salinity driven thermocline transients in a wind and thermohaline forced isopycnic coordinate model of the north atlantic abstract an isopycnic coordinate oceanic circulation model formulated with the aim of simulating thermodynamically and mechanically driven flow in realistic basins is presented special emphasis is placed on the handling of diabatic surface processes and on thermocline ventilation the model performance is illustrated by a 30 year spinup run with coarse horizontal resolution 2 mesh in a domain with north atlantic topography extending from 10 to 60 n latitude the vertical structure encompasses 10 isopycnic layers in steps of 0 2 units capped by a thermodynamically active mixed layer from an initially isohaline state with isopycnals prescribed by zonally averaged climatology the model is forced by seasonally varying wind stress radiative and freshwater fluxes and by a thermal relaxation process at the surface after a mechanical spinup time of about 15 years a quasi stationary pattern of mean circulation and annual variability ensues characterized by pronounced subtropical mode water formation

a vertically flow following icosahedral grid model for medium range and seasonal prediction part i model description abstracta hydrostatic global weather prediction model based on an icosahedral horizontal grid and a hybrid terrain following isentropic vertical coordinate is described the model is an extension to three spatial dimensions of a previously developed icosahedral shallow water model featuring user selectable horizontal resolution and employing indirect addressing techniques the vertical grid is adaptive to maximize the portion of the atmosphere mapped into the isentropic coordinate subdomain the model best described as a stacked shallow water model is being tested extensively on real time medium range forecasts to ready it for possible inclusion in operational multimodel ensembles for medium range to seasonal prediction

mantle discontinuities and temperature under the north american continental keel a ubiquitous feature of upper mantle seismic velocity models has been the presence of high velocity keels beneath stable continental interiors1 2 3 4 5 uncertainty remains however regarding the maximum depth to which continental keels extend the degree to which they have cooled the mantle that surrounds them and their role in mantle flow here we investigate thermal anomalies across the eastern margin of the north american continental keel by imaging the seismic discontinuities at depths of 410 and 660 km with compressional to shear converted waves recorded by a 1 500 km long seismometer deployment in the eastern united states the thickness of the transition zone the region nominally between depths of 410 and 660 km and the depth to the 410 km discontinuity indicate that cold keel material and sub keel downwellings must be largely confined to the upper mantle and may impinge on the transition zone only in localized regions and with thermal anomalies of less than 150 k a 20 km depression of the 660 km discontinuity to the south of the westernmost stations coincides with a region of fast velocity in the deep transition zone2 and may be associated with the remnants of the subducted farallon plate1 2 4

simulated variability of the atlantic meridional overturning circulation to examine the multi annual to decadal scale variability of the atlantic meridional overturning circulation amoc we conducted a four member ensemble with a daily reanalysis forced medium resolution global version of the isopycnic coordinate ocean model micom and a 300 years integration with the fully coupled bergen climate model bcm the simulations of the amoc with both model systems yield a long term mean value of 18 sv and decadal variability with an amplitude of 1 3 sv the power spectrum of the inter annual to decadal scale variability of the amoc in bcm generally follows the theoretical red noise spectrum with indications of increased power near the 20 years period comparison with observational proxy indices for the amoc e g the thickness of the labrador sea water the strength of the baroclinic gyre circulation in the north atlantic ocean and the surface temperature anomalies along the mean path of the gulf stream shows similar trends and phasing of the variability indicating that the simulated amoc variability is robust and real mixing indices have been constructed for the labrador the irminger and the greenland iceland norwegian gin seas while convective mixing in the labrador and the gin seas are in opposite phase and linked to the nao as observations suggest the convective mixing in the irminger sea is in phase with or leads the labrador sea newly formed deep water is seen as a slow anomalous cold and fresh plume flowing southward along the western continental slope of the atlantic ocean with a return flow of warm and saline water on the surface in addition fast travelling topographically trapped waves propagate southward along the continental slope towards equator where they go east and continue along the eastern rim of the atlantic for both types of experiments the northern hemisphere sea level pressure and 2 m temperature anomaly patterns computed based on the difference between climate states with strong and weak amoc yields a nao like pattern with intensified icelandic low and azores high and a warming of 0 25 0 5 c of the central north atlantic sea surface temperature sst the reanalysis forced simulations indicate a coupling between the labrador sea water production rate and an equatorial atlantic sst index in accordance with observations this coupling is not identified in the coupled simulation

circulation characteristics in three eddy permitting models of the north atlantic a systematic intercomparison of three realistic eddy permitting models of the north atlantic circulation has been performed the models use different concepts for the discretization of the vertical coordinate namely geopotential levels isopycnal layers terrain following sigma coordinates respectively although these models were integrated under nearly identical conditions the resulting large scale model circulations show substantial differences the results demonstrate that the large scale thermohaline circulation is very sensitive to the model representation of certain localised processes in particular to the amount and water mass properties of the overflow across the greenland scotland region to the amount of mixing within a few hundred kilometers south of the sills and to several other processes at small or sub grid scales the different behaviour of the three models can to a large extent be explained as a consequence of the different model representation of these processes

simulation of the atlantic circulation with a coupled sea ice mixed layer isopycnal general circulation model part i model description abstract a diabatic ocean general circulation model based on primitive equations is described it uses isopycnals as lagrangian coordinates in the vertical and predicts a free surface prognostic fields of temperature and salinity enter the dynamics as active tracers through a realistic equation of state the surface boundary layer is parameterized by a detailed mixed layer model a sea ice model with a viscous plastic rheology is coupled to the mixed layer thermal forcing wind stress and surface input of turbulent kinetic energy are determined from monthly mean values of atmospheric quantities while the freshwater flux still is parameterized by a newtonian relaxation towards the observed surface salinity the model equations are written in layer formulation each interface represents an isopycnal as the equations are written in flux form the mass flux and the content of mass heat and salt are conserved in the model domain a potential vorticity conserving scheme is included except for the mixed

variability of the denmark strait overflow a numerical study mesoscale variability in the denmark strait overflow is investigated using a version of the miami isopycnic coordinate ocean model that includes a recently developed intermittent and vigorous turbulent and diffusive diapycnal mixing scheme earlier idealized modeling work on the subject is further extended in that a realistic replica of the shelf slope topography and irregular coastline geometry of the denmark strait area is also employed compared with earlier studies our experiments reveal that 1 the introduction of the new diapycnal scheme and the true shelf slope topography do not affect the formation of the intense cyclonic eddies south of the sill and along the continental slope and 2 the new diapycnal scheme has a significant effect on the bottom plume in that the distribution volume transport and properties of the bottom plume appear to be more realistic and more in line with what is observed the first conclusion adds support to the vortex stretching mechanism suggested in earlier studies as the cause for the formation of the cyclonic eddies this mechanism is therefore a robust feature and provides an explanation for the observed variability in the denmark strait overflow the second conclusion underscores the importance of including realistic parameterizations of diapycnal mixing in isopycnal coordinate ocean models specifically the results show that the water that descends along the bottom south of the sill becomes lighter and is more voluminous compared to experiments without the new mixing scheme even when including the mixing scheme the bottom plume separates into distinct boluses of enhanced thickness moreover these boluses are also associated with water of anomalously high density as well as with the cyclonic eddies in the upper water column

response of the overturning circulation to high latitude fresh water perturbations in the north atlantic studies have suggested that sea ice cover east and west of greenland fluctuates out of phase as a part of the atlantic decadal climate variability and greater changes are possible under global warming conditions in this study the response of the atlantic meridional overturning circulation moc to the distribution of surface fresh water flux is explored using a global isopycnal ocean model an arctic ice related fresh water flux of 0 1 sv entering the nordic seas is shown to reduce the maximum overturning by 1 to 2 sv 106 m3 s 1 a further decrease of 3 to 5 sv in the moc is observed when the fresh water flux is shifted from the fram strait to the southern baffin bay area surprisingly the salinity in much of the upper nordic seas actually increases when the arctic fresh water source is the strongest there as a result of enhanced global overturning it reflects the great influence of labrador sea convection on this model s moc by applying a weaker surface fresh water transport perturbation 0 02 sv on the baffin bay area and therefore perturbing the labrador sea water lsw formation we have also investigated the interaction between the overflows across the greenland scotland ridge and the lsw and find that with the same surface forcing conditions in the nordic seas volume transport of the overflows weakens when the lsw formation intensifies

gravity field over northern eurasia and variations in the strength of the upper mantle the correlation of long wavelength gravity anomalies in northern eurasia with seismic velocity anomalies in the upper mantle reverses in sign between western and eastern eurasia the difference between western and eastern eurasia can be explained by the presence of a low viscosity zone in the uppermost mantle beneath eastern eurasia that is absent to the west the location of the lateral change in viscosity corresponds with the geologic boundary between the older shields and platforms of the baltics russia and siberia and the younger geologically active mountain belts of eastern asia this relation provides evidence that differences in the strength of the upper mantle control the locus of intracontinental deformation

influence of abyssal mixing on the multilayer circulation in the south china sea abstractby parameterizing the abyssal mixing as the exchange velocity entrainment detrainment between the middle and deep layers of the south china sea scs its effects on the multilayer circul

an inversion for radial viscosity structure using seismic tomography using a uniform velocity density scaling we have inverted the seismically inferred 3 dimensional structure of the whole manfie for the radial viscosity structure which best fits the geoid we are able to obtain 60 72 variance reductions for three different s wave tomographic models the resulting viscosity structures are remarkably similar showing a high viscosity lid a low viscosity zone in the transition region and a high viscosity lower manfie a resolution analysis indcates that the viscosity structure in the upper manfie is well resolved by the data however the resolution in the lower manfie is poorer our models axe in general agreement with previous studies except that our inversions prefer a low viscosity layer at 400 670 km as opposed to 100 400 kin

vertical mixing and cabbeling in layered models abstract a consistent scheme for vertical mixing in layered numerical models is derived in this paper the fact that the vertical coordinate density depends on the properties being transported namely salinity and potential temperature renders the inclusion of vertical mixing in layered models a subtle problem the approach the authors have taken is based upon the entrainment into a layer being proportional to the turbulent activity in that layer across each interface there are then two entrainment velocities one upward velocity that is the entrainment of fluid into the layer above the interface and one downward velocity being the entrainment velocity into the layer below the interface this double entrainment accounts for both the diffusive and the advective consequences of turbulent mixing the proposed scheme works without approximation for a nonlinear equation of state and can readily handle the production of density caused by cabbeling several examples are given

simultaneous inversion for 3 d variations in shear and bulk velocity in the mantle until recently most of the seismic tomographic modeling has been addressing the question of lateral heterogeneity either in p or s wave velocities the s wave velocity variations are larger and hence provide stronger signal on long period waveforms the direct p travel times being the first arrivals on the other hand are most frequently reported in the international seismological centre isc bulletins in mineral physics experiments the variation in bulk velocity is more often measured to better understand the differences between vp and vp patterns and better link the results from mineral physics to those of seismic tomography we formulate the inverse problem in terms of relative perturbations in the shear velocity vs 12 and bulk sound velocity v k 12 we use a large data set which consists of waveforms waveform derived travel times and travel times from the isc bulletins the earthquakes are relocated using corrections for lateral heterogeneity the events which cannot be reliably determined are discarded the model is defined as spherical harmonics to degree 12 horizontally and as chebyshev polynomials to order 13 radially for both shear and bulk sound velocity the inversion is performed under smoothness constraint the resolution tests and bootstrapping analysis indicate that the model is well recovered particularly at long wavelength the results indicate a much larger variability of shear than bulk sound velocity the model explains observations well the most intriguing result obtained in this study is that the variations in shear velocity and bulk sound velocity are negatively correlated in the lowermost mantle the explanation is not very clear from the mineral physics point of view it is not unlikely that this could be explained in terms of thermal variation even though we are unwilling to rule out the possibility of large wavelength compositional variations

seismic constraints on mantle flow and topography of the 660 km discontinuity evidence for whole mantle convection recent seismic models of three dimensional mantle structure and topography on the transition zone seismic discontinuities permit the direct evaluation of the buoyancy forces that drive large scale mantle flow this buoyancy distribution coupled with radial viscosity models that are consistent with the observed geoid predicts flow patterns with significant vertical flow through the 660 km phase boundary the observed topography on the 660 km discontinuity acts to inhibit convection across the boundary but is two to four times too small to prevent whole mantle convection

comment on dynamic surface topography a new interpretation based upon mantle flow models derived from seismic tomography by a m forte w r peltier a m dziewonski and r l woodward in a recent paper in this journal forte et al 1993 have proposed a model of global dynamic topography with an amplitude of three kilometers six kilometers peak to peak if north america australia and other continents were dynamically depressed by the one to two kilometers predicted then these continents would today be below sea level and nearly covered by epeiric seas since the continents are nearly entirely exposed and have become progressively exposed since the late mesozoic the amplitude of the forte et al model is clearly much too large

changes in coiling direction habitat depth and abundance in two menardellid species abstract we present a detailed study of menardellid speciation abundance and coiling changes between 6 34 and 5 1 ma latest miocene and earliest pliocene menardellids are widely distributed in tropical to subtropical waters from miocene to modern time revealing a stable isotopic signature characteristic for the top of the thermocline and shallower rather than deeper habitat depth menardellid response to its environment reveals a tripartite pattern the first interval from 6 34 to 5 75 ma is marked by a dominance of menardella limbata frequent changes in coiling direction and variable abundance with strongest reductions during intervals of dextral dominance the onset of an interval of cooling and ice build up at 5 82 ma coincides with a weakening of the mixed layer leading to nearly 70 kyr of strongly reduced menardellid abundance at 5 75 ma menardella multicamerata replaces m limbata as the prevailing menardellid species at the same time as the overall abundance of menardellids stabilises initial stabilisation of sinistral coiling until the end of the cold interval at 5 49 ma suggests the development of a temperature preference in sinistral cold and dextral warm m multicamerata a strong increase in menardellid 13c values relative to the thermocline gradient difference between the 18o records of surface dwelling globigerinoides trilobus and menardella spp following 5 77 ma suggests a move to shallower habitat depths of both m multicamerata morphotypes initiated by mixed layer destabilisation both the development of a temperature preference and the move to shallower habitat depth in m multicamerata appear to identify its adjustment to a new niche driving the replacement of m limbata as the dominant menardellid species

deep water properties and surface buoyancy flux as simulated by a z coordinate model including eddy induced advection abstract a parameterization for the adiabatic transport effect of eddies is introduced into a world ocean model based on the bryan cox code the model topography is only lightly smoothed and retains realistic sill depths and representation of continental shelves commensurate with the model s 1 6 latitude by 2 8 longitude resolution the parameterization allows the model to be run without horizontal diffusivity though only under certain conditions as discussed a first control run features a typical horizontal diffusivity and no eddy induced transport a second run features the eddy induced transport scheme and zero horizontal diffusivity substantial changes occur between the runs in subsurface temperature salinity and density throughout the model ocean the most profound changes occur in the deep ocean and feature a marked increase in density in the second run associated with a substantial decline in temperature especially in the atlantic and an increase in salinity especially in the southern

dynamic surface topography a new interpretation based upon mantle flow models derived from seismic tomography the very long wavelength i e in the degree range l 1 8 dynamic topography at the earth s surface estimated by isostatic reduction of the observed topography is shown to be in good agreement with the topography predicted by a model of viscous flow in the mantle this flow model was previously derived by independent consideration of the observed nonhydrostatic geoid and is based upon a recent model of large scale seismic shear velocity heterogeneity in the mantle our estimate and prediction of the long wavelength dynamic surface topography reveals significant depressions 2 3 km of the continental shields relative to their hydrostatic reference positions

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

the sensitivity of the atlantic meridional overturning circulation to enhanced freshwater discharge along the entire eastern and western coast of greenland the possible responses of the atlantic meridional overturning circulation amoc to increased freshwater discharge along the greenland coast has become an issue of growing concern given the increasing rate of the greenland ice sheet gris melting a recent model study suggested a weakened amoc of about 13 30 when a freshwater anomaly of 0 1 sv 1 sv 106 m3 s 1 was released along the entire greenland coast during the late twentieth century 1965 2000 in this study we use a fully coupled climate model to examine the sensitivity of amoc to a similar amount of freshwater forcing but released separately along the eastern the western and the entire greenland coast our results show that in all three cases there is a general weakening of the amoc mainly due to a reduced formation of labrador sea water moreover when additional freshwater is released along the eastern coast of greenland the amoc weakens more compared to the other two cases the different degree of convective mixing reduction in the irminger sea is the main reason for the spread in amoc responses in the three freshwater hosing experiments compared to the other two experiments the eastern coast experiment shows a relative warming in the labrador sea and the generation of a negative greenland tip jet like wind pattern anomaly these anomalies lead to a weaker convective mixing in the southern irminger sea and result subsequently in less formation of the simulated upper labrador sea water ulsw in the eastern coast experiment this study therefore highlights a potential important role for ulsw formation in determining the sensitivity of the amoc in response to large gris melting

a conceptual model of ocean heat uptake under climate change abstracta conceptual model of ocean heat uptake is developed as a multilayer generalization of gnanadesikan the roles of southern ocean ekman and eddy transports north atlantic deep water nadw formation and diapycnal mixing in controlling ocean stratification and transient heat uptake are investigated under climate change scenarios including imposed surface warming increased southern ocean wind forcing with or without eddy compensation and weakened meridional overturning circulation moc induced by reduced nadw formation with realistic profiles of diapycnal mixing ocean heat uptake is dominated by southern ocean ekman transport and its long term adjustment controlled by the southern ocean eddy transport the time scale of adjustment setting the rate of ocean heat uptake increases with depth for scenarios with increased southern ocean wind forcing or weakened moc deepened stratification results in enhanced ocean heat uptake in each of these experiments the role of diapycnal mixing in settin

an assessment of orthobaric density in the global ocean abstract orthobaric density has recently been advanced as a new density variable for displaying ocean data and as a coordinate for ocean modeling here the extent to which orthobaric density surfaces are neutral is quantified and it is found that orthobaric density surfaces are less neutral in the world ocean than are potential density surfaces referenced to 2000 dbar another property that is important for a vertical coordinate of a layered model is the quasi material nature of the coordinate and it is shown that orthobaric density surfaces are significantly non quasi material these limitations of orthobaric density arise because of its inability to accurately accommodate differences between water masses at fixed values of pressure and in situ density such as occur between the northern and southern hemisphere portions of the world ocean it is shown that special forms of orthobaric density can be quite accurate if they are formed for an individual ocean basin and used only in that basin while orthobari

adaptation of an isopycnic coordinate ocean model for the study of circulation beneath ice shelves abstract much of the antarctic coastline comprises large floating ice shelves beneath which waters from the open ocean circulate the interaction of the seawater with the base of these ice shelves has a bearing both on the rate at which antarctic bottom water is formed and on the mass balance of the ice sheet an isopycnic coordinate ocean general circulation model has been modified so as to allow the incorporation of a floating ice shelf as an upper boundary to the model domain the modified code admits the introduction of an arbitrary surface pressure field and includes new algorithms for the diagnosis of entrainment into and detrainment from the surface mixed layer special care is needed in handling the cases where the mixed layer and isopycnic interior layers interact with surface and basal topography the modified model is described in detail and then applied to an idealized ice shelf ocean geometry simple tests with zero surface buoyancy forcing indicate that the introduction of the static s

the geoid effect of compensated topography and uncompensated oceanic trenches the geoid is becoming increasingly important in interpretation of global tectonics most of the topography of the earth is isostatically compensated so removal of its effect from the geoid is appropriate before tectonic modeling the oceanic trenches however are dynamically depressed features and cannot be isostatically compensated in the classical way continental topography compensated at 35 km gives intracontinental geoidal undulations of up to 15 m over mountain ranges in a spherical harmonic expansion to order and degree 22 oceanic topography compensated at 40 km reasonable for the thermally supported long wavelengths matches the 10 m difference between old continents and old oceans in a detailed nasa gsfc geoid removing the assumed compensation for the oceanic trenches leaves negative anomalies of up to 9 m amplitude caused by their uncompensated mass deficit this mass deficit acts as a partial regional compensation for the excess mass of the subducting slabs and partly explains why geoidal and gravity anomalies over the cold slabs are less than thermal models predict

plate tectonics and aspherical earth structure the importance of poloidal toroidal coupling we derive poloidal flow internal loading green functions for incompressible fluid models of the mantle consisting either of a single constant viscosity spherical shell or of two adjacent spherical shells having different viscosities from the green function we obtain kernels connecting the surface divergence the geoid and the surface topography fields to the lateral density heterogeneity inferred on the basis of the application of seismic tomographic imaging techniques and with these kernels we argue that both the surface divergence and geoid fields consisting of harmonic degrees 2 5 may be reasonably fit with only a factor of 8 viscosity increase at a depth of 1200 km we point out however that the coupling from poloidal to toroidal flow which is required to understand surface velocity spectra may allow these observations to be understood in terms of a viscosity increase at depth which is smaller than required by nonhydrostatic geoid data in the context of pure poloidal models using the observed kinetic energy in the surface plate motions as a constraint allows us to infer a value for the steady state upper mantle viscosity of 2 0 0 5 1021 pa s we comment on the implication of the difference between this number and the somewhat lower value 1 1021 pa s which has been derived on the basis of analyses of signatures of the glacial isostatic adjustment process

continent ocean chemical heterogeneity in the mantle based on seismic tomography seismic models of global scale lateral heterogeneity in the mantle show systematic differences below continents and oceans that are too large to be purely thermal in origin an inversion of the geoid based on a seismic model that includes viscous flow in the mantle indicates that the differences beneath continents and oceans can be accounted for by differences in composition in the upper mantle superposed on mantle wide thermal heterogeneities the net continent ocean density differences integrated over depth are small and cause only a low flux of mass and heat across the asthenosphere and mantle transition zone

hydraulics and mixing in a laterally divergent channel of a highly stratified estuary author posting american geophysical union 2017 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in journal of geophysical research oceans 122 2017 4743 4760 doi 10 1002 2016jc012455

temporal and spatial variability of the sea surface salinity in the nordic seas 1 in this paper the temporal and spatial variability of the sea surface salinity sss in the nordic seas is investigated the data include a russian hydrographical database for the nordic seas and daily to weekly observations of salinity at ocean weather station mike owsm located at 66 n 2 e in the norwegian sea in addition output from a medium resolution version of the miami isopycnic coordinate ocean model micom forced with daily national center for environmental prediction national center for atmospheric research ncep ncar reanalysis data is used to complement the analysis of the temporal and spatial fields constructed from the observational data sets the nordic seas show a strong seasonal variability in the vertical density stratification and the mixed layer ml depth with a weak stratification and a several hundred meters deep ml during winter and a well defined shallow ml confined to the upper few tens of meters during summer the seasonal variability strongly influences the strength of the high frequency variability and to what extent subsurface anomalies are isolated from the surface high frequency variability has been investigated in terms of standard deviation of daily sss calculated for the different months of the year from observations at owsm typical winter values range from 0 03 to 0 04 psu and summer values range from 0 06 to 0 07 psu results from the model simulation show that highest variability is found in frontal areas and in areas with strong stratification and lowest variability in the less stratified areas in the central norwegian sea and south of iceland investigation of the interannual variability over the last 50 years shows a marked freshening of the atlantic water in the norwegian and greenland seas moreover the strength of the southern sector of the polar front as defined by the 34 8 35 0 psu isohalines along the western boundary of the inflowing atlantic water undergoes significant interannual variability with gradient stretching reaching up to 300 km in comparison the variability in the strength of the eastern front and northern sector of the polar front seemingly controlled by the shelf break off norway and the ridge between the norwegian and the greenland seas typically undergoes stretching only between 60 and 80 km the investigation also demonstrates that the low frequency variability in the upper ocean density field in the greenland sea a key factor for the deep water convection is governed by the variability in the sea surface field since the early 1960s there has been a negative trend in the salinity probably contributing to the observed decrease in the deep water production in that period

geoid anomalies in a dynamic earth in order to obtain a dynamically consistent relationship between the geoid and the earth s response to internal buoyancy forces we have calculated potential and surface deformation love numbers for internal loading these quantities depend on the depth and harmonic degree of loading they can be integrated as green functions to obtain the dynamic response due to an arbitrary distribution of internal density contrasts spherically symmetric self gravitating flow models are constructed for a variety of radial newtonian viscosity variations and flow configurations including both whole mantle and layered convection we demonstrate that boundary deformation due to internal loading reaches its equilibrium value on the same time scale as postglacial rebound much less than the time scale for significant change in the convective flow pattern by calculating relaxation times for a series of spherically symmetric viscous earth models for uniform mantle viscosity the geoid signature due to boundary deformations is larger than that due to internal loads resulting in net negative geoid anomalies for positive density contrasts geoid anomalies from intermediate wavelength density contrasts are amplified by up to an order of magnitude geoid anomalies are primarily the result of density contrasts in the interior of convecting layers density contrasts near layer boundaries are almost completely compensated layered mantle convection results in smaller geoid anomalies than mantle wide flow for a given density contrast viscosity stratification leads to more complicated spectral signatures because of the sensitivity of the dynamic response functions to model parameters forward models for the geoid can be used to combine several sources of geophysical data e g subducted slab locations seismic velocity anomalies surface topography to constrain better the structure and viscosity of the mantle

parameter sensitivity of primitive equation ocean general circulation models abstract experiments with a low resolution primitive equation ocean general circulation model with idealized basin geometry and surface forcing have been carried out in order to identify the processes controlling the climatically important aspects of the circulation emphasis was placed on the sensitivity of the model solutions to the magnitude of the vertical diffusivity scaling arguments suggest and the numerical experiments confirm that the solutions are most sensitive to the magnitudes of the wind stress curl and the vertical diffusivity for small vertical diffusivity wind forcing dominates the solution the vertical scale of the thermocline is set by the strength of the ekman pumping and there is a multiple gyre circulation in the upper layers for large vertical diffusivity diabatic surface forcing dominates the solution vertical diffusion controls the vertical scale of the thermocline and there is a single large anticyclonic gyre in the upper layers both the meridionally and zonally inte