Editorial Type:
Article
Article Type:
Research Article

Interactions of Baroclinic Isolated Vortices: The Dominant Effect of Shielding

S. Valcke CNRS, Laboratoire des Ecoulements Géophysiques et Industriels, Institut de Mécanique de Grenoble, Grenoble, France

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J. Verron CNRS, Laboratoire des Ecoulements Géophysiques et Industriels, Institut de Mécanique de Grenoble, Grenoble, France

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Print Publication:
01 Apr 1997
DOI:
https://doi.org/10.1175/1520-0485(1997)027<0524:IOBIVT>2.0.CO;2
Page(s):
524–541
Restricted access

Abstract

The interactions of two quasigeostrophic isolated shielded vortices are considered in a two-layer model and in the reduced-gravity approximation. Each shielded vortex is defined by a realistic horizontal profile of relative vorticity in the upper layer. In the numerical experiments, the initial separation distance between the vortices, d, and the degree of the ambient baroclinicity (i.e., the density stratification) are varied.

The results show that the interactions of shielded vortices are dictated by their horizontal structure of potential vorticity, which depends on the baroclinicity of the system. Globally, the critical distance of merging is dc/R = 2.4 ± 0.3 (where R is the radius of the vortices). The results denote also a favoring effect of baroclinicity on the merging efficiency, which increases when the baroclinicity increases.

Furthermore, a new mechanism of interaction inhibiting the merging is identified. When two vortices characterized by an annulus of opposite-sign potential vorticity surrounding their core interact, the potential vorticity of the annuli is redistributed and forms two lateral poles. Under the action of these poles, the vortices move apart from one another and their merging is inhibited. It is therefore concluded that the merging of vortices possessing a shielded potential vorticity structure is very unlikely. To apply these results to the oceanic reality, a better knowledge of the horizontal structure of oceanic vortices remains essential.

Corresponding author address: Sophie Valcke, SEOS/CEOR, University of Victoria, P.O. Box 1700, Victoria, BC V8W 2Y2, Canada.

Abstract

The interactions of two quasigeostrophic isolated shielded vortices are considered in a two-layer model and in the reduced-gravity approximation. Each shielded vortex is defined by a realistic horizontal profile of relative vorticity in the upper layer. In the numerical experiments, the initial separation distance between the vortices, d, and the degree of the ambient baroclinicity (i.e., the density stratification) are varied.

The results show that the interactions of shielded vortices are dictated by their horizontal structure of potential vorticity, which depends on the baroclinicity of the system. Globally, the critical distance of merging is dc/R = 2.4 ± 0.3 (where R is the radius of the vortices). The results denote also a favoring effect of baroclinicity on the merging efficiency, which increases when the baroclinicity increases.

Furthermore, a new mechanism of interaction inhibiting the merging is identified. When two vortices characterized by an annulus of opposite-sign potential vorticity surrounding their core interact, the potential vorticity of the annuli is redistributed and forms two lateral poles. Under the action of these poles, the vortices move apart from one another and their merging is inhibited. It is therefore concluded that the merging of vortices possessing a shielded potential vorticity structure is very unlikely. To apply these results to the oceanic reality, a better knowledge of the horizontal structure of oceanic vortices remains essential.

Corresponding author address: Sophie Valcke, SEOS/CEOR, University of Victoria, P.O. Box 1700, Victoria, BC V8W 2Y2, Canada.

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