Motivated in part by recent satellite and radar observations of asymmetric convective bursts near incipient tropical vortices and full-fledged hurricanes, we examine the nonlinear non-axisymmetric vortex adjustment problem on an initially circular basic state vortex in gradient balance. For simplicity, a barotropic shallow water primitive equation model is used to illustrate the basic physics.
Convective bursts are parameterized as localized disturbances in the asymmetric wind or mass field. The adjustment process consists of radiating gravity-inertia waves and vortex Rossby waves. Unlike gravity-inertia waves which propagate to infinity with little or no wave mean-flow interaction, vortex Rossby waves are bound to the near-vortex region and yield the principal contribution to the wave, mean-flow interaction. As long as the vortex core region is not saturated with gravity wave activity, vortex Rossby waves spin up the vortex by transporting like-sign PV anomalies into the parent vortex and orbiting filaments and ejecting opposite-sign PV anomalies to the vortex periphery.
Application of these findings to the problems of hurricane formation and rapid intensification will be discussed