Climatic variations of the work done by the wind on the ocean's general circulation

Lauderdale, J.M., Naveira Garabato, A.C., Oliver, K.I.C. and Thomas, L.N. (2012) Climatic variations of the work done by the wind on the ocean's general circulation. Journal of Geophysical Research, 117 (C9), C09017. (doi:10.1029/2012JC008135).

Abstract

The Southern Hemisphere westerlies exert an important influence on global climate, supplying nearly half of the mechanical energy for the deep overturning circulation. In a coarse-resolution ocean model, northward-shifted winds increase the work done on surface geostrophic flows due to enhanced velocities associated with the Antarctic Circumpolar Current (ACC). Alternatively, energy supply is diminished by southward-shifted winds, primarily through reduced correspondence between wind stress and surface velocity in the Southern Ocean due to dynamical and topographic constraints on the ACC. When combined perturbations in latitude and magnitude of the westerlies are applied, these results are reconciled with estimates of recent trends in wind work and volume transport in the Southern Ocean from observations and coupled climate models. This indicates that the strength of the winds exerts a dominant effect that masks the opposing consequences of latitudinal migration. In particular, transport through Drake Passage shows a clear relationship with wind work and velocity when the winds move poleward leading to a reduction in all three quantities. However, under equatorward-shifted winds, stronger polar easterlies adjacent to the Antarctic continent establishes a recirculation gyre leading to increased mechanical energy input and swifter currents but reduced transport. Significant (O(25%)) changes in the mechanical energy supply from the winds may be possible on climatic time scales, particularly associated with the spatial correlation between winds and the ACC that does not depend critically on unresolved eddy processes in this model, leading to a pathway for altering abyssal diapycnal mixing rates and stratification of the ocean interior.

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Contributors

Author: A.C. Naveira Garabato

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