Symmetric and Asymmetric Intensification Processes in Tropical Cyclones

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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. For developing storms, these areas of convection are highly asymmetric and often displaced from the storm center. In previous work, the Principal Investigator has shown how the heat energy released in asymmetric convection is converted into kinetic energy of the axisymmetric wind field through a sequence of asymmetric and then symmetric adjustment processes. From previous work using balance models of axisymmetric dynamics, it is already known that the efficiency of this process (the amount of vortex intensification per unit heating) is quite small, on the order of 5%, and depends strongly on both the location of the convection and the structure of the cyclone itself. The new model used for this work resolves the unbalanced, fully nonhydrostatic dynamics of both asymmetric and symmetric motions. This project will further analyze the symmetric and asymmetric processes, which mediate these energy transfers, and in particular will document the efficiency of the intensification process for particular heating distributions and storm structures. The interaction of outward propagating gravity waves with the symmetric wind field also will be examined, along with a new possible mechanism connecting gravity waves to spiral band formation.This work potentially will lead to better understanding and forecasting of tropical cyclone development and rapid intensification phenomena. The computer programs used to simulate the symmetric and asymmetric adjustment processes will be made available to the community for general use. This project may also lay the foundation for a new approach to hurricane intensity forecasting, which would combine satellite observations of precipitation and convective heating with a simple dynamical model to predict short-term intensity change.