the initial response of a stratified lake to a surface shear stress laboratory experiments are used to study the initial response of a stratified fluid to the action of a wind stress the experiments are described in the context of a parameterization scheme that quantifies the strength of the applied stress relative to the bulk stability of the fluid and also the duration of the wind stress relative to the periods of the waves generated by the stress this study concentrates on the first fundamental internal wave period in experiments where the fluid is considered to have upwelled i e the stratified region of the fluid reaches the surface at the upwind endwall the majority of the experiments use three layer initial density profiles as an approximation to a continuously stratified water column a linear model using normal modes proved successful prior to the commencement of upwelling and this enabled an estimate to be made of the time at which upwelling occurred at this point the wave development ceased and the flows developed via entrainment mechanisms consideration of the energy budget showed that little of the input energy was stored in the system the initial mixing efficiency defined as the ratio of the mean potential energy gained to the energy imparted by the belt never exceeded 30 peak efficiency occurred when the surface stress was just sufficient to bring the interfacial region to the surface

earthʼs inner core innermost inner core or hemispherical variations the structure of earth s deep inner core has important implications for core evolution since it is thought to be related to the early stages of core formation previous studies have suggested that there exists an innermost inner core with distinct anisotropy relative to the rest of the inner core using an extensive new data set of handpicked absolute travel time observations of the inner core phase pkikp we find that the data are best explained by variations in anisotropy between two hemispheres and do not require an innermost inner core we demonstrate that observations of an innermost inner core are an artifact from averaging over lateral anisotropy variations more significantly we show that hemispherical variations in anisotropy previously only imaged in the upper inner core continue to its centre the eastern region has 0 5 1 5 anisotropy whereas the western region has 3 5 8 8 anisotropy increasing with depth with a slow direction at 57 61 to the earth s rotation axis at all depths such anisotropy is consistent with models of aligned hcp or bcc iron aggregates

modal response of reservoirs to wind stress an analysis of the response of a density stratified reservoir to surface shear stress is presented the reservoir is assumed to be two dimensional and to have a constant depth in the limit that the bulk wedderburn number wb and the bulk richardson number rib are both infinite the resulting equations are linear and solutions can be found in terms of the individual responses of a set of orthogonal normal modes for the case of a steady wind stress the solution consists of periodic motions and steady isopycnal displacements however the steady state isopycnal slope at the base of the mixed layer is infinite implying that upwelling can occur when the wedderburn number is quite large this is attributed to blocking of the stratified fluid below the mixed layer by the endwall the modal theory presented in this paper is compared with experimental observations made using a belt to impart shear stress to a stratified fluid contained in a box the comparison shows that the present theory is qualitatively corr

baroclinic effects on wind driven lateral circulation in chesapeake bay abstractthe 2 month long mooring data were collected in a straight midsection of chesapeake bay to document the lateral circulation driven by along channel winds under upestuary winds the lateral circulation featured a clockwise looking into estuary circulation in the surface layer with lateral ekman forcing as the dominant generation mechanism under downestuary winds however the lateral circulation displayed a structure dependent on the wedderburn number w a counterclockwise circulation at small w and two counterrotating vortices at large w the surface lateral velocity was phase locked to the along channel wind speed analysis of the streamwise vorticity equation showed that the strength and structure of the lateral circulation in this stratified estuary were largely determined by the competition between the tilting of planetary vorticity by along channel currents and lateral baroclinic forcing due to sloping isopycnals under strong downestuary winds the lateral baroclinic forcing offset or

an experimental study of the upwelling response of stratified reservoirs to surface shear stress an experimental study of the dynamic response of non rotating stratified reservoirs to the application of surface shear stresses is presented the experiments were made using two layered and linear stratifications a moving belt was used to supply a shear stress to the fluid detailed measurements of the density field show that upwelling occurs at all values of the wedderburn number w rather than only occurring when w 1 differences between the two layer theory and the present observations are attributed to the fact that the experimental stratifications were continuous rather than layered shearflow dispersion is observed to be an important mechanism for distributing the effects of localized upwelling over the entire length of the mixed layer a model of mixed layer deepening based on upwelling and shearflow dispersion is presented and is compared to the observations of this and other experimental studies

wind induced entrainment in a stably stratified fluid experiments on mixed layer deepening in a straight wind flume initially containing a two layer fluid were carried out in order to simulate an effectively unlimited water body or a situation where the presence of end walls is not yet noticeable the water from the upper layer was withdrawn at the downstream end and supplied again at the upstream end in part of the experiments upper layer depths and mean density and mean velocity profiles were measured for overall richardson numbers based on the surface friction velocity ranging from 22 to 1090 gradient richardson numbers in the transition layer between the mixed layer and the undisturbed layer and in the mixed layer were estimated the correction of the results for the effects of recirculation is discussed

formulae for pressure gradients in one dimensional lake models formulae for barotropic and baroclinic pressure gradients suitable for one dimensional lake models are derived and explored the derivation is based on the equation for free standing oscillations and a continuity relation the formulae which are easy to derive and use give the correct external and internal seiche frequencies for nonrotating rectangular one or two layered basins of constant depth when applied to situations with continuous stratification further assumptions need to be introduced these are discussed in the paper applications to a laboratory experiment dealing with wind induced entrainment show that pressure gradients for the entrainment process are significant and that the pressure formulae derived capture this effect the formulae are also used in combination with a one dimensional lake model comparisons with field measurements of the seasonal stratification show that the inclusion of pressure gradients improves the predictive capabilities of the lake model

the feasibility of thermal and compositional convection in earth s inner core inner core convection and the corresponding variations in grain size and alignment has been proposed to explain the complex seismic structure of the inner core including its anisotropy lateral variations and the f layer at the base of the outer core we develop a parametrized convection model to investigate the possibility of convection in the inner core focusing on the dominance of the plume mode of convection versus the translation mode we investigate thermal and compositional convection separately so as to study the end members of the system in the thermal case the dominant mode of convection is strongly dependent on the viscosity of the inner core the magnitude of which is poorly constrained furthermore recent estimates of a large core thermal conductivity result in stable thermal stratification hindering convection however an unstable density stratification may arise due to the pressure dependant partition coefficient of certain light elements we show that this unstable stratification leads to compositionally driven convection and that inner core translation is likely to be the dominant convective mode due to the low compositional diffusivity the style of convection resulting from a combination of both thermal and compositional effects is not easy to understand for reasonable parameter estimates the stabilizing thermal buoyancy is greater than the destabilizing compositional buoyancy however we anticipate complex double diffusive processes to occur given the very different thermal and compositional diffusivities

stability and meromixis in a water filled mine pit a field experiment examined stability and stratification in a disused mine fit filled with 1 75 x lo7 m3 of water vertical profiles of conductivity and temperature indicated that due to substantial chemical stratification spring and autumn overturn did not penetrate to the base of the pit although parameterization indicated that double diffusion should be expected we found only circumstantial evidence of associated step structure the available data suggest that groundwater inflow created a warm salty pool of water at the base of the water column giving the appearance of a meromictic structure with a monimolimnion however this pool was noi a consistent feature suggesting both a variable inflow and significant diffusion rates from the temperature data estimates indicated that hypolimnetic vertical eddy diffusivity varied between 1 x 10e7 and 5 x lo m s l the observations identify short term relatively energetic internal wave events that may have a significant impact on this value the present study is useful in two ways first it shows how pit lakes form a natural laboratory fcr a range of processes and second it illustrates how these processes relate to diffusion paranieterization it is clear that reliable parameterization is vital for long term modeling required for prediction of water quality over decadal timescales with the closure of an open cut mining operation come the dual problems of rehabilitation of the mine pit and containment of deleterious material generated by the mine during its life in many cases the pit fills with water either naturally or through mine activities thus an artificial lake of moderate volume is created davis and ashenberg 1989 characterization of the transport processes within the water column is important for two reasons first the pit is likely to contain hazardous levels of dissolved metals and second if vertical transport rates are low then the pit may prove suitable as a storage location for hazardous material water filled mine pit lakes pit lakes have received consideration in the literature but with a biological or geochemical emphasis e g klapper and schultz 1995 crater lakes are the natural system most similar to these artificial water bodies martin 1985 macintyre and melack 1985 pit lakes are unique for several reasons they are often deep relative to natural lakes of similar surface area they have high surrounding walls that often generate a microclimate different to that outside the pit they typically have very thin sediment layers they may undergo substantial and rapid changes in water level and they are likely to contain significant concentrations of dissolved material the final point is important if the dissolved material is environmentally harmful or if it leads to meromixis with these departures from what might be associated with typical natural lakes

ab initio calculations on the free energy and high p t elasticity of face centred cubic iron ab initio finite temperature molecular dynamics simulations have been used to calculate the free energy and elasticity of face centred cubic fcc iron at a state point representative of the earth s inner core whilst the free energy of this phase is found to be higher than that of hexagonal close packed hcp iron the difference is only 14 mev atom it is possible that this difference might be overcome by the presence of light elements as previous calculations at zero kelvin have shown that the addition of elements such as silicon stabilise fec fe with respect to hcp fe by at least 40 mev atom the calculated elastic constants at core pressures and temperatures of pure fec fe and of alloys of fe with sulphur and nickel fe3s and fe3ni derived from the fee structure lead to average shear wave velocities that are considerably higher than those inferred from seismology however these mineralogical and seismological results could be reconciled by the presence of partial melt in the inner core the calculated p wave anisotropy of fec fe is comparable with the seismological values but only if there is a high degree of crystal alignment although the necessity for alignment can be reduced if a layered model for the inner core is invoked the results presented in this paper therefore suggest that fcc fe cannot be ruled out as a candidate for the dominant phase of the earth s inner core c 2008 elsevier b v all rights reserved

an extraordinary upwelling event in a deep thermally stratified lake 1 a unique combination of temporal and spatial measurements provides a description of an extraordinarily large upwelling event in lake tahoe ca nv the 4 d event which engulfed half of the lake s surface and had an amplitude of 500 m was recorded with in situ and space borne instruments the vertical mixing that ensued was characterized by a large transfer of heat across the thermocline resulting in the replacement of the distinct two layer thermal structure by a diffuse temperature gradient prior to the event mixing energy due to the cooling flux at the surface was two orders of magnitude larger than the mixing energy associated with the wind this dominance by cooling yielded the two layer structure during the event wind energy was of similar magnitude to the cooling energy the large bottom velocities that were produced at the end of the event were sufficient to re suspend sediment into the water column

facies analysis and depositional mechanisms of hydroclastite breccias acicastello eastern sicily abstract hydroclastite beds are interbedded with pillow lavas in an overturned section exposed near acicastello on the ionian coast of sicily two distinct hydroclastite facies are recognized in a continuous 15 m section in a cliff face overlying pillow lavas the first an hyaloclastite facies comprises black hyaloclasts and pillow fragments many of which retain a partial pillow shape and glassy rim in a matrix of smaller partially devitrified and palagonitized hyaloclasts beds of this facies are predominantly inversely graded exhibit both matrix and clast support and commonly contain outsize clasts at or near the bed top beds of the hyaloclastite facies beds are interpreted as the deposits of noncohesive submarine debris flows transporting fragments formed primarily by cooling contraction granulation the second a pillow fragment breccia facies forms wedge shaped beds that are interbedded with the hyaloclastite facies pillow fragment breccias comprise non graded breccias of basalt blocks that formed by spalling of joint blocks from pillow lavas beds of this facies are clast supported and contain a matrix of marly sediment this facies formed by accumulation of pillow fragments along the sides of pillow lava ridges creating wedges of talus which interfinger with the debris flow deposits of the hyaloclastite facies

basin evolution in southern east greenland an outcrop analog for cretaceous paleogene basins on the north atlantic volcanic margins the cretaceous paleogene kangerlussuaq basin in southern east greenland represents a unique outcrop analog for the frontier petroleum provinces along the deep water volcanic margins of the northern north atlantic the 1 km thick sedimentary succession comprises six facies associations 1 alluvial plain and shallow marine late aptian 2 fluvio estuarine late aptian early albian 3 offshore marine late cretaceous early paleocene 4 submarine fan and channel levee early paleocene 5 fluvial mid paleocene and 6 volcanic late paleocene sedimentation was terminated in the late paleocene by extrusion of flood basalts related to continental breakup the basin fill is divided into two depositional megasequences related to regional tectonic events and sea level changes the oldest megasequence sq1 spans the late aptian to the earliest paleocene with sea level rise in the late aptian and maximum flooding in the late albian cenomanian followed by sea level highstand in the late cretaceous early paleocene sq1 is truncated by a basin wide unconformity related to regional uplift and basin reorganization in the mid paleocene the upper megasequence sq2 spans the mid to late paleocene and comprises sediments deposited during early sea level rise extensive volcanic deposits and continental flood basalts overlie it deep burial 6 km and middle eocene early oligocene uplift excludes the kangerlussuaq basin as a petroleum basin in itself however to evaluate the petroleum potential of similar volcanic influenced offshore basins such as the west shetland faeroe more and voring basins we discuss three conceptual play models based on the kangerlussuaq basin 1 early albian stratigraphic trap 2 early paleocene structural trap and 3 paleocene stratigraphic trap

wind driven lateral circulation in a stratified estuary and its effects on the along channel flow 1 in the stratified rotating estuary of chesapeake bay the ekman transport drives a counterclockwise lateral circulation under down estuary winds and a clockwise lateral circulation under up estuary winds looking into estuary the clockwise circulation is about twice as strong as the counterclockwise circulation analysis of the streamwise vorticity equation reveals a balance among three terms titling of the planetary vorticity by vertical shear in the along channel current baroclinic forcing due to sloping isopycnals at cross channel sections and turbulent diffusion the baroclinic forcing is highly asymmetric between the down and up estuary winds while the counter clockwise lateral circulation tilts isopycnals vertically and creates lateral barolinic pressure gradient to oppose the ekman transport under the down estuary wind the clockwise circulation initially flattens the isopycnals and the baroclinic forcing reinforces the ekman transport under the up estuary wind the coriolis acceleration associated with the lateral flows is of the first order importance in the along channel momentum balance it has a sign opposite to the stress divergence in the surface layer and the pressure gradient in the bottom layer thereby reducing the shear in the along channel current compared with the non rotating system the shear reduction is about 30 40 two summary diagrams are constructed to show how the averaged streamwise vorticity and along channel current shear vary with the wedderburn w and kelvin ke numbers

cretaceous palaeogene sub basaltic and intrabasaltic sediments of the kangerdlugssuaq area central east greenland

boundary mixing in a rotating stratified fluid extension d une experience de laboratoire sur le melange en couche limite dans un fluide stratifie pour inclure les effets de rotation la combinaison du melange vertical a la frontiere et du melange horizontal par des tourbillons d echelle moyenne conduit a l affaiblissement du gradient de densite interieur

the oceanic response of the turkish straits system to an extreme drop in atmospheric pressure moorings across all four entry exit sections of the dardanelles strait and the bosphorus strait simultaneously measured the response of the turkish straits system to the passage of a severe cyclonic storm that included an atmospheric pressure drop of more than 30 mbar in less than 48 h the bottom pressure response at the aegean sea side of the dardanelles strait was consistent with an inverted barometer response but the response at the other sections did not follow an inverted barometer leading to a large bottom pressure gradient through the turkish straits system upper layer flow toward the aegean sea was reversed by the storm and flow toward the black sea was greatly enhanced bottom pressure across the sea of marmara peaked 6 h after the passage of the storm s minimum pressure the response on the dardanelles side was a combination of sea elevation and pycnocline depth rise and the response on the bosphorus side was an even greater sea elevation rise and a drop in pycnocline depth the peak in bottom pressure in the sea of marmara was followed by another reverse in the flow through the dardanelles strait as flow was then directed away from the sea of marmara in both straits a simple conceptual model without wind is able to explain fluctuations in bottom pressure in the sea of marmara to a 0 89 0 96 level of correlation this stresses the importance of atmospheric pressure dynamics in driving the mass flux of the turkish strait system for extreme storms

topographically controlled circulation and mixing in a lake it is well known that the wind driven circulation in a wide lake may be controlled by its topography wind stress acting on the smaller mass of the water column in the shallows results in downwind flow there and return flow in the deeper water in lakes with large areas of shallow water this circulation may cause rapid mixing in weakly stratified conditions in more strongly stratified conditions topographically induced horizontal wind driven circulation may influence the vertical stratification of the lake lough mask is about 10 km long and has a maximum width of about 8 km the lake may be divided into shallow eastern and deeper western portions with mean depths of 10 and 35 m respectively in late autumn water at depth in the deep part of the lake moves upwind at speeds of up to 50 cm s 1 in response to axial winds of up to 15 m s 1 at the same location a weaker upwind flow is observed in the near surface water this return flow is topographically driven temperature differences between near surface and near bottom meters were small 20 m surface mixed layer and a cooler layer at depth whose temperature fluctuates in response to wind stress along the axis of the lake modelling results supported by drogue measurements indicate that the return flow associated with axial winds in these summer conditions is confined to the surface mixed layer if this layer is thin shear between the surface layer and the underlying water can be sufficient to cause mixing and a thickening of the surface layer until the richardson number is 1 thus the vertical temperature structure of the deep part of the lake can be influenced by flows driven by the lake topography in the shallow part of the lake there is evidence of thermally driven motion in periods of calm weather in summer

influence of sulfur on the electrical resistivity of a crystallizing core in small terrestrial bodies abstract electrical experiments were performed on core analogues in the fe s system and on fesi2 up to 8 gpa and 1850 c in the multi anvil apparatus electrical resistivity was measured using the four electrode method for all samples resistivity increases with increasing temperature the higher the s content the higher the resistivity and the resistivity increase upon melting at 4 5 gpa liquid fes is up to 10 times more resistive than fe 5 wt s and twice more resistive than fesi2 suggesting a stronger influence of s than si on liquid resistivity electrical results are used to develop crystallization resistivity paths considering both equilibrium and fractional crystallization in the fe s system at 4 5 gpa equilibrium crystallization as expected locally in thin snow zones during top down core crystallization presents electrical resistivity variations from about 300 to 190 microhm cm for a core analogue made of fe 5 wt s depending on temperature fractional crystallization which is relevant to core scale cooling leads to more important electrical resistivity variations depending on s distribution across the core temperature and pressure estimates of the lower bound of thermal resistivity are calculated using the wiedemann franz law comparison with previous works indicates that the thermal conductivity of a metallic core in small terrestrial bodies is more sensitive to the abundance of alloying agents than that of the earth s core application to ganymede using core adiabat estimates from previous studies suggests important thermal resistivity variations with depth during cooling with a lower bound value at the top of the core that can be as low as 3 w m k it is speculated that the generation and sustainability of a magnetic field in small terrestrial bodies might be favored in light element depleted cores

elastic anisotropy in textured hcp iron to 112 gpa from sound wave propagation measurements we report the first experimental determination of elastic anisotropy in highly textured polycrystalline hexagonal closed packed hcp iron obtained at room temperature and 112 gpa by inelastic x ray scattering ixs in a diamond anvil cell dac the compressional sound velocity vp at 50 and 90 from the c axis was determined to be vp 50 9900 200 m s and vp 90 9450 150 m s respectively the difference of 4 5 between the two velocities is of the same order of the seismic observations of the anisotropy in earth s inner core combining our new results with the equation of state of hcp iron we derive the pressure dependence of the shear velocity vs the vs values extrapolated to inner core densities are 30 higher than the prem results the extrapolated vp values are instead in fair agreement with the prem seismic model though differences in the slope remain furthermore assuming a strong texture characterized by cylindrical symmetry we provide an estimate for the single crystal elastic modulus c11 as a function of pressure while our results are in general agreement with the predominant existence of hcp iron in earth s inner core the remaining differences might be assigned to the presence of another solid iron phase light elements or liquid inclusions as well as anharmonic high temperature effects

thermotectonic evolution of a rifted continental margin fission track evidence from the kangerlussuaq area se greenland fission track analyses of apatites from sediments precambrian gneisses and caledonian to tertiary intrusive rocks from the kangerlussuaq region reveal its post caledonian thermotectonic history inland the history involves cooling to temperatures within the high temperature part of the apatite annealing interval and slow cooling or reheating continued in cretaceous times through this interval apatites from coastal areas between kangerlussuaq and tasiilaq reveal only tertiary cooling in tertiary times cooling accelerated after the main intrusive phase in the tertiary the evolution is taken as evidence for a general uplift erosion since caledonian times probably disturbed by basin formation and sedimentation and reheating due to magmatic activity thermal subsidence of the rift shoulders following the opening of the adjacent oceanic basin is not indicated annealing patterns inland of the plume centre in the kangerlussuaq provide no evidence for the earlier movement of the plume from a westerly direction

the elastic properties of hcp fe alloys under the conditions of the earth s inner core abstract geophysical and cosmochemical constraints suggest the inner core is mainly composed of iron with a few percent of light elements however despite extensive studies over many years no single alloying light element has been found that is able to simultaneously match the observed inner core density and both seismic velocities this has motivated a number of suggestions of other mechanism to lower velocities such as anelasticity or premelting however an unexplored possibility is that a combination of two or more light elements might produce the desired reduction in velocities and densities of the inner core in order to test this we use ab initio molecular dynamics calculations to map the elastic property space of hcp fe alloyed with s si and c at 360 gpa up to the melting temperature based on a mixing solid solution model together with direct simulations on the ternaries we found a number of compositions which are able to match the observed properties of the inner core this is the first time that the density v p v s and the poisson s ratio of the inner core have been matched directly with an hcp fe alloy

observations of the lateral structure of wind driven flow in a coastal plain estuary abstract wind stress is one of the main drivers of estuarine circulation the lateral structure of wind induced flows in estuaries has been described mainly with analytical and numerical models the aim of this study is to investigate with observations the lateral structure of wind induced flow in a coastal plain estuary the james river virginia such structure was explored with the first empirical orthogonal function eof1 mode derived from month long moored adcps deployed at two cross sections in the estuary mode 1 explained 53 of the variance and was attributed to wind forcing its lateral structure eigenvectors consisted of upwind flow centered in the channel at middle depth downwind flow over the shoals and a vertically sheared bidirectional flow over the channel slope wavelet coherence analysis showed that along estuary wind was highly coherent with mode 1 coherence squared 0 9 especially at the period band between 4 and 6 days the along estuary wind stress and the temporal variation of mode 1 showed an anti phase coherence with the wind stress leading mode 1 persistently in addition an analytical solution showed a lateral structure similar to the eigenvectors obtained with eof1 the conclusion is that the lateral structure described by eof1 was induced by wind stress and was consistent with analytical and numerical model results these results are among the handful available that confirm the theoretical structure of wind driven flows over laterally varying bathymetry

effects of winds on stratification and circulation in a partially mixed estuary 1 numerical experiments are conducted to investigate how axial winds affect stratification and circulation in the partially mixed estuary of chesapeake bay in the absence of rotational effects stratification in the estuary decreases following both down estuary and up estuary winds but stratification experiences larger reduction and takes longer to recover under up estuary winds in the presence of rotational effects wind driven lateral circulations cause the lateral straining of density field and weaken the shear in the along channel flows under the down estuary winds a counterclockwise lateral circulation steepens isopycnals in the cross channel sections while the coriolis force acting on it decelerates the downwind current in the surface layer and the upwind directed current in the bottom layer under the up estuary winds a clockwise lateral circulation flattens isopycnals in the cross channel sections and reduces the shear between the surface and bottom currents hence in the presence of rotational effects the lateral straining offsets the effects of longitudinal straining such that the asymmetry in stratification reduction is significantly reduced between the down estuary and up estuary winds regime diagrams based on wedderburn w and kelvin ke numbers are constructed to summarize the net effects of winds on estuarine stratification during both wind perturbation and postwind adjustment periods

differential mixing in a stratified fluid we present an experimental and theoretical study of the effects of localized mixing on a stratified fluid contained in a reservoir in the experiments mixing is accomplished by means of a vertically oscillating horizontal grid located near the water surface at one end of the reservoir once the grid is set in motion a mixed layer forms immediately beneath it as this layer deepens a horizontal pressure gradient builds up which drives an outflow of mixed fluid into the unmixed interior of the reservoir this outflow slows and eventually brings to a halt mixed layer deepening under the grid at this equilibrium depth the vertical velocity of the entrainment interface induced by the outflow exactly equals the velocity at which the entrainment interface would move downwards because of mixing this equilibrium state persists until the outflow intrusion is blocked by the far wall of the reservoir at which time deepening resumes under the grid asymptotically the fluid reaches a state in which mixed layer deepening is independent of position

differential cooling drives large scale convective circulation in lake tanganyika field data scaling analysis and three dimensional numerical experiments demonstrate that the dominant large scale circulation pattern during the southeast trade winds in lake tanganyika east africa is a downwind flow in the metalimnion with a returning southward upwind flow in the upper region of the epilimnion this is in the opposite direction to all prior literature available on the lake which has assumed that the southeast trade winds must drive a northward surface flow due to momentum induced by the wind the gradient in wind speed and humidity along the length of the lake and the resulting gradient in heat exchange with the atmosphere result in warm water accumulating at the northern end of the lake the north basin of lake tanganyika thus acts as a heat sink while the south basin is a net source of heat to the atmosphere the resulting variation in buoyancy flux is strong enough to drive a convective flow in the upper layer in the opposite direction to the wind a large scale convective circulation results in an annual exchange of 6 2 1012 m3 of water and an annual net transport of heat averaging 0 2 terawatt from the northern to the southern region of the lake currents in the upper 100 m layer with a mean flow of 0 2 sverdrup and flow speed of 0 08 m s 1 can be described by the superposition of a parallel convective flow with the internal seiche motion

internal hydraulic jumps in a long narrow lake high resolution three dimensional numerical modeling and field observations were used to describe the nonlinear response of cayuga lake to surface wind forcing the degeneration of the basin scale internal wave field was characterized according to the composite froude number g2 wedderburn number wn and lake number ln which are measures of hydraulic control and bulk and integral wind disturbance force to the baroclinic restoring force respectively the typical cayuga lake response was a nonlinear surge when 1 1 in a lake the occurrence of the hydraulic jump was correctly predicted using scaling parameters it was also shown that topographically induced internal hydraulic jumps form when the nonlinear surges interact with a sill contraction topographic feature in contrast to published literature the observed high frequency nonlinear internal waves were preferentially associated with internal jumps as opposed to steepened internal surges computed vertical diffusivities showed mixing was enhanced by two orders of magnitude within both the surges and hydraulic jumps as they propagated through the basin and interacted with topography our results can be generalized to other lakes and fjords with similar long narrow geometry and topographically separate side basins

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

the elastic properties of hcp fe1 xsix at earth s inner core conditions the density of the earth s inner core is less than that of pure iron and the p wave velocities and particularly the s wave velocities in the inner core observed from seismology are lower than those generally obtained from mineral physics on the basis of measurements of compressional sound velocities to 100 gpa in diamond anvil cells extrapolated to inner core pressures it has been suggested that both the inner core density and p wave velocity can be matched simultaneously by the properties of a hexagonal close packed hcp fe si or fe ni si alloy in this paper we present the results of ab initio molecular dynamics simulations of hcp fe si alloys at 360 gpa and at temperatures up to melting we find that although the inner core density can be readily matched by an fe si alloy the same is not true for the wave velocities at inner core temperatures the p wave velocity in hcp fe si remains equal to or slightly above that of hcp fe and shows little change with silicon content the s wave velocity is reduced with respect to that of pure hcp iron except for temperatures immediately prior to melting where the velocities are almost equal this is a consequence of the fact that the strong temperature dependence of the shear modulus that was seen in similar simulations of hcp fe just prior to melting was not found in hcp fe si and so in this temperature range the reduced s wave velocity of pure iron closely matches that of the alloy our results show that for an hcp fe si alloy matching the inner core density both the p wave and the s wave velocities will be higher than those observed by seismology and we conclude therefore that our calculations indicate that inner core velocities cannot be explained by an hcp fe si alloy the opposite conclusion obtained previously from experimental data measured at lower pressures is a consequence of i the necessarily large extrapolation in pressure and temperature required to extend the experimental results to inner core conditions and ii the use of a velocity density relationship for pure hcp iron that is now considered to be incorrect

katabatic wind driven exchange in fjords the general issue of katabatic wind driven exchange in fjords is considered using an idealized numerical model theory and observations two regimes are identified for fjords narrower than a viscous boundary layer width the exchange is limited by a balance between wind and friction in lateral boundary layers for the nonlinear viscous parameterization used here this boundary layer thickness depends on the properties of the fjord such as stratification and length as well as on the wind stress and numerical parameters such as grid spacing and an empirical constant for wider fjords typical of east greenland the balance is primarily between wind the along fjord pressure gradient and acceleration in general agreement with previous two layer nonrotating theories it is expected that o 10 of the surface layer will be flushed out of the fjord by a single wind event application of the idealized model to a typical katabatic wind event produces outflowing velocities that are in general agreement with observations in sermilik fjord the presence of a sill has only a minor influence on the exchange until the sill penetrates over most of the lower layer thickness in which cases the exchange is reduced it is concluded that the multiple katabatic wind events per winter that are experienced by the fjords along east greenland represent an important mechanism of exchange between the fjord and shelf with implications for the renewal of warm salty waters at depth and for the export of glacial freshwater in the upper layer

composition of the earth s inner core from high pressure sound velocity measurements in fe ni si alloys article i nfo we performed room temperature sound velocity and density measurements on a polycrystalline alloy fe0 89ni0 04si0 07 in the hexagonal close packed hcp phase up to 108 gpa over the investigated pressure range the aggregate compressional sound velocity is 9 higher than in pure iron at the same density the measured aggregate compressional vp and shear vs sound velocities extrapolated to core densities and corrected for anharmonic temperature effects are compared with seismic profiles our results provide constraints on the silicon abundance in the core suggesting a model that simultaneously matches the primary seismic observables density p wave and s wave velocities for an inner core containing 4 to 5 wt of ni and 1 to 2 wt of si

mixed layer dynamics in a lake exposed to a spatially variable wind field1 field measurements are described detailing the formation of frontal structures in the surface mixed layer near the entrance of an embayment in a medium sized lake the observed evolution of the fronts is interpreted in terms of three well defined dynamical regimes the first differential heating is defined as the variable heat capture due to decreased surface heat losses and warmer surface water in the sheltered embayments the second variable deepening of the mixed layer is induced by a sudden increase in wind speed in the open central areas of the lake with only minimal mixing in the sheltered parts of the lake the third is the horizontal gravitational motion driven by the horizontal density gradients set up by the active deepening of the mixed layer in the exposed parts of the lake although detailed wind data were not available observations of the temperature and salinity fields show the existence of fronts in lakes and strongly suggest the importance of the above mechanisms in determining the horizontal variability of these fields in the surface mixed layer of medium sized lakes

ab initio calculations of the elasticity of iron and iron alloys at inner core conditions evidence for a partially molten inner core abstract ab initio finite temperature molecular dynamics simulations have been used to calculate the elasticity of hcp fe bcc fe fes and fesi at core conditions the calculated compressional wave velocities are in excellent agreement with the most recent experimental data however the calculated shear wave velocities of all phases studied are significantly higher than those inferred from seismology this discrepancy can only be explained if the inner core is partially molten containing more than 8 liquid

constraints from material properties on the dynamics and evolution of earth s core the material properties of the earth s core have been better constrained by recent technical and computational advances the properties imply that the core was once hot but is cooling quickly and the inner core is young

configurational thermodynamics of fe ni alloys at earth s core conditions by means of ab initio calculations we perform an analysis of the configurational thermodynamics effects of disorder and structural energy differences in fe ni alloys at the pressure and temperat

the existence of radial anisotropy in earth s upper inner core revealed from seismic normal mode observations as we strive to understand the most remote region of our planet one critical area of investigation is the uppermost inner core since its structure is related to solidification of outer core material at the inner core boundary icb previous seismic studies have used body waves to show that the top 100 km of the inner core is isotropic however radial anisotropy cannot be uniquely determined by body wave observations alternatively normal mode center frequencies are sensitive to spherically symmetric earth structure therefore may provide a constraint on the existence of radial anisotropy in the inner core here we show that normal mode center frequency measurements are compatible with 2 5 radial anisotropy in the top 100 km of the inner core with a fast direction radially outward and a slow direction along the icb given the uncertainties in the mineral physics and processes that produce anisotropy the observed radial anisotropy may be reconciled with predictions based on either solidification processes or from texturing due to anisotropic growth

numerical simulation of coastal upwelling and inerfacial instability of a rotaion and stratified fluid the evolution of the coastal upwelling and interfacial instability of a stratified and rotating fluid is studied numerically by using large eddy simulation upwelling is generated near the sidewall of a rotating annulus by the shear at the top the fluid initially consists of a stably stratified two layer structure with a narrow interface separating the two layers the large scale motion of the flow is simulated by solving the time dependent non hydrostatic incompressible navier stokes and scalar transport equations while the small scale motion is represented by a dynamic subgrid scale model the upwelling process contains both stable and unstable stratification the vertical structure of upwelling consists of a persistent primary front a trailing mixing zone on the shore side of the front and a temporary secondary front which leads a top inversion layer the longshore velocity profile has two maxima which occur at the edge of the sidewall boundary layer and at the density front the upwelled density front is unstable to azimuthal perturbations and baroclinic waves develop and grow to large amplitude pairs of cyclonic and anticyclonic waves appear at the front which form jet streams the secondary front is unstable to azimuthal perturbations its instability and the associated drop of the top inversion layer take the form of radial bands which subsequently break up into isolated patches and eventually sink the computed values of various upwelling time and length scales are compared to and are in good agreement with past experimental data

shear wave anisotropy of textured hcp fe in the earth s inner core abstract many seismological studies have confirmed that vp travels 3 4 faster along the rotation axis of the earth than along the equatorial plane in the inner core indicating that the inner core is elastically anisotropic however seismic and mineral physics observations of the polarized vs are still emerging thus far the vs anisotropy of the constitute iron crystals at relevant pressures of the earth s core has remained mostly theoretical mainly because of the technical difficulties involved in measuring reliable vs velocities of iron crystals here we have measured azimuthal vs anisotropy of highly textured hcp fe at high pressures using nuclear resonant inelastic x ray scattering a technique sensitive to vs in a diamond anvil cell our results show that the azimuthal vs is 2 4 faster along the crystallographic c axis than along the a axis at 158 gpa and 172 gpa if one describes the vp anisotropy of the inner core as a result of the textured hcp fe crystals it is conceivable that azimuthal and polarized vs anisotropies with a magnitude of a few percent also exist in the region since vp and vs of candidate iron phases behave quite differently in theoretical predictions our results here indicate that future seismic observations of the vs and vp anisotropies of the inner core thus hold the key to deciphering the causes for the seismic and dynamic signatures as well as constitute iron phase s of the region

subtidal hydrodynamics in a tropical lagoon a dimensionless numbers approach abstract observations in a tropical lagoon of the yucatan peninsula motivated a non dimensional number analysis to examine the relative influence of tidal stress density gradients and wind stress on subtidal hydrodynamics a two month observation period in chelem lagoon covered the transition from the dry to the wet season chelem lagoon is influenced by groundwater inputs and exhibits a main sub basin central sub basin a west sub basin and an east sub basin subtidal hydrodynamics were associated with horizontal density gradients that were modified seasonally by evaporation precipitation and groundwater discharge a tidal froude number fr 0 a wedderburn number w and a stress ratio s 0 were used to diagnose the relative importance of dominant subtidal driving forces the froude number fr 0 compares tidal forcing and baroclinic forcing through the ratio of tidal stress to longitudinal baroclinic pressure gradient the wedderburn number w relates wind stress to baroclinicity the stress ratio s 0 sizes tidal stress and wind stress s 0 is a new diagnostic tool for systems influenced by tides and winds and represents the main contribution of this research results show that spring tide subtidal flows in the tropical lagoon had log fr 0 0 and log s 0 0 i e driven mainly by tidal stresses advective accelerations neap tides showed log fr 0 0 and log s 0 0 i e flows driven by baroclinicity especially at the lagoon heads of the east and west sub basins however when the wind stress intensified over the lagoon the relative importance of baroclinicity decreased and the wind stress controlled the dynamics log w 0 each sub basin exhibited a different subtidal response according to the dimensionless numbers the response depended on the fortnightly tidal cycle the location and magnitude of groundwater input and the direction and magnitude of the wind stress

ab initio elasticity and thermal equation of state of mgsio3 perovskite we have used high temperature ab initio molecular dynamic simulations to study the equation of state of orthorhombic mgsio3 perovskite under lower mantle pressure temperature conditions we have determined the gru neisen parameter q as a function of volume our state of the art simulations accurate to within 10 resolve the long standing controversy on thermal expansion k and gru neisen parameter of mgsio3 perovskite under ambient conditions we find the values for k and q of 1 86u10 35 k 31 and 1 51 respectively in excellent agreement with the latest experimental studies calculated elastic constants and the static equation of state at 0 k agree well with previous simulations we have found no evidence for the high temperature phase transitions of orthorhombic mgsio3 perovskite to cubic or tetragonal phases at mantle temperatures fl 2001 elsevier science b v all rights reserved

observed flow variability along the thalweg and on the coastal slopes of the gulf of finland baltic sea abstract bottom mounted adcp measurements from 10 installations collected between 2009 and 2014 and each lasting several months are analysed in order to distinguish between different flow regimes and to detect variability a along the thalweg of the elongated basin with different regimes in summer and in winter and b on the coastal slopes in the deep thalweg area the mean flow speed amounts to 6 13 cm s 1 whereas the maximum speeds appear in winter near the bottom of the basin and in summer within the halocline around 70 m depth the mean zonal flow component reveals a nearly depth uniform inflow during winter and a layered inflow outflow during summer in years where up estuary w to sw winds are stronger during the summer inflow dominates in upper layers and anti estuarine outflow dominates in deeper layers this causes the export of a salt wedge and the weakening of haline stratification infra low frequency zonal currents i e excluding topographic waves etc with periods of less than 10 days have a structure which is uniform with depth for 53 of the time in winter in summer a layered structure is present 65 of the time however during both periods the reversed estuarine flow inflow in upper layers and outflow in the bottom layer appears on average for 30 of the time the deep flow zonal component is well correlated with westward winds during summer r 0 84 and south westward winds during winter r 0 77 on the coastal slopes the speed of the currents are lower than in the thalweg region and they decay with depth in the vertical the flow exhibits a layered structure in both the winter and summer seasons

wind driven upwelling in opunohu bay moorea french polynesia abstract opunohu bay is a narrow straight 3 km long bay on the island of moorea french polynesia the bay is open to the ocean with a water depth of about 80 m at the mouth the sea floor slope reaches one third offshore field observations show that a wind blowing to offshore along the axis of the bay generates an outflow at the surface and an inflow below 20 m depth a localized upwelling results at the mouth of the bay which may also be detected in the phytoplankton population this situation is modelled numerically and the results suggest that the wind stress must be taken to be not only a function of the wind speed but also of the wind fetch

ab initio calculations of the elasticity of hcp fe as a function of temperature at inner core pressure ab initio finite temperature molecular dynamics simulations have been used to calculate the elastic constants of hexagonal close packed hcp fe as a function of temperature at similar to 300 gpa the longitudinal modulus c 1 1 decreases with temperature in stark contrast to previous calculations but in agreement with experimental observations on other transition metals at ambient pressures c 33 and c 44 also decrease with temperature while c 12 and c 23 slightly increase when these moduli are used to calculate p wave velocities through the crystal the sense of the anisotropy is such that v p is fastest along the c axis up to 5000 k however by 5500 k the anisotropy reverses with v p becoming faster in the a b plane this suggests that for an inner core dominated by crystals of hcp fe aligned with the c axis in the polar direction the observed isotropic outer inner core could result from the hcp fe being at a temperature close to melting where the axial wave velocities parallel and perpendicular to the c axis become similar while at greater depths in the inner inner core where iron is further from melting stronger anisotropy is achieved with the faster p wave velocities parallel to the polar axis no other mechanisms such as changes in composition or crystal alignment are therefore required to account for the observed change in seismic anisotropy of the earth s inner core with depth c 2009 elsevier b v all rights reserved

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

high pressure elastic properties of major materials of earth s mantle from first principles the elasticity of materials is important for our understanding of processes ranging from brittle failure to flexure to the propagation of elastic waves seismologically revealed structure of the earth s mantle including the radial one dimensional profile lateral heterogeneity and anisotropy are determined largely by the elasticity of the materials that make up this region despite its importance to geophysics our knowledge of the elasticity of potentially relevant mineral phases at conditions typical of the earth s mantle is still limited measuring the elastic constants at elevated pressure temperature conditions in the laboratory remains a major challenge over the past several years another approach has been developed based on first principles quantum mechanical theory first principles calculations provide the ideal complement to the laboratory approach because they require no input from experiment that is there are no free parameters in the theory such calculations have true predictive power and can supply critical information including that which is difficult to measure experimentally a review of high pressure theoretical studies of major mantle phases shows a wide diversity of elastic behavior among important tetrahedrally and octahedrally coordinated mg and ca silicates and mg ca al and si oxides this is particularly apparent in the acoustic anisotropy which is essential for understanding the relationship between seismically observed anisotropy and mantle flow the acoustic anisotropy of the phases studied varies from zero to more than 50 and is found to depend on pressure strongly and in some cases nonmonotonically for example the anisotropy in mgo decreases with pressure up to 15 gpa before increasing upon further compression reaching 50 at a pressure of 130 gpa compression also has a strong effect on the elasticity through pressure induced phase transitions in several systems for example the transition from stishovite to cacl2 structure in silica is accompanied by a discontinuous change in the shear s wave velocity that is so large 60 that it may be observable seismologically unifying patterns emerge as well eulerian finite strain theory is found to provide a good description of the pressure dependence of the elastic constants for most phases this is in contrast to an evaluation of birch s law which shows that this systematic accounts only roughly for the effect of pressure composition and structure on the longitudinal p wave velocity the growing body of theoretical work now allows a detailed comparison with seismological observations the athermal elastic wave velocities of most important mantle phases are found to be higher than the seismic wave velocities of the mantle by amounts that are consistent with the anticipated effects of temperature and iron content on the p and s wave velocities of the phases studied an examination of future directions focuses on strategies for extending first principles studies to more challenging but geophysically relevant situations such as solid solutions high temperature conditions and mineral composites

dynamics of wind driven circulation in a shallow lagoon with strong horizontal density gradient 1 albemarle pamlico sound aps is a shallow lagoonal estuary with weak stratification but strong horizontal density gradient idealized and realistic model simulations are conducted to examine the dynamics of wind driven circulation in aps two dimensionless parameters the ekman ek and wedderburn w numbers are found to be two key parameters in controlling the flow pattern and dynamics circulation in albemarle sound and northern pamlico sound is primarily driven by wind forcing and shows laterally sheared flows withek approaching 1 and wexceeding 1 analysis of the along channel momentum equation shows a balance among the wind stress barotropic pressure gradient due to sea level setup and bottom friction while the vertical vorticity is primarily determined by the balance between the wind stress curl and bottom stress curl in contrast circulation in southern pamlico sound is driven by both wind and gravitational forces and shows vertically sheared two layer flows with lowek and waround 1 both baroclinic and barotropic pressure gradients act against the wind stress to drive the two layer flows a regime diagram in the parameter space ofek and w is used to summarize variability of circulation pattern on the seasonal time scale northern pamlico sound is characterized by high ek and high w values and laterally sheared currents southern pamlico sound is usually characterized by low ek and low w values and vertically sheared flows but featuring laterally sheared flows during the fall when ek averages to over 0 5

a parametric study of the generation and degeneration of wind forced long internal waves in narrow lakes the generation and energy downscaling of wind forced long internal waves in strongly stratified small to medium sized narrow lakes are studied a two layer nonlinear model with forcing and damping is employed even though the wave field is fundamentally bidirectional in nature a domain folding technique is employed to simulate the leading order internal wave field in terms of a weakly nonlinear weakly dispersive model equation of korteweg devries type parametric effects of wind forcing and environmental conditions including variable topography and variable basin width are examined energy downscaling from basin scale waves to shorter scales are quantified by means of a time evolution of the wave energy spectra it is demonstrated that an internal wave resonance is possible when repetitive wind forcing events arise with a frequency near the linear seiche frequency an attempt is made to apply the model to describe the shoaling of long waves on sloping endwall boundaries modelling of the energy loss and energy reflection during a shoaling event is calibrated against laboratory experiments

ab initio simulations of iron nickel alloys at earth s core conditions we report ab initio density functional theory calculations on iron nickel fe ni alloys at conditions representative of the earth s inner core we test different concentrations of ni up to 39 wt using ab initio lattice dynamics and investigate the thermodynamic and vibrational stability of the three candidate crystal structures bcc hcp and fcc first of all at inner core pressures we find that pure fe transforms from the hcp to the fcc phase at around 6000 k secondly in agreement with low pressure experiments on fe ni alloys we find the fcc structure is stabilised by the incorporation of ni under core pressures and temperatures our results show that the fcc structure may therefore be stable under core conditions depending on the temperature in the inner core and the ni content lastly we find that within the quasi harmonic approximation there is no stability field for fe ni alloys in the bcc structure under core conditions

undercurrent driven upwelling in the northwestern arafura sea a three dimensional process oriented model is applied to explore the circulation in the arafura sea during the southeasterly monsoon during this period widespread phytoplankton blooms develop in a large area 300 km 300 km in the northwestern arafura sea the model findings indicate that undercurrents are the principal source of nutrient rich banda sea slope water for the region it is demonstrated that these undercurrents operate to flush the northwestern arafura sea with banda sea slope water on a time scale of 1 3 months which is consistent with observational evidence the simulated undercurrents are the signature of the classical lee effect frequently observed in lakes that comes into play in the arafura sea given its bay like geometry shallow water depth 40 50 m and close vicinity to the equator it is also shown that density stratification and rotational effects have important influences on the pathway and intensity of the overturning circulation in the northwestern arafura sea which needs to be further explored in the future

mixed layer deepening in lakes after wind setup laboratory experiments on wind driven mixed layer deepening in a wind flume are described for the situation where the wind shear stress has become balanced by a streamwise pressure gradient so that the mean mixed layer velocity has vanished the results were obtained at two lengths of the flume and include visual observations entrainment rates density profiles velocity profiles and profiles of turbulence intensities an intermediate upwind wedge formed by accumulation of mixed water was observed in all experiments the entrainment law obtained agrees with kraus and turner s relationship and is almost independent of the length of the flume

the transition from sedimentation to flood volcanism in the kangerlussuaq basin east greenland basaltic pyroclastic volcanism during initial palaeogene continental break up primary basaltic pyroclastic deposits compose volumetrically c 35 50 of the lower palaeogene vandfaldsdalen mikis and haengefjeldet formations within the lower volcanic series of the east greenland flood basalt province the eruption and emplacement mechanisms of these deposits can be used to evaluate the volcanotectonic evolution of continental break up and initiation of flood basalt volcanism we present a revised stratigraphy for the pre volcanic sedimentary rocks and synvolcanic pyroclastic and epiclastic deposits and lavas from the kangerlussuaq basin east greenland primary basaltic pyroclastic deposits range from airfall tuffs to bomb beds surge deposits and vent sites with cinder cones early volcanism was apparently restricted to localized basins and formed shield volcano structures 30 40 km in diameter that are characterized by a heterogeneous sequence of intercalated hyaloclastites sediments pyroclastic deposits and lavas the lateral variation of deposit morphology reflects distance from source and indicates a migrating locus of volcanism along the axis of rifting towards the ne paired with continued down dropping of inactive volcanic centres the complex stratigraphic architecture of the initial volcanic deposits reflects local tectonic and sedimentary processes interacting with regional flood basalt volcanism and continental rifting

an observation of pkjkp inferences on inner core shear properties the seismic phase pkjkp which traverses the inner core as a shear wave and would provide direct evidence for its solidity has been difficult to detect using stacked broadband records from the grafenberg array in germany we documented a high signal to noise phase the arrival time and slowness of which agree with theoretical predictions for pkjkp the back azimuth of this arrival is also consistent with predictions for pkjkp as is the comparison with a pseudoliquid inner core model envelope modeling of the pkjkp waveform implies a shear velocity gradient with depth in the inner core that is slightly larger than that in the preliminary reference earth model

dynamic response of the fluid mud to a tropical storm fluidmud fm isauniquesedimentaryfeatureinhigh turbidityestuaries whereitcanmake a rapid contribution to morphodynamics insuf cient eld measurements and xed point monitoring lead to de cient understandings of the formation transport and breakdown of the fm under extreme weather conditions a eld survey was conducted in the changjiang estuary during the period of turbidity maximum just after typhoon haikui the measurements captured the formation of the fm beneath the suspended layers particularly around the lower reach of the north passage the thickness of the observed fm gradually decreased landward along the channel with the maximum value reaching 0 9 m the major features of the observed storm induced fm were simulated using the finite volume community ocean model the results indicated that the initial appearance of the fm was the result of a typhoon intensi ed salinity induced strati cation in the outlet region the subsequent landward propagation of the fm was driven by the combined effects of the fm induced mud surface pressure gradient force and saltwater intrusion near the bottom weak mixing during the subsequent neap tidal period sustained the fm as it rapidly extended into the middle region of the north passage this produced a large velocity shear at the interface of the fm and upper suspension layer increasing the entrainment from the fm to the upper suspensionlayer asaresultoftheincreasedtidalmixing thefmweakenedandthen nallybrokedownin the subsequent spring tidal period

wind forced motions in stratified lakes and their effect on mixed layer shear the solution for the response of a rectangular n layered stratified lake to an arbitrarily varying in time wind stress is presented the case n 3 is considered in detail for a three layered lake the response is made up of the individual responses of one external and two internal modes when the upper layer is shallow relative to the other two layers the mixed layer shear is due almost entirely to the slower second mode response moreover the upper interface can tilt quite severely while the lower interface remains nearly flat calculations based on the three layer model are compared with measurements made in wellington reservoir western australia

constraints on grain size and stable iron phases in the uppermost inner core from multiple scattering modeling of seismic velocity and attenuation we propose to model the uppermost inner core as an aggregate of randomly oriented anisotropic patches a patch is defined as an assemblage of a possibly large number of crystals with identically oriented crystallographic axes this simple model accounts for the observed velocity isotropy of short period body waves and offers a reasonable physical interpretation for the scatterers detected at the top of the inner core from rigorous multiple scattering modeling of seismic wave propagation through the aggregate we obtain strong constraints on both the size and the elastic constants of iron patches we perform a systematic search for iron models compatible with measured seismic velocities and attenuations an iron model is characterized by its symmetry cubic or hexagonal elastic constants and patch size independent of the crystal symmetry we infer a most likely size of patch of the order of 400 m recent it bcc iron models from the literature are in very good agreement with the most probable elastic constants of cubic crystals found in our inversion our study 1 suggests that the presence of melt may not be required to explain the low shear wavespeeds in the inner core and 2 supports the recent experimental results on the stability of cubic iron in the inner core at least in its upper part

the effect of nickel on the properties of iron at the conditions of earth s inner core ab initio calculations of seismic wave velocities of fe ni alloys abstract we have performed athermal periodic plane wave density functional calculations within the generalised gradient approximation on the bcc fcc and hcp structures of fe 1 x ni x alloys x 0 0 0625 0 125 0 25 and 1 in order to obtain their relative stability and elastic properties at 360 gpa and 0 k for the hcp structure using ab initio molecular dynamics we have also calculated the elastic properties and wave velocities for x 0 0 0625 and 0 125 at 360 gpa and 5500 k with further calculations for x 0 and 0 125 at 360 gpa and 2000 k at 0 k the hcp structure is the most stable for x 0 0 0625 0 125 and 0 25 with the fcc structure becoming the most stable above x 0 45 the bcc structure is not the most stable phase for any composition at 0 k compressional and shear wave velocities are structure dependent in the case of fcc the velocities are very similar to pure fe but for the hcp structure the addition of ni strongly reduces v s ni also reduced velocities in fcc iron but to a lesser extent however at 5500 k and 360 gpa ni has little effect on the wave velocities of the hcp structure which remain similar to those of pure iron throughout the range of compositions studied and in the case of v s 30 greater than that from seismological models the effect of temperature on fe ni alloys is therefore very significant indicating that conclusions based on the extrapolation of results obtained at much lower temperatures must be treated with great caution the significance of temperature is confirmed by the additional simulation at 2000 k for x 0 and 0 125 which reveals a remarkably linear temperature dependence of the change in v s relative to that of pure iron at 0 k the maximum anisotropy in v p is found to be only very weakly dependent on nickel content but dependent on structure being 15 for fcc and 8 for hcp for the hcp structure at 2000 and 5500 k the maximum anisotropy in v p is also 8 and almost independent of the ni content we conclude that ni can safely be ignored when considering its effect on the seismic properties of hcp fe under core pressures and temperatures and that the negligible effect of nickel on the physical properties of iron in the core arises not because of the chemical similarities between iron and nickel but because of the high temperature of the system

phase relations of iron and iron nickel alloys up to 300 gpa implications for composition and structure of the earth s inner core abstract we have investigated the phase relations of iron and iron nickel alloys with 18 to 50 wt ni up to over 300 gpa using a laser heated diamond anvil cell the synchrotron x ray diffraction measurements show the wide stability of hcp iron up to 301 gpa and 2000 k and 319 gpa and 300 k without phase transition to dhcp orthorhombic or bcc phases on the other hand the incorporation of nickel has a remarkable effect on expanding the stability field of fcc phase the geometry of the temperature composition phase diagram of iron nickel alloys suggests that the hcp fcc liquid triple point is located at 10 to 20 wt ni at the pressure of the inner core boundary the fcc phase could crystallize depending on the nickel and silicon contents in the earth s core both of which are fcc stabilizer