Extended Abstract (68K)15A.3
Mechanics and efficiency of symmetric and asymmetric intensification processes
David S. Nolan, University of Miami/RSMAS, Miami, FL
Tropical cyclone development and intensification is driven in large part by the release of latent heat of condensation in cumulonimbus convection organized around the center of the storm. This heat energy is converted into kinetic and potential energy of the symmetric vortex through a series of asymmetric and symmetric hydrostatic and gradient wind adjustment processes. In recent years the author has developed a model of the linearized dynamics of nonhydrostatic, three-dimensional perturbations to basic-state vortices modeled after tropical cyclones. This model is used to simulate and understand these adjustment processes under fully nonhydrostatic dynamics.
Using a balance model of axisymmetric dynamics, Hack and Schubert (1986) showed that the "efficiency" of this process (the amount of vortex intensification per unit heating) depends strongly on both the location and distribution of the heating and on the structure of the cyclone itself. The linearized nonhydrostatic model is used to make similar calculations, computing the amount of energy retained as kinetic energy per unit heating at each altitude and radius from the center of the vortex. Maximum efficiency rates range from just a few percent for weak vortices to nearly 30 percent for strong hurricanes. These plots also show some interesting structure, such as an efficiency maximum at high altitudes above the radius maximum winds, and an efficiency minimum at low altitudes just outside the radius of maximum winds, which has interesting implications regarding the effect of spiral bands. Other measures of intensification efficiency, such as changes in the central pressure or maximum winds speeds, will also be presented.
Session 15A, Tropical cyclone intensity change IV: Numerical Modeling Studies
Thursday, 6 May 2004, 3:45 PM-5:00 PM, Le Jardin Room
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