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.

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.

Variability in Southern Hemisphere Ocean Circulation from the 1980s to the 2000s

2013 ◽  
Vol 43 (9) ◽  
pp. 1981-2007 ◽  
Author(s):  
K. Katsumata ◽  
S. Masuda
Keyword(s):  
Southern Hemisphere ◽  
Ocean Circulation ◽  
General Circulation ◽  
Antarctic Circumpolar Current ◽  
General Circulation Models ◽  
Polar Front ◽  
Inverse Model ◽  
Meridional Overturning Circulation ◽  
Steady Increase ◽  
Circumpolar Current

Abstract Interannual-to-decadal variability of ocean circulation in the Southern Hemisphere was examined using data from the 1980s to the 2000s in a box inverse model to estimate transport across hydrographic sections and three ocean general circulation models (OGCMs). The westerly wind stress over the OGCM Southern Ocean showed a steady increase of 5%–8% decade−1. The meridional overturning circulation was quantified by the transport across 30°S. The OGCMs suggested a slight strengthening [from 0.2 ± 1.0 to 0.8 ± 1.3 Sv decade−1 (1 Sv ≡ 106 m3 s−1)] of the upper meridional cell (Deacon cell) and two OGCMs showed a weakening (−0.8 ± 0.6 and −1.0 ± 0.3 Sv decade−1) of the lower meridional [Antarctic Bottom Water (AABW)] cell, partly explained by contraction of the AABW volume. The box inverse estimates did not contradict these two findings. For Antarctic Circumpolar Current transport, quantified by zonal transport across four key sections, the box inverse model estimated a decrease of 5–21 Sv. Decomposition of the decrease into baroclinic transport by the Subantarctic and Polar Fronts, barotropic transport, and others shows that the decrease is mostly due to barotropic transport and transport carried by the flow north of the Subantarctic Front and south of the Polar Front. In the OGCMs, the variability of transport across key sections is often correlated with transport carried by a flow south of the Polar Front and with the southern annular mode index. In all models, then, the transport of the Antarctic Circumpolar Current, defined as the transport carried by the fronts, has not decreased significantly over the study period.

Energy Cascades and Loss of Balance in a Reentrant Channel Forced by Wind Stress and Buoyancy Fluxes

2015 ◽  
Vol 45 (1) ◽  
pp. 272-293 ◽  
Author(s):  
Roy Barkan ◽  
Kraig B. Winters ◽  
Stefan G. Llewellyn Smith
Keyword(s):  
Kinetic Energy ◽  
Wind Stress ◽  
General Circulation ◽  
Large Fraction ◽  
Energy Cascade ◽  
Turbulence Theory ◽  
Inverse Energy Cascade ◽  
Loss Of Balance ◽  
Small Scales ◽  
Eddy Field

AbstractA large fraction of the kinetic energy in the ocean is stored in the “quasigeostrophic” eddy field. This “balanced” eddy field is expected, according to geostrophic turbulence theory, to transfer energy to larger scales. In order for the general circulation to remain approximately steady, instability mechanisms leading to loss of balance (LOB) have been hypothesized to take place so that the eddy kinetic energy (EKE) may be transferred to small scales where it can be dissipated. This study examines the kinetic energy pathways in fully resolved direct numerical simulations of flow in a flat-bottomed reentrant channel, externally forced by surface buoyancy fluxes and wind stress in a configuration that resembles the Antarctic Circumpolar Current. The flow is allowed to reach a statistical steady state at which point it exhibits both a forward and an inverse energy cascade. Flow interactions with irregular bathymetry are excluded so that bottom drag is the sole mechanism available to dissipate the upscale EKE transfer. The authors show that EKE is dissipated preferentially at small scales near the surface via frontal instabilities associated with LOB and a forward energy cascade rather than by bottom drag after an inverse energy cascade. This is true both with and without forcing by the wind. These results suggest that LOB caused by frontal instabilities near the ocean surface could provide an efficient mechanism, independent of boundary effects, by which EKE is dissipated. Ageostrophic anticyclonic instability is the dominant frontal instability mechanism in these simulations. Symmetric instability is also important in a “deep convection” region, where it can be sustained by buoyancy loss.

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.

scholarly journals Nonlinear Cascades of Surface Oceanic Geostrophic Kinetic Energy in the Frequency Domain*

2012 ◽  
Vol 42 (9) ◽  
pp. 1577-1600 ◽  
Author(s):  
Brian K. Arbic ◽  
Robert B. Scott ◽  
Glenn R. Flierl ◽  
Andrew J. Morten ◽  
James G. Richman ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Frequency Domain ◽  
General Circulation ◽  
General Circulation Models ◽  
Altimeter Data ◽  
Satellite Altimeter ◽  
Frequency Spectra ◽  
Low Frequencies ◽  
Spectral Flux ◽  
Satellite Altimeter Data

Abstract Motivated by the ubiquity of time series in oceanic data, the relative lack of studies of geostrophic turbulence in the frequency domain, and the interest in quantifying the contributions of intrinsic nonlinearities to oceanic frequency spectra, this paper examines the spectra and spectral fluxes of surface oceanic geostrophic flows in the frequency domain. Spectra and spectral fluxes are computed from idealized two-layer quasigeostrophic (QG) turbulence models and realistic ocean general circulation models, as well as from gridded satellite altimeter data. The frequency spectra of the variance of streamfunction (akin to sea surface height) and of geostrophic velocity are qualitatively similar in all of these, with substantial variance extending out to low frequencies. The spectral flux Π(ω) of kinetic energy in the frequency ω domain for the QG model documents a tendency for nonlinearity to drive energy toward longer periods, in like manner to the inverse cascade toward larger length scales documented in calculations of the spectral flux Π(k) in the wavenumber k domain. Computations of Π(ω) in the realistic model also display an “inverse temporal cascade.” In satellite altimeter data, some regions are dominated by an inverse temporal cascade, whereas others exhibit a forward temporal cascade. However, calculations performed with temporally and/or spatially filtered output from the models demonstrate that Π(ω) values are highly susceptible to the smoothing inherent in the construction of gridded altimeter products. Therefore, at present it is difficult to say whether the forward temporal cascades seen in some regions in altimeter data represent physics that is missing in the models studied here or merely sampling artifacts.

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 Nonlinear Differential Equations Modeling the Antarctic Circumpolar Current

2021 ◽  
Vol 23 (4) ◽  
Author(s):  
Jifeng Chu ◽  
Kateryna Marynets
Keyword(s):  
Fixed Point ◽  
Differential Equations ◽  
Boundary Conditions ◽  
Topological Degree ◽  
Antarctic Circumpolar Current ◽  
Fixed Point Theorems ◽  
Nonlinear Differential Equations ◽  
Existence Results ◽  
Circumpolar Current ◽  
The Antarctic

AbstractThe aim of this paper is to study one class of nonlinear differential equations, which model the Antarctic circumpolar current. We prove the existence results for such equations related to the geophysical relevant boundary conditions. First, based on the weighted eigenvalues and the theory of topological degree, we study the semilinear case. Secondly, the existence results for the sublinear and superlinear cases are proved by fixed point theorems.

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