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Mesoscale subduction at the Antarctic Polar Front driven by baroclinic instability

Naveira Garabato, A.C., Allen, J.T., Leach, H., Strass, V.H. and Pollard, R.T. (2001) Mesoscale subduction at the Antarctic Polar Front driven by baroclinic instability Journal of Physical Oceanography, 31, (8, Pt.1), pp. 2087-2107.

Record type: Article

Abstract

A study of mesoscale subduction at the Antarctic Polar Front (PF) is conducted by use of hydrographic data from a high-resolution, quasi-synoptic survey of the front. The geostrophic velocity and isopycnal potential vorticity (PV) fields are computed, and the ageostrophic flow diagnosed from the semigeostrophic omega equation. It is found that the ageostrophic circulation induced by baroclinic instability counteracts the frontogenesis and frontolysis effected by the confluence and difluence, respectively, of the geostrophic velocity field. Though the sense of the ageostrophic circulation is reversed repeatedly along the front, the existence of PV gradients along isopycnals leads to a net cross-front ‘‘bolus’’ transport. In response to a reversal of this gradient with depth (a necessary condition for the onset of baroclinic instability), the bolus transport is northward at the protruding temperature minimum layer that characterizes the PF, and southward above. This net cross-front overturning circulation acts to flatten the isopycnals of the front and results in a subduction of the temperature minimum layer as it progresses northward along isopycnals. Consistently, a net baroclinic conversion rate of approximately 1 cm^2 s^-2 d^-1, corresponding to a net subduction rate of O(20 m yr^-1), is calculated in the survey area. The similarity between the PV field of the PF and other Southern Ocean fronts suggests that the authors’ results may also be applicable there. This has profound implications for the understanding of the zonation of the Antarctic Circumpolar Current.

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Published date: 2001

Identifiers

Local EPrints ID: 37539
URI: http://eprints.soton.ac.uk/id/eprint/37539
ISSN: 0022-3670
PURE UUID: 12bc1a66-e032-4eb0-9103-912fdd3d4587

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Date deposited: 24 May 2006
Last modified: 18 Sep 2017 00:16

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Contributors

Author: J.T. Allen
Author: H. Leach
Author: V.H. Strass
Author: R.T. Pollard

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