modeling basin scale internal waves in a stratified lake basin scale internal waves provide the driving forces for vertical and horizontal fluxes in a stratified lake below the wind mixed layer thus correct modeling of lake mixing and transport requires accurate modeling of basin scale internal waves examining this capability with a hydrostatic z coordinate three dimensional 3d numerical model at coarse grid resolutions is the focus of this paper it is demonstrated that capturing the correct thermocline forcing with a 3d mixed layer model for surface dynamics results in a good representation of low frequency internal wave dynamics the 3d estuary and lake computer model elcom is applied to modeling lake kinneret israel and is compared with field data under summer stratification conditions to identify and illustrate the spatial structure of the lowest mode basin scale kelvin and poincarewaves that provide the largest two peaks in the internal wave energy spectra the model solves the unsteady reynolds averaged navier stokes equations using a semi implicit method similar to the momentum solution in the trim code with the addition of quadratic euler lagrange dis cretization scalar e g temperature transport using a conservative flux limited approach and elimination of vertical diffusion terms in the governing equations a detailed description is provided of turbulence closure for the vertical reynolds stress terms and vertical turbulent transport using a 3d mixed layer model parameterized on wind and shear energy fluxes instead of the convential eddy viscosity diffusivity assumption this approach gives a good representation of the depth of the mixed layer at coarse vertical grid resolutions that allows the internal waves to be energized correctly at the basin scale wind stresses surface heating and density currents form the driving energy fluxes of a stratified lake the basin scale energy flux from the wind is of particular interest because of its dominant role in setting the thermocline in motion which in the absence of inflows and outflows is the primary energy store for transport and mixing below the wind mixed layer thus modeling the basin scale internal wave behavior is an a priori requirement to modeling and quantifying the flux paths of nutrients in a stratified lake imberger 1994 this paper takes a first step in this direction by analyzing our ability to model basin scale internal waves that are seen in lake kinneret israel energy flux path in a stratified lake energy flux through a stratified lake has a fundamental dependence on forced and free baroclinic motions the wind imparts both momentum and turbulent kinetic energy tke to the water in the sur face layer the tke distributes momentum vertically in the

particle dispersal due to interplay of motions in the surface layer of a small reservoir horizontal dispersion mechanisms must be well defined in order to determine the origin and fate of heterogeneous distributions of biogeochemical material here data from an intensive field campaign in valle de bravo reservoir mexico was used to run a three dimensional hydrodynamic model and the simulated flow field was used to characterize the horizontal motions and investigate the dispersal of waterborne particles driven by the dominant circulation patterns the surface layer horizontal motions included an oscillatory component associated with two basin scale internal wave modes and a spatially and temporally complex flow field associated mostly with topographic circulation modeling of particle advection by the horizontal motions led to areal dispersal rates of o 1 to o 10 m2 s 1 comparable with bulk dispersion rates observed in other surface layer studies the aperiodic topographic component of the horizontal flow field not the oscillatory motion or a combination of both sustained most of the particle dispersal in particular local flow features such as stagnation points were shown to be a significant driver for horizontal dispersion and should be taken into consideration when analyzing horizontal distributions of waterborne material

lithospheric structure of the chaco and parana basins of south america from surface wave inversion surface wave data from a portable broadband array have been used to invert for the velocity structure of the crust and upper mantle beneath the chaco and parana basins of central south america the upper mantle velocity structure beneath the parana basin is cratonic in character whereas that beneath the chaco basin is tectonic or asthenospheric in character the surface wave analysis used broadband recordings from a subset of a 14 station array deployed in a roughly east west sawtooth arrangement along 20 s latitude with a total e w aperture of 1 400 km results from receiver function analysis as well as direct p wave regional travel time data were used in the inversions to help constrain moho depths and crust and upper mantle velocities s wave structure for the intracratonic parana basin was determined using interstation phase and group velocities for rayleigh waves fundamental and first higher mode and love waves fundamental mode only based on seven events with paths which traverse the eastern parana basin and one event with a path across the western parana basin the average moho depth in the eastern parana basin is 42 km the high velocity upper mantle lid has a maximum s wave velocity of 4 7 km s with no resolvable low velocity zone to at least 200 km depth this cratonic velocity structure indicates the presence of a lithospheric root beneath the parana basin despite emplacement of the parana plume the limited data from the western parana basin are consistent with a homogeneous upper mantle structure throughout the parana basin waveform inversion of fundamental mode and first higher mode rayleigh waves from a single subandean event was used to obtain estimates for pure path dispersion along propagation paths through the chaco basin and the western half of the parana basin the data were partitioned to isolate the partial path contribution of the phase and group velocities for the chaco basin the phase and group velocities from this somewhat sparse data set were inverted to obtain a velocity depth model for the chaco basin the distinguishing features of the chaco model consist of a rather shallow moho depth 32 km and low asthenospheric upper mantle s wave velocities about 4 2 km s with velocity increasing only slightly to about 4 3km s at 150 km depth

upper mantle structure under western europe from fundamental and higher mode surface waves using the nars array summary a generalized inversion of a new data set consisting of surface wave phase velocities and sn traveltimes has resulted in a new shear velocity and density model for the west european platform wepl 2 the surface wave phase velocity data set consists of fundamental and higher mode mode 1 6 measurements from 25 to 70mhz using the network of autonomously recording stations nars array which was specifically designed for higher mode surface wave measurements the sn traveltime data set consists of isc readings for selected european events major features of wepl 2 are a high velocity lid of 80 140 km depth underlain by a pronounced low velocity zone between 160 and 220 km depth the transition zone 400 650 km depth is characterized by high shear velocities with respect to prem the density shows a positive gradient from 60 to 140 km depth followed by an approximately constant value down to 400 km depth a model for the baltic shield scsh 2 is obtained by combination of nolet s 1977 higher mode phase velocity data set for western europe including the baltic shield and the present phase velocities for the platform this shield model shows an absence of the low velocity layer and low shear velocities in the top of the transition layer with respect to wepl 2 density although less well resolved shows lower values for the shield structure between 200 and 350 km depth

numerical simulation of internal kelvin waves and coastal upwelling fronts two three dimensional primitive equation numerical ocean models are applied to the problem of internal kelvin waves and coastal upwelling in the great lakes one is the princeton ocean model pom with a terrain following sigma vertical coordinate and the other is the dietrich center for air sea technology diecast model with constant z level coordinates the sigma coordinate system is particularly convenient for simulating coastal upwelling while the z level system might be better for representing abrupt topographic changes the models are first tested with a stratified idealized circular lake 100 km in diameter and 100 m deep two bottom topographies are considered a flat bottom and a parabolic depth profile three rectilinear horizontal grids are used 5 2 5 and 1 25 km the pom was used with 13 vertical levels while the diecast model was tested with both 13 and 29 vertical levels the models are driven with an impulsive wind stress imitating the passage of a weather system in the case of the flat bottom basin the dynamical response to light wind forcing is a small amplitude internal kelvin wave for both models the speed of the kelvin wave in the model is somewhat less than the inviscid analytic solution wave speed in the case of strong wind forcing the thermocline breaks the surface full upwelling and a strong surface thermal front appears after the wind ceases the edges of this thermal front propagate cyclonically around the lake quite similar to an internal kelvin wave in the case of parabolic bathymetry kelvin wave and thermal front propagation is modified by interaction with a topographic wave and a geostrophic circulation in both models higher horizontal resolution gives higher wave and frontal speeds horizontal resolution is much more critical in the full upwelling case than in the kelvin wave case vertical resolution is not as critical the models are also applied to lake michigan to determine the response to strong northerly winds causing upwelling along the eastern shore the results are more complex than for the circular basin but clearly show the characteristics of cyclonically propagating thermal fronts the resulting northward warm front propagation along the eastern shore compares favorably with observations of temperature fluctuations at municipal water intakes after a storm although the model frontal speed was less than the observed speed

uniqueness and stability analysis of hydrogeophysical inversion for time lapse ground penetrating radar estimates of shallow soil hydraulic properties precise measurement of soil hydraulic properties at field scales is one of the prerequisites to simulate subsurface flow and transport processes which is crucial in many research and engineering areas in our study we numerically analyze uniqueness and stability for integrated hydrogeophysical inversion of time lapse off ground ground penetrating radar gpr data in estimating the unsaturated soil hydraulic properties in the inversion hydrodynamic modeling based on the one dimensional 1 d richards equation is used to physically constrain a full waveform radar electromagnetic model synthetic gpr data in terms of 3 d multilayered media green s functions were generated for three different textured soils coarse medium and fine and assuming different infiltration events inversion was performed iteratively to estimate three key soil hydraulic parameters n and ks of the mualem van genuchten model using the global multilevel coordinate search optimization algorithm for the coarse and medium textured soils inversions converged to the actual solution for all scenarios for the fine soil estimation errors occurred mainly because of the higher attenuation of the electromagnetic waves in such a soil high electric conductivity the procedure appeared to be generally stable with respect to possible errors in the hydrodynamic and petrophysical model parameterization however we found that particular attention should be given to an accurate estimation of the saturated water content and infiltration flux for real field applications the results from our numerical experiments suggest that in theory the proposed method is promising for the noninvasive identification of the shallow soil hydraulic properties at the field scale with a high spatial resolution

surface wave dispersion crustal structure and sediment thickness variations across the barents shelf summary rayleigh and love wave group velocities were determined for 21 paths across the barents shelf those group velocities exhibit regional variations of 1 0 km or more at short periods depending upon the location of the path within the shelf only two different crustal shear velocity models beneath sedimentary layers are required however to explain all of the group velocity data one model pertains to most of the shelf from a longitude near the eastern coast of svalbard to novaya zemlya the other pertains to a 200 or 300km wide region at the western edge of the shelf shear velocities in the upper crust of the western region are significantly higher and the crust is much thinner than they are for the rest of the shelf that region is known to have moved to its present prosition from a point several hundred kilometres to the north during the caledonian orogeny surface wave group velocities within each of the two regions are strongly influenced by sediments which have accumulated in basins within the barents shelf some of these basins in the southern portion of the shelf may be 10 km or more in thickness

polarization anisotropy and fine scale structure of the eurasian upper mantle we have observed shear wave splitting with tsh tsv tsv up to 1 5 on long period records of multiply reflected s waves bottoming in the upper mantle beneath the russian and siberian platforms the dispersion of love and rayleigh waves over these paths shows discrepancies of comparable or larger magnitude with respect to smooth isotropic si structures consistent with a model of the uppermost mantle having significant apparent vertical anisotropy although the splitting and dispersion data can be fit by smooth anisotropic sa models we have investigated the apparent anisotropy associated with fine scale rough structure beneath stable eurasia we fit the data with a rough isotropic ri model having an rms shear velocity fluctuation that varies from 14 in the uppermost mantle to zero at 400 km depth these fluctuations are larger than the variation in isotropically averaged parameters expected for even a diverse assemblage of upper mantle ultrabasic rocks which we take to be evidence for some sort of intrinsic local anisotropy

global anisotropy in the upper mantle inferred from the regionalization of phase velocities a data set of 2600 paths for rayleigh waves and 2170 paths for love waves was selected in order to resolve azimuthal anisotropy of surface waves in the period range 70 250 s the epicenters were chosen so that the paths provide uniform spatial and azimuthal coverage of earth a synthetic seismogram is computed for each path and compared to the observed seismogram in order to infer the phase velocity along each path to process such a large data set a new tomographic technique is designed a good correlation is found with surface tectonics in the whole period range for love waves and at shorter periods for rayleigh waves the directions of maximum velocities are also well correlated with plate tectonics motions for the 2 azimuthal term of rayleigh waves when the power spectrum of heterogeneities is computed it is found that for love waves the even orders are usually larger than the odd orders for rayleigh waves the degrees 2 and 6 dominate only at long periods suggesting a deep origin for these components

damping mechanisms of internal waves in continuously stratified rotating basins damping mechanisms damping rates and the dissipative modal structure of internal waves in stratified rotating circular basins are investigated analytically the damping is shown to be due to a combination of the internal wave cancelling where waves emitted by the oscillatory boundary layers destructively interact with the parent wave and drain energy from it and spin down modified by the periodicity where the energy is drained by the sinks and sources at the bottom corner caused by a discontinuity in the ekman transport it is shown that super inertial poincare waves and sub inertial kelvin waves are damped predominantly by the internal wave cancelling and modified spin down respectively these processes also modify the internal wave structure for super inertial waves the boundary layer generated waves intensify the interior flow in the lower part of the water column and delay the phase relative to the isopycnal displacements but for sub inertial waves the ekman pumping and the corner sinks and sources add a horizontal circular flow that slants the crest and trough backwards near the wall

surface wave propagation in an ocean basin with an anisotropic upper mantle numerical modelling summary the characteristics of surface wave propagation in ocean basins are examined numerically for models with two types of anisotropic alignment in the upper mantle one resulting from glide plane slip in olivine with horizontal or vertical slip planes and the other from syntectonic recrystallization of olivine in a zone of horizontal shear glide plane slip can cause highly anomalous inclined rayleigh particle motion in the third generalized mode corresponding to the isotropic second rayleigh mode the amplitude of this anomaly is rather insensitive to details of the structure syntectonic recrystallization can cause an anomalous combination of inclined and tilted rayleigh motion in all modes the variation with period of the amplitude of the anomaly in the fundamental mode can indicate the approximate depth to the anisotropic layer in both types of alignment the sense of tilt and the inclination varies with direction of propagation in a manner characteristic of the structural symmetry

the physical regime and the respective biogeochemical processes in the lower water mass of lake kinneret physical measurements made in lake kinneret during the stratified period indicate that the lower water mass lwm consists of two layers a turbulent benthic boundary layer bbl and a hypolimnetic layer overlying the bbl the water in the lwm moves in response to vertical mode one seiching of the metalimnion this movement is accentuated near the perimeter of the metalimnion due to shoaling of the seiche and breaking of internal waves the motion associated with this phenomena induce a well mixed benthic boundary layer bbl adjacent to the lake bottom the bbl and hypolimnion were distinguished chemically because transport of solutes between these water bodies was very small compared to the hypolimnion the bbl was characterized by more intensive biomineralisation processes as indicated by the faster depletion of do and no3 by higher levels of nh4 h 2s and soluble reactive phosphorus srp and by lower ph values srp levels in the hypolimnion were particularly low suggesting that phosphorus was either preferentially removed by sedimentation from the hypolimnion or it was not released from particles as a result nh4 over srp ratios in the hypolimnion were significantly higher than in the bbl and diffusional fluxes of both nutrients from the lwm to the trophogenic epipelagic water should therefore be characterized by relatively high n p ratios

dynamics of large polymictic lake i field observations the internal dynamics of clear lake california a large multibasin and polymictic lake under stratified conditions is described in this work particular attention is paid to one of the subbasins of clear lake oaks arm several field experiments were conducted in the lake to obtain data of wind currents and water temperature using a wide range of devices based on field observations and previously published results on basin responses to wind stress a conceptual model of the internal circulation of the oaks arm is proposed its internal dynamics are characterized by diurnal cycles of setup and relaxation of horizontal temperature gradients driven by the wind forcing the setup and relaxation processes are modulated by the influence of the earth s rotation and create a residual cyclonic circulation this circulation mechanism is here referred to as baroclinic pumping it is in all likelihood not exclusive to clear lake but probably exists in other large and relatively shallow lakes forced by strong and almost periodic wind events where basin scale internal waves do not play a major role in the dynamics of the system

three dimensional simulation of high frequency nonlinear internal wave dynamics in cayuga lake three dimensional 3d hydrostatic and nonhydrostatic versions of the mitgcm were applied to simulate the dynamics of the internal wave field basin scale seiches nonlinear surges and high frequency nonlinear internal waves nliws in cayuga lake ny the simulations were performed using up to 226 million computational cells with several horizontal grid resolutions varying from 450 450 m to 22 22 m vertical grid spacing was not varied and ranged from 0 5 m to 2 95 m the 22 22 m nonhydrostatic grid reproduced qualitatively the formation propagation and shoaling of observed nliws using 10 grid points along the wavelength and a grid lepticity of o 1 this ensured respectively that the waves were not aliased and physical dispersion predominated over numerical dispersion using a sensitivity analysis we generalize that correctly simulating nliws in real domains using second order discretization requires grid resolutions that are an order of magnitude smaller than the wavelength and amplitude with 2 consistent with published work on idealized domains local gyre like circulation was simulated near mid basin headlands and transverse shoaling of nliw packets on lateral boundaries was associated with topographic reflection and refraction in agreement with published field observations from estuaries which show nliw propagation in long narrow quasi 2d systems e g finger lakes lochs fjords estuaries and straits is fundamentally 3d these results therefore help fill the gap in understanding and correctly modelling the multiscale 3d dynamics of nliws in complex natural systems this article is protected by copyright all rights reserved

imaging global body wave phases by stacking long period seismograms stacked record sections combining over 5 years of long period global digital seismograph network gdsn seismograms from shallow events show dozens of seismic body wave phases separate images are obtained for the vertical radial and transverse components using an automatic gain control algorithm which normalizes the amplitude of each trace prior to stacking these images provide an indication of the relative signal to noise characteristics of different parts of the gdsn data set core mantle boundary diffracted phases are particularly prominent in these stacks which show pdiff to 150 pkpdiff to 200 ppdiff to 230 sdiff to 160 and ssdiff to 220 high order s surface multiples can be seen extending through the surface wave train up to ranges of 540 two examples of possible upper mantle discontinuity reflected phases are visible one following ppp between about 95 and 125 the other following scs3 between about 210 and 240 an apparent offset between sh and sv arrivals is seen which becomes larger for the higher order s multiples sss ssss etc and appears consistent with models containing transverse isotropy in the upper mantle

resolving a low velocity zone with surface wave data summary the main purpose of seismic inversion is the retrieval of seismic velocities and densities in the earth inversion of body wave traveltimes cannot uniquely determine the seismic velocities as a function of depth when a low velocity layer is present it is generally assumed that surface waves do not suffer from the same non uniqueness the issue is addressed whether it is possible to remove the non uniqueness of traveltime inversions with a realistic set of surface wave data this requires the exact determination of the velocity distribution within and around the low velocity zone waveforms phase velocities as well as group velocities are investigated qualitatively synthetic love wave phase and group velocities are actually inverted waveforms are shown to be sensitive to the exact velocity distribution of a low velocity layer but it is concluded that the removal of the non uniqueness with the use of waveforms is difficult because the differences of the waveforms are generally small and because complications such as lateral heterogeneity and poorly known source parameters reduce the accuracy of waveform inversions the inversions of love phase and group velocities indicate that it is difficult to determine the velocity distribution of a low velocity layer in a statistically significant way with a realistic set of dispersion data group velocities are shown to be more sensitive to the low velocity structure than phase velocities unfortunately group velocity data suffers from a practical non uniqueness because in general only fundamental mode group velocities can be measured it is concluded that the non uniqueness in the detailed structure caused by a low velocity layer cannot readily be resolved by using surface wave dispersion data

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

boundary mixing in lakes 1 modeling the effect of shear induced convection 1 recent studies in lakes have shown evidence for a strong influence of shear induced stratification on mixing in turbulent bottom boundary layers bbls on sloping topography these observations suggest that the periodic near bottom shear resulting from internal wave motions may lead to alternating periods of gravitationally stable and unstable stratification in the bbl with relevant implications for turbulence and mixing in the entire basin the impact of these processes for basin scale mixing is investigated here in a three dimensional processes oriented modeling study using a well investigated system lake alpnach switzerland as an example consistent with available observations our results indicate that the bbl becomes gravitationally unstable in areas with upslope flow covering a substantial fraction of the total bottom area of the lake while near bottom convection associated with the unstable stratification in these areas results in strong turbulence its contribution to net mixing is negligible since the bbl is already well mixed conversely in areas with downslope flow the near bottom shear generates stable stratification leading to a suppression of turbulence but also to larger mixing rates due to an enhanced mixing efficiency overall bbl mixing is found to dominate basin scale mixing these mechanisms are likely to be important for a large class of stratified natural waters in which boundary layer mixing is energized by periodic internal waves or basin scale motions

on the inversion of love and rayleigh wave dispersion and implications for earth structure and anisotropy summary various factors can make it difficult to explain observations of love and rayleigh wave dispersion with the same relatively simple isotropic model these factors include systematic errors which might occur in determinations of observed group and phase velocities lateral variations in structure along the path of travel and the attempt to explain observations with a model comprised of only a small number of thick layers the last of these factors is illustrated by an inversion of dispersion data in the central united states where shear wave anisotropy had previously been invoked as one way to explain incompatible love and rayleigh wave velocities it is shown that the data can be satisfied equally well by an isotropic model consisting of several thin layers in cases where the incompatibility of love and rayleigh wave data might be produced by intrinsic anisotropy it is necessary to invert those data using an anisotropic theory rather than by separate isotropic inversions of love and rayleigh waves inversions of fundamental mode data for a region of the pacific assuming anisotropic media in which the layers are transversely isotropic with a vertical axis of symmetry lead to models which are highly non unique even if the inversions solve only for shear velocities in the litho sphere and asthenosphere it is not possible without supplementary information to ascertain the depth interval over which anisotropy occurs or to determine the thickness of the lithosphere or asthenosphere with much precision

interference pattern of the sound field in the presence of an internal kelvin wave in a stratified lake internal kelvin waves ikws initiated by rotation of the earth are one of the main hydrodynamic phenomena in large stratified lakes where baroclinic rossby radius of deformation is smaller than the horizontal scale of the lake ikws can be identified using the spectra of internal waves where in the presence of ikws the inertial frequency is at maximum ikws play a rather important role in the lake s dynamics for different processes both in the water layer and sediment especially at the periphery of lake due to influence of internal waves on the sound propagation acoustical methods can be used for estimation of behaviour of ikws in this paper the spatiotemporal variability of the mid frequency 1 khz sound field in the presence of ikws in a deep stratified lake kinneret is studied using numerical simulations based on normal mode theory due to the specific character of perturbation of the water layer ikws can cause specific variations of interference pattern in particular a significant shift of the sound interference pattern both in spatial and frequency domain these shifts can be easily measured and used for reconstruction of ikw parameters

physical limitations on detecting tunnels using underground focusing spotlight synthetic aperture radar this paper examines the feasibility of underground focusing spotlight synthetic aperture radar uf sl sar systems for tunnel detection applications a general formulation is reviewed for generating uf sl sar imaging by using multiple frequencies across a wide band and by focusing in space to subsurface points using well known ray refraction at the nominal ground surface a full wave finite difference frequency domain model is used to consider wave propagation in realistic soil with loss and frequency dependent dielectric constant and a randomly rough ground surface both of which serve to obscure and distort the returned tunnel target signal imaging results are presented for two representative soil scenarios dry sand and moist clay loam considering the ground surface ray refraction for focusing greatly improves the sar image relative to conventional sar focusing at the ground surface using uf sl sar a small shallow tunnel is reasonably imaged for the sand case despite the roughness of the ground interface however for higher conductivity moist clay loam the clutter from the rough surface overwhelms the significantly attenuated target signal which must propagate through the lossy intervening soil it is demonstrated that despite ideal focusing the tunnel is successfully imaged only for the sand case

a seismic cross section through the east european continent summary a 2 d pro le for the shear wave velocity and anisotropybetween egypt and spitsbergen is presented the pro le is constructed using fundamental and higher mode love and rayleigh waves recorded by stations of the nars deep iris and geofon networks the surface wave data have been inverted for shear velocity and anisotropy using a waveform inversion in the eastern mediterranean lithosphere we observe a large diierence 7 per cent between sh and sv velocities we interpret this anomaly as an anisotropic oceanic lithosphere beneath the eastern mediterranean an interpretation which is consistent with tectonic reconstructions of the region the east european continent is imaged as a high velocity body whose thickness increases with the estimated age of the lithosphere the continental root of the ukrainian and baltic shields and east european platform extends to a depth of 200 km this is in contrast to the surrounding younger continental regions which appear to be less than 100 km thick we further studied the structure of the continental lithosphere by investigating a possible relation between seismic velocities and tectonic age both a logarithmic and a square root relation have been tted to the average seismic velocities in each tectonic region the data slightly favour a logarithmic relation but a square root relation cannot be excluded

upper mantle shear velocities beneath southern california determined from long period surface waves we used long period surface waves from teleseismic earthquakes recorded by the terrascope network to determine phase velocity dispersion of rayleigh waves up to periods of about 170 sec and of love waves up to about 150 sec this enabled us to investigate the upper mantle velocity structure beneath southern california to a depth of about 250 km ten and five earthquakes were used for rayleigh and love waves respectively the observed surface wave dispersion shows a clear love rayleigh wave discrepancy that cannot be accounted for by a simple isotropic velocity model with smooth variations of velocity with depth separate isotropic inversions for love and rayleigh wave data yield velocity models that show up to 10 anisotropy transverse isotropy however tests with synthetic love waves suggest that the relatively high love wave phase velocity could be at least partly due to interference of higher mode love waves with the fundamental mode even after this interference effect is removed about 4 anisotropy remains in the top 250 km of the mantle this anisotropy could be due to intrinsic anisotropy of olivine crystals or due to a laminated structure with alternating high and low velocity layers other possibilities include the following upper mantle heterogeneity in southern california such as the transverse range anomaly may affect love and rayleigh wave velocities differently so that it yields the apparent anisotropy higher mode love wave interference has a stronger effect than suggested by our numerical experiments using model 1066a if the high love wave velocity is due to causes other than anisotropy the rayleigh wave velocity model would represent the southern california upper mantle velocity structure the shear velocity in the upper mantle moho to 250 km of this structure is on average 3 to 4 slower than that of the tna model determined for western north america

forced resonant oscillations as a response to periodic winds in a stratified reservoir the response of the sau reservoir to a wind field characterized by having marked periodicities of 12 h and 24 h has been studied measurements of temperature with a thermistor string and currents with an acoustic doppler current meter show that the reservoir also responds with the same water periodicities during certain times of the stratified period some of the natural oscillation modes of the reservoir are close to these forcing wind periods in particular in mid july the vertical mode v2 is close to 12 h and in mid to end of september the vertical mode v3 is close to 24 h in these situations these modes are selected out of the spectrum of possible internal waves and the reservoir behaves as a forced oscillator in resonance with the wind the structure and the period of these vertical modes have been elucidated by using the 3d model elcom both modes are affected by the earth s rotation at the widest part of the reservoir

spatial temporal variability in surface layer deepening and lateral advection in an embayment of lake victoria east africa vertical and horizontal exchanges in pilkington bay a shallow 9 m embayment of lake victoria were determined from a surface energy budget time series measurements of temperature and quasi synoptic transects of conductivity temperature and depth conducted over a 2 d period the surface energy budget is the first from a tropical lake over a diurnal timescale strong stratification developed during morning and early afternoon 40 cycles h 21 but was eroded beginning in the afternoon by the combination of wind and heat loss surface heat losses contributed 70 of the energy for surface layer deepening 82 of the time from midafternoon until midmorning circulation times of the surface layer were 2 min as it deepened to 1 5 m in the afternoon and were 12 min at night even when mixing extended to the lake bottom spatial differences in the rates of heating and cooling and in the depth of wind mixing caused fronts to develop on spatial scales of kilometers within the bay convergence of these fronts led to downwelling of surface waters and upwelling of deep waters during the stratified period horizontal pressure gradients due to differential heating contributed to thermocline downwelling lateral movement of deep anoxic waters and generation of high frequency internal waves all of which contribute to vertical and horizontal transports although wind and heat loss at one location generally determine the depth of the surface layer and thermocline the depths of these key features may be strongly influenced by rates of heating and cooling elsewhere in a basin the temporal and spatial scales of advection and vertical mixing determine the flux paths of particles and solutes in aquatic ecosystems and ultimately lacustrine productivity time series measurements of surface meteorology from which surface energy budgets can be calculated and water column temperatures can be used as an indirect approach to determine these pathways the data also can be used to determine internal wave dynamics the energetics of mixing and the role of intrusions and density driven flows in advection with this information the rates of circulation within the upper mixed layer and vertical and horizontal transports can be assessed the diurnal cycle of stratification and mixing is deter

inversion of multimode surface wave data evidence for sub lithospheric anisotropy summary multiparameter inversions of multimode dispersion data are performed for two large regions the pacific ocean and north america anisotropy is taken into account by considering transversely isotropic structures with a vertical axis of symmetry two fundamental questions are studied in detail 1 how to make the inverted models consistent when using different sets of parameters 2 what is the significance of transversely isotropic inversion for the actual earth s structure it is proved that full consistency of the inverted models can be achieved by properly taking into account some a priori informations on the model and it is shown that the use of transversely isotropic models with vertical axis of symmetry does not cause severe limitations when interpreting the data the models we have obtained are discussed in the light of these investigations considering an olivine rich upper mantle we make a tentative interpretation of these models in terms of preferred orientation of the a axis of the crystals in one fixed horizontal direction

combination of advanced inversion techniques for an accurate target localization via gpr for demining applications we used advanced ground penetrating radar gpr inversion techniques for detecting landmines in laboratory conditions the radar data were acquired with a calibrated vector network analyzer combined with an off ground monostatic horn antenna thereby setting up a stepped frequency continuous wave radar major antenna effects and interactions with the soil and targets were filtered out using frequency dependent complex antenna transfer functions the proposed strategy first exploits inversion approaches that are able to give an accurate characterization of the antenna soil interaction and a reliable estimate of the soil permittivity the outcomes of this first phase are at the basis of the application of a microwave tomographic approach based on the born approximation to achieve the imaging of the subsurface the algorithms were applied for imaging three landmines of different sizes and buried at different depths in sand although the radar system was off the ground the results showed that it was possible to reconstruct all mines including a shallow plastic mine as small as 5 6 cm in diameter this last mine was invisible in the raw radar data and the use of common gpr imaging techniques did not lead to satisfactory results the proposed integrated method shows great promise for shallow subsurface imaging in a demining context particularly because it automatically provides accurate information on the shallow soil dielectric permittivity

mass transport between a semienclosed basin and the ocean maracaibo system 1 field data and three dimensional numerical estuary and lake computer model simulations are used to investigate exchange between lake maracaibo and the gulf of venezuela this exchange occurs along a dredged shipping lane 100 km long and 14 m deep it is driven by a density difference between the lake and gulf and modulated at tidal and subtidal timescales by water level fluctuations in the gulf propagating to the lake at tidal frequencies exchange is modulated by barotropic forcing and nonlinear baroclinic response leading to a severance of high salinity bottom water into seaward and landward segments bottom water in the landward segment is moved lakeward along the shipping lane where it is mixed vertically and flushed out subtidal water level fluctuations in the gulf force barotropic currents along the shipping lane dominating variability of volume and salt flux at timescales of 1 4 weeks the barotropic component of simulated salt flux decreases from the gulf to the lake as depth averaged salinity decreases while simulated baroclinic exchange is only 20 of that predicted by quasi steady two layer hydraulic theory these reductions in salt flux are due to intense mixing that occurs throughout the shipping lane

gpr phase based techniques for profiling rough surfaces and detecting small low contrast landmines under flat ground we present a new technique whereby phase variation signatures are used to profile two dimensional 2 d rough surfaces and to discern shallowly buried small low contrast landmines under a flat ground the method has been tested using data measured over a composite surface containing two rough dielectric surface patches and over a flat ground under which small low contrast antipersonnel landmines are shallowly buried the results show that the phase based technique is capable of profiling rough surfaces and of detecting small low contrast landmines with different internal structures buried underneath a flat ground

near inertial waves in lake erie near inertial poincare waves with a period t p similar to 17 h are the dominant wind induced internal wave motions in central lake erie and consequently have a substantial influence on lake circulation mixing and biogeochemistry however due to the complex three basin bathymetry in lake erie the vertical and horizontal modal structure of these waves remain poorly understood in this study we analyze field data to show wind events energize frequent vertical mode one poincare waves the horizontal modal structure was also investigated in a sensitivity analysis using a calibrated three dimensional hydrodynamic transport model forced with observed and idealized spatially uniform wind events strong horizontal mode one poincare wave cells form in both the central and eastern basins when wind events have a duration of 0 25 t p to 0 5 t p are impulsive and periodic at t p or have anticyclonic rotation with a duration of t p momentum transfer from longer wind events 0 5 tp will oppose the coriolis force rotated currents and damp poincare wave generation in agreement with theory the most efficient wind events are observed and computationally modeled to have a duration of 0 25 t p causing an excitation peak at similar to 0 4 t p and converting similar to 0 8 of the wind energy input to poincare waves the efficiency of wind work in generating poincare wave kinetic energy is given by 1 cos 2 pi f t t 1 where f is the inertial frequency and t is the wind duration therefore the efficiency peaks during each nt p period where n is a non negative integer and decreases significantly for longer wind events

wind and buoyancy driven horizontal exchange in shallow embayments of a tropical reservoir lake argyle western australia many factors including depth vegetation density wind and gyres may act to influence the littoral exchange in a water body but very few studies have investigated the interaction between more than two of these factors at any time to investigate these controls on horizontal exchange in a large tropical reservoir we conducted a 9 d intensive field experiment in lake argyle western australia the experiment began with a 7 d cooling period that generated water in the shallows of the reservoir embayments that was persistently cooler than the interior this led to an underflow of dense water that moved from the lake boundary toward the center of the reservoir a three dimensional hydrodynamic model elcom was able to adequately reproduce this thermal structure and was used to demonstrate its sensitivity to wind sheltering effects and submerged macrophyte presence further analysis of the predictions indicated that when the ratio of the shear and buoyancy force averaged over 6 h b6h and 6 h averaged wind speed in the direction of the embayment u6h was 1 greater than 0 5 ms 1 and 4 5 ms 1 respectively the exchange was dominated by a topographic gyre formation 2 when 0 1 b6h 0 5 and 2 4 ms 1 u6h 4 5 ms 1 the resulting circulation was a combination of differential cooling flows and a topographic gyre circulation and 3 when u6h fell below 2 4 ms 1 purely buoyancy driven flow occurred but only if the buoyancy forces across the embayments were an order of magnitude greater than wind induced velocity shear

effect of stair step and piecewise linear topography on internal wave propagation in a geophysical flow model 1 the paper describes the effect of a stair step representation of bottom topography common in most numerical models on the propagation of internal waves in a geophysical flow an analytical solution was used to predict the effect of stair step and piecewise linear representations of topography on the reflection and transmission of internal waves the estuary lake and coastal model elcom was used to simulate the transmission of a train of small amplitude internal gravity waves propagated along a variable depth rectangular channel containing a linearly stratified fluid the effect of the different obstacle approximations was examined in terms of the interference of the resulting wave number content and hence the associated reflection coefficients which could be directly compared to the analytical theory it was shown that for gaussian obstacles of varying lengths and heights the full bottom cells and partial bottom cells solutions from elcom agree with the stair step and piecewise linear solutions from the theory respectively it was shown that when gaussian obstacles with weak slopes are represented by stair steps an aliasing that is similar to that in discrete fourier transform can occur resulting in reflection coefficients that are much higher than the exact solution on the other hand piecewise linear approximations produce significantly attenuated aliasing an immersed boundary technique that enforces a no flux condition at the actual sloping bottom similar to that of the analytical solution is found not to produce better numerical results

a novel signal processing technique for clutter reduction in gpr measurements of small shallow land mines a signal processing technique is developed to reduce clutter due to ground bounce in ground penetrating radar gpr measurements this technique is especially useful when a gpr is used to detect subsurface antipersonnel mines the gpr clutter is modeled using a simple parametric model buried mine and clutter contributions are separated through a pair of coupled iterative procedures the algorithm outperforms existing clutter reduction approaches and also yields target features that are useful for detection and identification of these mines the proposed technique effectively reduces clutter resulting in a significant decrease in false alarm rates

processes affecting horizontal mixing and dispersion in winam gulf lake victoria several large rivers enter winam gulf a large shallow semi enclosed embayment of lake victoria given the vast spatial scale of this embayment 1400 km 2 horizontal transport of waterborne material plays a major role in determining its biochemical properties to identify the dominant hydrodynamic characteristics of this horizontal transport a combination of field data and three dimensional numerical modeling were employed to investigate effects due to variable wind forcing riverine inflows and interactions with the rest of lake victoria including astronomical tides and a complex bathymetry currents in the gulf were oscillatory due to periodic wind and tidal forcing leading to surface seiching with a residual circulation component in the western region of the gulf near the connection with lake victoria substantial vertical and horizontal shear in the currents resulted in efficient horizontal dispersion with rates of up to 160 m 2 s 1 simulated using numerical tracers in the eastern region however rates of horizontal dispersion were reduced to around 12 m 2 s 1 this spatial variability in hydrodynamic conditions underpins regional differences in ecological properties of winam gulf

internal wave weather in a stratified lake thermistor chain data collected in lake biwa japan during a period of strong stratification were used to determine the nature of the water column response to wind forcing the evolution of the basin scale waves in the lake were reproduced in three dimensional numerical simulations and the time variability of the internal wave spectrum is discussed based on spectral analysis of the thermistor chain records severe winds associated with the passage of three typhoons during the sampling period excited basin scale kelvin and poincare waves which by interaction with the topography of the lake and non linear effects generate trains of high frequency internal waves time frequency analysis of the temperature signals suggests that the 2 slope of the internal wave spectrum is probably the result of the composition of groups of waves with high intermittence travelling through the wave guide the observed rapid decay of internal wave energy after severe wind events seemed to be due mostly to high dissipation at the sloping boundaries of the lake

formation of magnetite enriched zones in and offshore of a mesotidal estuarine lagoon an environmental magnetic study of tauranga harbour and bay of plenty new zealand 1 magnetic iron minerals are widespread and indicative sediment constituents in estuarine coastal and shelf systems we combine environmental magnetic sedimentological and numerical methods to identify magnetite enriched placer like zones in a complex coastal system and delineate their formation mechanisms magnetic susceptibility and remanence measurements on 245 surficial sediment samples collected in and around tauranga harbour the largest barrier enclosed tidal estuary of new zealand reveal several discrete enrichment zones controlled by local hydrodynamic conditions active magnetite enrichment takes place in tidal channels which feed into two coast parallel nearshore magnetite enriched belts centered at water depths of 6 10 m and 10 20 m a close correlation between magnetite content and magnetic grain size was found where higher susceptibility values are associated within coarser magnetic crystal sizes two key mechanisms for magnetite enrichment are identified first tide induced residual currents primarily enable magnetite enrichment within the estuarine channel network a coast parallel fine sand magnetite enrichment belt in water depths of less than 10 m along the barrier island has a strong decrease in magnetite content away from the southern tidal inlet and is apparently related to active coast parallel transport combined with mobilizing surf zone processes a second less pronounced but more uniform magnetite enrichment belt at 10 20 m water depth is composed of non mobile medium coarse grained relict sands which have been reworked during post glacial sea level transgression we demonstrate the potential of magnetic methods to reveal and differentiate coastal magnetite enrichment patterns and investigate their formative mechanisms

surface wave propagation in an ocean basin with an anisotropic upper mantle observations of polarization anomalies summary observations of surface waves crossing ocean basins indicate that at least in some cases a better interpretation of what was previously considered to be the simultaneous arrival of fundamental love and second rayleigh modes with similar group velocities is the coupled motion of the second generalized mode surface wave propagating in an anisotropic upper mantle this mode displays the polarization anomalies expected from anisotropic alignments caused by syntectonic recrystallization of olivine in a zone of horizontal shear the polarity of the pattern of anomalies found in waves crossing the pacific basin suggests that the lithosphere is dragging the asthenosphere

global tomography from rayleigh and love wave dispersion effect of ray path bending summary a large data set of fundamental mode rayleigh and love wave phases has been employed for global tomographic inversions these data represent observations of the first arriving surface waves r1 and l1 from approximately 850 seismic events with about 10 observations of dispersion per event the inversion for laterally varying depth dependent structure is performed in several steps at discrete periods from 111s 250s for love waves and from 111s 200s for rayleigh waves we first determine simultaneously the global distribution of phase velocity anomaly and the relocations of the seismic events each phase velocity distribution is then corrected for laterally varying moho depth and bathymetry followed by inversion for 3 d earth structure in the depth range 0 240 km in order to lie within the limits of ray theory we restrict all model perturbations to a degree 0 16 spherical harmonic expansion a second order scattering ray path correction is included in the inversions the phase velocity perturbations show a high correlation with surface tectonics at shorter periods comparison of inversions shows that those performed without the ray path correction exhibit a complicated pattern of fast and slow velocity bias the only common feature in the patterns of bias with respect to period or wave type is that fast velocity bias is concentrated in regions of large structural gradient the amplitude pattern of the depth dependent model has pronounced peaks in the intervals 0 70 km and 140 210 km the deeper peak is associated with lateral variations in asthenosphere structure we derive new estimates for the spherically averaged phase velocities of the fundamental mode rayleigh and love waves the spherically averaged phase velocities are decreased by about 0 1 per cent by including the ray path correction these phase velocity dispersions can be simultaneously fit well with an isotropic model either with or without the ray path correction but particularly well when the ray path correction is included in both cases a pronounced low velocity zone of the global extent is required in the depth range 120 190 km

reducing numerical diffusion effects with pycnocline filter numerical or artificial diffusion is the unintentional smoothing of gradients associated with the discretization of the transport equations in lakes and reservoirs where through flow is small the effects of numerical diffusion of mass are cumulative leading to a progressive weakening of vertical density stratification this density field misrepresentation precludes accurate long term three dimensional 3d hydrodynamic simulations on fixed grids in closed basins with an active thermocline an ad hoc technique to limit the destratifying effects of numerical diffusion of mass is presented and tested for a 3d hydrostatic z coordinate numerical model the technique quantifies the domain integrated numerical diffusion by assessing the change in the background potential energy eb at each time step the change in eb associated with numerical diffusion is calculated then removed using a sharpening filter applied to each water column in idealized test cases the filtering technique is effective in maintaining density stratification over one year while undergoing periodic large amplitude forcing by internal waves forty day simulations of lake kinneret compared to field measurements demonstrate improved representation of density stratification using the filtering technique

mixing dynamics at the confluence of two large rivers undergoing weak density variations simulations of tracer experiments conducted with a three dimensional primitive equation hydrodynamic and transport model are used to understand the processes controlling the rate of mixing between two rivers ebro and segre with distinct physical and chemical properties at their confluence upstream of a meandering reservoir ribarroja reservoir mixing rates downstream of the confluence are subject to hourly scale oscillations driven partly by changes in inflow densities and also as a result of turbulent eddies that develop within the shear layer between the confluent rivers and near a dead zone located downstream of the confluence even though density contrasts are low at most o 10 1 kg m 3 difference among sources and almost negligible from a dynamic point of view compared with inertial forces they are important for mixing mixing rates between the confluent streams under weakly buoyant conditions can be of up to 40 larger than those occurring under neutrally buoyant conditions the buoyancy effects on mixing rates are interpreted as the result of changes in the contact area available for mixing distortion of the mixing layer for strong density contrasts though when the contact area between the streams becomes nearly horizontal larger density differences between streams will lead to weaker mixing rates as a result of the stabilizing effect of vertical density gradients

what controls the transition from confined to unconfined flow analysis of hydraulics in a river delta abstractrecent field work at the wax lake delta wld in coastal louisiana indicates lateral outflow from channels to islands upstream of the receiving basin in this region of the delta the flow t

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

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

the seasonal evolution of high vertical mode internal waves in a deep reservoir the causal mechanism and seasonal evolution of the internal wave field in a deep warm monomictic reservoir are examined through the analysis of field observations and numerical techniques the study period extends from the onset of thermal stratification in the spring until midsummer in 2005 during this time wind forcing was periodic with a period of 24 h typical of land sea breezes and the thermal structure in the lake was characterized by the presence of a shallow surface layer overlying a thick metalimnion typical of small to medium sized reservoirs with deep outtakes basin scale internal seiches of high vertical mode ranging from mode v3 to v5 were observed in the metalimnion the structure of the dominant modes of oscillation changed as stratification evolved on seasonal timescales but in all cases their periods were close to that of the local wind forcing i e 24 h suggesting a resonant response nonresonant oscillatory modes of type v1 and v2 became dominant after large frontal events which disrupted the diurnal periodicity of the wind forcing

shallow anisotropy in the mediterranean mantle from surface waves 1 we present new evidence for the existence of the love rayleigh discrepancy in the mediterranean region and constrain the average polarization anisotropic structure of the mediterranean mantle we analysed regional rayleigh and love waveforms recorded at 3 component broadband seismic stations none of the 3 component seismograms could be fit with a single 1d isotropic and smooth velocity model however satisfactory fits for individual rayleigh and love waveforms could often be obtained using realistic 1d velocity models we used these 1d path average velocity structures to derive 3d s velocity models for the mediterranean region our results show that love waves require higher velocities about 200 m s compared to rayleigh waves between 30 and 120 km depth we relate the observed anisotropy to lattice preferred orientation of crystallographic axes of elastically anisotropic minerals such as olivine

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

three dimensional imaging of multicomponent ground penetrating radar data scalar imaging algorithms originally developed for the processing of remote sensing measurements e g the synthetic aperture radar method or seismic reflection data e g the gazdag phase shift method are commonly used for the processing of ground penetrating radar gpr data unfortunately these algorithms do not account for the radiation characteristics of gpr source and receiver antennas or the vectorial nature of radar waves we present a new multicomponent imaging algorithm designed specifically for vector electromagnetic wave propagation it accounts for all propagation effects including the vectorial characteristics of the source and receiver antennas and the polarization of the electromagnetic wavefield a constant offset source receiver antenna pair is assumed to overlie a dielectric medium to assess the performance of the scalar and multicomponent imaging algorithms we compute their spatial resolution function which is defined as the image of a point scatterer at a fixed depth using a

the influence of eddy viscosity formulation bottom topography and wind wave effects upon the circulation of a shallow bay abstract a three dimensional hydrodynamic model taking account of enhanced bed stress due to wave current interaction is used to examine the wind induced circulation and flushing time of an idealized homogeneous bay or estuary the model uses a spectral approach in the vertical and hence computes a continuous current profile from sea surface to seabed calculations show that in the case of an estuary of nearly constant cross sectional depth with an along estuary wind the intensity of differential flow in the vertical is critical in determining the flushing time in this case the three dimensional circulation and hence flushing time is sensitive to the formulation of vertical eddy viscosity and in the case of a tidal estuary its variation over the spring neap cycle and with wind intensity must be included for an estuary with a deep central channel horizontal rather than vertical circulations dominate the flow is more uniform in the vertical and hence the circulation is fairly insensitive to ed

physical controls on the spatial evolution of a dinoflagellate bloom in a large lake a set of satellite images of chlorophyll a concentration for lake kinneret israel from the period february to april 2007 captured the temporal evolution of horizontal patchiness that developed during the typical spring bloom of the dinoflagellate peridinium gatunense narrow bands of high concentration located adjacent to the shoreline at the start of the bloom were followed by progressive propagation of this high concentration region from the shoreline toward the center of the lake as the bloom proceeded a three dimensional 3 d hydrodynamic numerical model and an analytical model for a flat bottomed elliptical basin together explain the observed phenomenon the spatial structure of kelvin waves which were demonstrated to most likely be present in february and april due to resonance produced regions of high velocity gradient contributing to horizontal dispersion close to the shoreline this region of high dispersion was narrow and close to the shoreline at the start of the bloom when the burger number was relatively small but it widened over the course of the season as the burger number increased due to increasing stratification in addition an increase in the dispersion rate with time in the lake interior was inferred from numerical simulation due to increasing wind speeds and a thinner surface layer physical processes in this case horizontal dispersion as a result of both kelvin waves and wind can play an important role in governing the dynamics and spatial evolution of dinoflagellate blooms in lakes spatial heterogeneity of phytoplankton is a ubiquitous occurrence in lakes coastal waters and the open ocean phytoplankton patchiness can be defined by localized abruptly elevated concentrations phytoplankton patches may occur at a broad range of spatial scales and such

downscaling model resolution to illuminate the internal wave field in a small stratified lake this paper presents the application of hydrostatic and nonhydrostatic three dimensional hydrodynamic models to a stratified lake focus was given to the multiscale response of the internal wave field to strong wind gusts exceeding 20 m s 1 simulations were performed using different horizontal grid resolutions with uniform grid sizes varying from 100 100 to 10 10 m results of the hydrostatic models were used to investigate the large scale features of the internal wave motion with the intent of investigating the high frequency waves observed results of these simulations were used as initial conditions for nonhydrostatic simulations using smaller grids wavelength of the high frequency waves decreased with grid resolution however none of the uniform grids were sufficiently fine to capture the waves of the highest frequency simulations performed using a nonuniform grid produced internal waves of similar frequency of the waves observed in the field the simulations showed that these waves were shear u

seasonal evolution of the basin scale internal wave field in a large stratified lake the response of the water column to varying conditions of stratification and wind forcing was investigated in lake kinneret israel using data collected from thermistor chains and acoustic doppler current profilers during 1997 and 1998 the strong daily sea breeze was found to generate a vertical mode 1 internal kelvin wave and basin scale internal poincarewaves of vertical modes 1 2 and 3 the kelvin wave the dominant component of the internal wave field was responsible for alongshore velocities in the nearshore regions in the upwind nearshore regions velocities were dominated by the forced response to the wind and were cross shore in nature in the lake interior the kelvin wave effect on the horizontal velocity field was minor compared to the higher vertical mode poincarewaves the kelvin wave is shown to exist in resonant and nonforced states with the wind whereas the vertical mode 1 poincarewave energy remained relatively constant despite large variability in the forcing condi tions the energy in the higher mode poincarewaves varied greatly both on daily and seasonal timescales the results demonstrate that the wind energy forces multiple basin scale internal wave modes and that prior motion in the water column must be considered when determining the subsequent internal wave response in periodically forced systems lake kinneret israel has long been an important regional resource providing a substantial supply of drinking water as well as supporting a commercial fishery the monomictic lake is forced daily during the summer by a powerful sea breeze with stratification and wind patterns showing little variation from year to year these factors along with a fa vorable bathymetric pattern combine to make lake kinneret an ideal place for the field investigation of large scale inter nal waves and related phenomena such as the benthic bound ary layer horizontal transport and vertical mixing processes in addition to providing substantial insight into the local pro cesses and hence influencing local management study of the lake also provides fundamental knowledge of the dynam ics of enclosed basins on a geophysical scale during summer the internal rossby radius in lake kin neret is typically one half the basin width hence large scale motion in the lake will be affected by the earth s rotation and basin scale internal waves may be of topographic ross by kelvin or poincareform topographic rossby waves are sub inertial frequency oscillations that exist only in rotating fluids with variable bathymetry mysak et al 1985 stocker and hutter 1987 and these waves result from changes in depth affecting the relative vorticity of fluid elements in the absence of vertical boundaries wavelike solutions to the lin ear inviscid equations of motion for a flat bottomed region of homogeneous fluid with a constant rate of rotation are 1

modeling a plunging underflow a coupled three dimensional hydrodynamics and two dimensional underflow model is adapted to provide simulation of plunging inflows in reservoirs the new approach accounts for the effect of the barotropic term prior to the plunge point of the inflow simulations of plunging flows in constant width and constant slope channels are conducted and the resulting plunge depths are in agreement with prior empirical models simulation of a previously measured underflow in wellington reservoir australia demonstrates the model application to a plunging inflow in a natural water body and good agreement between field and model results

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

structure of the earth mantle and core the deep interior structure of the earth has been extensively analyzed using a wide variety of seismic phases and techniques during the last four years most studies have emphasized quantitative three dimensional mapping of the lateral velocity heterogeneity of the mantle and core these aspherical velocity variations are believed to be direct manifestations of thermal and compositional heterogeneity associated with convective processes a first generation of global models for the lateral velocity variations in the deep earth has been produced providing tantalizing images of large scale structures suggestive of a non steady state thermal convection system the upper 400 km of the mantle has the strongest lateral velocity variations of up to 10 for shear velocity surface wave analyses that do not require a priori regionalizations have demonstrated that there is a strong association between surface tectonic provinces and the uppermost mantle velocity variations thus the thermal and convective state of the upper 200 km of the mantle can be reliably interpreted in the context of plate tectonics the upper mantle models support the contention that continents have deep roots with differences in velocity structure from oceanic and active tectonic regions extending as deep as 400 km very long wavelength lateral velocity variations of a few percent have been detected in the transition zone at depths from 400 to 670 km as well as throughout the lower mantle these deep seated variations have little correspondence to surface tectonics and efforts to interpret their nature are just beginning the lowermost 200 km of the mantle d region has lateral velocity fluctuations comparable to those in the upper mantle and evidence has been presented for the presence of a sizable velocity discontinuity at the top of the d layer a combined thermal and compositional boundary layer roughly mirroring the lithosphere is a likely explanation for this anomalous zone the core mantle boundary appears to have significant 10 km long wavelength topography presumably sustained by dynamic stresses from deep mantle convection the inner core may have strong lateral heterogeneity or axially symmetric anisotropy suggesting a complex thermal and compositional state significant progress has been made in characterizing the frequency dependence of anelastic attenuation in the mantle in the short period body wave band models for teleseismic p wave attenuation operators have converged with t values of 0 7 1 0 s appropriate at 1 hz and t values of 0 4 0 6 s appropriate at 4 hz regional variations of attenuation are slowly being mapped out as well

a simple model of mixing in stratified tidal flows we use a simple model of vertical mixing in a stratified tidal flow to study flows that might be observed in shallow estuaries in the model flow is driven by a specified surface pressure gradient due to barotropic tidal motions the model incorporates two means for accomplishing vertical mixing 1 shear instability and 2 bottom mixed layer deepening by turbulence produced at the estuary bottom and in the shear layer at the top of the mixed layer we discuss model results that show how the combined action of shear instability and tidal stirring accomplishes vertical mixing the interaction between the instabilities that develop because of the substantial tidal timescale velocity shear caused by stratification is the key feature of mixing shear instability weakens the stability of the mixed layer allowing stirring to efficiently entrain lighter fluid into the mixed layer the importance of shear is found to depend on the stability of the water column and on the relative importance of frictional forces

preliminary results from higher mode surface wave measurements in western europe using the nars array abstract for the first time fundamental and higher mode rayleigh wave phase velocity data for the west european platform have been measured using teleseismic recordings from the mobile broad band nars array measurements could be obtained from 30 to 70 mhz this is an extension of 30 mhz towards higher frequencies with regard to previous measurements in the frequency range of 10 to 40 mhz for western europe including the scandinavian shield nolet 1977 inversion of the new data for isotropic shear wave velocity and density model wepl1 shows a broad low shear wave velocity layer from 120 to 260 km depth without a lehmann discontinuity at larger depths the model resembles the m7 model nolet 1977 the density model shows a steep positive gradient from 60 to 100 km depth followed by a slight decrease down to 300 km depth no pronounced low density layer as present in the m7 model could be resolved reinversion of nolet s data using the same starting model as for the wepl1 model and calculation of the difference structure yields a model for the scandinavian shield scsh1 the shield has higher shear wave velocities than the west european platform down to about 300 km depth

effect of wind variability on topographic waves lake kinneret case 1 we studied the winter wind driven circulation in lake kinneret northern israel using state of the art atmospheric regional atmosphere modeling system rams and oceanic regional ocean modeling system roms general circulation models during winter the lake is completely mixed and mainly forced by the passage of synoptic weather systems the lake s dynamic response was identified using various wind regimes the response of the lake to a uniform wind stress resulted in the formation of a double gyre circulation pattern after removal of the wind stress the double gyre pattern slowly rotated cyclonically with a time period of several days around the lake perimeter consistent with the pattern of the lowest mode basin scale topographic vorticity wave the use of rams simulated wind fields resulted in a less symmetric structure of the double gyre pattern due to the presence of a curl in the wind field using various wind regimes to force the lake indicated that the presence of a positive or negative curl in the wind field might result in a shift in the topographic wave frequency to a higher or lower value respectively this result may be easily applied to motions on the geophysical scale the currents predicted by rams roms agree well with measured data near the center of the lake forcing the model with a spatially uniform wind field constructed from a single station resulted in poor agreement with the observed currents indicating the importance of the wind field spatial pattern

spatial structure of the dominant basin scale internal waves in lake kinneret field data and numerical simulations were used to investigate the effects of basin shape continuous stratification and rotation on the three dimensional structure of the dominant natural basin scale internal wave modes in lake kinneret a stratified lake large enough so that the earth s rotation influences the wave motion the structure of the modes was inferred from power spectral density of measured and simulated isotherm vertical displacements and from rotary power spectral density of isopycnal velocities obtained from numerical simulations the shape of the lake at the level of the thermocline in conjunction with the dispersion relationship determines the horizontal configuration of the natural modes the dominant response to wind forcing was an azimuthal and vertical mode 1 kelvin wave with a natural period of 22 6 h that propagated around the entire basin the second most dominant response was a vertical mode 1 wave with a natural period close to 10 5 h and composed of two counter rotating

filtering soil surface and antenna effects from gpr data to enhance landmine detection the detection of antipersonnel landmines using ground penetrating radar gpr is particularly hindered by the predominant soil surface and antenna reflections in this paper we propose a novel approach to filter out these effects from 2 d off ground monostatic gpr data by adapting and combining the radar antenna subsurface model of lambot with phase shift migration first the antenna multiple reflections originating from the antenna itself and from the interaction between the antenna and the ground are removed using linear transfer functions second a simulated green s function accounting for the surface reflection is subtracted the green s function is derived from the estimated soil surface dielectric permittivity using full wave inversion of the radar signal for a measurement taken in a local landmine free area third off ground phase shift migration is performed on the 2 d data to filter the effect of the antenna radiation pattern we validate the approach in laboratory conditions for four differently detectable landmines embedded in a sandy soil compared to traditional background subtraction this new filtering method permits a better differentiation of the landmine and estimation of its depth and geometrical properties this is particularly beneficial for the detection of landmines in low contrast conditions

crustal structure and possible anisotropy in turkey from seismic surface wave dispersion summary the velocity structure of two regions of turkey are determined using single station measurements of rayleigh and love wave group velocities in the period range 8 50s a differential inversion scheme yields models for turkey in which crustal and upper mantle shear wave velocities are slower than those of most of europe comparisons of upper mantle shear wave velocities we have obtained with reported p velocities leads to poisson s ratio values in the upper mantle between 0 29 and 0 30 for eastern turkey and between 0 27 and 0 31 for western turkey crustal velocities are slightly slower and upper mantle velocities are slightly faster in western turkey than in eastern turkey the crust mantle boundary obtained in our studies is gradational but if a shear velocity of 4 2 km s l is taken to define the upper mantle then the crust appears to be about 40 km thick throughout all of turkey a sharp crust mantle boundary may occur but cannot be resolved the data of this study require neither a low velocity zone in the upper mantle nor polarization anisotropy in the crust or upper mantle azimuthal variations of rayleigh and love wave group velocities in western turkey are consistent with velocities predicted by an azimuthally anisotropic upper crust in which vertical cracks are orientated in an approximate e w direction this interpretation is consistent with geological information fault plane solutions lineations mapped from satellite observations and reported heat flow values but the possibility that these variations are caused by lateral changes of velocity in the crust of western turkey cannot be completely ruled out at the present time