reconstructability of three dimensional upper ocean circulation from swot sea surface height measurements abstractutilizing the framework of effective surface quasigeostrophic esqg theory this study explores the potential of reconstructing the 3d upper ocean circulation structures including the balanced vertical velocity w field from high resolution sea surface height ssh data of the planned surface water and ocean topography swot satellite mission specifically the authors utilize the 1 30 submesoscale resolving ofes model output and subject it to the swot simulator that generates the along swath ssh data with expected measurement errors focusing on the kuroshio extension region in the north pacific where regional rossby numbers range from 0 22 to 0 32 this study finds that the esqg dynamics constitute an effective framework for reconstructing the 3d upper ocean circulation field using the modeled ssh data as input the esqg reconstructed relative vorticity and w fields are found to reach a correlation of 0 7 0 9 and 0 6 0 7 respectively in the 1000 m upper ocean when compared to the orig

on the skewness of vorticity in the upper ocean conservation of potential vorticity suggests that when the magnitude of relative vorticity approaches the planetary vorticity cyclonic vorticity should be preferred small scale 3 km relative vorticity is examined using shipboard acoustic doppler current profiler adcp velocity measurements and p code global positioning system gps navigation from a cruise in the north pacific the skewness of relative vorticity in the mixed layer is positive consistent with theory the probability density function of vorticity reveals that positive skewness occurs because large vorticities are more likely to be cyclonic than anticyclonic the skewness is shown to be significant relative to measurement and random errors in contrast skewness in the thermocline has no preferred sign the skewness peaks at the surface and decays to zero at the base of the mixed layer

seasonal variation and instability nature of the north pacific subtropical countercurrent and the hawaiian lee countercurrent 1 the relation between baroclinic instability of the north pacific subtropical countercurrent stcc and the hawaiian lee countercurrent hlcc and seasonal evolution of mesoscale sea surface height ssh variability was investigated by using historical hydrographic data and altimeter derived ssh anomaly data during 1992 2000 the annual and monthly mean dynamic height climatologies show two robust eastward flowing countercurrents the stcc extends typically along 24 n from 130 e to 160 w and slightly shifts to the north as it flows toward the east and the hlcc is located typically along 20 n and extends from about 150 e to just west of the hawaiian islands seasonal variations of the stcc in the western north pacific and the hlcc west of the hawaiian island where the eddy variability is relatively larger than the background were quite different the stcc hlcc is strong in winter summer to summer winter and weak in fall spring in contrast seasonal evolution of mesoscale ssh variability has almost the same cycle in the two countercurrent regions the eddy kinetic energy eke is a maximum in spring and a minimum in fall the dominant zonal scales are shortest in late winter and become longer with time a linear quasigeostrophic stability analysis using a three layer model indicates that instability properties are very similar between the two countercurrent regions the stcc and the hlcc become baroclinically more unstable during winter and late fall to winter respectively due to strong vertical velocity shear and weak stratification between the stcc hlcc and underlying westward flow and the most unstable wave during this season has an e folding timescale of about 2 3 months and a zonal wavelength of about 300 400 km the same behavior of the seasonal evolution of the mesoscale variability in the two countercurrent regions is a manifestation of these similarities in terms of increasing nonlinearity of the unstable waves and an inverse cascade of the eddy energy we discussed generation processes of the mesoscale ssh disturbances

seasonal mesoscale and submesoscale eddy variability along the north pacific subtropical countercurrent abstractlocated at the center of the western north pacific subtropical gyre the subtropical countercurrent stcc is not only abundant in mesoscale eddies but also exhibits prominent submesoscale eddy features output from a high resolution ogcm simulation and a gridded satellite altimetry product are analyzed to contrast the seasonal stcc variability in the mesoscale versus submesoscale ranges resolving the eddy scales of 150 km the altimetry product reveals that the stcc eddy kinetic energy and rms vorticity have a seasonal maximum in may and april respectively a weak positive vorticity skewness without seasonal dependence and an inverse forward kinetic energy cascade for wavelengths larger shorter than 250 km in contrast the submesoscale resolving ogcm simulation detects that the stcc eddy kinetic energy and rms vorticity both appear in march a large positive vorticity skewness with strong seasonality and an intense inverse kinetic energy cascade whose short wave cutoff migrates seaso

frontogenesis subduction and cross front exchange at upper ocean fronts the subduction of water at upper ocean fronts driven by internal instabilities is investigated a simple analytic model which assumes conservation of potential density and potential vorticity is used to characterize the expected structure of subducted parcels as a function of the surface layer depth and the length scale of the parcel parcels subducted from a deep surface layer will be characterized by anomalously low potential vorticity and anticyclonic circulation while shallow surface layers result in subducted parcels with high potential vorticity and cyclonic circulation a nonlinear isopycnal primitive equation model is used to demonstrate how baroclinic instability and the resulting frontogenesis force the subduction of parcels below and across the front frontogenesis generates vertical velocities of 0 30 m d and ageostrophic cross front flows of 3 to 5 cm s the subduction is achieved by the deep ageostrophic flow which carries water from the surface layer below and across the front the subducted parcels quickly develop a circulation through balanced adjustment anticyclonic for deep surface layers and cyclonic for shallow surface layers the characteristics of parcels subducted in winter conditions closely resemble a class of eddies called submesoscale coherent vortices the horizontal and vertical scales of the vortices are determined by the frontogenetic mechanism and the depth of the surface layer the total permanent subduction rate is estimated to be 20 m yr for frontal subduction driven by frontogenesis although local and temporary subduction can be much larger the subducted anticyclonic vortices are often coupled to upper ocean cyclonic vortices thus forming a baroclinic dipole that propagates at approximately 3 5 cm s and is capable of transporting the anomalous water properties far from the region of formation similarities with observations in the north atlantic subtropical convergence zone and near the gulf stream are discussed

molecular stratigraphy of the santa barbara basin comparison with historical records of annual climate change abstract the molecular record of 20th century climatic variability in laminated sediments of the santa barbara basin has been compiled distributions and abundance profiles of alkenones and selected sterols reveal annual oscillations in sea surface temperatures and phytoplankton productivity positive excursions in alkenone temperature profiles coincide with all major 20th century el nino events recording oceanic warming downcore abundance profiles for dinosterol brassicasterol cholesterol and alkenones reflect productivity trends in phytoplankton and illustrate the comparative resilience of their molecular records series of subsurface concentration maxima for dinosterol a dinoflagellate derived sterol appear synchronous with regional historical reports of dinoflagellate blooms

characterizing the transition from balanced to unbalanced motions in the southern california current author s chereskin teresa k rocha cesar b gille sarah t menemenlis dimitris passaro marcello

reconstructing upper ocean vertical velocity field from sea surface height in the presence of unbalanced motion abstractreconstructability of upper ocean vertical velocity w and vorticity fields from high resolution sea surface height ssh data is explored using the global 1 48 horizontal resolution mitg

seasonality of submesoscale flows in the ocean surface boundary layer a signature of submesoscale flows in the upper ocean is skewness in the distribution of relative vorticity expected to result for high rossby number flows such skewness has implications for mixing dissipation and stratification within the upper ocean an array of moorings deployed in the northeast atlantic for one year as part of the osmosis experiment reveals that relative vorticity is positively skewed during winter even though the scale of the rossby number is less than 0 5 furthermore this skewness is reduced to zero during spring and autumn there is also evidence of modest seasonal variations in the gradient rossby number the proposed mechanism by which relative vorticity is skewed is that the ratio of lateral to vertical buoyancy gradients as summarized by the inverse gradient richardson number restricts its range during winter but less so at other times of the year these results support recent observations and model simulations suggesting the upper ocean is host to a seasonal cycle in submesoscale turbulence

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

spring snow albedo feedback analysis over the third pole results from satellite observation and cmip5 model simulations the snow albedo feedback is a crucial component in high altitude cryospheric change but is poorly quantified over the third pole encompassing the karakoram and tibetan plateau here we present an analysis of present day and future spring snow albedo feedback over the third pole using a 28 year satellite based albedo and the latest climate model simulations we show that present day spring snow albedo feedback strength is primarily determined by the decrease in albedo due to snow metamorphosis rather than that due to reduced snow cover in the karakoram but not found in southeastern tibet we further demonstrate an emergent relationship between snow albedo feedback from the seasonal cycle and that from climate change across models combined with contemporary satellite based snow albedo feedback from seasonal cycle this relationship enables us to estimate that the feedback strength for the karakoram with a relatively high glaciated area is 2 42 0 48 k 1 under an unmitigated scenario which is much stronger than that for southeastern tibet 1 64 0 48 k 1 and for the third pole 0 89 0 44 k 1 respectively moreover it is noteworthy that the magnitude of the constrained strength is only half of the unconstrained model estimate for the third pole suggesting that current climate models generally overestimate the feedback of spring snow change to temperature change based on the unmitigated scenario

on the seasonal eddy variability in the kuroshio extension abstractusing a recently developed tool multiscale window transform mwt and the mwt based canonical energy transfer theory this study investigates the seasonal eddy variability in the kuroshio

parameterization of mixed layer eddies part i theory and diagnosis ageostrophic baroclinic instabilities develop within the surface mixed layer of the ocean at horizontal fronts and efficiently restratify the upper ocean in this paper a parameterization for the restratification driven by finite amplitude baroclinic instabilities of the mixed layer is proposed in terms of an overturning streamfunction that tilts isopycnals from the vertical to the horizontal the streamfunction is proportional to the product of the horizontal density gradient the mixed layer depth squared and the inertial period hence restratification proceeds faster at strong fronts in deep mixed layers with a weak latitude dependence in this paper the parameterization is theoretically motivated confirmed to perform well for a wide range of mixed layer depths rotation rates and vertical and horizontal stratifications it is shown to be superior to alternative extant parameterizations of baroclinic instability for the problem of mixed layer restratification two companion papers discuss the numerical implementation and the climate impacts of this parameterization

energetics of eddy mean flow interactions along the western boundary currents in the north pacific abstractthe energetics of eddy mean flow interactions along two western boundary currents of the north pacific the kuroshio and ryukyu currents are systematically investigated using 22 years of n

spatial and temporal variability of the north atlantic eddy field from two kilometric resolution ocean models ocean circulation is dominated by turbulent geostrophic eddy fields with typical scales ranging from 10 to 300 km at mesoscales 50 km the size of eddy structures varies regionally following the rossby radius of deformation the variability of the scale of smaller eddies is not well known due to the limitations in existing numerical simulations and satellite capability nevertheless it is well established that oceanic flows 50 km generally exhibit strong seasonality in this study we present a basin scale analysis of coherent structures down to 10 km in the north atlantic ocean using two submesoscale permitting ocean models a nemo based north atlantic simulation with a horizontal resolution of 1 60 natl60 and an hycom based atlantic simulation with a horizontal resolution of 1 50 hycom50 we investigate the spatial and temporal variability of the scale of eddy structures with a particular focus on eddies with scales of 10 to 100 km and examine the impact of the seasonality of submesoscale energy on the seasonality and distribution of coherent structures in the north atlantic our results show an overall good agreement between the two models in terms of surface wave number spectra and seasonal variability the key findings of the paper are that i the mean size of ocean eddies show strong seasonality ii this seasonality is associated with an increased population of submesoscale eddies 10 50 km in winter and iii the net release of available potential energy associated with mixed layer instability is responsible for the emergence of the increased population of submesoscale eddies in wintertime

scale selection of baroclinic instability effects of stratification and nongeostrophy abstract a simple two dimensional linear stability analysis is presented to study the characteristics of the scale selection and structure of baroclinic cyclogenesis effects of a realistic vertical thermal structure of the environment and the related nongeostrophic wind are investigated in detail both short mesoscale waves trapped in the lower layer with a small static stability and long waves extending throughout the column are unstable which supports blumen s results the integral constraints imply that the vertical structure of the stratification can provide an internal lid to confine the wave into the mixed layer nongeostrophic effects become important as richardson number decreases as pointed out by stone the scale of the most unstable eady s mode becomes sensitive to the change of shear unlike the geostrophic case the measure of the horizontal scale of the disturbance is the modified rossby radius of deformationwhere is the vertical shear and provides o ri correction to the conventio

isopycnal eddy mixing across the kuroshio extension stable versus unstable states in an eddying model the kuroshio extension ke jet transitions between stable and unstable states on interannual time scales cross jet eddy mixing in the two states is contrasted in the ke region 28 40 n 125 165 e using a global eddying 0 1 configuration of the parallel ocean program with online numerical particles the four year period chosen june 1994 to may 1998 covers a full cycle of the stable state unstable state and the transition period large values of cross jet eddy diffusivities within the ke jet are concentrated in the upper 1000m in the upper ocean elevated cross jet mixing within the ke jet is mainly concentrated in the downstream part of the ke jet where the jet is weak but eddy activity is strong the simulated time mean ke jet is more intense and extends further east in the stable state than in the unstable state consequently strong cross jet mixing within the ke jet is located west of 150oe during june 1996 may 1997 a typical unstable state but east of 150oe during june 1995 may 1996 a typical stable state however average mixing within the ke jet is indistinguishable in the typical stable and unstable states in the deep ocean mixing is strongly influenced by topography and thus their horizontal structures have less inter annual variability than in the upper ocean one caveat is that results here cover one representative cycle of the two states to obtain the climate mean mixing structures for the stable or unstable state one would need numerical output covering a period much longer than four years

seasonality in transition scale from balanced to unbalanced motions in the world ocean abstractthe transition scale lt from balanced geostrophic motions to unbalanced wave motions including near inertial flows internal tides and inertia gravity wave continuum is explored using the output from a global 1 48 horizontal resolution massachusetts institute of technology general circulation model mitgcm simulation defined as the wavelength with equal balanced and unbalanced motion kinetic energy ke spectral density lt is detected to be geographically highly inhomogeneous it falls below 40 km in the western boundary current and antarctic circumpolar current regions increases to 40 100 km in the interior subtropical and subpolar gyres and exceeds in general 200 km in the tropical oceans with the exception of the pacific and indian sectors of the southern ocean the seasonal ke fluctuations of the surface balanced and unbalanced motions are out of phase because of the occurrence of mixed layer instability in winter and trapping of unbalanced motion ke in shallow mixed layer in summe

length scales of eddy generation and nonlinear evolution of the seasonally modulated south pacific subtropical countercurrent the dynamical processes behind the seasonal modulation of the two dimensional eddy kinetic energy eke wavenumber spectrum in the subtropical countercurrent region of the south pacific are investigated with 14 yr of satellite altimeter data and climatological hydrographic data the authors find a seasonally modulated generation of eke via baroclinic instability in modes with larger meridional length scales subsequent nonlinear eddy eddy interactions redistribute the eke to larger total horizontal length scales and larger zonal scales in particular this is confirmed by diagnosing the spectral transfer of eke in the surface geostrophic flow which is found to drive an anisotropic inverse cascade being redirected in the sense consistent with the effect as predicted by geostrophic turbulence theory on the plane because of the seasonal renewal of meridionally elongated anomalies by baroclinic instability and possibly because of the barotropization process however the net outcome for the formation of surface zonal flows is observed to be limited

mixed layer instabilities and restratification abstract the restratification of the oceanic surface mixed layer that results from lateral gradients in the surface density field is studied the lateral gradients are shown to be unstable to ageostrophic baroclinic instabilities and slump from the horizontal to the vertical these instabilities which are referred to as mixed layer instabilities mlis differ from instabilities in the ocean interior because of the weak surface stratification spatial scales are o 1 10 km and growth time scales are on the order of a day linear stability analysis and fully nonlinear simulations are used to study mlis and their impact on mixed layer restratification the main result is that mlis are a leading order process in the ml heat budget acting to constantly restratify the surface ocean climate and regional ocean models do not resolve the scales associated with mlis and are likely to underestimate the rate of ml restratification and consequently suffer from a bias in sea surface temperatures and ml depths in a

submesoscale eddy vertical covariances and dynamical constraints from high resolution numerical simulations abstractwe analyze high resolution 1 km simulations of the western pacific gulf of mexico and arabian sea to understand submesoscale eddy dynamics a mask based on the okubo weiss parameter iso

small meanders of the kuroshio extension and associated northward spreading of warm water three vessel simultaneous observations and an eddy resolving ocean model simulation

characterizing meso to submesoscale features in the south china sea abstract in this study the mesoscale and submesoscale features in the south china sea scs are characterized based on a submesoscale permitting numerical simulation mitgcm llc4320 with nominal horizontal grid spacing of 1 48 2 2 km in the scs the simulation includes tidal forcing which is particularly crucial in the scs where tides play a key role in many aspects of regional dynamics evaluation against observations demonstrates that the simulation is capable of reproducing a wide spectrum of dynamical features in the scs the simulation is then used to characterize meso to submesoscale features in the scs and the key findings are summarized as follows i the scs is rich in submesoscale features e g vortices filaments which undergo significant seasonal variations in many regions ii there is a clear dominance of positive surface relative vorticity in most regions of the scs presumably due to the centrifugal instability but large negative also emerges in areas with strong flow topography interactions iii the vertical motions in the upper scs are dominated by tidal modulations with strong vertical velocities up to 0 01 m s 1 about an order of magnitude larger than those due to the quasi balanced sub inertial motions and iv both the wintertime and summertime horizontal wavenumber spectra of kinetic energy scale roughly as k 2 with k being the horizontal wavenumber for wavelengths below 100 km in addition four key regions are highlighted with distinctive characteristics of submesoscale turbulence including the northern scs luzon strait the scs western boundary current region in winter and east of vietnam in summer a number of model deficiencies are noted along with suggestions for improving model accuracy in order to better characterize the local submesoscale features as well as the underlying dynamics

zonal jets in equilibrating baroclinic instability on the polar beta plane experiments with altimetry results from the laboratory experiments on the evolution of baroclinically unstable flows generated in a rotating tank with topographic effect are presented we study zonal jets of alternating direction which occur in these flows the primary system we model includes lighter fluid in the south and heavier fluid in the north with resulting slow meridional circulation and fast mean zonal motion in a two layer system the velocity shear between the layers results in baroclinic instability which equilibrates with time and due to interaction with effect generates zonal jets this system is archetypal for various geophysical systems including the general circulation and jet streams in the earth s atmosphere the antarctic circumpolar current or the areas in the vicinity of western boundary currents where baroclinic instability and multiple zonal jets are observed the gradient of the surface elevation and the thickness of the upper layer are measured in the experiments using the altimetric imaging velocimetry and the optical thickness velocimetry techniques respectively barotropic and baroclinic velocity fields are then derived from the measured quantities the results demonstrate that the zonal jets are driven by eddy forcing due to continuously created baroclinic perturbations the flow is baroclinic to a significant degree and the jets are surface intensified the meridional wavelength of the jets varies linearly with the baroclinic radius of deformation and is also in a good agreement with a modified rhines scale this suggests a linear dependence of the perturbation velocity in the equilibrated baroclinically unstable flow on the parameter

submesoscale activity over the argentinian shelf 1 submesoscale activity over the argentinian shelf is investigated by means of high resolution primitive equation numerical solutions these reveal energetic turbulent activity visually similar to the one occasionally seen in satellite images at scales o 5 km in fall and winter that is linked to mixed layer baroclinic instability the air sea heat flux responsible for i deepening the upper ocean boundary layer at these seasons and ii maintaining a cross shelf background density gradient is the key environmental parameter controlling submesoscale activity implications of submesoscale turbulence are investigated its mixing efficiency estimated by computing a diffusivity coefficient is above 30 m2 s 1 away from the shallowest regions aggregation of surface buoyant material by submesoscale currents occurs within hours and is presumably important to the ecosystem

simulations of temperature and turbulence structure of the oceanic boundary layer with the improved near surface process an improved model for the oceanic boundary layer is presented in view of the recent observation of the microstructure of the upper ocean including the high dissipation rate near the sea surface in the new model the surface boundary conditions for both the turbulent kinetic energy flux and the roughness length scale are modified the parameterization of stratification effects on turbulence is improved and the convective process is reformulated on the basis of the observation of uniform temperature and velocity profiles within the convective mixed layer evolutions of the profiles of both the dissipation rate and temperature of the observation data patches experiment as well as the time series of the sea surface temperature over the observation days are successfully simulated during a diurnal cycle for the first time it is also shown that the model reproduces various important features of the oceanic boundary layer for example the formation of a diurnal thermocline the profiles of buoyancy flux and the magnitudes of the buoyancy gradients both within the mixed layer and at the diurnal thermocline performance of the model is compared with that of the widely used mellor yamada model

intraseasonal variability of the surface zonal currents in the western tropical pacific ocean characteristics and mechanisms abstractthe surface circulation of the tropical pacific ocean is characterized by alternating zonal currents such as the north equatorial current nec north equatorial countercurrent necc south equatorial current sec and south equatorial countercurrent secc in situ measurements of subsurface moorings and satellite observations reveal pronounced intraseasonal variability isv 20 90 days of these zonal currents in the western tropical pacific ocean wtpo the amplitude of isv is the largest within the equatorial band exceeding 20 cm s 1 and decreases to 10 cm s 1 in the necc band and further to 4 8 cm s 1 in the nec and secc the isv power generally increases from high frequencies to low frequencies and exhibits a peak at 50 60 days in the necc sec and secc these variations are faithfully reproduced by an ocean general circulation model ogcm forced by satellite winds and parallel model experiments are performed to gain insights into the underlying mechanisms it is found that large sca

mesoscale to submesoscale transition in the california current system part i flow structure eddy flux and observational tests in computational simulations of an idealized subtropical eastern boundary upwelling current system similar to the california current a submesoscale transition occurs in the eddy variability as the horizontal grid scale is reduced to o 1 km this first paper in a series of three describes the transition in terms of the emergent flow structure and the associated time averaged eddy fluxes in addition to the mesoscale eddies that arise from a primary instability of the alongshore wind driven currents significant energy is transferred into submesoscale fronts and vortices in the upper ocean the submesoscale arises through surface frontogenesis growing off upwelled cold filaments that are pulled offshore and strained in between the mesoscale eddy centers in turn some submesoscale fronts become unstable and develop submesoscale meanders and fragment into roll up vortices associated with this phenomenon are a large vertical vorticity and rossby number a large vertical velocity relatively flat horizontal spectra contrary to the prevailing view of mesoscale dynamics a large vertical buoyancy flux acting to restratify the upper ocean a submesoscale energy conversion from potential to kinetic a significant spatial and temporal intermittency in the upper ocean and material exchanges between the surface boundary layer and pycnocline comparison with available observations indicates that submesoscale fronts and instabilities occur widely in the upper ocean with characteristics similar to the simulations

dynamics of the atlantic meridional overturning circulation and southern ocean in an ocean model of intermediate complexity abstract a steady state variable density 2 layer ocean model vlom is used to investigate basic dynamics of the atlantic meridional overturning circulation and southern ocean the domain consists of idealized rectangular representations of the atlantic southern and pacific oceans the model equations represent the depth averaged layer 1 response except for one solution in which they represent the depth integrated flow over both layers to allow for overturning water can cross the bottom of layer 1 at the velocity w e w d w m w n the three parts representing interior diffusion w d that increases the layer 1 thickness h throughout the basin mixed layer entrainment w m that ensures h is never less than a minimum value h m and diapycnal cooling processes external to the basin w n that adjust h to h n for most solutions horizontal mixing has the form of rayleigh damping with coefficient which we interpret to result from baroclinic instability through the closure v f 2 p where p 1 2 g h 2 is the depth integrated pressure gradient g is the reduced gravity coefficient and is a mixing coefficient with this interpretation the layer 1 flow corresponds to the sum of the eulerian mean and eddy mean v transport widths that is the residual circulation finally layer 1 temperature cools polewards in response to a surface heat flux q and the cooling can be strong enough in the southern ocean for g 0 south of a latitude y 0 in which case layer 1 vanishes and the model reduces to a single layer 2 solutions are obtained both numerically and analytically the analytic approach splits fields into interior and boundary layer parts from which a coupled set of integral constraints can be derived the set allows properties of the circulation upwelling driven transport out of the southern ocean m downwelling transport in the north atlantic transport of the antarctic circumpolar current and stratification atlantic thermocline depth and the latitudes y and y 0 where h thins to h m or layer 1 vanishes in the southern ocean to be evaluated in terms of model forcings southern ocean wind strength a q entrainment due to w d processes v in the southern ocean northern sinking upwelling within the atlantic subpolar gyre and to the presence of the pacific ocean a hierarchy of solutions is reported in which forcings and processes are individually introduced the complete solution set includes a wide variety of solution types with m 0 and m 0 with and without wind forcing with without and for two parameterizations of northern boundary sinking that represent cooling external to and within the north atlantic for a wide range of and a and for different closures novel aspects of the model and solutions include the following use of vlom which allows q forcing to be introduced realistically the aforementioned closure which allows v to be determined when layer 1 represents both the surface mixed layer h h m and the depth of subsurface isopycnals h h m latitude y where layer 1 outcrops in the southern ocean being internally determined rather than externally specified and a boundary layer based on gill s 1968 solution that smoothly connects the southern and atlantic ocean responses across the latitude of the southern tip of south america finally some solutions in the set are comparable to solutions to idealized ocean general circulation models ogcms in these cases our solutions provide insight into the underlying dynamics of the ogcm solutions for example pointing toward processes that may be involved in eddy saturation and compensation

ssh wavenumber spectra in the north pacific from a high resolution realistic simulation abstractfollowing recent studies based on altimetric data this paper analyses the spectral characteristics of the sea surface height ssh using a new realistic simulation of the north pacific ocean with high resolution in the horizontal and 100 vertical levels this simulation resolves smaller scales down to 10 km than altimetric data limited to 70 km because of the noise level in high eddy kinetic energy eke regions as in the western part ssh spectral slope almost follows a k 4 with k the wavenumber or slightly steeper law in agreement with altimeter studies the new result is that unlike altimeter studies such a k 4 slope is also observed in low eke regions as in the eastern part in these regions this slope mostly concerns scales not well resolved by altimetric data such k 4 ssh spectral slopes are weaker from what is expected from quasigeostrophic turbulence theory but closer to surface quasigeostrophic sqg turbulence theory the consequence is that the small scales concerned

migration of the kuroshio extension in the northwest pacific since the last glacial maximum abstract the 18o values of planktic and benthic foraminifera and faunal assemblage of planktic foraminifera were investigated at a northwest pacific site 32 16 n 158 13 e 2514 m water depth to understand the oceanographic changes in the kuroshio extension ke region over the past 23 kyr the 18o differences between species and the relative abundances of the dominant planktic foraminiferal species have not changed greatly over the study period suggesting that the subarctic boundary and the subarctic subtropical transition zone have remained north of study site while the study site itself has been under the influence of ke nevertheless increased abundances of foraminiferal taxa that populated the subarctic subtropical transition zone during the last glacial maximum lgm indicate the input of transition zone water through the ke manifest as meandering cold core ring eddies generated along the ke since this unstable surface environment is most pronounced along the main axis of the ke it could have been induced by the southward displacement of the ke main axis to the vicinity of the study site in tandem with the overall southward displacement of the kuroshio oyashio extension system during the lgm the input of transition zone water mass has also increased during the deglacial northern hemisphere cold intervals i e heinrich stadial 1 and the younger dryas suggesting that the strengthened surface wind system regulated the surface ocean condition this demonstrates that the northern high latitudes are the dominant control on post glacial oceanographic changes in the northwest pacific ke region

instability of the north pacific subtropical countercurrent abstractthe north pacific subtropical countercurrent stcc has a weak eastward velocity near the surface but the region is populated with eddies studies have shown that the stcc is baroclinically unstable with a peak growth rate of 0 015 day 1 in march and the 60 day growth time has been used to explain the peak eddy kinetic energy eke in may observed from satellites it is argued here that this growth time from previously published normal mode instability analyses is too slow growth rates calculated from an initial value problem without the normal mode assumption are found to be 1 5 to 2 times faster and at shorter wavelengths due to the existence of i nonmodal solutions and ii sea surface temperature front in the mixed layer in winter at interannual time scales it is shown that because of rapid surface adjustments the stcc geostrophic shear hence also the instability growth is approximately in phase with surface forcing leading to eke modulation that peaks approximately 10 months later

interannual variability of the north pacific subtropical countercurrent and its associated mesoscale eddy field interannual changes in the mesoscale eddy field along the subtropical countercurrent stcc band of 188 258n in the western north pacific ocean are investigated with 16 yr of satellite altimeter data enhanced eddy activities were observed in 1996 98 and 2003 08 whereas the eddy activities were below average in 1993 95 and 1999 2002 analysis of repeat hydrographic data along 1378e reveals that the vertical shear between the surface eastward flowing stcc and the subsurface westward flowing north equatorial current nec was larger in the eddy rich years than in the eddy weak years by adopting a 2 layer reduced gravity model it is shown that the increased eddy kinetic energy level in 1996 98 and 2003 08 is because of enhanced baroclinic instability resulting from the larger vertical shear in the stcc nec s background flow the cause for the stcc nec s interannually varying vertical shear can be sought in the forcing by surface ekman

on eddy viscosity energy cascades and the horizontal resolution of gridded satellite altimeter products motivated by the recent interest in ocean energetics the widespread use of horizontal eddy viscosity in models and the promise of high horizontal resolution data from the planned wide swath satellite altimeter this paper explores the impacts of horizontal eddy viscosity and horizontal grid resolution on geostrophic turbulence with a particular focus on spectral kinetic energy fluxes p k computed in the isotropic wavenumber k domain the paper utilizes idealized two layer quasigeostrophic qg models realistic highresolution ocean general circulation models and present generation gridded satellite altimeter data adding horizontal eddy viscosity to the qg model results in a forward cascade at smaller scales in apparent agreement with results from present generation altimetry eddy viscosity is taken to roughly represent coupling of mesoscale eddies to internal waves or to submesoscale eddies filtering the output of either the qg or realistic models before computing p k also greatly increases the forward cascade such filtering mimics the smoothing inherent in the construction of present generation gridded altimeter data it is therefore difficult to say whether the forward cascades seen in present generation altimeter data are due to real physics represented here by eddy viscosity or to insufficient horizontal resolution the inverse cascade at larger scales remains in the models even after filtering suggesting that its existence in the models and in altimeterdata is robust however themagnitudeofthe inverse cascadeis affectedbyfiltering suggestingthat the wide swath altimeter will allow a more accurate determination of the inverse cascade at larger scales as well as providing important constraints on smaller scale dynamics

diagnosing ocean wave turbulence interactions from space numerical studies indicate that interactions between ocean internal gravity waves especially those textless100 km and geostrophic or balanced motions associated with mesoscale eddy turbulence involving eddies of 100 300 km impact the ocean s kinetic energy budget and therefore its circulation results from these studies have never been confirmed by observations in regional or basin scale domains here we show that internal gravity waves have a spectral signature on sea surface height during summer that significantly differs from that of balanced motions these spectral differences lead us to propose a new dynamical framework that quantifies the interactions between internal gravity waves and balanced motions in physical space from sea surface height snapshots and in particular the energy exchanges between them our results using this dynamical framework highlight the strong potential of future satellite altimeter missions to make critical advances in assessing the ocean s kinetic energy budget from observations in large domains

new cnes cls09 global mean dynamic topography computed from the combination of grace data altimetry and in situ measurements 1 an accurate knowledge of the ocean mean dynamic topography mdt is mandatory for the optimal use of altimetric data including their assimilation into operational ocean forecasting systems a new global 1 4 resolution mdt was computed for the 1993 1999 time period with improved data and methodology compared to the previous rio05 mdt field first a large scale mdt is obtained from the cls01 altimetric mean sea surface and a recent geoid model computed from 4 5 years of grace gravity recovery and climate experiment data altimetric sea level anomalies and in situ measurements are then combined to compute synthetic estimates of the mdt and the corresponding mean currents while the rio05 mdt was based on 10 years of in situ dynamic heights and drifting buoy velocities the new field benefits from an enlarged data set of in situ measurements ranging from 1993 to 2008 and includes all hydrological profiles from the argo array moreover the processing of the in situ data has been updated a new ekman model was developed to extract the geostrophic velocity component from the drifting buoy measurements the handling of hydrologic measurements has also been revisited compared to the previous rio05 solution the new global mdt resolves much stronger gradients in western boundary currents with mean velocities being doubled in some places moreover in comparison to several other recent mdt estimates we find that the new cnes cls09 mdt is in better agreement with independent in situ observations

eddy transport of heat and thermocline waters in the north pacific a key to interannual decadal climate variability abstract high resolution xbt transects in the north pacific ocean at an average latitude of 22 n are analyzed together with topex poseidon altimetric data to determine the structure and transport characteristics of the mesoscale eddy field based on anomalies in dynamic height 410 eddies are identified in 30 transects from 1991 to 1999 including eddies seen in multiple transects over a year or longer their wavelength is typically 500 km with peak to trough temperature difference of 2 2 c in the center of the thermocline the features slant westward with decreasing depth by 0 8 of longitude on average from 400 m up to the sea surface this tilt produces a depth varying velocity temperature correlation and hence a vertical meridional overturning circulation in the mean 3 9 sv sv 106 m3 s 1 of thermocline waters are carried southward by the eddy field over the width of the basin balanced mainly by northward flow in the surface layer corresponding northward heat transport is 0 086 0 012 pw