Development and applications of an index for tropical cyclone genesis

Michael K. Tippett(1),  Suzana J. Camargo(2), Adam H. Sobel(3),
Gabriel A. Vecchi(4), and Ming Zhao(4)

(1) International Research Institute for Climate and Society, Columbia
(2) Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY
University, Palisades, NY
(3) Department of Applied Physics and Applied Mathematics, Department
of Earth and Environmental Sciences, Columbia University, New York, NY
(4) NOAA - Geophysical Fluid Dynamics Laboratory, Princeton, NJ

We present a new index for tropical cyclone genesis.  As in the earlier work of Emanuel and Nolan (and originally, that of Gray) the index is based on large-scale environmental quantities. Here, the index is constructed in the framework of Poisson regression which provides an objective basis for the selection of large-scale environmental quantities and a direct interpretation of the index parameters. We examine the impact of using relative sea surface temperature instead of potential intensity and compare the use of satellite-based column-integrated relative humidity with midlevel reanalysis relative humidity.  The sensitivity of tropical cyclone genesis to absolute vorticity is found to vary with absolute vorticity.  Although the index is derived from climatological data, it is able reproduce some degree of observed interannual variability. Finally, we apply the index to present and future climate simulations from the GFDL high-resolution global model HIRAM.