Interaction of Barotropic Vortices with Coastal Topography: Laboratory Experiments and Numerical Simulations

L. Zavala Sansón Eindhoven University of Technology, Eindhoven, Netherlands

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G. J. F. van Heijst Eindhoven University of Technology, Eindhoven, Netherlands

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Abstract

The interaction of a barotropic cyclonic vortex on a β plane with a strong topographic slope is studied by means of laboratory experiments and numerical simulations. In the laboratory, the vortex is produced in a rectangular rotating tank with a weak uniformly sloping bottom (slope angle 3.5°) in order to simulate the β effect. The cyclonic vortex moves in the northwestward direction and interacts with an additional, pronounced linear topography (slope angle 35°) along the western boundary of the tank. The laboratory experiments revealed that the original northwestward trajectory changes to the south until the vortex is dissipated by viscous effects and bottom friction. As it moves upslope, the exterior ring of the vortex forms a strong current to the northeast. From this current a new cyclonic vortex is created, repeating approximately the behavior of the original one. Later, two more vortices are formed in the same way.

A finite difference numerical model is used to solve the nondivergent barotropic equation. Despite the presence of the strong slope, agreement between laboratory results and numerical runs suggests that conservation of potential vorticity is indeed the basic mechanism involved in the southward motion of the vortex and the northeastward meandering current.

Corresponding author address: Luis Zavala Sansón, Fluid Dynamics Laboratory, Dept. of Physics, Building Cascade 2.14, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, Netherlands.

luis@kiev.phys.tue.nl

Abstract

The interaction of a barotropic cyclonic vortex on a β plane with a strong topographic slope is studied by means of laboratory experiments and numerical simulations. In the laboratory, the vortex is produced in a rectangular rotating tank with a weak uniformly sloping bottom (slope angle 3.5°) in order to simulate the β effect. The cyclonic vortex moves in the northwestward direction and interacts with an additional, pronounced linear topography (slope angle 35°) along the western boundary of the tank. The laboratory experiments revealed that the original northwestward trajectory changes to the south until the vortex is dissipated by viscous effects and bottom friction. As it moves upslope, the exterior ring of the vortex forms a strong current to the northeast. From this current a new cyclonic vortex is created, repeating approximately the behavior of the original one. Later, two more vortices are formed in the same way.

A finite difference numerical model is used to solve the nondivergent barotropic equation. Despite the presence of the strong slope, agreement between laboratory results and numerical runs suggests that conservation of potential vorticity is indeed the basic mechanism involved in the southward motion of the vortex and the northeastward meandering current.

Corresponding author address: Luis Zavala Sansón, Fluid Dynamics Laboratory, Dept. of Physics, Building Cascade 2.14, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, Netherlands.

luis@kiev.phys.tue.nl

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