On the Patterns of Wind-Power Input to the Ocean Circulation

Fabien Roquet Department of Earth, Atmosphere and Planetary Science, Massachusetts Institute of Technology, Cambridge, Massachusetts

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Carl Wunsch Department of Earth, Atmosphere and Planetary Science, Massachusetts Institute of Technology, Cambridge, Massachusetts

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Gurvan Madec Laboratoire d’Océanographie Dynamique et de Climatologie, Paris, France

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Abstract

Pathways of wind-power input into the ocean general circulation are analyzed using Ekman theory. Direct rates of wind work can be calculated through the wind stress acting on the surface geostrophic flow. However, because that energy is transported laterally in the Ekman layer, the injection into the geostrophic interior is actually controlled by Ekman pumping, with a pattern determined by the wind curl rather than the wind itself. Regions of power injection into the geostrophic interior are thus generally shifted poleward compared to regions of direct wind-power input, most notably in the Southern Ocean, where on average energy enters the interior 10° south of the Antarctic Circumpolar Current core. An interpretation of the wind-power input to the interior is proposed, expressed as a downward flux of pressure work. This energy flux is a measure of the work done by the Ekman pumping against the surface elevation pressure, helping to maintain the observed anomaly of sea surface height relative to the global-mean sea level.

Corresponding author address: Fabien Roquet, Department of Earth, Atmosphere and Planetary Science, Massachusetts Institute of Technology, Cambridge, MA 02139. E-mail: roquet@mit.edu

Abstract

Pathways of wind-power input into the ocean general circulation are analyzed using Ekman theory. Direct rates of wind work can be calculated through the wind stress acting on the surface geostrophic flow. However, because that energy is transported laterally in the Ekman layer, the injection into the geostrophic interior is actually controlled by Ekman pumping, with a pattern determined by the wind curl rather than the wind itself. Regions of power injection into the geostrophic interior are thus generally shifted poleward compared to regions of direct wind-power input, most notably in the Southern Ocean, where on average energy enters the interior 10° south of the Antarctic Circumpolar Current core. An interpretation of the wind-power input to the interior is proposed, expressed as a downward flux of pressure work. This energy flux is a measure of the work done by the Ekman pumping against the surface elevation pressure, helping to maintain the observed anomaly of sea surface height relative to the global-mean sea level.

Corresponding author address: Fabien Roquet, Department of Earth, Atmosphere and Planetary Science, Massachusetts Institute of Technology, Cambridge, MA 02139. E-mail: roquet@mit.edu
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