Vortex stability in a large-scale internal wave shear

Abstract

The effect of a large-scale internal wave on a multipolar compound vortex was simulated numerically using a 3DBoussinesq pseudospectral model. Asuite of simulations tested the effect of a background internal wave of various strengths, including a simulation with only a vortex. Without the background wave, the vortex remained apparently stable for many hundreds of inertialperiods but then split into two dipoles. With increasing background wave amplitude, and hence shear, dipole splitting occurredearlier and was less symmetric in space. Theoretical considerations suggest that the vortex alone undergoes a self-induced mixed barotropic-baroclinic instability. For a vortex plus background wave, kinetic energy spectra showed that the internal wave supplied energy for the dipole splitting. In this case, it was found that the presence of the wave hastened the time to instability by increasing the initial perturbation to the vortex. Results suggest that the stability and fate of submesoscale vortices in the ocean may be significantly modified by the presence of largescale internal waves. This could in turn have a significant effect on the exchange of energy between the submesoscale and both larger and smaller scales. © 2012 American Meteorological Society.