Effects of Bottom Topography in the Large-Scale Circulation of the Southern Ocean

Christopher W. Hughes Proudman Oceanographic Laboratory, Bidston Observatory, Birkenhead, Merseyside, United Kingdom

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Peter D. Killworth Institute of Oceanographic Sciences, Deacon Laboratory, Wormley, Godalming, Surrey, United Kingdom

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Abstract

The characteristics of an unforced, stratified f-plane geostrophic flow over topography are described, and scaling arguments are made to justify the use of such a flow as a first-order approximation to a real, large-scale circulation. Consideration of integral constraints then provides an insight into the ways in which second-order processes must balance the wind forcing. The importance of bottom pressure in this model is used to test the scalings and theory on a dataset taken from the Fine Resolution Antarctic Model. Two plots of bottom pressure, each with depth dependence filtered out in a different way, confirm the scalings producing the following conclusions: The effect of topography on the bottom boundary condition (no flow through the boundary) is important to the first-order (f-plane geostrophic) circulation; the turning of horizontal velocities with depth is limited, especially in regions of strong flow; and a picture of bottom pressure, appropriately filtered for depth dependence, contains a wealth of valuable information about the importance of second-order processes, demonstrating that they are most important in particular localized regions associated with topographic features.

Abstract

The characteristics of an unforced, stratified f-plane geostrophic flow over topography are described, and scaling arguments are made to justify the use of such a flow as a first-order approximation to a real, large-scale circulation. Consideration of integral constraints then provides an insight into the ways in which second-order processes must balance the wind forcing. The importance of bottom pressure in this model is used to test the scalings and theory on a dataset taken from the Fine Resolution Antarctic Model. Two plots of bottom pressure, each with depth dependence filtered out in a different way, confirm the scalings producing the following conclusions: The effect of topography on the bottom boundary condition (no flow through the boundary) is important to the first-order (f-plane geostrophic) circulation; the turning of horizontal velocities with depth is limited, especially in regions of strong flow; and a picture of bottom pressure, appropriately filtered for depth dependence, contains a wealth of valuable information about the importance of second-order processes, demonstrating that they are most important in particular localized regions associated with topographic features.

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