different from those of the anhydrous carbonates as the former do not have the strong spectral features typically associated with anhydrous carbonates such as calcite and siderite theoretical mixing indicates that depending on the type of hydrous carbonate 10 20 wt can be incorporated into the regolith without contradicting the spectral observations or the viking x ray fluorescence chemical analysis hydrous carbonates form as weathering products of mafic minerals in the presence of h2o and co2 even in the antarctic their formation as evaporite minerals from either original magmas or hydrothermally altered rocks is consistent with the martian environment provided liquid water is or has been at least transiently present on earth formation of hydrous mg carbonates is associated with the production of amorphous iron oxides which is consistent with both the environment and the inferred surface mineralogy of mars these minerals are about 60 wt h2o co3 and oh if they are abundant everywhere at the 10 level then about 6 of the surface weight could be volatiles bound in this type of mineral although the stability of hydrous carbonates in a martian environment is uncertain there may be kinetic factors inhibiting the dehydration of these minerals which may persist metastably in the current environment although the spectroscopic evidence for anhydrous carbonates is scant the possible presence of hydrous carbonates provides an appealing mechanism for the existence of carbonates on mars

residual circulation and tidal stress in the gulf of california 1 results of a three dimensional nonlinear barotropic shelf model are used to study the effect of the m2 tidal stress on the residual current in the gulf of california the tidal stress summarizes the nonlinear interactions and forces the residual circulation it is calculated following the method developed by nihoul and ronday 1975 the vertical structure of the tidal stress reveals clearly the zones where the interaction between tidal currents and the basin geometry is strong the highest values of tidal stress were found over the salsipuedes sill and in the ballenas channel in the central archipelago and in the colorado river delta relatively high values of tidal stress were also found in deeper layers in the southern part the high tidal stress values coincide well with the anomalous cold water patches observed in the archipelago area attributed to tidal mixing the calculated residual currents show a maximum of about 15 cm s 1 in the upper layers in the archipelago area at subsurface layers an anticyclonic circulation is observed divergence patterns in the upper layers suggest that m2 tide residuals contribute to significant upward movements of water on the west side of tiburon island this barotropic process may contribute to the generation of the observed cold patches

wind driven surface transport in stratified closed basins direct versus residual circulations a numerical model has been used to investigate the wind driven circulation in a stratified basin of moderate size lake tahoe california nevada two types of circulation are identified direct circulations in which the current directions remain relatively constant and the mean circulation formed over several days resembles the instantaneous circulation and residual circulations in which the currents fluctuate continuously and the mean circulation is characterized by small net displacements of parcels after large oscillations previous studies of stratified closed basins have emphasized residual circulations caused by cyclonically propagating internal basin modes resulting in a single cyclonic mean gyre during light to moderate winds observations at lake tahoe have shown currents which are more constant in direction with a double gyre pattern of surface circulation dominated by an anticyclonic northern gyre model experiments of lake tahoe demonstrate that the curl of the wind stress must be included to obtain a direct double gyre circulation similar to the observations horizontally uniform winds cause a residual circulation similar to that reported at other lakes use of the model to calculate the vorticity budget clarifies the role of the wind stress curl in creating the direct double gyre

wave driven along channel subtidal flows in a well mixed ocean inlet observations of waves flows and water levels collected for a month in and near a long narrow shallow 3000 m long 1000 m wide and 5 m deep well mixed ocean inlet are used to evaluate the subtidal periods 30 h along inlet momentum balance maximum tidal flows in the inlet were about 1 5 m s and offshore significant wave heights ranged from about 0 5 to 2 5 m the dominant terms in the local across the km wide ebb shoal along inlet momentum balance are the along inlet pressure gradient the bottom stress and the wave radiation stress gradient estimated nonlinear advective acceleration terms roughly balance in the channel onshore radiation stress gradients owing to breaking waves enhance the flood flows into the inlet especially during storms

assessment of earthquake location accuracy and confidence region estimates using known nuclear tests i have used the known epicenters and depths of 307 nuclear tests at the nevada test site nts and 75 tests at the east kazakhstan test site to compare the distances between actual and calculated hypocenters mislocations with calculated location confidence limits errors each test was located using its isc compiled p first arrivals a starting depth of 33 km and the iasp91 velocity model i also applied azimuth and incident angle dependent station corrections to the arrival times the most accurately located tests are those at the kazakhstan test site where all of the mislocations in latitude and longitude are less than 10 km and 90 of the depth mislocations are less than 20 km bayesian confidence limits calculated from the least squares covariance matrix satisfactorily account for these mislocations at the nevada test site 90 of the mislocations are less than 9 km in longitude 15 km in latitude and 33 km in depth the overestimates in depth are compensated for by origin times that are 2 to 5 sec late the larger mislocations at nts occur in spite of the fact that the closest recording sites are less than 200 km away compared to 1800 km away at the kazakhstan test site a significant fraction of the depth mislocations at nts are much larger than their calculated errors i interpret this failure of the calculated errors to adequately account for the nts mislocations as being due to systematically late arrivals at northwestern american stations relative to the predicted iasp91 values by using a locally determined three layer velocity model for the travel times of phases recorded at distances of less than 1500 km i was able to reduce 90 of the depth mislocations to less than 11 km as well as significantly reducing the latitude longitude and origin time mislocations i conclude that differences between the iasp91 model and velocities in the vicinity of the explosions may introduce a significant bias into the determined depths of nuclear tests a similar bias would therefore be expected in the similarly determined depths of shallow earthquakes

interbasin exchange and mixing in the hypolimnion of a large lake the role of long internal waves we conducted a combined field and numerical study of the effects of episodic internal kelvin type waves on bottom boundary turbulence and the exchange of a passive tracer between the main basin and the side basin of a large lake lake geneva high resolution measurements of the vertical current structure near the entrance of the 25 km long and 70 m deep side basin revealed that hypolimnetic current speeds frequently exceed 0 2 m s 21 leading to a turbulent bottom boundary layer several meters thick with logarithmic current profiles and to a region of strong shear across the thermocline the time series and vertical structure of the currents were reproduced by a threedimensional numerical model of the lake it was demonstrated that after episodes of strong winds from the northeast and southwest exchange flows due to internal kelvin waves were able to temporarily half or double the hypolimnetic volume of the side basin leading to an irreversible exchange of up to 40 of the hypolimnetic water in the side basin of lake geneva within only a few wave cycles with the help of the numerical model it was shown that the key mechanisms of exchange are horizontal dispersion by resolved scales and to a small extent shear dispersion in the bottom boundary layer it is suggested that bottom boundary layer turbulence and the interbasin exchange can explain the structural differences in the oxygen profiles observed in the side basin and the main basin respectively

on tide induced lagrangian residual current and residual transport 2 residual transport with application in south san francisco bay california the transports of solutes and other tracers are fundamental to estuarine processes the apparent transport mechanisms are convection by tidal current and current induced shear effect dispersion for processes which take place in a time period of the order of a tidal cycle however as emphasis is shifted toward the effects of intertidal processes the net transport is mainly determined by tide induced residual circulation and by residual circulation due to other processes the commonly used intertidal conservation equation takes the form of a convection dispersion equation in which the convective velocity is the eulerian residual current and the dispersion terms are often referred to as the phase effect dispersion or sometimes as the tidal dispersion the presence of these dispersion terms is merely the result of a fickian type hypothesis since the actual processes are not fickian thus a fickian hypothesis obscures the physical significance of this equation recent research results on residual circulation have suggested that long term transport phenomena are closely related to the lagrangian residual current or the lagrangian residual transport in this paper a new formulation of an intertidal conservation equation is presented and examined in detail in a weakly nonlinear tidal estuary the resultant intertidal transport equation also takes the form of a convection dispersion equation without the ad hoc introduction of phase effect dispersion in a form of dispersion tensor the convective velocity in the resultant equation is the first order lagrangian residual current the sum of the eulerian residual current and the stokes drift the remaining dispersion terms are important only in higher order solutions they are due to shear effect dispersion and turbulent mixing there exists a dispersion boundary layer adjacent to shoreline boundaries an order of magnitude estimate of the properties in the dispersion boundary layer is given the present treatment of intertidal transport processes is illustrated by an analytical solution for an amphidromic system and by a numerical application in south san francisco bay california the present formulation reveals that the mechanism for long term transport of solutes is mainly convection due to the lagrangian residual current in the interior of a tidal estuary this result also points out the weakness in the tidal dispersion formulation and explains the large variability of the observed values for tidal dispersion coefficients further research on properties of the dispersion boundary layer is needed

on the structure of transient upwelling events abstract nearshore transcends following the development of transient coastal upwelling characteristically show intermediate density fluid occupying the immediate nearshore band large cross shore particle excursions during the development of upwelling may be inferred from be fore and after transects and the movement of surface layers seaward intermediate density fluid shoreward through a distance of the order of kilometers and the bottom layers also shoreward by a 1esser amount some inevitable vertical mixing together with the large cross shore displacements results in efficient cross shore mass exchange the main dynamical features of similar events may be investigated by means of three layer models linear theory is conveniently discussed first the conclusions of which are easily generalized to multilayer models finite amplitude i e full upwelling is then considered using a potential vorticity conserving impulsive model the results show that the wind peels off the surface layer over w

characterization of etnean soils and application to mars we present the results of a study of some petromineralogical chemical and spectral properties of etnean palagonitic soils these soils exhibit highly variable mineralogy although they are considered among the best candidates as martian soil analogs five specimens of etnean volcanic soil were collected at different altitudes four of these are weathered and reworked pyroclasts from the historic eruptive activity the fifth represents an ancient paleosoil 5420 2370 years b p the chemical composition is hawaiitic petrography and mineralogy of grain mounts show they mainly consist of glass particles black and red orange containing microphenocrystals of plagioclase clinopyroxene olivine and ti magnetite in order of abundance one sample also contains rare amphiboles ir 2 3 25 m transmittance and uv visible near ir 0 4 2 6 m diffuse reflectance spectra were obtained and compared with those of martian dust

predicting the vertical structure of tidal current and salinity in san francisco bay california a two dimensional laterally averaged numerical estuarine model is developed to study the vertical variations of tidal hydrodynamic properties in the central north part of san francisco bay california tidal stage data current meter measurements and conductivity temperature and depth profiling data in san francisco bay are used for comparison with model predictions an extensive review of the literature is conducted to assess the success and failure of previous similar investigations and to establish a strategy for development of the present model a plane transformation is used in the vertical dimension to alleviate problems associated with fixed grid model applications in the bay where the tidal range can be as much as 20 25 of the total water depth model predictions of tidal stage and velocity compare favorably with the available field data and prototype salinity stratification is qualitatively reproduced conclusions from this study as well as future model applications and research needs are discussed

can internal processes sustain reversals of the ocean upper circulation the ionian sea example 1 in 1997 an inversion in the ionian upper layer circulation was documented and ascribed to a massive inflow of aegean dense waters associated with the eastern mediterranean transient emt and not to the wind stress borzelli et al 2009 here we generalize the concept hypothesizing that such inversions are possible even in the absence of the aegean influence indeed salinity and density data collected in the southern adriatic the main source of the eastern mediterranean deep water show decadal variations coherent with changes in the sea level height in the northern ionian scaling considerations suggest that the redistribution of ionian water masses resulting from changes in the thermohaline properties of waters entering the basin can sustain inversions of the upper layer circulation therefore we propose a feedback mechanism named the adriatic ionian bimodal oscillating system bios between variations in the thermohaline properties of waters formed in the southern adriatic and the ionian circulation

could mars be dark and altered there is a long known dichotomy in the martian albedo with an associated but mostly assumed mineralogical split as well the bright red regions are inferred to be weathered oxidized dust and the dark grey regions unaltered volcanic material a number of recent analyses suggest this division is unnaturally simplistic and the association of many dark regions with the former presence of water requires a re examination of the spectra in light of potential alteration minerals i present an alternate interpretation of the reflectance spectral characteristics of some dark regions on mars that includes dark layer silicates if their presence is confirmed on mars this will have implications for sequestration of current and past volatile inventories clues to the extent and type of geochemical weathering and potential zones where bacterial life forms may have emerged

evidence for platy hematite grains in sinus meridiani mars 1 midinfrared 1600 200 cm 1 spectral data received from the mars global surveyor thermal emission spectrometer mgs tes have provided evidence for a large hematite bearing fe2o3 deposit in sinus meridiani mars we report here the results of a laboratory spectroscopic investigation of 24 hematite samples including polycrystalline hand samples massive and schistose textures single crystal hand samples and particle size fractions single crystal and polycrystalline discrete particles laboratory midinfrared analyses of crystallographically oriented hematite samples suggest that the hematite emission in sinus meridiani sm is predominantly from the crystallographic c face of hematite this observation implies the presence of platy hematite particles with the plate face being the crystallographic c face the observations are consistent with a formational model where the platy gray hematite originated as an iron oxide chemically precipitated from fe rich aqueous and or hydrothermal solutions on early mars that was buried recrystallized to platy hematite and subsequently reexposed as lenses of schistose hematite in a friable consolidated stratigraphic unit unconsolidated platy hematite particles are also likely to be present as a physical weathering product of the schistose hematite lenses

the effect of channel length on the residual circulation in tidally dominated channels with an analytic model this paper describes the subtidal circulation in tidally dominated channels of different lengths with arbitrary lateral depth variations the focus is on an important parameter associated with the reversal of the exchange flows this parameter is defined as the ratio between the channel length and one quarter of the tidal wavelength which is determined by water depth and tidal frequency in this study a standard bottom drag coefficient cd 0 0025 is used for a channel with smaller than 0 6 0 7 short channels the exchange flow at the open end has an inward transport in deep water and an outward transport in shallow water this situation is just the opposite of channels with a value larger than 0 6 0 7 long channels for a channel with a value of about 0 35 0 5 the exchange flow at the open end reaches the maximum of a short channel for a channel with a value of about 0 85 1 0 the exchange flow at the open end reaches the maximum of a long channel with the inward flux of water occurring over the shoal area and the outward flow in the deep water area however near the closed end of a long channel the exchange flow appears as that in a short channel that is the exchange flow changes direction along the channel from the head to the open end of the channel for a channel with a value of about 0 6 0 7 the tidally induced subtidal exchange flow at the open end reaches its minimum when there is little flow across the open end and the water residence time reaches its maximum the mean sea level increases toward the closed end for all values however the spatial gradient of the mean sea level in a short channel is much smaller than that of a long channel the differences between short and long channels are caused by a shift in dynamical balance of momentum or equivalently a change in tidal wave characteristics from a progressive wave to a standing wave

mineralogical composition of sands in meridiani planum determined from mars exploration rover data and comparison to orbital measurements constraints on the mineralogical composition of low albedo low sulfur sands at meridiani planum are determined from mars exploration rover mer opportunity miniature thermal emission spectrometer mini tes mossbauer and alpha proton x ray spectrometer measurements results of this work show that the sand is olivine basaltic in composition with minor amounts of sulfate and a high silica phase glass or secondary amorphous silica measurements from all three instruments indicate that pyroxene is twice as abundant as olivine and that the pyroxene composition is dominated by the low calcium variety the volume abundance of olivine is constrained to be 10 15 results from detailed analyses of mer data are used to ground truth the spectral emissivity and mineral abundances derived from orbit with mars global surveyor tes data tes derived mineral abundances are within 5 of those derived from mer data which is generally within the statistical errors associated with tes derived phase abundances the agreement lends support to global and regional scale variations in mineralogical composition determined from tes data in previous studies an alternative method of least squares minimization is used for modeling the tes and mini tes data the benefits of this method are demonstrated by comparison with conventional least squares techniques previously used by tes data users

the structure of basin scale internal waves in a stratified lake in response to lake bathymetry and wind spatial and temporal distribution lake iseo italy field data theoretical analyses and numerical simulations were used to investigate the effects of lake basin bathymetry and spatial and temporal structures of the wind field on the basin scale internal wave spectrum in lake iseo this deep italian basin is characterized by the presence of a large island imparting attributes of an annulus to the lake during the summer of 2010 the internal wave activity was dominated by a basin scale internal wave of vertical and horizontal modes 1 v1h1 superimposed on which were occasional higher vertical modes v2h1 and higher horizontal modes v1h5 trapped by the main island the occurrence of these motions was interpreted as forcing by the wind components with similar horizontal structures and with energies at frequencies near the natural oscillations of the excited modes the modifications of the wind field by the topography in particular controlled the excitation of an anticyclonic wave trapped around the island whose features were investigated on the basis of an extension of the circular model to the case of an annular basin of constant depth

low temperature mechanism for formation of coarse crystalline hematite through nanoparticle aggregation we have discovered a low temperature mechanism for the formation of coarse specular hematite grains either freezing and subsequent thawing or cryodesiccation of aqueous nanoparticle suspensions under confinement leads to aggregation of hematite platelets with initial diameters of 10 nm into domains 100 nm in diameter crystallographic alignment of particles in the 001 basal plane only occurs on the scale of the 50 100 nm domains is absent for air dried grains and increases for freeze thawed and freeze dried samples stacking of the domains accommodates curvature at the microscale leading to final grain sizes greater than 1 mm with curved but smooth surfaces reflective to visible light confinement of freezing suspensions increases ordering of aggregates no spherules were produced however thermal emission spectra of the nanoparticle aggregates are consistent with coarse crystalline spectra from mars tir spectra of air dried freeze thawed and cryodesiccated samples are similar suggesting that the crystallographic alignment observed at the nanoscale is not responsible for the lack of 390 cm 1 feature aqueous alteration of fe bearing sulfates has been demonstrated to form hematite nanoparticles in systems analogous to meridiani planum evaporation and aggregation of resulting nanoparticles is consistent with the context of low temperature playa groundwater models while freezing and or cryodesiccation are consistent with models of low temperature ice hosted weathering additionally this new mechanism for specular hematite formation may lead to re evaluation and re interpretation of coarse hematite formation throughout earth history

tidally driven residual circulation in shallow estuaries with lateral depth variation tidally driven residual circulation in shallow estuaries with lateral depth variation has been studied analytically using a two dimensional depth averaged model the solution is presented for a v shaped channel exchange flow is found to be correlated with the topography the magnitude of this exchange flow depends mainly on four parameters the ratio between the minimum depth on the shoal and the maximum depth in the channel the ratio between the tidal amplitude at the mouth and the mean depth the ratio between the length of the estuary and the tidal wave length and the ratio between the tidal timescale and the decay timescale due to friction generally a net landward flow occurs over the shoals and is balanced by a return flow in the channel the along channel residual velocity changes nearly linearly across the estuary the residual velocity decreases monotonically toward the head of the estuary the transverse residual velocity is convergent in the channel and divergent on the shoals the residual velocity is highly dependent on the length of the estuary when the length of the estuary is much smaller than a quarter of the wave length the residual velocity is relatively small when the length of the estuary is about a quarter of the wave length the magnitude of the residual velocity reaches its maximum when the length of the estuary is much larger than a quarter of the wave length the residual circulation approaches the pattern found in an infinite length estuary on the basis of the analysis of the solution we conclude that exchange flow generated by tides in a shallow estuary is the result of competition among several processes an inward flux is caused by local nonlinearity both in the bottom friction and from propagation of the tidal wave of finite amplitude this inward flux is larger on the shoals and smaller in the channel owing to larger nonlinearity in the shallow water the residual inward flow creates a setup residual surface elevation of water at the head of the estuary that produces a pressure gradient this residual pressure gradient is approximately uniform across the estuary and drives an outward flow that is larger in the channel than on the shoals in all of the parameter space the competition results in a net inflow on the shoals and a net outflow in the channel

two dimensional horizontal modeling of fine sediment transport at the south channel north passage of the partially mixed changjiang river estuary china tidal flow and fine sediment transport at the south channel north passage of the partially mixed changjiang river estuary were studied using a two dimensional horizontal 2dh numerical model this 2dh model was achieved by depth integrating the momentum and convection diffusion equations the alternating direction implicit scheme was used to solve the governing equations the iterative method was adopted for the calculation of convection and diffusion terms of momentum equation comparisons between calculated and measured results tidal elevations and depth averaged velocities have shown reasonable agreement horizontal distributions of tidal current velocity and suspended sediment concentration were qualitatively consistent with observations those modeled results were analyzed to elucidate the mechanisms for the formation of the turbidity maximum and intratidal variations in fine sediment transport processes

the origin of neap spring tidal cycles abstract the origin of oceanic tides is a basic concept taught in most introductory college level sedimentology geology oceanography and astronomy courses tides are typically explained in the context of the equilibrium tidal theory model yet this model does not take into account real tides in many parts of the world not only does the equilibrium tidal model fail to explicate amphidromic circulation it also does not explain diurnal tides in low latitude positions it likewise fails to explain the existence of tide dominated areas where neap spring cycles are synchronized with the 27 32 day orbital cycle of the moon tropical month rather than with the more familiar 29 52 day cycle of lunar phases synodic month both types of neap spring cycles can be recognized in the rock record a complete explanation of the origin of tides should include a discussion of dynamic tidal theory in the dynamic tidal model tides resulting from the motions of the moon in its orbit around the earth and the earth in its orbit around the sun are modeled as products of the combined effects of a series of phantom satellites the movement of each of these satellites relative to the earth s equator creates its own tidal wave that moves around an amphidromic point each of these waves is referred to as a tidal constituent the geometries of the ocean basins determine which of these constituents are amplified thus the tide raising potential for any locality on earth can be conceptualized as the result of a series of tidal constituents specific to that region a better understanding of tidal cycles opens up remarkable opportunities for research on tidal deposits with implications for among other things a more complete understanding of the tidal dynamics responsible for sediment transport and deposition changes in earth moon distance through time and the possible influences tidal cycles may exert on organisms

integration of bed characteristics geochemical tracers current measurements and numerical modeling for assessing the provenance of beach sand in the san francisco bay coastal system abstract over 150 million m3 of sand sized sediment has disappeared from the central region of the san francisco bay coastal system during the last half century this enormous loss may reflect numerous anthropogenic influences such as watershed damming bay fill development aggregate mining and dredging the reduction in bay sediment also appears to be linked to a reduction in sediment supply and recent widespread erosion of adjacent beaches wetlands and submarine environments a unique multi faceted provenance study was performed to definitively establish the primary sources sinks and transport pathways of beach sized sand in the region thereby identifying the activities and processes that directly limit supply to the outer coast this integrative program is based on comprehensive surficial sediment sampling of the san francisco bay coastal system including the seabed bay floor area beaches adjacent rock units and major drainages analyses of sample morphometrics and biological composition e g foraminifera were then integrated with a suite of tracers including 87sr 86sr and 143nd 144nd isotopes rare earth elements semi quantitative x ray diffraction mineralogy and heavy minerals and with process based numerical modeling in situ current measurements and bedform asymmetry to robustly determine the provenance of beach sized sand in the region

harmonic analysis of tides and tidal currents in south san francisco bay california abstract water level observations from tide stations and current observations from current meter moorings in south san francisco bay south bay california have been harmonically analysed at each tide station 13 harmonic constituents have been computed by a least squares regression without inference tides in south bay are typically mixed there is a phase lag of approximately 1 h and an amplification of 1 5 from north to south for a mean semi diurnal tide because most of the current meter records are between 14 and 29 days only the five most important harmonics have been solved for east west and north south velocity components the eccentricity of tidal current ellipse is generally very small which indicates that the tidal current in south bay is strongly bidirectional the analyses further show that the principal direction and the magnitude of tidal current are well correlated with the basin bathymetry patterns of eulerian residual circulation deduced from the current meter data show an anticlockwise gyre to the west and a clockwise gyre to the east of the main channel in the summer months due to the prevailing westerly wind opposite trends have been observed during winter when the wind was variable

relative effects of wind stress curl topography and stratification on large scale circulation in lake michigan 1 this paper uses the results from two multiseason numerical model simulations of lake michigan hydrodynamics to examine the relative effects of wind stress curl topography and stratification on large scale circulation the multiseason simulations provide a period long enough to encompass the full range of atmospheric and thermal conditions that can occur in the lake the purpose of this paper is to diagnose the relative importance of various mechanisms responsible for the large scale circulation patterns by analyzing the vorticity balance in the lake on a monthly timescale five different model scenarios are used to isolate the predominant mechanisms 1 baroclinic lake spatially variable wind stress 2 barotropic lake spatially variable wind stress 3 baroclinic lake spatially uniform wind stress 4 barotropic lake spatially uniform wind stress and 5 barotropic lake linearized equations spatially uniform wind stress by comparing the results of these five model scenarios it is shown that the cyclonic wind stress curl in the winter and the effect of baroclinicity in the summer are primarily responsible for the predominantly cyclonic flow in the lake topographic effects are also important but are not as significant as wind stress curl and baroclinic effects nonlinear effects are much smaller

subtidal sea level and current variations in the northern reach of san francisco bay abstract analyses of sea level and current meter data using digital filters and a variety of statistical methods show a variety of phenomena related to non local coastal forcing and local tidal forcing in the northern reach of san francisco bay a partially mixed estuary low frequency variations in sea level are dominated by non local variations in coastal sea level and also show a smaller influence from tidally induced fortnightly sea level variations low frequency currents demonstrate a gravitational circulation which is modified by changes in tidal current speed over the spring neap tidal cycle transients in gravitational circulation induce internal oscillations with periods of two to four days

comparison between predicted and observed physical features of sandbanks a linear stability analysis has been carried out to investigate the influence of parameters like tidal current depth and coriolis force on sand bank formation the applied analytical model allowed the computation of the horizontal wave number corresponding to the fastest initial growth rate of seabed form perturbations sandbank wavelength and the angle between the crest of the sandbank and tidal current direction were also obtained the experiments show an exponential decay of this angle for increasing values of tidal currents at a particular depth the sand bank wavelength grows almost linearly with the velocity we compared these theoretical results with observations of sandbank features in several geographic areas persian gulf the gulf of korea gulf of california and the north sea the results show that all observed sand bank wavelengths and angles are in very close agreement with the calculated theoretical curves

evidence for mechanical and chemical alteration of iron nickel meteorites on mars process insights for meridiani planum 1 the weathering of meteorites found on mars involves chemical and physical processes that can provide clues to climate conditions at the location of their discovery beginning on sol 1961 the opportunity rover encountered three large iron meteorites within a few hundred meters of each other in order of discovery these rocks have been assigned the unofficial names block island shelter island and mackinac island each rock presents a unique but complimentary set of features that increase our understanding of weathering processes at meridiani planum significant morphologic characteristics interpretable as weathering features include 1 a large pit in block island lined with delicate iron protrusions suggestive of inclusion removal by corrosive interaction 2 differentially eroded kamacite and taenite lamellae in block island and shelter island providing relative timing through crosscutting relationships with deposition of 3 an iron oxide rich dark coating 4 regmaglypted surfaces testifying to regions of minimal surface modification with other regions in the same meteorites exhibiting 5 large scale cavernous weathering in shelter island and mackinac island we conclude that the current size of the rocks is approximate to their original postfall contours their morphology thus likely results from a combination of atmospheric interaction and postfall weathering effects among our specific findings is evidence supporting 1 at least one possible episode of aqueous acidic exposure for block island 2 ripple migration over portions of the meteorites 3 a minimum of two separate episodes of wind abrasion alternating with 4 at least one episode of coating forming chemical alteration most likely at subzero temperatures

lake of lugano and topographic waves during the summer of 1979 wind water temperature and current measurements were made in the lake of lugano switzerland to study its response to meteorological forcing analysis of the collected data revealed the presence of wind induced internal gravity wave seiches with periods of 24 h and less1 however during this study an intriguing 3 day oscillation in the temperature and horizontal current records was also noted1 we present here evidence which suggests that this low frequency oscillation is a free topographic rossby wave that travels around the lake in an anticlockwise direction

global distribution of neutrons from mars results from mars odyssey global distributions of thermal epithermal and fast neutron fluxes have been mapped during late southern summer northern winter using the mars odyssey neutron spectrometer these fluxes are selectively sensitive to the vertical and lateral spatial distributions of h and co 2 in the uppermost meter of the martian surface poleward of 60 latitude is terrain rich in hydrogen probably h 2 o ice buried beneath tens of centimeter thick hydrogen poor soil the central portion of the north polar cap is covered by a thick co 2 layer as is the residual south polar cap portions of the low to middle latitudes indicate subsurface deposits of chemically and or physically bound h 2 o and or oh