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Barotropic quasi-geostrophic f-plane flow over anisotropic topography

Published online by Cambridge University Press:  26 April 2006

G. F. Carnevale ,
R. Purini ,
P. Orlandi  and
P. Cavazza
G. F. Carnevale
Affiliation:
Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, USA
R. Purini
Affiliation:
Istituto di Fisica dell'Atmosfera, P.le Luigi Sturzo 31, 00144 Roma, Italy
P. Orlandi
Affiliation:
Dipartimento di Meccanica e Aeronautica, Universita di Roma, “La Sapienza,” Via Eudossiana 16, 00184 Roma, Italy
P. Cavazza
Affiliation:
Dipartimento di Meccanica e Aeronautica, Universita di Roma, “La Sapienza,” Via Eudossiana 16, 00184 Roma, Italy
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Abstract

For an anisotropic topographic feature in a large-scale flow, the orientation of the topography with respect to the flow will affect the vorticity production that results from the topography–flow interaction. This in turn affects the amount of form drag that the ambient flow experiences. Numerical simulations and perturbation theory are used to explore these effects of change in topographic orientation. The flow is modelled as a quasi-geostrophic homogeneous fluid on an f-plane. The topography is taken to be a hill of limited extent, with an elliptical cross-section in the horizontal. It is shown that, as a result of a basic asymmetry of the quasi-geostrophic flow, the strength of the form drag depends not only on the magnitude of the angle that the topographic axis makes with the oncoming stream, but also on the sign of this angle. For sufficiently low topography, it is found that a positive angle of attack leads to a stronger form drag than that for the corresponding negative angle. For strong topography, this relation is reversed, with the negative angle then resulting in the stronger form drag.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 285 , 25 February 1995 , pp. 329 - 347
Copyright
© 1995 Cambridge University Press

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