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Dynamics of ventilated coherent cold eddies on a sloping bottom

Published online by Cambridge University Press:  26 April 2006

Gordon E. Swaters  and
Glenn R. Flierl
Gordon E. Swaters
Affiliation:
Applied Mathematics Institute, Department of Mathematics and Institute of Earth and Planetary Physics, University of Alberta, Edmonton, Alberta, T6G 2G1, Canada
Glenn R. Flierl
Affiliation:
Center for Meteorology and Physical Oceanography, Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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Abstract

A theory is presented to describe the propagation and structure of coherent cold-core (mesoscale) eddies on a sloping bottom including dynamical and thermodynamical interaction with the surrounding fluid. Based on parameter values suggested by oceanographic and rotating-tank experimental data, the evolution of the baroclinic eddy is modelled with nonlinear ‘intermediate lengthscale’ geostrophic dynamics which is coupled to the surrounding fluid. The process of ventilation is modelled with a simple cross-interfacial mass flux parameterization. The surrounding fluid is governed by nonlinear quasi-geostrophic dynamics including eddy-induced vortex-tube compression. Assuming a relatively weak ventilation rate, a multiple-scale asymptotic theory is constructed to describe the propagation of an initially isolated or coherent baroclinic eddy. Throughout the evolution the eddy is assumed to be interacting strongly with the surrounding fluid. To leading order, the eddy and surrounding fluid satisfy the Stern isolation constraint. The magnitude of the Eulerian velocity field in the surrounding fluid above the eddy is shown to be larger than the swirl velocities in the eddy interior as suggested by experimental data. Also, to leading order, the along-shelf translation speed is given by the Nof formula. The process of ventilation is shown to induce a slowly decaying upslope translation in the propagating eddy, and acts to stimulate a weak slowly decaying topographic Rossby wave field in the surrounding fluid. The important features of the theory are illustrated with a simple example calculation.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 223 , February 1991 , pp. 565 - 587
Copyright
© 1991 Cambridge University Press

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