residual mean solutions for the antarctic circumpolar current and its associated overturning circulation abstract residual mean theory is applied to the streamwise averaged antarctic circumpolar current to arrive at a concise description of the processes that set up its stratification and meridional overturning circulation on an f plane simple solutions are found in which transfer by geostrophic eddies colludes with applied winds and buoyancy fluxes to determine the depth and stratification of the thermocline and the pattern of associated residual meridional overturning circulation

estimating eddy stresses by fitting dynamics to observations using a residual mean ocean circulation model and its adjoint a global ocean circulation model is formulated in terms of the residual mean and used to study eddy mean flow interaction adjoint techniques are used to compute the three dimensional eddy stress field that minimizes the departure of the coarse resolution model from climatological observations of temperature the resulting 3d maps of eddy stress and residual mean circulation yield a wealth of information about the role of eddies in large scale ocean circulation in eddy rich regions such as the southern ocean the kuroshio and the gulf stream eddy stresses have an amplitude comparable to the wind stress of order 0 2 n m 2 and carry momentum from the surface down to the bottom where they are balanced

topographic steering of the antarctic circumpolar current abstract an analytic model of the antarctic circumpolar current acc is presented in which information contained in a hydrographic section is propagated along characteristics the characteristics are obtained by assuming that potential vorticity is uniform on density surfaces they lie between the f h contours found in a homogeneous ocean and the f contours found in a strongly stratified ocean solutions describe an inviscid adiabatic circulation in which fluid parcels negotiate a variable bottom topography while conserving density and conserving potential vorticity a family of solutions are obtained for a realistic spherical geometry including coastlines and major topographic features in the limit of weak bottom currents the acc transports 160 sv sv 106 m3 s 1 of fluid around antarctica with circumpolar flow in the upper three kilometers and abyssal gyres bounded by the bottom topography in the limit of large bottom currents the acc exhibits increased sensitivity to the topograph streamlines

subduction of pacific antarctic intermediate water in an eddy resolving model the subduction process of pacific antarctic intermediate water paaiw in the pacific is investigated using output from an eddy resolving ocean model focus is on contribution of eddies to the subduction process to separate the subduction rate into contributions by eddies and mean flows the temporal residual mean trm velocity is used in the mean subduction rate lateral induction caused by the strong eastward flow of the antarctic circumpolar current acc is dominant the largest rate is located in the drake passage the estimated eddy induced subduction rate is comparable with the mean subduction rate and it tends to cancel the vertical mean component in many regions in the west of the drake passage however the eddy induced subduction is larger than the vertical mean component and this eddy induced subduction was not detected in previous studies using the thickness diffusion parameterization and an eddy permitting model results of idealized sensitivity studies to model resolution suggest that the subduction rate would be larger using a model with higher vertical resolution therefore the vertical resolution should be paid more attention in model studies investigating eddy induced subduction and not just the horizontal resolution

jets and topography jet transitions and the impact on transport in the antarctic circumpolar current the southern ocean s antarctic circumpolar current acc naturally lends itself to interpretations using a zonally averaged framework yet navigation around steep and complicated bathymetric obstacles suggests that local dynamics may be far removed from those described by zonally symmetric models in this study both observational and numerical results indicate that zonal asymmetries in the form of topography impact global flow structure and transport properties the conclusions are based on a suite of more than 1 5 million virtual drifter trajectories advected using a satellite altimetry derived surface velocity field spanning 17 years the focus is on sites of cross front transport as defined by movement across selected sea surface height contours that correspond to jets along most of the acc cross front exchange is localized in the lee of bathymetric features with more than 75 of crossing events occurring in regions corresponding to only 20 of the acc s zonal extent these observations motivate a series of numerical experiments using a two layer quasigeostrophic model with simple zonally asymmetric topography which often produces transitions in the front structure along the channel significantly regimes occur where the equilibrated number of coherent jets is a function of longitude and transport barriers are not periodic jet reorganization is carried out by eddy flux divergences acting to both accelerate and decelerate the mean flow of the jets eddy kinetic energy is amplified downstream of topography due to increased baroclinicity related to topographic steering the combination of high eddy kinetic energy and recirculation features enhances particle exchange these results stress the complications in developing consistent circumpolar definitions of the acc fronts

eddy overturning across a shelf edge front kongsfjorden west spitsbergen 1 eddy overturning across a shelf edge front has been investigated in a simplified model setup comprising an along slope uniform shelf and slope with a slope current results from three model runs are presented each initiated with and nudged toward a sharp shelf edge front in temperature salinity density and velocity data collected off kongsfjorden at spitsbergen were used for initiating the model runs three distinctly different density fronts were used to initialize the model runs one with a negative cross frontal density gradient toward the shelf one with a positive density gradient and one with a combination of negative density gradient in the upper water column and a positive in the lower water column the model results indicate that the initial cross frontal density gradients determine the eddy overturning direction acting toward flattened or terrain following isopycnals the steady state modeled fronts resemble quite well the observed front structures as well as temperature and salinity fields this indicates that eddy overturning plays an important role in cross frontal exchange of water masses along the shelf edge front off west spitsbergen the eulerian mean cross slope flow is close to zero and the corresponding fluxes do not describe the correct vertical distribution

a laboratory model of thermocline depth and exchange fluxes across circumpolar fronts a laboratory experiment has been constructed to investigate the possibility that the equilibrium depth of a circumpolar front is set by a balance between the rate at which potential energy is created by mechanical and buoyancy forcing and the rate at which it is released by eddies in a rotating cylindrical tank the combined action of mechanical and buoyancy forcing builds a stratification creating a large scale front at equilibrium the depth of penetration and strength of the current are then determined by the balance between eddy transport and sources and sinks associated with imposed patterns of ekman pumping and buoyancy fluxes it is found that the depth of penetration and transport of the front scale like l and wel2 respectively where fw g9 e we is the ekman pumping g9 is the reduced gravity across the front f is the coriolis parameter and l is the width scale of the front last the implications of this study for understanding those processes that set the stratification and transport of the antarctic circumpolar current acc are discussed if the laboratory results scale up to the acc they suggest a maximum thermocline depth of approximately h 5 2 km a zonal current velocity of 4 6 cm s 21 and a transport t 5 150 sv 1 sv 106 m3 s 21 not dissimilar to what is observed

potential vorticity constraints on the dynamics and hydrography of the southern ocean abstract constraints on the hydrography and geostrophic velocity shear of the southern ocean implicit in its potential vorticity field are discussed and illustrated by diagnostic study of observed and modeled potential vorticity fields a stress driven thermodynamically inactive eddy resolving quasigeostrophic model of the southern ocean suggests that through the systematic erosion of potential vorticity gradients by geostrophic eddies the large scale flow equilibrates toward a state in which interior potential vorticity gradients are small observations of the large scale isopycnal distribution of potential vorticity ipv deduced from climatological hydrographic data reveal a much richer structure the most striking feature of the ipv field is the presence of large near surface gradients of ipv a vortocline coinciding with the axis of the antarctic circumpolar current acc to the south of this front potential vorticity pv is large to its north pv has low values and relative to those foun

transformed eulerian mean theory part ii potential vorticity homogenization and the equilibrium of a wind and buoyancy driven zonal flow the equilibrium of a modeled wind and buoyancy driven baroclinically unstable flow is analyzed using the transformed eulerian mean tem approach described in part i within the near adiabatic interior of the flow ertel potential vorticity is homogenized along mean isopycnals a finding readily explained using tem theory given the geometry of the domain the equilibrium zonal mean buoyancy structure at the surface is determined entirely by a balance between imposed surface fluxes and residual mean and eddy buoyancy transport within a surface diabatic layer balance between these same processes and the wind stress determines the stratification and hence potential vorticity immediately below this layer ertel potential vorticity homogenization below then determines the mean buoyancy structure everywhere accordingly the equilibrium structure of this flow can be described and quantitatively reproduced from knowledge of the eddy mixing rates within the surface diabatic zone and the depth of this zone together with potential vorticity homogenization beneath these results emphasize the need to include near surface buoyancy transport as well as interior pv transport in eddy parameterization schemes they also imply that in more realistic models the surface buoyancy balances may be impacted by processes in remote locations that allow diapycnal flow

water mass transformations driven by ekman upwelling and surface warming in subpolar gyres abstractthe sverdrup relationship when applied to the southern ocean suggests that some isopycnals that are deep in the eastern pacific will shoal in the atlantic cold waters surfacing in the south atlantic at midlatitudes would be warmed by the atmosphere the potential for water mass transformations in this region is studied by applying a three layer planetary geostrophic model to a wide ocean basin driven by the ekman upwelling typical of the southern ocean surface winds the model uses a simple physically based parameterization of the entrainment of mass into the surface layer with zonally symmetric atmospheric surface fields to find steady state subpolar gyre solutions the solutions are found numerically by specifying suitable boundary conditions and integrating along characteristics with reasonable parameter settings transformations of more than 10 sverdrups sv 1 sv 106 m3 s 1 of water between layers are obtained the water mass transformations are sensitive to the strength of the wind stre

the stability of primary alluaudites in granitic pegmatites an experimental investigation of the na 2 mn 2 2 x fe 1 2 x po 4 3 system in order to assess the geothermometric potential of the na2 mn2 2xfe1 2x po4 3 system x 0 1 which represents the compositions of natural weakly oxidized alluaudites we performed hydrothermal experiments between 400 and 800 c at 1 kbar under an oxygen fugacity f o2 controlled by the ni nio nno fe2o3 fe3o4 hm cu2o cuo ct and fe fe3o4 mi buffers when f o2 is controlled by nno single phase alluaudites crystallize at 400 and 500 c whereas the association alluaudite maricite appears between 500 and 700 c the limit between these two fields corresponds to the maximum temperature that can be reached by alluaudites in granitic pegmatites because maricite has never been observed in these geological environments because alluaudites are very sensitive to variations of oxygen fugacity the field of hagendorfite na2mnfe2 fe3 po4 3 has been positioned in the f o2 t diagram and provides a tool that can be used to estimate the oxygen fugacity conditions that prevailed in granitic pegmatites during the crystallization of this phosphate

inferring the pattern of the oceanic meridional transport from the air sea density flux abstract an extension of walin s water mass transformation analysis is proposed that would make it possible to assess the strength of the adiabatic along isopycnal component of the meridional overturning circulation moc it is hypothesized that the substantial fraction of the adiabatic moc component can be attributed to the difference in subduction rates at the northern and southern outcrops of each density layer the push pull mechanism the gcm generated data are examined and it is shown that the push pull mode accounts for approximately two thirds of the isopycnal water mass transport in the global budget and dominates the atlantic transport much of the difference between the actual interhemispheric flux and the push pull mode can be ascribed to the influence of the antarctic circumpolar current characterized by the elevated at least in the gcm values of the diapycnal transport when the diagnostic model is applied to observations it is discovered that the reconstructed moc is consistent in te

semi adiabatic model of the deep stratification and meridional overturning abstractan analytical model of the atlantic deep stratification and meridional overturning circulation is presented that illustrates the dynamic coupling between the southern ocean and the midlatitude gyres the model expressed here in terms of the two and a half layer framework predicts the stratification and meridional transport as a function of the mechanical and thermodynamic forcing at the sea surface the approach is based on the classical elements of large scale circulation theory ideal thermocline inertial western boundary currents and eddy controlled antarctic circumpolar current acc models which are combined to produce a consistent three dimensional view of the global overturning the analytical tractability is achieved by assuming and subsequently verifying that the pattern of circulation in the model is largely controlled by adiabatic processes the time mean and eddy induced isopycnal advection of buoyancy the mean stratification of the lower thermocline is determined by the surface fo

the surface branch of the zonally averaged mass transport circulation in the troposphere the near surface branch of the overturning mass transport circulation in the troposphere containing the equatorward flow is examined in isentropic and geometric coordinates a discussion of the zonal momentum balance within isentropic layers shows that the equatorward flow at a given latitude is confined to isentropic layers that typically intersect the surface at that latitude as a consequence of mass transport within the surface mixed layer much of the equatorward flow occurs in layers with potential temperatures below the mean surface potential temperature in the conventional transformed eulerian mean formulation for geometric coordinates the surface branch of the overturning circulation is represented in an unrealistic manner streamlines of the residual circulation do not close above the surface a modified residual circulation is introduced that is free from this defect and has the additional advantage that its computation unlike that of the conventional residual circulation does not require division by the static stability which may approach zero in the planetary boundary layer it is then argued that cold air advection by the residual circulation is responsible for the formation of surface inversions at all latitudes in idealized gcms with weak thermal damping also included is a discussion of how a general circulation theory for the troposphere must be built upon a theory for the near surface meridional mass fluxes

meridional overturning circulations driven by surface wind and buoyancy forcing abstractthe meridional overturning circulation moc can be considered to consist of a downwelling limb in the northern hemisphere nh and an upwelling limb in the southern hemisphere sh that are connected via western boundary currents steady state analytical gyre scale solutions of the planetary geostrophic equations are derived for a downwelling limb driven in the nh solely by surface heat loss in these solutions the rates of the water mass transformations between layers driven by the surface heat loss determine the strength of the downwelling limb simple expressions are obtained for these transformation rates that depend on the most southerly latitudes where heat loss occurs and the depths of the isopycnals on the eastern boundary previously derived expressions for the water mass transformation rates in subpolar gyres driven by the ekman upwelling characteristic of the sh are also summarized explicit expressions for the moc transport and the depths of isopycnals on the eastern boundary are then

heat flux carried by the antarctic circumpolar current mean flow 1 a stream function projection of historical hydrographic data is applied to study the heat flux problem in the antarctic circumpolar current acc the acc is defined as a circumpolar band consisting of mean streamlines passing through drake passage its mean path exhibits a globally meandering pattern the calculation of zonal heat transport shows that the acc warms along its equatorward segments south atlantic and indian ocean and cools along its poleward segment south pacific the primary heat sources for the acc system are two western boundary currents the brazil current and the agulhas current the mean baroclinic flow relative to 3000 dbar carries 0 14 pw poleward heat flux across 56 s and 0 08 pw across 60 s

a multibasin residual mean model for the global overturning circulation the ocean s overturning circulation is inherently three dimensional yet modern quantitative estimates of the overturning typically represent the subsurface circulation as a two dimensional two cell streamfunction that varies with latitude and depth only this approach suppresses information about zonal mass and tracer transport in this article the authors extend earlier zonally averaged overturning theory to explore the dynamics of a figure eight circulation that cycles through multiple basins a three dimensional residual mean model of the overturning circulation is derived and then simplified to a multibasin isopycnal box model to explore how stratification and diabatic water mass transformations in each basin depend on the basin widths and on deep and bottom water formation in both hemispheres the idealization to multiple two dimensional basins permits zonal mass transport along isopycnals in a southern ocean like channel while retaining the dynamical framework of residual mean theory the model qualitatively reproduces the deeper isopycnal surfaces in the pacific basin relative to the atlantic this supports a transfer of antarctic bottom water from the atlantic sector to the pacific sector via the southern ocean which subsequently upwells in the northern pacific basin a solution for the full isopycnal structure in the southern ocean reproduces observed stratification differences between atlantic and pacific basins and provides a scaling for the diffusive boundary layer in which the zonal mass transport occurs these results are consistent with observational indications that north atlantic deep water is preferentially transformed into antarctic bottom water which undermines the importance of an adiabatic upper overturning cell in the modern ocean

the antarctic circumpolar current in three dimensions a simple theory is developed for the large scale three dimensional structure of the antarctic circumpolar current and the upper cell of its overturning circulation the model is based on a perturbation expansion about the zonal average residual mean model developed previously by marshall and radko the problem is solved using the method of characteristics for idealized patterns of wind and buoyancy forcing constructed from observations the equilibrium solutions found represent a balance between the eulerian meridional overturning eddy induced circulation and downstream advection by the mean flow depth and stratification of the model thermocline increase in the atlantic indian oceans sector where the mean wind stress is large residual circulation in the model is characterized by intensification of the overturning circulation in the atlantic indian sector and reduction in strength in the pacific ocean region predicted three dimensional patterns of stratification and residual circulation in the interior of the acc are compared with observations

the role of eddy transfer in setting the stratification and transport of a circumpolar current abstract high resolution numerical experiments of a circumpolar current are diagnosed to study how lateral and vertical transfer of buoyancy by geostrophic eddies balances advection by a meridional circulation driven by surface wind stresses and buoyancy fluxes a theory is developed in the framework of the residual circulation to relate the vertical and horizontal stratification set up to the transfer properties of eddies and the patterns of imposed wind and buoyancy forcing simple expressions are found for the depth of penetration stratification baroclinic transport and residual circulation of the current finally the ideas are applied to the antarctic circumpolar current acc and yield predictions for how its properties depend on wind and buoyancy forcing