Using Tropical Cyclone Genesis Indices to Assess Changes in Tropical Cyclone Seasonality Due to a Warming Climate

Recent studies suggest that a warming climate could have a significant impact on tropical cyclone (TC) frequency and intensity, as well as event seasonality. Consensus states that a decrease of TC frequency and an increase in intensity is expected in the future. However, there is no agreement as to the definitive expected changes in seasonality across the different basins. Furthermore, the current resolution of the general circulation models (GCM) used when studying climate change is inadequate to accurately represent systems like tropical cyclones, thus exacerbating the challenge of projecting future changes in tropical cyclone activity.

This project aims to examine the possible changes in tropical cyclone seasonality over the North Atlantic, East Pacific, and West Pacific Ocean basins by using tropical cyclone genesis indices to diagnose cyclogenesis in simulated present-day and future-day large scale environmental conditions. Genesis indices use large scale environmental parameters (like vorticity at 850 hPa and vertical wind shear between 200 hPa and 850 hPa) to identify areas where cyclogenesis is favorable. As such, their results are not highly dependent on model resolution. For this study, the revised Genesis Potential Index (GPI) and the Cyclone Genesis Index (CGI) will be applied to ensembles of monthly twentieth century historical (1980-2005) and twenty-first- century, representative concentration pathway RCP8.5 (2080-2105) CMIP5 model simulations. These results will be validated using reanalysis data (e.g. 0.75^∘ ERA Interim) and distributions of genesis location observations obtained from best track data (genesis location is defined as the location where a recorded storm first reached 35 kt wind speeds).

Special attention will be paid to understanding the possible physical and thermodynamical mechanisms that could contribute to potential seasonal changes. Some studies suggest that alterations to the saturation deficit can reduce TC frequency, while condensational heating can offset this effect during the cooler months of the TC seasons; this project will examine how these parameters, and all the parameters used as genesis index inputs, behave during different stages of the TC season.