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Original Research Papers

The effect of mechanical stirring on horizontal convection

Authors:

R. Tailleux ,

Department of Meteorology, University of Reading, Earley Gate, PO Box 243, Reading RG6 6BB, GB
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L. Rouleau

Department of Meteorology, University of Reading, Earley Gate, PO Box 243, Reading RG6 6BB, GB
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Abstract

An important experimental result, as yet poorly understood, is that mechanical stirring can significantly enhance the strength of horizontal convection. A contentious issue is whether this necessarily implies that the mechanical stirring replaces the buoyancy forcing as the main source of energy driving the observed overturning circulation, as has been suggested for the Atlantic meridional overturning circulation (AMOC). In this paper, rigorous energetics considerations and idealized numerical experiments reveal that the rate at which the surface buoyancy forcing supplies energy to the fluid, as measured by the production rate of available potential energy G(APE), does not solely depend upon the buoyancy forcing, as is often implicitly assumed, but also upon the vertical stratification, such that the deeper the thermocline depth, the larger G(APE). This suggests that mechanical stirring enhances horizontal convection because it causes more energy to be extracted from the buoyancy forcing. It does so by enhancing turbulent mixing, which allows surface heating to reach greater depths, which increases the thermocline depth and hence G(APE). This paper therefore proposes a new hypothesis, namely that mechanically stirred horizontal convection and the AMOC are best described as mechanically controlled heat engines.

How to Cite: Tailleux, R. and Rouleau, L., 2010. The effect of mechanical stirring on horizontal convection. Tellus A: Dynamic Meteorology and Oceanography, 62(2), pp.138–153. DOI: http://doi.org/10.1111/j.1600-0870.2009.00426.x
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  Published on 01 Jan 2010
 Accepted on 12 Nov 2009            Submitted on 2 May 2009

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