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On the motion of linearly stratified rotating fluids past capes

Published online by Cambridge University Press:  21 April 2006

Don L. Boyer  and
Lijun Tao
Don L. Boyer
Affiliation:
Department of Mechanical Engineering, University of Wyoming, Laramie, WY 82071, USA
Lijun Tao
Affiliation:
Department of Mechanical Engineering, University of Wyoming, Laramie, WY 82071, USA
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Abstract

This is an experimental investigation of the flow of an impulsively started linearly stratified, rotating fluid past obstacles located on either the right or left side of a channel of rectangular cross-section. The obstacle has plane sloping sides so as to represent a cape-like feature extending from a shoreline. Emphasis is given to the temporal flow development in the lee of the obstacle. The pertinent dimensionless parameters are the Rossby. Burger and Ekman numbers, the ratio of the fluid depth to obstacle width and the obstacle-to-channel-width ratio.

For sufficiently small Burger numbers and for a range of Rossby numbers the right-side obstacle produces fully attached flows at all levels. At larger Burger numbers attached lee anticyclones develop during a period of the order of ten advective timescales. At still larger Burger numbers the starting lee anticyclone is shed and followed by a weaker secondary anticyclone.

No fully attached regime could be found for the left-side obstacle for the range of parameters considered. For the smallest Burger numbers studied and for a range of Rossby numbers, a lee cyclone is formed on the order of one advective timescale; this eddy spins down at large times leaving a quiescent wake. At larger Burger numbers and for a range of Rossby numbers, cyclonic eddy shedding occurs.

Measurements of the streamwise location of the eddy centres, the streamwise extent of the eddies and the vorticities of the eddy cores are made as functions of a dimensionless time and the system parameters. It is found, for example, that the vorticity of the starting eddies at small times in the eddy-shedding regimes for both anticyclones and cyclones is strongest at the lowest observation levels. Ekman suction, however, tends to more strongly decrease the vortex strength in the lower levels compared to the middle levels so that at large times the vorticity in the middle levels exceeds that near the channel floor. Eddies with similar characteristics are found in the open ocean.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 180 , July 1987 , pp. 429 - 449
Copyright
© 1987 Cambridge University Press

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