Environmental Influences on Tropical Cyclone Variability and Trends

The power dissipation index (PDI), a measure of the total mechanical energy generated by tropical cyclones over their lifetimes, exhibits secular trends and regional multi-decadal variability, both well correlated with sea surface temperature. In the Atlantic, in particular, both the trend and the variability exhibit somewhat more sensitivity to sea surface temperature than had been predicted in earlier theoretical and modeling studies. Here we examine more closely the various environmental influences on tropical cyclone activity and show that the potential intensity, a more meaningful measure of the thermodynamic environment of tropical cyclones than sea surface temperature (SST), has varied more rapidly with SST than is predicted by single column climate models, and further show that this is a consequence of the variation of the surface wind speed of the Trades, which in the Atlantic had varied in concert with SST. The effect on PDI of other factors, such as low level vorticity, mid-level humidity and wind shear, are also quantified.