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The residual circulation of the Southern Ocean: Which spatio-temporal scales are needed?

The residual circulation of the Southern Ocean: Which spatio-temporal scales are needed?
The residual circulation of the Southern Ocean: Which spatio-temporal scales are needed?
he Southern Ocean circulation consists of a complicated mixture of processes and phenomena that arise at different time and spatial scales which need to be parametrized in the state-of-the-art climate models. The temporal and spatial scales that give rise to the present-day residual mean circulation are here investigated by calculating the Meridional Overturning Circulation (MOC) in density coordinates from an eddy-permitting global model. The region sensitive to the temporal decomposition is located between 38°S and 63°S, associated with the eddy-induced transport. The “Bolus” component of the residual circulation corresponds to the eddy-induced transport. It is dominated by timescales between 1 month and 1 year. The temporal behavior of the transient eddies is examined in splitting the “Bolus” component into a “Seasonal”, an “Eddy” and an “Inter-monthly” component, respectively representing the correlation between density and velocity fluctuations due to the average seasonal cycle, due to mesoscale eddies and due to large-scale motion on timescales longer than one month that is not due to the seasonal cycle. The “Seasonal” bolus cell is important at all latitudes near the surface. The “Eddy” bolus cell is dominant in the thermocline between 50°S and 35°S and over the whole ocean depth at the latitude of the Drake Passage. The “Inter-monthly” bolus cell is important in all density classes and is maximal in the Brazil–Malvinas Confluence and the Agulhas Return Current. The spatial decomposition indicates that a large part of the Eulerian mean circulation is recovered for spatial scales larger than 11.25°, implying that small-scale meanders in the Antarctic Circumpolar Current (ACC), near the Subantarctic and Polar Fronts, and near the Subtropical Front are important in the compensation of the Eulerian mean flow.
Overturning, Stream function, Southern Ocean, Bolus, Deacon Cell
1463-5003
46-55
Ballarotta, Maxime
9d04b373-79e4-4544-b224-37c1288080c2
Drijfhout, Sybren
a5c76079-179b-490c-93fe-fc0391aacf13
Kuhlbrodt, Till
2b5ab80d-f09e-49f1-9514-a24fcc65ab6f
Döös, Kristofer
f983e388-b9e9-4405-a51d-adf432410c2e
Ballarotta, Maxime
9d04b373-79e4-4544-b224-37c1288080c2
Drijfhout, Sybren
a5c76079-179b-490c-93fe-fc0391aacf13
Kuhlbrodt, Till
2b5ab80d-f09e-49f1-9514-a24fcc65ab6f
Döös, Kristofer
f983e388-b9e9-4405-a51d-adf432410c2e

Ballarotta, Maxime, Drijfhout, Sybren, Kuhlbrodt, Till and Döös, Kristofer (2013) The residual circulation of the Southern Ocean: Which spatio-temporal scales are needed? Ocean Modelling, 64, 46-55. (doi:10.1016/j.ocemod.2013.01.005).

Record type: Article

Abstract

he Southern Ocean circulation consists of a complicated mixture of processes and phenomena that arise at different time and spatial scales which need to be parametrized in the state-of-the-art climate models. The temporal and spatial scales that give rise to the present-day residual mean circulation are here investigated by calculating the Meridional Overturning Circulation (MOC) in density coordinates from an eddy-permitting global model. The region sensitive to the temporal decomposition is located between 38°S and 63°S, associated with the eddy-induced transport. The “Bolus” component of the residual circulation corresponds to the eddy-induced transport. It is dominated by timescales between 1 month and 1 year. The temporal behavior of the transient eddies is examined in splitting the “Bolus” component into a “Seasonal”, an “Eddy” and an “Inter-monthly” component, respectively representing the correlation between density and velocity fluctuations due to the average seasonal cycle, due to mesoscale eddies and due to large-scale motion on timescales longer than one month that is not due to the seasonal cycle. The “Seasonal” bolus cell is important at all latitudes near the surface. The “Eddy” bolus cell is dominant in the thermocline between 50°S and 35°S and over the whole ocean depth at the latitude of the Drake Passage. The “Inter-monthly” bolus cell is important in all density classes and is maximal in the Brazil–Malvinas Confluence and the Agulhas Return Current. The spatial decomposition indicates that a large part of the Eulerian mean circulation is recovered for spatial scales larger than 11.25°, implying that small-scale meanders in the Antarctic Circumpolar Current (ACC), near the Subantarctic and Polar Fronts, and near the Subtropical Front are important in the compensation of the Eulerian mean flow.

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More information

Published date: 2013
Keywords: Overturning, Stream function, Southern Ocean, Bolus, Deacon Cell
Organisations: Physical Oceanography

Identifiers

Local EPrints ID: 352577
URI: https://eprints.soton.ac.uk/id/eprint/352577
ISSN: 1463-5003
PURE UUID: c0a11148-b373-4952-bd79-b6e1e30dc351

Catalogue record

Date deposited: 15 May 2013 14:04
Last modified: 16 Jul 2019 21:33

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