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Two-layer model of shear-driven coastal upwelling in the presence of bottom topography

Published online by Cambridge University Press:  20 April 2006

Siavash Narimousa  and
Tony Maxworthy
Siavash Narimousa
Affiliation:
Department of Mechanical Engineering, University of Southern California, Los Angeles, CA 90089-1453
Tony Maxworthy
Affiliation:
Department of Mechanical Engineering, University of Southern California, Los Angeles, CA 90089-1453
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Abstract

A stratified two-layer fluid is brought to solid-body counterclockwise rotation inside a cylindrical tank having a conical bottom with a radial topographic ridge. A stress is then applied to the top surface by means of a clockwise differentially rotating disk. The resulting Ekman-layer flux causes the top layer to spin-down and the interface to rise near the wall and to descend a t the centre of the tank. As this process continues, the interface (front) between the two layers intersects the disk surface, and after that migrates away from the wall and allows the bottom fluid to contact the disk directly. The migration of the front continues until a steady state is reached, the front becomes stationary and the system is in geostrophic balance. The first sign of upwelled flow at the surface always occurs as a high-speed jet-like plume at the bottom topography, and only at a later time does a uniform upwelled flow appear a t the surface upstream of the topography. This plume, which always forms near the downstream edge of the topography, migrates in advance of the upstream front to produce an upwelling maximum at the bottom topography.

The final width of the upstream flow in steady-state conditions is estimated by a simple theoretical model, which is in good agreement with the experimental results. We have an experimental criterion to predict the occurrence of travelling baroclinic waves on the upstream front. On the downstream side of the ridge, large standing waves are observed, with significant upwelling within them. Under some circumstances cyclones pinch-off from the upstream front, the plume on the ridge and the crests of the large downstream standing waves. We present criteria to predict the occurrence of these pinch-off processes.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 159 , October 1985 , pp. 503 - 531
Copyright
© 1985 Cambridge University Press

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