UNIVERSITY OF MIAMI
Research over the past few decades has established that much and perhaps most of the interannual to interdecadal variation of tropical cyclone activity integrated over ocean basins is controlled by the large-scale atmospheric and oceanic environment in which the storms develop. Both statistical and model-based hindcasts of Atlantic tropical cyclone activity are able to capture as much as 65% of the interannual variability of tropical cyclone frequency in spite of making little or no account of potential initiating disturbances such as African easterly waves. But these same techniques, when applied to global warming scenarios, produce greatly divergent results, highlighting the pressing need for a better physical understanding of the link between tropical cyclones and climate. This proposal details plans for pursuing such an understanding by addressing the problem using several different, but complimentary, approaches. The first approach builds on our previous research by investigating the formation of, or failure to form, tropical cyclones from seed cyclonic disturbances in large-scale environments of radiative-convective equilibrium with shear. Our previous results with this method will be extended to a wider range of wind profiles that include both speed and directional shear, thus allowing for a careful study of cyclogenesis (or failure) in more realistic environments that can still be systematically adjusted and compared. A second approach builds on the success of our Genesis Potential Index (GPI), which, when applied to NCAR/NCEP reanalysis data, has been shown to explain much of the interannual variance and long-term trend of tropical cyclones, by using it to understand the physical factors responsible for predicted variations in the GPI in climate models simulating the response to global warming. We intend to improve this index using results from the aforementioned cloud-resolving model simulations. Finally, we will analyze one or two cases of genesis in the cloud-resolving model in some depth and attempt to test the hypothesis that tropical cyclones can only develop in mesoscale patches that are nearly saturated through most of the troposphere, and suggest that such patches must necessarily be colder than their environments at low levels when they first develop.