Oscillatory Instabilities to Zonally Varying Barotropic Flows

Abstract

The barotropic instability of a forced, axisymmetric vortex patch is examined and linked to prior work on the destabilization of a single Rossby wave via triad interactions. Both oscillatory instabilities, which share certain qualitative aspects with Rossby wave triads, as well as stationary instabilities are studied. It is shown that instability is confined to quite limited regions of the parameter space described by the magnitude of flow variation along the vortex edge and the zonally averaged flow along the vortex edge. However, more realistic flow variations along the vortex edge expand the region of parameter space where instability is found. The nonlinear manifestation of these instabilities is examined, and it is found that the leading oscillatory branch of instabilities can lead to large perturbations of the vortex patch, and its ultimate filamentation. Extension of these results to observed structures in the troposphere and stratosphere is discussed.