The propagation and decay of a coastal vortex on a shelf

TL;DR

This paper models a coastal vortex as a barotropic eddy on a shelf, analyzing its interaction with shelf waves, energy transfer, and evolution, supported by analytic solutions and numerical simulations.

Contribution

It provides analytic expressions for wave wake and energy flux, predicts vortex evolution, and introduces a numerical method for steady vortex solutions.

Findings

Analytic expressions for wave wake and energy flux derived.

Predictions for vortex speed and radius evolution made.

Numerical solutions for steady vortices explored.

Abstract

A coastal eddy is modelled as a barotropic vortex propagating along a coastal shelf. If the vortex speed matches the phase speed of any coastal trapped shelf wave modes, a shelf wave wake is generated leading to a flux of energy from the vortex into the wave field. Using a simply shelf geometry, we determine analytic expressions for the wave wake and the leading order flux of wave energy. By considering the balance of energy between the vortex and wave field, this energy flux is then used to make analytic predictions for the evolution of the vortex speed and radius under the assumption that the vortex structure remains self similar. These predictions are examined in the asymptotic limit of small rotation rate and shelf slope and tested against numerical simulations. If the vortex speed does not match the phase speed of any shelf wave, steady vortex solutions are expected to exist. We present a numerical approach for finding these nonlinear solutions and examine the parameter dependence of their structure.