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The dynamics of equatorially asymmetric thermohaline circulations

The dynamics of equatorially asymmetric thermohaline circulations
The dynamics of equatorially asymmetric thermohaline circulations
The three-dimensional dynamics of equatorially asymmetric thermohaline flow are investigated using an ocean general circulation model in a highly idealized configuration with no wind forcing and nearly fixed surface density. Small asymmetries in surface density lead to strongly asymmetric meridional overturning patterns, with deep water formed in the denser (northern) hemisphere filling the abyss. The poleward deep transport in the lighter hemisphere implies that the deep zonal-mean zonal pressure gradient reverses across the equator. Density along the eastern boundary and the zonally averaged density are nearly symmetric about the equator except at very high latitudes; the Southern Hemisphere western boundary thermocline, in contrast, is balanced by weaker upwelling and is hence broader than its northern counterpart. This pattern is explained through the spinup of the asymmetric circulation from a symmetric one, the timescale of which is set through advection by the mean deep western boundary current.
For the strength of the interhemispheric transport, a lower bound of one-half the one-hemisphere overturning strength is derived theoretically for small finite forcing asymmetries, implying that the symmetric circulation is unlikely to be realized. Under asymmetric surface forcing, enhanced mixing in the denser hemisphere suppresses interhemispheric transport. Conversely, very strong cross-equatorial transport is caused by enhanced mixing in the lighter hemisphere. These results indicate that, once the surface densities determine that North Atlantic Deep Water is the dominant ventilating source, its export rate from the North Atlantic is controlled by mixing and upwelling in the rest of the World Ocean.
WOCE, THERMOHALINE CIRCULATION, OCEAN CIRCULATION, OCEAN MODELS
0022-3670
955-970
Marotzke, J.
6047bfd1-68a3-4abe-95ce-e1df9a56ce76
Klinger, B.A.
85e68361-bf4c-49c3-8a86-3faca1f3900c
Marotzke, J.
6047bfd1-68a3-4abe-95ce-e1df9a56ce76
Klinger, B.A.
85e68361-bf4c-49c3-8a86-3faca1f3900c

Marotzke, J. and Klinger, B.A. (2000) The dynamics of equatorially asymmetric thermohaline circulations. Journal of Physical Oceanography, 30 (5), 955-970. (doi:10.1175/1520-0485(2000)030<0955:TDOEAT>2.0.CO;2).

Record type: Article

Abstract

The three-dimensional dynamics of equatorially asymmetric thermohaline flow are investigated using an ocean general circulation model in a highly idealized configuration with no wind forcing and nearly fixed surface density. Small asymmetries in surface density lead to strongly asymmetric meridional overturning patterns, with deep water formed in the denser (northern) hemisphere filling the abyss. The poleward deep transport in the lighter hemisphere implies that the deep zonal-mean zonal pressure gradient reverses across the equator. Density along the eastern boundary and the zonally averaged density are nearly symmetric about the equator except at very high latitudes; the Southern Hemisphere western boundary thermocline, in contrast, is balanced by weaker upwelling and is hence broader than its northern counterpart. This pattern is explained through the spinup of the asymmetric circulation from a symmetric one, the timescale of which is set through advection by the mean deep western boundary current.
For the strength of the interhemispheric transport, a lower bound of one-half the one-hemisphere overturning strength is derived theoretically for small finite forcing asymmetries, implying that the symmetric circulation is unlikely to be realized. Under asymmetric surface forcing, enhanced mixing in the denser hemisphere suppresses interhemispheric transport. Conversely, very strong cross-equatorial transport is caused by enhanced mixing in the lighter hemisphere. These results indicate that, once the surface densities determine that North Atlantic Deep Water is the dominant ventilating source, its export rate from the North Atlantic is controlled by mixing and upwelling in the rest of the World Ocean.

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Published date: 2000
Keywords: WOCE, THERMOHALINE CIRCULATION, OCEAN CIRCULATION, OCEAN MODELS

Identifiers

Local EPrints ID: 8757
URI: https://eprints.soton.ac.uk/id/eprint/8757
ISSN: 0022-3670
PURE UUID: 65493b3f-f42b-42bc-b835-5e874d646722

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Date deposited: 25 Aug 2004
Last modified: 17 Jul 2017 17:12

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Author: J. Marotzke
Author: B.A. Klinger

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