The Vertical Structure of Hurricane Rainbands and Their Interaction with the Mean Vortex

Abstract

The model of hurricane rainbands developed by Willoughby (1977a, 1978) is here extended to simulate linear waves on a baroclinic mean vortex. Although the energetics are more complicated than in the case of barotropic mean flow, these results support the plausibility of Willoughby's model of rainbands as inward-propagating inertia-buoyancy waves. These waves are excited with small amplitude at the storm's periphery and amplify in consequence of the Eliassen-Palm theorem as they are Doppler-shifted to higher frequency during their propagation toward the storm's center. In a baroclinic mean flow, as in a barotropic one, the energy for the amplification comes primarily from the kinetic energy of the mean flow. The primary process which effects this energy exchange is associated with a horizontal export of angular momentum from the vortex center. A baroclinic mean vortex also supplies a lesser amount of energy to the perturbations at the expense of the mean available potential energy. In the upper troposphere, inward-propagating waves are absorbed as a quasi-horizontal critical layer; this leads to some loss of perturbation energy to the mean flow associated with the vertical momentum flux. The waves also experience critical radius absorption in the eye-wall region.