scholarly journals Energy of the jets of the Antarctic circumpolar current and of their eddies in the surface layer of the Southern Ocean

2019 ◽  
Vol 59 (3) ◽  
pp. 325-334
Author(s):  
M. N. Koshlyakov ◽  
D. S. Savchenko ◽  
R. Yu. Tarakanov
Keyword(s):  
Surface Layer ◽  
Kinetic Energy ◽  
Antarctic Circumpolar Current ◽  
The Internet ◽  
Satellite Altimeter ◽  
Synoptic Eddies ◽  
Ocean Layer ◽  
The Mean ◽  
Circumpolar Current ◽  
The Antarctic

Kinetic energy of six jets of the Antarctic Circumpolar Current (ACC) and of the cyclonic and anticyclonic synoptic eddies generated by these jets is studied in application to the surface layer of Antarctic Circle. The study is based on the data of satellite altimeter observations during 1993–2015 available in the Internet (http://aviso.altimetry.fr). Main results of the study: a) five times excess of the mean energy of jets proper over the mean summary (cyclones plus anticyclones) energy of eddies; b) prevalence of the energy of middle jet of Subantarctic Current over energy of the rest ACC jets in the whole of Antarctic Circle; c) two times excess of mean energy of cyclonic eddies over energy of anticyclones in the upper ocean layer.

scholarly journals ENERGY INTERACTION OF THE JETS AND EDDIES OF ANTARCTIC CIRCUMPOLAR CURRENT IN THE NEAR-SURFACE LAYER OF THE SOUTHERN OCEAN

2019 ◽  
Vol 47 (3) ◽  
pp. 39-57
Author(s):  
M. N. Koshlyakov ◽  
R. Yu. Tarakanov ◽  
D. S. Savchenko
Keyword(s):  
Surface Layer ◽  
Antarctic Circumpolar Current ◽  
Altimeter Data ◽  
Satellite Altimeter ◽  
Near Surface ◽  
Synoptic Eddies ◽  
The Mean ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Satellite Altimeter Data

Kinetic energy six jets of the Antarctic Circumpolar Current (ACC), and of synoptic eddies generated by these jets is studied in application to the near-surface layer of the Antarctic Circle on the base of the satellite altimeter data during 1993–2015. The main results of the study were as follows: a) prevalence of the energy of middle jet of the Subantarctic Current over energy of the rest ACC jets in the whole of the Antarctic Circle; b) five times excess of the mean energy of jets proper over the mean summary (cyclones plus anticyclones) energy of eddies; c) two times excess of mean energy of cyclonic eddies over energy of anticyclones.

scholarly journals Circulation and Stirring in the Southeast Pacific Ocean and the Scotia Sea Sectors of the Antarctic Circumpolar Current

2016 ◽  
Vol 46 (7) ◽  
pp. 2005-2027 ◽  
Author(s):  
Dhruv Balwada ◽  
Kevin G. Speer ◽  
Joseph H. LaCasce ◽  
W. Brechner Owens ◽  
John Marshall ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
Kinetic Energy ◽  
Antarctic Circumpolar Current ◽  
Scotia Sea ◽  
Eddy Diffusivities ◽  
Southeast Pacific ◽  
The Mean ◽  
The Cross ◽  
Circumpolar Current ◽  
The Antarctic

AbstractThe large-scale middepth circulation and eddy diffusivities in the southeast Pacific Ocean and Scotia Sea sectors between 110° and 45°W of the Antarctic Circumpolar Current (ACC) are described based on a subsurface quasi-isobaric RAFOS-float-based Lagrangian dataset. These RAFOS float data were collected during the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). The mean flow, adjusted to a common 1400-m depth, shows the presence of jets in the time-averaged sense with speeds of 6 cm s−1 in the southeast Pacific Ocean and upward of 13 cm s−1 in the Scotia Sea. These jets appear to be locked to topography in the Scotia Sea but, aside from negotiating a seamount chain, are mostly free of local topographic constraints in the southeast Pacific Ocean. The eddy kinetic energy (EKE) is higher than the mean kinetic energy everywhere in the sampled domain by about 50%. The magnitude of the EKE increases drastically (by a factor of 2 or more) as the current crosses over the Hero and Shackleton fracture zones into the Scotia Sea. The meridional isopycnal stirring shows lateral and vertical variations with local eddy diffusivities as high as 2800 ± 600 m2 s−1 at 700 m decreasing to 990 ± 200 m2 s−1 at 1800 m in the southeast Pacific Ocean. However, the cross-ACC diffusivity in the southeast Pacific Ocean is significantly lower, with values of 690 ± 150 and 1000 ± 200 m2 s−1 at shallow and deep levels, respectively, due to the action of jets. The cross-ACC diffusivity in the Scotia Sea is about 1200 ± 500 m2 s−1.

scholarly journals Time-Mean Flow as the Prevailing Contribution to the Poleward Heat Flux across the Southern Flank of the Antarctic Circumpolar Current: A Case Study in the Fawn Trough, Kerguelen Plateau

2013 ◽  
Vol 43 (3) ◽  
pp. 583-601 ◽  
Author(s):  
H. Sekma ◽  
Y.-H. Park ◽  
F. Vivier
Keyword(s):  
Heat Flux ◽  
Southern Ocean ◽  
Antarctic Circumpolar Current ◽  
Mean Flow ◽  
Kerguelen Plateau ◽  
The Mean ◽  
The Cross ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Southern Flank

Abstract The major mechanisms of the oceanic poleward heat flux in the Southern Ocean are still in debate. The long-standing belief stipulates that the poleward heat flux across the Antarctic Circumpolar Current (ACC) is mainly due to mesoscale transient eddies and the cross-stream heat flux by time-mean flow is insignificant. This belief has recently been challenged by several numerical modeling studies, which stress the importance of mean flow for the meridional heat flux in the Southern Ocean. Here, this study analyzes moored current meter data obtained recently in the Fawn Trough, Kerguelen Plateau, to estimate the cross-stream heat flux caused by the time-mean flow and transient eddies. It is shown that the poleward eddy heat flux in this southern part of the ACC is negligible, while that from the mean flow is overwhelming by two orders of magnitude. This is due to the unusual anticlockwise turning of currents with decreasing depth, which is associated with significant bottom upwelling engendered by strong bottom currents flowing over the sloping topography of the trough. The circumpolar implications of these local observations are discussed in terms of the depth-integrated linear vorticity budget, which suggests that the six topographic features along the southern flank of the ACC equivalent to the Fawn Trough case would yield sufficient poleward heat flux to balance the oceanic heat loss in the subpolar region. As eddy activity on the southern flank of the ACC is too weak to transport sufficient heat poleward, the nonequivalent barotropic structure of the mean flow in several topographically constricted passages should accomplish the required task.

Barotropic and baroclinic inverse kinetic energy cascade in the Antarctic Circumpolar Current

2021 ◽  
Author(s):  
Hongjie Li ◽  
Yongsheng Xu
Keyword(s):  
Kinetic Energy ◽  
General Circulation ◽  
Antarctic Circumpolar Current ◽  
General Circulation Models ◽  
Energy Cascade ◽  
Turbulence Theory ◽  
Inverse Cascade ◽  
Spectral Flux ◽  
Circumpolar Current ◽  
The Antarctic

AbstractStratified geostrophic turbulence theory predicts an inverse energy cascade for the barotropic (BT) mode. Satellite altimetry has revealed a net inverse cascade in the baroclinic (BC) mode. Here the spatial variabilities of BT and BC kinetic energy fluxes in the Antarctic Circumpolar Current (ACC) were investigated using ECCO2 data, which synthesizes satellite data and in situ measurements with an eddy-permitting general circulation models containing realistic bathymetry and wind forcing. The BT and BC inverse kinetic energy cascades both reveal complex spatial variations that could not be explained fully by classical arguments. For example, the BC injection scales match better with most unstable scales than with the first-mode deformation scales, but the opposite is true for the BT mode. In addition, the BT and BC arrest scales do not follow the Rhines scale well in term of spatial variation, but show better consistency with their own energy-containing scales. The reverse cascade of the BT and BC modes was found related to their EKE, and better correlation was found between the BT inverse cascade and barotropization. Speculations of the findings were proposed. however, further observations and modeling experiments are needed to test these interpretations. Spectral flux anisotropy exhibits a feature associated with oceanic jets that is consistent with classical expectations. Specifically, the spectral flux along the along-stream direction remains negative at scales up to that of the studied domain (~2000km), while that in the perpendicular direction becomes positive close to the scale of the width of a typical jet.

The Antarctic Circumpolar Current in Three Dimensions

2006 ◽  
Vol 36 (4) ◽  
pp. 651-669 ◽  
Author(s):  
Timour Radko ◽  
John Marshall
Keyword(s):  
Antarctic Circumpolar Current ◽  
Three Dimensional ◽  
Perturbation Expansion ◽  
Dimensional Structure ◽  
Residual Circulation ◽  
Mean Flow ◽  
Overturning Circulation ◽  
The Mean ◽  
Circumpolar Current ◽  
The Antarctic

Abstract 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.

scholarly journals Equilibration of the Antarctic Circumpolar Current by Standing Meanders

2014 ◽  
Vol 44 (7) ◽  
pp. 1811-1828 ◽  
Author(s):  
Andrew F. Thompson ◽  
Alberto C. Naveira Garabato
Keyword(s):  
Antarctic Circumpolar Current ◽  
Relative Vorticity ◽  
Alternative Mechanism ◽  
Mean Flow ◽  
Spatially Correlated ◽  
Eddy Characteristics ◽  
Rapid Changes ◽  
The Mean ◽  
Circumpolar Current ◽  
The Antarctic

Abstract The insensitivity of the Antarctic Circumpolar Current (ACC)’s prominent isopycnal slope to changes in wind stress is thought to stem from the action of mesoscale eddies that counterbalance the wind-driven Ekman overturning—a framework verified in zonally symmetric circumpolar flows. Substantial zonal variations in eddy characteristics suggest that local dynamics may modify this balance along the path of the ACC. Analysis of an eddy-resolving ocean GCM shows that the ACC can be broken into broad regions of weak eddy activity, where surface winds steepen isopycnals, and a small number of standing meanders, across which the isopycnals relax. Meanders are coincident with sites of (i) strong eddy-induced modification of the mean flow and its vertical structure as measured by the divergence of the Eliassen–Palm flux and (ii) enhancement of deep eddy kinetic energy by up to two orders of magnitude over surrounding regions. Within meanders, the vorticity budget shows a balance between the advection of relative vorticity and horizontal divergence, providing a mechanism for the generation of strong vertical velocities and rapid changes in stratification. Temporal fluctuations in these diagnostics are correlated with variability in both the Eliassen–Palm flux and bottom speed, implying a link to dissipative processes at the ocean floor. At larger scales, bottom pressure torque is spatially correlated with the barotropic advection of planetary vorticity, which links to variations in meander structure. From these results, it is proposed that the “flexing” of standing meanders provides an alternative mechanism for reducing the sensitivity of the ACC’s baroclinicity to changes in forcing, separate from an ACC-wide change in transient eddy characteristics.

scholarly journals The South Atlantic in the Fine-Resolution Antarctic Model

1994 ◽  
Vol 12 (9) ◽  
pp. 826-839 ◽  
Author(s):  
D. P. Stevens ◽  
S. R. Thompson
Keyword(s):  
Antarctic Circumpolar Current ◽  
Geographical Area ◽  
South Atlantic ◽  
The South ◽  
The Indian Ocean ◽  
The Mean ◽  
Circumpolar Current ◽  
Fine Resolution ◽  
The Antarctic ◽  
Good Agreement

Abstract. The geographical area covered by the Fine-Resolution Antarctic Model (FRAM) includes that part of the South Atlantic south of 24°S. A description of the dynamics and thermodynamics of this region of the model is presented. Both the mean and eddy fields in the model are in good agreement with reality, although the magnitude of the transients is somewhat reduced. The heat flux is northward and in broad agreement with many other estimates. Agulhas eddies are formed by the model and propagate westward into the Atlantic providing a mechanism for fluxing heat from the Indian Ocean. The confluence of the Brazil and Falkland currents produces a strong front and a large amount of mesoscale activity. In the less stratified regions to the south, topographic steering of the Antarctic circumpolar current is important.

scholarly journals Eddies in Numerical Models of the Antarctic Circumpolar Current and Their Influence on the Mean Flow

1999 ◽  
Vol 29 (3) ◽  
pp. 328-350 ◽  
Author(s):  
S. E. Best ◽  
V. O. Ivchenko ◽  
K. J. Richards ◽  
R. D. Smith ◽  
R. C. Malone
Keyword(s):  
Antarctic Circumpolar Current ◽  
Numerical Models ◽  
Mean Flow ◽  
The Mean ◽  
Circumpolar Current ◽  
The Antarctic

scholarly journals Suppression of Eddy Diffusivity across Jets in the Southern Ocean

2010 ◽  
Vol 40 (7) ◽  
pp. 1501-1519 ◽  
Author(s):  
Raffaele Ferrari ◽  
Maxim Nikurashin
Keyword(s):  
Kinetic Energy ◽  
Southern Ocean ◽  
Antarctic Circumpolar Current ◽  
Eddy Diffusivity ◽  
Simple Expression ◽  
Ongoing Debate ◽  
The Core ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Mean Current

Abstract Geostrophic eddies control the meridional mixing of heat, carbon, and other climatically important tracers in the Southern Ocean. The rate of eddy mixing is typically quantified through an eddy diffusivity. There is an ongoing debate as to whether eddy mixing in enhanced in the core of the Antarctic Circumpolar Current or on its flanks. A simple expression is derived that predicts the rate of eddy mixing, that is, the eddy diffusivity, as a function of eddy and mean current statistics. This novel expression predicts suppression of the cross-jet eddy diffusivity in the core of the Antarctic Circumpolar Current, despite enhanced values of eddy kinetic energy. The expression is qualitatively and quantitatively validated by independent estimates of eddy mixing from altimetry observations. This work suggests that the meridional eddy diffusivity across the Antarctic Circumpolar Current is weaker than presently assumed because of the suppression of eddy mixing by the strong zonal current.

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