Exploring Genesis Potential Indices

That the large-scale environment has a role in determining tropical cyclone genesis has been understood since the earliest analyses of the association between cyclones and the general circulation in the tropics. Gray summarized the state of science and demonstrated the potential for assessing genesis potential (GP) utilizing such environmental parameters as ocean thermal content, midlevel moisture, a conditionally unstable atmosphere, low-level vorticity, and vertical wind shear through a deep atmospheric layer. Building on this earlier work, a number of GP indices has since been developed and are currently widely used to assess potential changes in GP on climate scales. These indices, although developed based on the hemispheric seasonal cycle of the mean genesis climatology, is often used in specific TC basins and for interannual and decade studies, without verification of the index's skill in the given basin or its ability to capture interannual variability.

Bruyère et al. (2012, J. Climate, 25, 8611–8626) showed that, at least for the NA basin, most indices are not well suited as a proxy for interannual TC frequency. Key findings from this study showed that 1) for the North Atlantic basin potential intensity and shear played dominant roles in TC predictions, and 2) that the mean large-scale environment in one specific hotspot (the this case the main development region of Africa (MDR)) correlated much better with TC genesis than using a basin-wide average.

Following on from this study we set out to find indices with basin specific predictors, as well as key hot spots associated with these basins. With specific focus the development of indices specific to regions of interest like the Gulf of Mexico (GOM). The presentation will discuss theses indices together with their use in Global and Regional Climate Models to evaluate changes in tropical cyclone frequency under climate variability and change.