Thursday, 11 June 2009: 8:40 AM
Pinnacle BC (Stoweflake Resort and Confernce Center)
This study examines (in part) the emergence of hurricanes from chaotic swirling motions in a 3-layer model of the tropical troposphere that includes basic parameterizations of cumulus convection and air-sea interaction. The chaotic flow of vortices and filaments is referred to as Diabatic Ekman Turbulence (DET), in order to emphasize that cumulus convection and Ekman pumping are critical to its behavior. The time required for hurricane formation in DET is examined over a broad range of sea-surface temperatures, tropical latitudes, and surface exchange coefficients for moist entropy and momentum. The mean results show sensible trends, but the specific genesis time can vary significantly with subtle details of the initial turbulence. Moreover, hurricanes do not always form. In the event that a tropical depression develops into a hurricane, the process is highly asymmetric. Intensification involves a shear-flow instability, the production of mesovortices, and contraction of the basic circulation. Despite the complex evolution, the intensification rate is fairly consistent with the expectations of a quasi-linear stability analysis. In fully developed DET, filaments play a more active role than in ordinary 2D turbulence: hurricanes can develop outer eyewalls by entraining filaments, and free filaments can spawn new hurricanes.
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