Damping and Pumping of a Vortex Rossby Wave in a Monotonic Cyclone: Critical Layer Stirring Versus Gravity Wave Emission
Abstract
This work further examines the rate at which potential vorticity in the core of a monotonic cyclone becomes vertically aligned and horizontally axisymmetric. We consider the case in which symmetrization occurs by the damping of a vortex Rossby (VR) wave. The damping of the VR wave is caused by its stirring of potential vorticity at a critical radius r_*, outside the core of the cyclone. The decay rate generally increases with the radial gradient of potential vorticity at r_*. Previous theories for the decay rate were based on ``balance models'' of the vortex dynamics. Such models filter out inertiabuoyancy (IB) oscillations, i.e. gravity waves. However, if the Rossby number is greater than unity, the core VR wave can excite a frequencymatched outward propagating IB wave. To accurately account for this radiation, we here develop a theory for the decay rate that is based on the primitive equations. Starting from conservation of wave activity (angular pseudomomentum), an expression is derived for the decay rate. This expression explicitly demonstrates a competition between the destabilizing influence of IB wave radiation, and the stabilizing influence of potential vorticity stirring at r_*. It shows that if the radial gradient of potential vorticity at r_{*} exceeds a small threshold, the VR wave will decay, and the vortex will symmetrize, even at large Rossby numbers. Preliminary numerical simulations verify this theory. Implications concerning the robustness of intense geophysical vortices will be summarized.
 Publication:

APS Division of Fluid Dynamics Meeting Abstracts
 Pub Date:
 November 2003
 Bibcode:
 2003APS..DFD.JN010S