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Standing and Transient Eddies in the Response of the Southern Ocean Meridional Overturning to the Southern Annular Mode

Standing and Transient Eddies in the Response of the Southern Ocean Meridional Overturning to the Southern Annular Mode
Standing and Transient Eddies in the Response of the Southern Ocean Meridional Overturning to the Southern Annular Mode
To refine the understanding of how the Southern Ocean responds to recent intensification of the southern annular mode (SAM), a regional ocean model at two eddy-permitting resolutions was forced with two synthetic interannual forcings. The first forcing corresponds to homogeneously intensified winds, while the second concerns their poleward intensification, consistent with positive phases of the SAM. Resulting wind-driven responses differ greatly between the nearly insensitive Antarctic Circumpolar Current (ACC) and the more sensitive meridional overturning circulation (MOC). As expected, eddies mitigate the response of the ACC and MOC to poleward-intensified winds. However, transient eddies do not necessarily play an increasing role in meridional transport with increasing resolution. As winds and resolution increase, meridional transport from standing eddies becomes more efficient at balancing wind-enhanced overturning. These results question the current paradigms on the role of eddies and present new challenges for eddy flux parameterization. Results also indicate that spatial patterns of wind anomalies are at least as important as the overall change in intensity in influencing the Southern Ocean’s dynamic response to wind events. Poleward-intensified wind anomalies from the positive trend in the SAM are far more efficient in accelerating the ACC than homogeneous wind anomalies.
0894-8755
6958-6974
Dufour, C.O.
30f6030d-afd0-4e8b-8a62-9494e5d2130d
Le Sommer, J.
b2f7856c-9030-4d9e-bda6-dbfea753d329
Zika, J.D.
1843cce7-77ce-4ef6-9f79-bcf4f9db30e5
Gehlen, M.
ea0e4efc-ebd0-453c-ae9d-ba5c931867a3
Orr, J.C.
59198c8e-f89d-40ec-90b5-1d94de00ac5a
Mathiot, P.
3a3b8745-dbb0-4da5-a9a2-6c95a55425d0
Barnier, B.
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Dufour, C.O.
30f6030d-afd0-4e8b-8a62-9494e5d2130d
Le Sommer, J.
b2f7856c-9030-4d9e-bda6-dbfea753d329
Zika, J.D.
1843cce7-77ce-4ef6-9f79-bcf4f9db30e5
Gehlen, M.
ea0e4efc-ebd0-453c-ae9d-ba5c931867a3
Orr, J.C.
59198c8e-f89d-40ec-90b5-1d94de00ac5a
Mathiot, P.
3a3b8745-dbb0-4da5-a9a2-6c95a55425d0
Barnier, B.
0179fa7c-ed1b-45df-9e81-5a959268d99b

Dufour, C.O., Le Sommer, J., Zika, J.D., Gehlen, M., Orr, J.C., Mathiot, P. and Barnier, B. (2012) Standing and Transient Eddies in the Response of the Southern Ocean Meridional Overturning to the Southern Annular Mode. Journal of Climate, 25 (20), 6958-6974. (doi:10.1175/JCLI-D-11-00309.1).

Record type: Article

Abstract

To refine the understanding of how the Southern Ocean responds to recent intensification of the southern annular mode (SAM), a regional ocean model at two eddy-permitting resolutions was forced with two synthetic interannual forcings. The first forcing corresponds to homogeneously intensified winds, while the second concerns their poleward intensification, consistent with positive phases of the SAM. Resulting wind-driven responses differ greatly between the nearly insensitive Antarctic Circumpolar Current (ACC) and the more sensitive meridional overturning circulation (MOC). As expected, eddies mitigate the response of the ACC and MOC to poleward-intensified winds. However, transient eddies do not necessarily play an increasing role in meridional transport with increasing resolution. As winds and resolution increase, meridional transport from standing eddies becomes more efficient at balancing wind-enhanced overturning. These results question the current paradigms on the role of eddies and present new challenges for eddy flux parameterization. Results also indicate that spatial patterns of wind anomalies are at least as important as the overall change in intensity in influencing the Southern Ocean’s dynamic response to wind events. Poleward-intensified wind anomalies from the positive trend in the SAM are far more efficient in accelerating the ACC than homogeneous wind anomalies.

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Published date: 2012
Organisations: Physical Oceanography

Identifiers

Local EPrints ID: 344701
URI: https://eprints.soton.ac.uk/id/eprint/344701
ISSN: 0894-8755
PURE UUID: 2b9e638a-dd06-44eb-85e0-b740e6476271

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Date deposited: 29 Oct 2012 10:28
Last modified: 16 Jul 2019 21:50

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