Fundamental Studies In Tropical Cyclone Structure & Intensity Change

Abstract

Abstract : LONG-TERM GOALS AND OBJECTIVES. Focusing on dynamical and thermodynamical processes germane to the hurricane s core region, the objectives of this research project are to obtain a more complete understanding of atmospheric processes governing hurricane development, structure and intensity. This year we have continued our basic research on the dynamics and thermodynamics of the hurricane eye/eyewall region, and the dry adiabatic dynamics of a hurricane-like vortex in vertical shear. We have also begun an applied research thrust, in collaboration with Dr. s N. Davidson and K. Tory of Australia s BMRC. New insight and discoveries have been advanced in all areas. These are summarized below. A New Look at the Problem of Tropical Cyclones in Vertical Shear Flow: Vortex Resiliency APPROACH. A simple model based on the Boussinesq Primitive Equations (PE), linearized about a mean barotropic vortex in gradient and hydrostatic balance is used as a baseline model for exploring the tilting behavior of tropical-cyclone-like vortices in unidirectional vertical shear flow. In our previous work (Reasor and Montgomery 2001; Schecter, Montgomery, and Reasor 2002) a self-alignment mechanism was identified which reduces departures from an upright state (i.e., the vortex tilt). The mechanism involves the projection of the vortex tilt onto vortex Rossby waves (VRWs) and their subsequent damping. The question we sought to address in this work was how this VRW damping mechanism operates when the vortex is embedded in a vertical shear flow. The linear PE model is used for acquiring a first order understanding of the basic dynamics of the vortex-shear interaction. It is well known, however, that for a given vortex strength, as the shear strength increases, the vortex crosses a threshold and irreversibly shears apart.