Numerical Studies of Tropical Cyclogenesis and Hurricane Andrew (1992)

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Adequate understanding of the genesis and inner core structure of tropical cyclones is a high priority research area under the U.S. Weather Research Program. Although there have been numerous studies of tropical cyclogenesis in the past decades, little work has been done to investigate cyclogenesis from mesoscale convective systems (MCSs) and the inner-core structures of hurricanes. Thus, the objectives of this research are to a) test the hypothesis that convectively generated mid-level mesovortices could induce tropical cyclogenesis under optimum environmental conditions; and b) simulate and investigate the inner-core structures and evolution of Hurricane Andrew (1992). To gain insight into the nature of tropical cyclogenesis, emphasis will be placed on a) the processes leading to the generation and amplification of lower-level cyclonic vorticity in tropical storms in relation to mid-level mesovortices, and b) the mechanisms responsible for the transformation from MCSs with a low-level cold pool into intense mesocyclones that are characterized by deep warm-cored structures. Finally, model-based diagnosis will be performed to examine the roles of air-sea interaction, cloud-radiation interaction and meso-larger scale interaction in the transformation from MCSs to tropical storms.For the second objective, numerical studies of hurricane intensity will be performed. Specifically, 1) aircraft observations during the rapid intensification of Andrew and SSM/I data will be used to help understand the predictability of the inner-core structures by nudging the model integration towards the observations during a pre-forecast period; 2) higher resolution (i.e. 2 - 3 km) explicit simulations will be conducted to demonstrate the capability of reproducing inner-core structure and intensity and, thereby, gain insight into the double eyewall cycle that is associated with the rapid decay followed by explosive deepening of the storm; 3) an advanced oceanic and atmospheric mesoscale model will be coupled in order to study the impact of local sea-surface temperature changes on the development of inner-core structures; and 4) various sensitivity simulations will be performed to examine the effects of different cumulus parameterization schemes, shallow convection, cloud microphysical processes (water vs. ice), cloud-radiation interaction and air-sea interaction on the simulation of the storm.Successful completion of the proposed tasks will provide a better understanding of the dynamic effects of MCSs on larger-scale flows, the processes leading to tropical cyclogenesis from MCSs, the inner-core structures of hurricanes and various processes during rapid deepening. Satisfying results may open a new important era for tropical cyclogenesis research and for improving the numerical prediction of hurricanes and their structure at landfall.