The influence of mesoscale eddies and topology on southern ocean flow

Sinha, Bablu (1993) The influence of mesoscale eddies and topology on southern ocean flow. University of Southampton, Doctoral Thesis.

Abstract

The physical processes of eddy potential vorticity transport, momentum redistribution and jet formation in the Southern Ocean are studied with a view to understanding and parametrising their effects on the large scale circulation. Such a goal is desirable given the importance of the Southern Ocean in the world ocean circulation, and its role in the evolution of global climate.

The study is conducted using a wind driven quasigeostrophic channel model. Without topography the flow adopts a configuration with an intense meandering central jet flanked by eddies. In the presence of a centrally located Gaussian topographic hill the flow configuration is drastically altered, taking on a double jet structure upstream of the hill and exhibiting a Rossby wave wake downstream of it. The mean mass transport is halved.

The transient eddies are found to follow a simple closure hypothesis based on a diffusive parameterisation of of eddy potential vorticity transport in both topographic and flat bottomed cases provided that the dynamically irrelevant nondivergent part of the eddy potential vorticity flux is discarded in the topographic case.

The standing and transient eddies are found to have distinct roles in the momentum balance, depending on the location in the channel, and the closeness to topography.

In the presence of a zonally symmetric Gaussian ridge, the flow characteristics are again profoundly altered with a number of distinct zonal jets formed whose spacing is shown to be related to the topographic slope and the eddy energy of the flow. The phenomenon is observed in the Fine Resolution Antarctic Model.

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