the front speed of intrusions into a continuously stratified medium this paper examines intrusive boussinesq gravity currents propagating into a continuously stratified fluid we develop a model based on energy arguments to predict the front speed of such an intrusive gravity current from a lock release we find that the depth at which the intrusion occurs which corresponds to the level of neutral buoyancy i e the depth where the intrusion density equals the stratified fluid density affects the front speed the maximum speeds occur when the intrusion travels along the top and bottom boundaries and the minimum speed occurs at mid depth experiments and numerical simulations were conducted to compare to the theoretically predicted values and good agreement was found

mars orbiter camera observations of the martian south polar cap in 1999 2000 the spring summer recession of the south polar cap of mars in 1999 2000 has been investigated using the wide angle cameras of the mars orbiter camera experiment on mars global surveyor the 1999 2000 regression closely resembles the recession observed by viking orbiters in 1977 although the rates of recession are quite similar the current recession was slightly ahead of that in 1977 throughout spring the rapid development of dark terrain dubbed cryptic terrain by hugh kieffer in one sector of the south cap between ls 198 and 223 is documented the emergence and separation of the mountains of mitchel has also been recorded in detail culminating with its complete disappearance at solstice the 2000 residual cap is almost identical to that in 1977 this observation does not resolve the mystery of the very different appearance of the residual cap in 1972 the albedos in the residual cap region and in bright seasonal frost increase rapidly to high values at around solstice and then level out until the seasonal frost disappears observations of more martian years will be needed to constrain the amount of interannual variability and its relation to other phenomena such as dust storms

near infrared imaging of mars from hst surface reflectance photometric properties and implications for mola data abstract we report initial results from hubble space telescope hst images of mars obtained at a near ir wavelength of 1042 nm between february 1995 and june 1997 the images provide the highest spatial resolution global near ir measurements of mars obtained to date the data have been calibrated to radiance factor i f to an absolute accuracy of 2 to 5 including new refinements to several hst calibration parameters and now exist as a set of coregistered map projected images spanning a range of phase angles between 10 and 41 the relatively high spatial resolution 20 30 km pixel global maps when compared with viking era global albedo maps reveal that substantial variations in mars surface albedo patterns have occurred in the past 20 years the most obvious changes include several classical dark regions that have become substantially brighter and a few formerly bright regions that have darkened the normal albedo of typical surface regions in the near ir is derived from the multiple phase angle observations and is found to be bimodal with typical bright and dark values of 0 36 and 0 18 respectively the surface near ir phase coefficient ranges from 0 0 to 0 013 mag deg and there is no systematic correlation between phase coefficient and normal albedo this observation is consistent with the diffusely scattering nature of the martian atmosphere even during times of low dust opacity the data presented here may facilitate the planning and optimization of measurements to be obtained by the mars global surveyor mgs mars orbiter laser altimeter mola which will begin mapping the planet in 1999 these hst data also provide a basis for comparison with future mola and mars orbiter camera moc data in searches for seasonal and interannual variations in surface and polar cap albedo

sedimentation by river induced turbidity currents field measurements and interpretation turbidity currents initiated from spring runoffs of an influent river were observed in the upper region of a reservoir in hokkaido japan by measuring water temperature velocity and suspended sediment concentration their profiles offer some physical parameters for the sedimentary conditions assuming the turbidity currents to be quasi uniform the bottom sediment deposited by the turbidity currents was then collected by a portable core sampler the bottom sediment consists of more than 90 silt and clay and thus offers a hydraulically smooth bed for shear flow a plane bed as a bed configuration was formed on the reservoir bed probably because of the low shear velocity and small grain size of sediment using a graphic method with log normal probability paper the bottom sediment is divided into several overlapping log normal subpopulations grain size analysis indicates that the bottom sediment may be regarded as cohesionless criteria for complete deposition of transported grains can then be incorporated into the extended shields diagram giving the minimum shear stress to erode bottom sediment applying the new diagram to the grain size distribution of the bottom sediment it is suggested that each of the log normal subpopulations was deposited in each of four different modes of deposition i e traction saltation or intermittent suspension suspension and suspension under equilibrium the last mode may be observed under a sedimentary condition where upward flux of suspended sediment by eddy diffusion is almost equal to its depositional flux due to gravity the mean and critical grain sizes for bottom sediment and each of the corresponding subpopulations decrease consistently with an increase of fd2 log10re fd is the densimetric froude number and re is the flow reynolds number correlates inversely with shear velocity which bears a linear relationship to mean velocity these results lead to the conclusion that relatively fine suspended sediment is deposited as a result of decreasing bottom friction with a relative decrease of turbulent energy

apollo 12 breccia 12013 impact induced partial pb loss in zircon and its implications for lunar geochronology abstract apollo 12 breccia 12013 is composed of two portions one grey in colour the other black the grey portion of the breccia consists mainly of felsite thought to have formed during a single crystallisation event while the black part is characterized by presence of lithic fragments of noritic rocks and individual plagioclase crystals in this study u pb analyses of ca phosphate and zircon grains were conducted in both portions of the breccia the zircon grains within the grey portion yielded a large range of ages 4154 7 to 4308 6 ma 2 and show decreasing u and th concentrations within the younger grains moreover some grains exhibit recrystallisation features and potentially formation of neoblasts the latter process requires high temperatures above 1600 1700 c leading to the decomposition of the primary zircon grain and subsequent formation of new zircon occurring as neoblasts as a result of the high temperatures the u pb system of the remaining original zircon grains was most likely open for pb diffusion causing partial resetting and the observed range of 207pb 206pb ages the event that led to the pb loss in zircon could potentially be dated by the u pb system in ca phosphates which have a weighted average 207pb 206pb age across both lithologies of 3924 3 ma 95 conf this age is identical within error to the combined average 207pb 206pb age of 3926 2 ma that was previously obtained from ca phosphates within apollo 14 breccias zircon grains in apollo 12 impact melt breccias and the lunar meteorite sau 169 this age was interpreted to date the imbrium impact the zircon grains located within the black portion of the breccia yielded a similar range of ages 4123 13 to 4328 14 ma 2 to those in the grey portion given the brecciated nature of this part of the sample the interpretation of these ages as representing igneous crystallisation or resetting by impact events remains ambiguous since there is no direct link to their source rocks via textural relationships or crystal chemistry similarly the currently available zircon data set for all lunar samples may be distorted by partial pb loss resulting in meaningless and misleading age distribution patterns therefore it is crucial to fully understand and recognize the processes and conditions that may lead to partial resetting of the u pb system in zircon in order to better constrain the magmatic and impact history of the moon

mars south polar spring and summer behavior observed by tes seasonal cap evolution controlled by frost grain size thermal emission spectrometer tes observations of the recession phase of mars south polar cap are used to quantitatively map this recession in both thermal and visual appearance geographically nonuniform behavior interior to the cap is characterized by defining several small regions which exemplify the range of behavior for most of the cap while temperatures remain near the co2 frost point albedos slowly increase with the seasonal rise of the sun then drop rapidly as frost patches disappear over a period of 20 days a cryptic region remains dark and mottled throughout its cold period tes observations are compared with first order theoretical spectra of solid co2 frost with admixtures of dust and h2o the tes spectra indicate that the cryptic region has much larger grained solid co2 than the rest of the cap and that the solid co2 here may be in the form of a slab the mountains of mitchel remain cold and bright well after other areas at comparable latitude apparently as a result of unusually small size of the co2 frost grains we found little evidence for a significant presence of h2o although co2 grain size may be the major difference between these regions incorporated dust is also required to match the observations a self cleaning process carries away the smaller dust grains comparisons with viking observations indicate little difference in the seasonal cycle 12 martian years later the observed radiation balance indicates co2 sublimation budgets of up to 1250 kg m 2 regional atmospheric dust is common localized dust clouds are seen near the edge of the cap prior to the onset of a regional dust storm and interior to the cap during the storm

flocculation and sedimentation on the po river delta with the goal of improving understanding of the effect of flocculation on the formation of fine grained deposits on continental shelves hydrographic profiling in situ imaging of suspended matter and collection of surficial sediment samples were conducted at the po river delta in june 2001 these data show that during medium flow conditions 1920 m3 s sedimentation occurs rapidly immediately offshore of the main distributary po della pila rapid sedimentation is promoted by large rapidly sinking flocs forming in the river well upstream of the mouth the delivery of fine sediment to the seabed at the mouth of the po is sufficient to overwhelm the erosive effects of waves and currents leading to accumulation of mud in water depths as shallow as 4 m on cross shelf transects 2 km north and south of the mouth however suspended sediment supply from the river is reduced to the point that mud accumulates only seaward of the 8 m isobath along the central transect suspended sediment concentration decreases rapidly seaward of the 6 m isobath where the emergence of a more organic rich population of flocs along a mid water density interface is suggested energetic activity along the 15 m isobath likely promotes resuspension with the potential for removal of material from the delta further investigation of floc properties namely the relationship of floc size to settling velocity is necessary to establish the degree to which the suspension is flocculated during transport and deposition

influence of wind and lake morphometry on the interaction between two rivers entering a stratified lake the interaction of two rivers flowing into coeur d alene lake united states was investigated with a field experiment and three dimensional numerical simulations the focus was on the influence of basin morphology wind speed and wind direction on the fate and transport of the inflowing water data from the field campaign showed that intrusions from the two rivers propagated into the lake at different depths with the trace element polluted coeur d alene river flowing into the lake above the trace element poor and nutrient rich st joe river inflow the inflows initially intruded horizontally into the lake at their level of neutral buoyancy and later mixed vertically model results revealed that as the intrusions entered the main lake basin a forced horizontal mode two basin scale internal wave interacted with the intrusions to frequently siphon them into the lake proper and where rapid vertical mixing followed the results serve to show how detailed transport and mixing patterns in a lake can have im

how coriolis forces can limit the spatial extent of sediment deposition of a large scale turbidity current abstract the rotation rate of the earth controls the deposition scale of turbidity currents when their flow transit time is comparable to one day using laboratory experiments it is shown that the maximum length scale l of deposition is set by the scale where the rossby number of the current is equal to one the dimensionless rossby number is defined as ro u fl where u is a depth averaged velocity of the turbidity current and f is the coriolis parameter in these new laboratory experiments the coriolis parameter is varied by changing the platform rotation rate and there is good agreement between experimental observations and the prediction that the extent of the deposition scales as l 4 1 4 g v f 1 4 where g is the reduced gravity and v the initial volume of the sediment laden material this scaling implies that the depositional patterns will vary with latitude and that at higher latitudes one would expect smaller thicker deposits using this scaling implies that the 200 400 km spatial extent of the turbidite arising during the 1929 grand banks earthquake had ro 1 and so coriolis forces controlled the length scale of the turbidite deposition

sediment transport dynamics near a river inflow in a large alpine lake sediment dynamics were investigated in lake maggiore italy with field observations from october to mid december 2012 three moorings were deployed in pallanza bay a small embayment on the western side of the lake near the toce river inflow to measure temperature and currents throughout the water column and suspended sediment concentration ssc was estimated with acoustic instrumentation river intrusions are shown to dominate observed ssc although a small amount of sediment resuspension was observed at the site of the shallowest mooring during a large wind event that produced strong upwelling of the thermocline followed by downwelling although vertical turbulent sediment flux is typically assumed to indicate resuspension and the upward transport of sediment w c 0 downward turbulent sediment flux was observed w c 0 near the bed during the largest observed intrusion event the downward turbulent sediment flux significantly contributes to net deposition rates which are one order of magnitude larger than rates of erosion measured during the two major events observed horizontal transport of sediment occurs in vertically confined layers due to buoyancy driven intrusions beneath the intrusions sediment settles out of the water column at settling rates that appear to be constant with depth based on acoustic doppler current profiler backscatter measurements the effective settling velocities needed to produce the observed vertical transport of ssc during an inflow intrusion are one order of magnitude larger than those due to the stokes settling velocity ws alone particle flocculation and possible convective instabilities may play a role in generating the large observed effective settling rates

laboratory experiments simulating a coastal river inflow the dynamics of buoyant water entering a rotating basin are studied using a series of laboratory experiments designed to elucidate the alongshore transport mechanisms in river plumes inflowing water which is discharged perpendicular to the tank wall is observed to form a growing anticyclonic bulge and a coastal current downstream of the bulge detailed simultaneous measurements of the velocity and buoyancy fields in the plume confirm that the bulge momentum is in a gradient wind balance and the coastal current is geostrophic the growth of the bulge and accumulation of fluid within it coincides with a reduction in coastal current transport to approximately 50 of the inflow discharge the bulge is characterized by a depth scale h w hich is proportional to the geostrophic depth hg and two time dependent horizontal length scales yc the displacement of the bulge centre from the wall and rb the effective radius of the bulge these two length scales are proportional to the inertial radius

mars surface mineralogy from hubble space telescope imaging during 1994 1995 observations calibration and initial results visible to near infrared observations of mars were made with the hubble space telescope hst during 1994 1995 with the goals of monitoring seasonal variability of the surface and atmosphere and mapping specific spectral units to constrain the planet s surface mineralogy this paper presents the details of the collection and calibration of the data concentrating specifically on the near ir data that were obtained exclusively for the surface mineralogy aspect of our hst mars observing program we also present some initial results from the calibrated data set our calibration procedures included the standard pipeline processing steps supplemented by special procedures required for use with the linear ramp filters on the wide field planetary camera 2 instrument and an additional point spread function deconvolution procedure applied in order to realize the full potential spatial resolution of the images 23 to 64 km pixel between august 1994 and august 1995 the calibration results in a set of images projected onto a standard map grid and presented in radiance factor i f units having an estimated 5 photometric accuracy based on the performance of hst and comparisons with previous ground based and spacecraft mars spectra initial scientific analyses of these data reveal 1 distinct red blue color units within the classical bright regions similar to those seen in viking orbiter images and possibly related to variations in nanophase and or crystalline ferric mineral abundance 2 near ir spectral slope variations correlated with albedo on a large scale darker is bluer near ir slope but exhibiting wider variations among many of the small scale features visible in the data 3 an absorption at 860 nm that occurs in all regions but which is 3 to 5 stronger in many of the classical dark regions than in the bright regions possibly because of a greater abundance of a well crystalline ferric phase like hematite or a very low ca pyroxene or opx cpx mixture and 4 an absorption from pyroxene at 953 nm with a band depth that is inversely correlated with albedo bright regions 0 to 5 deep dark regions 7 to 15 deep and which shows the highest band depth values in individual craters calderas and other small geologic units that are resolved in the images

on the transport of buoyant coastal plumes abstract the role of discharge conditions and shelf geometry on the transport of coastal plumes is studied with a fully nonlinear primitive equation hydrodynamic model the physical setting is an estuarine channel with a small discharge rossby number by simulating different discharge magnitudes buoyant plumes are shown to be succinctly described by a simple coastal front model three results emerge from the model analysis first the plume transport is given by t 0 g ph2 2f where 0 is a parameter dependent on the ratio of the front and the plume widths g p is the plume reduced gravity h is the plume maximum depth and f is the coriolis parameter second this model links the plume transport directly to upstream river conditions with t qr where qr is the river outflow and is a parameter that relates to entrainment the geometry of the plume front and shelf slope and the fraction of freshwater carried downshelf third these equations reduce to analytic results previously established for

thermal and albedo mapping of the polar regions of mars using viking thermal mapper observations 1 north polar region we present the first maps of the apparent thermal inertia and albedo of the south polar region of mars the observations used to create these maps were acquired by the infrared thermal mapper irtm instruments on the two viking orbiters over a 30 day period in 1977 during the martian late southern summer season the maps cover the region from 60 s to the south pole at a spatial resolution of 1 of latitude thus completing the initial thermal mapping of the entire planet the analysis and interpretation of these maps is aided by the results of a one dimensional radiative convective model which is used to calculate diurnal variations in surface and atmospheric temperatures and brightness temperatures at the top of the atmosphere for a range of assumptions concerning dust optical properties and dust optical depths the maps show that apparent thermal inertias of bare ground regions decrease systematically from 60 s to the south pole in unfrosted regions close to the south pole apparent thermal inertias are among the lowest observed anywhere on the planet on the south residual cap apparent thermal inertias are very high due to the presence of co2 frost in most other regions of mars best fit apparent albedos based on thermal emission measurements are generally in good agreement with actual surface albedos based on broadband solar reflectance measurements however in the frost free region poleward of 75 s best fit apparent albedos are significantly higher than measured lambert albedos implying that measured brightness temperatures in this area are up to 15 k colder than would be expected for surfaces with the same measured albedos during this season the one dimensional atmospheric model calculations also predict anomalously cold brightness temperatures close to the pole during late summer and after considering a number of alternatives it is concluded that the net surface cooling due to atmospheric dust is the best explanation for this phenomenon the observed systematic decrease in apparent thermal inertia from 60 s to the south pole during this season is also consistent with the predictions of atmospheric model calculations the region of lowest apparent thermal inertia close to the pole which includes the south polar layered deposits is interpreted to be mantled by a continuous layer of aeolian material that must be at least a few millimeters thick the low thermal inertias mapped in the south polar region imply an absence of surface water ice deposits which is consistent with viking mars atmospheric water detector mawd measurements which show low atmospheric water vapor abundances throughout the summer season however these observations do not necessarily imply a complete absence of water thermal model calculations that can reproduce observed diurnal temperature variations in the south polar region show that annual maximum subsurface temperatures at depths ranging from 4 to 20 cm are cold enough to permit the stability of ground ice deposits even if they are in excellent diffusive contact with the atmosphere therefore the presence of near surface ground ice in the south polar region is not inconsistent with the viking irtm and mawd observations

a new parameterization for entrainment in overflows abstract dense overflows entrain surrounding waters at specific locations for example sills and constrictions but also along the descent over the continental slope the amount of entrainment dictates the final properties of these overflows and thus is of fundamental importance to the understanding of the formation of deep water masses even when resolving the overflows coarse resolution global circulation and climate models cannot resolve the entrainment processes that are often parameterized a new empirical parameterization is suggested obtained using an oceanic and laboratory dataset which includes two novel aspects first the parameterization depends on both the froude number fr and reynolds number of the flow second it takes into account subcritical fr 1 entrainment a weak but nonzero entrainment can change the final density and consequently the depth and location of important water masses in the open ocean this is especially true when the dense current follows a long path over

pathways of river water to the surface layers of stratified reservoirs this study uses tracer experiments to characterize the fate of a cold plunging river into a mediterranean reservoir under different stratification conditions three tracer experiments in lake beznar spain demonstrate that a significant fraction of the inflow may be quickly entrained into the surface mixed layer sml rather than flowing to lower depths we observe that a fraction and possibly all of river inflow entrains into the sml when the density current forms intrusions at the top of the metalimnetic layer intrusions near the base of the sml form due to lighter interfacial fluid at the top of the density current with intermediate properties between river reservior water when there is sufficient dilution of the cold inflow and abrupt density changes at the base of the sml consequently a layer of fluid splits from the denser part of the current and intrudes just below the sml while any remaining fluid flows to lower depths we parameterize this splitting behavior in terms of the transition richardson number ri12 2 1 0 1 where 0 1 and 2 are densities of the inflow the sml and the metalimnetic layer underneath respectively and is the total dilution through the plunge zone and subsequent entrainment splitting occurs when ri12 1 consistent with previous laboratory experiments we use this theory to predict the seasonal fate of river water during the stratification of lake beznar and identify the conditions that favor the formation of intrusions near the base of the sml

enhanced sedimentation beneath particle laden flows in lakes and the ocean due to double diffusive convection the transport rate of particles beneath sediment laden overflows and interflows in lakes and in the ocean can be enhanced by double diffusive and settling driven convection in previous experiments with sediment laden fluid overlaying a saline layer visual measurements could only be made in the optically clear lower layer hence there was difficulty distinguishing the two processes hindering predictions of when enhanced sedimentation occurs we used an acoustic doppler velocimeter adv to measure velocities and turbulence above and below the initial sediment salt interface the velocity of the sediment fingers in the lower layer were always larger than the stokes settling velocity of the particles leading to an asymmetry in the flow field of the two convective layers sediment fingers only dominated when there were marginal density differences between the two layers we conclude that double diffusive sediment fingers control sedimentation beneath interflows in most lakes whereas settling driven convection is dominant in most oceanic overflows

seasonal recession of martian south polar cap 1992 hst observations the seasonal recession of the south polar cap of mars has been studied using the wide field planetary camera images from hubble space telescope obtained during the summer of 1992 when the angular size of mars was between 5 and 6 arc sec the observations cover the interesting period betweenls 259 and 284 when the recession is rapid and the asymmetry in the cap is large these will be the only hst observations of this season during the 1990s because of the solar elongation constraint on telescope pointing the well known mountains of mitchel outlier which has been observed by viking and by many ground based observers nearls 260 is clearly present in the first set of hubble images the latitude of the cap edge the displacement of the center of the cap from the geographical pole and the albedo of the polar deposits determined from these images are consistent with observations of these quantities by viking in 1977 the data are not compatible with a recession as advanced as that deduced from the 1956 telescopic observations

mars global atmospheric oscillations annually synchronized transient normal mode oscillations and the triggering of global dust storms observation and analyses of the atmospheric pressure at the surface on mars for several martian years has led to the discovery of transient events in the daily pressure variations of an unusual nature these events last only a few sols mars days appear to repeat on an annual basis to within a few sols appear to cover a large portion of the hemisphere on the same sol or at least within a few sols occur in pairs with separations of 20 sols in some instances are coincident with the annual pressure minimum i e the maximum concentration of carbon dioxide in the southern hemisphere and consist of spectral components near to and sometimes identical in frequency to the diurnal and semidiurnal harmonics it is suggested that these events are kelvin normal mode transient global oscillations examination of the initiation of the 1977a 1977b and 1982a global dust storms indicate that pseudo diurnal and some times pseudo semidiurnal oscillations exist during the initiation phase and might be involved in triggering the global dust storms possibly in conjunction with winds due to longer period circulations the diurnal harmonic disappears prior to the 1977b global dust storm and is replaced by an oscillation at 1 1 cycles sol if the lack of a classical diurnal tide indicates the suppression of convection this might partially explain the slow growth of the 1977b storm the daily average pressure during the transient season which precedes the global dust storm season by almost one fourth of a year exhibits a different behavior during the global dust storm years than during the nonglobal dust storm years this implies that the global circulation must differ significantly in these cases and may be related to the presence or absence of global dust storms later in a given year these analyses suggest that an almost diurnal and an almost semidiurnal high frequency global oscillation different from the classical solar driven tides may be quite common on mars

martian dust storms 1999 mars orbiter camera observations the mars orbiter camera on board the mars global surveyor from march 9 1999 ls 107 where ls is the areocentric longitude of the sun measured in degrees from mars northern spring equinox to december 31 1999 ls 274 has obtained 7 5 km pixel 1 daily global maps of the martian surface in two wavelength bands blue 400 450 nm and red 575 625 nm visual inspection of these maps during the 1999 dust storm season has resulted in the detection of 783 dust storms ranging in size from local 102 km2 to regional 1 6 106 km2 no global storms were observed the difference in the numbers of dust storms occurring in the two hemispheres north 343 south 440 was not statistically significant fifty percent of the regional size dust storms formed as a result of the merger of two or more smaller local storms the regional storms from ls 207 to ls 223 were observed to move from the northern hemisphere into the southern hemisphere between 30 w and 50 w longitude this cross equatorial transport of dust suggests the location of the low lying southward flowing branch of the hadley circulation observations show that dust storms occur in several regions on mars at the two polar cap edges at the base of high elevation regions in the northern hemisphere near the polar hood during northern fall and at mid latitudes in both hemispheres specific regions such as solis planum and hesperia which were regions of significant dust activity in the past showed almost no dust storm activity in 1999 suggesting that regional dust sources are variable over a 20 year time frame one region of exceptional activity not noted previously was the arcadia amazonis border however other regions such as near elysium mons acidalia chryse hellas noachis argyre cimmeria and sirenum again were active dust storm regions relative dust opacities were modeled for 117 red wavelength events and ranged from 0 54 diffuse haze to 2 13 concentrated local events from the dust opacities we estimated the north polar sedimentation rate to be 6 0 10 10 4 g cm 2 yr 1 a factor of 40 smaller than previous estimates from the two 1977 global dust storms pollack et al 1979 along with the global dust mass loading 2 6 4 0 10 4 g cm 2 and cross equatorial dust mass loading 3 6 10 4 g cm 2 the 1999 cross equatorial mass dust loading suggests that the southern hemisphere subtropical latitudes require at least 2 3 martian years to replenish their dust sources before global storms can form

martian south polar cap boundary 1971 and 1973 data abstract international planetary patrol photographs of mars obtained during the 1971 and 1973 apparitions have been used to produce regression curves for the martian south polar cap for those years useful data span the range in areocentric longitude l s 186 261 in 1971 and l s 255 301 in 1973 these regression curves are compared to the 1977 regression curve obtained from viking observations and to the results of 1956 observations there is remarkable consistency between the 1971 ipp and 1977 viking data points and the 1973 regression does not appear to have differed significantly from those of 1971 or 1977

estimating suspended solids concentrations from backscatter intensity measured by acoustic doppler current profiler in san francisco bay california abstract the estimation of mass concentration of suspended solids is one of the properties needed to understand the characteristics of sediment transport in bays and estuaries however useful measurements or estimates of this property are often problematic when employing the usual methods of determination from collected water samples or optical sensors analysis of water samples tends to undersample the highly variable character of suspended solids and optical sensors often become useless from biological fouling in highly productive regions acoustic sensors such as acoustic doppler current profilers that are now routinely used to measure water velocity have been shown to hold promise as a means of quantitatively estimating suspended solids from acoustic backscatter intensity a parameter used in velocity measurement to further evaluate application of this technique using commercially available instruments profiles of suspended solids concentrations are estimated from acoustic backscatter intensity recorded by 1200 and 2400 khz broadband acoustic doppler current profilers located at two sites in san francisco bay california adcp backscatter intensity is calibrated using optical backscatterance data from an instrument located at a depth close to the adcp transducers in addition to losses from spherical spreading and water absorption calculations of acoustic transmission losses account for attenuation from suspended sediment and correction for nonspherical spreading in the near field of the acoustic transducer acoustic estimates of suspended solids consisting of cohesive and noncohesive sediments are found to agree within about 8 10 of the total range of concentration to those values estimated by a second optical backscatterance sensor located at a depth further from the adcp transducers the success of this approach using commercially available doppler profilers provides promise that this technique might be appropriate and useful under certain conditions in spite of some theoretical limitations of the method

dynamics of large polymictic lake ii numerical simulations the internal dynamics of clear lake california a large multibasin and polymictic lake are examined using simulations conducted with a three dimensional 3d hydrodynamic model the model is based on an accurate and efficient semi implicit finite difference algorithm for the hydrodynamic equations that has been previously subject to extensive verification with analytical test cases the high level of agreement without extensive calibration between the model results and the observations at several locations in the lake is comparable with previously published 3d modeling results the model results confirm the baroclinic pumping model of circulation proposed for the oaks arm of clear lake in part i the simulations show that the interaction of stratification periodic wind forcing and coriolis effects drive this circulation the diurnal readjustment of the circulation from being wind driven to baroclinically driven is examined and shown to vary spatially this transition in circulation type has a wavelike nature with a distinct frontal structure and converging currents at the surface asymmetries in the forcing and response combined with rotational effects impart a cyclonic residual circulation on the flow

horizontal structure and excitation of primary motions in a strongly stratified lake a modal analysis in the horizontal plane was extended to a layer stratified basin with irregular bathymetry and the theory was applied to lake biwa to investigate the horizontal structure and excitation of the basin scale internal waves and gyres the horizontal structure of the basin scale internal waves consisted of cyclonic and anticyclonic elliptic cells each of which appeared to follow the dispersion relationship of kelvin and poincare waves in elliptic basins the internal waves were preferentially excited depending on the arrangement of the cells and the wind direction but the spatial distribution of wind stress curl over the lake primarily determined the horizontal structure of the ensuing gyres decoupled evolutionary equations for the individual modes provided a good approximation for excitation of the internal waves and early stages of excitation of the gyres before nonlinear effects and damping become significant the modal decomposition of hydrodynamic simulation results also showed that the primary action of the wind was to excite the internal waves however these internal waves were damped within a few days and the dynamics during calm periods were dominated by the gyres illustrating the importance of internal waves on mixing and gyres on long term horizontal transport

selective withdrawal and spin up of a rotating stratified fluid we present an experimental study demonstrating that rotation has a pronounced effect on currents induced by selective withdrawal of fluid from a density stratified reservoir our observations show that initiating outflow from the reservoir generates kelvin shear waves these waves propagate cyclonically around the perimeter of the reservoir establishing an anticyclonic withdrawal layer flow this flow accelerates owing to the production of relative vorticity by compression of planetary vorticity the withdrawal layer thickness as shown by vertical profiles of the horizontal velocity grows with time separation of the side wall boundary layers in the corners of the tank causes the spun up flow to eventually break up into a series of counterrotating gyres we also present a model that describes many features of the spin up process observed before onset of separation and subsequent gyre formation the model shows that vertical diffusion of vorticity plays an important role in the spin up process leading us to conclude that apparent thickening of the withdrawal layer over time as seen in changes in the velocity profile is associated with the vertical diffusion of the spun up vorticity