A THEORY FOR VORTEX ROSSBY-WAVES AND ITS APPLICATION TO SPIRAL BANDS AND INTENSITY CHANGES IN HURRICANES

In this paper we examine further the physics of vortex axisymmetrizati on, with the goal of elucidating the dynamics of outward-propagating s piral bands in hurricanes. The basic physics is illustrated most simpl y for stable vorticity monopoles on an f-plane. Unlike the dynamics of sheared disturbances in rectilinear shear Bow, axisymmetrizing distur bances on a Vortex are accompanied by outward-propagating vortex Rossb y-waves whose restoring mechanism is associated with the radial gradie nt of storm vorticity. Expressions for both phase and group velocities are derived and verified; they confirm earlier speculations on the ex istence of vortex Rossby-waves in hurricanes. Effects of radially prop agating vortex Rossby-waves on the mean vortex are also analysed. In c onjunction with sustained injection of vorticity near the radius of ma ximum winds, these results reveal a new mechanism of vortex intensific ation. The basic theory is then applied to a hurricane-like vortex in a shallow-water asymmetric-balance model. The wave mechanics developed here shows promise in elucidating basic mechanisms of hurricane evolu tion and structure changes, such as the formation of secondary eye-wal ls. Radar observations possessing adequate temporal resolution are con sistent with the predictions of this work, though more refined observa tions are needed to quantify further the impact of mesoscale banded di sturbances on the evolution of the hurricane vortex.