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Sensitivity of Antarctic Circumpolar Current Transport and Eddy Activity to Wind Patterns in the Southern Ocean

Sensitivity of Antarctic Circumpolar Current Transport and Eddy Activity to Wind Patterns in the Southern Ocean
Sensitivity of Antarctic Circumpolar Current Transport and Eddy Activity to Wind Patterns in the Southern Ocean
The Southern Hemisphere westerly winds have intensified in recent decades associated with a positive trend in the southern annular mode (SAM). However, the response of the Antarctic Circumpolar Current (ACC) transport and eddy field to wind forcing remains a topic of debate. This study uses global eddy-permitting ocean circulation models driven with both idealized and realistic wind forcing to explore the response to interannual wind strengthening. The response of the barotropic and baroclinic transports and eddy field of the ACC is found to depend on the spatial pattern of the changes in wind forcing. In isolation, an enhancement of the westerlies over the ACC belt leads to an increase of both barotropic and baroclinic transport within the ACC envelope, with lagged enhancement of the eddy kinetic energy (EKE). In contrast, an increase in wind forcing near Antarctica drives a largely barotropic change in transport along closed f/H contours (“free mode”), with little change in eddy activity. Under realistic forcing, the interplay of the SAM and the El Niño–Southern Oscillation (ENSO) influences the spatial distribution of the wind anomalies, in particular the partition between changes in the wind stress over the ACC and along f/H contours. This study finds that the occurrence of a negative or positive ENSO during a positive SAM can cancel or double the wind anomalies near Antarctica, altering the response of the ACC and its eddy field. While a negative ENSO and positive SAM favors an increase in EKE, a positive ENSO and positive SAM lead to barotropic transport changes and no eddy response.
0022-3670
1051-1067
Langlais, Clothilde E.
23074aac-131a-481b-8e4c-632d111ff054
Rintoul, Stephen R.
ff078a21-d6cd-45bf-8c8f-f81f2e8ae410
Zika, Jan D.
1843cce7-77ce-4ef6-9f79-bcf4f9db30e5
Langlais, Clothilde E.
23074aac-131a-481b-8e4c-632d111ff054
Rintoul, Stephen R.
ff078a21-d6cd-45bf-8c8f-f81f2e8ae410
Zika, Jan D.
1843cce7-77ce-4ef6-9f79-bcf4f9db30e5

Langlais, Clothilde E., Rintoul, Stephen R. and Zika, Jan D. (2015) Sensitivity of Antarctic Circumpolar Current Transport and Eddy Activity to Wind Patterns in the Southern Ocean. Journal of Physical Oceanography, 45 (4), 1051-1067. (doi:10.1175/JPO-D-14-0053.1).

Record type: Article

Abstract

The Southern Hemisphere westerly winds have intensified in recent decades associated with a positive trend in the southern annular mode (SAM). However, the response of the Antarctic Circumpolar Current (ACC) transport and eddy field to wind forcing remains a topic of debate. This study uses global eddy-permitting ocean circulation models driven with both idealized and realistic wind forcing to explore the response to interannual wind strengthening. The response of the barotropic and baroclinic transports and eddy field of the ACC is found to depend on the spatial pattern of the changes in wind forcing. In isolation, an enhancement of the westerlies over the ACC belt leads to an increase of both barotropic and baroclinic transport within the ACC envelope, with lagged enhancement of the eddy kinetic energy (EKE). In contrast, an increase in wind forcing near Antarctica drives a largely barotropic change in transport along closed f/H contours (“free mode”), with little change in eddy activity. Under realistic forcing, the interplay of the SAM and the El Niño–Southern Oscillation (ENSO) influences the spatial distribution of the wind anomalies, in particular the partition between changes in the wind stress over the ACC and along f/H contours. This study finds that the occurrence of a negative or positive ENSO during a positive SAM can cancel or double the wind anomalies near Antarctica, altering the response of the ACC and its eddy field. While a negative ENSO and positive SAM favors an increase in EKE, a positive ENSO and positive SAM lead to barotropic transport changes and no eddy response.

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More information

Published date: April 2015
Additional Information: Supplemental information related to this paper is available at the Journals Online website: http://dx.doi.org/10.1175/JPO-D-14-0053.s1
Organisations: Physical Oceanography

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Local EPrints ID: 377285
URI: http://eprints.soton.ac.uk/id/eprint/377285
ISSN: 0022-3670
PURE UUID: d7e45898-95c5-433f-9a22-b8dd7d2a1e8e

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Date deposited: 19 May 2015 15:42
Last modified: 14 Mar 2024 20:00

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Contributors

Author: Clothilde E. Langlais
Author: Stephen R. Rintoul
Author: Jan D. Zika

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