Effect of Air-Sea Coupling on Tropical Cyclone Activity in a High-Resolution Coupled Climate Model

Tropical cyclone (TC)-ocean interactions are crucial in TC evolution. Strong surface winds associated with TCs extract a huge amount of heat out of the ocean, sustaining TC development, and at the same time vigorously mix warm surface waters with colder waters below, reducing sea surface temperatures (SSTs) and sea-to-air enthalpy fluxes and suppressing subsequent TC development. Here TC-ocean interactions and their influences on TC activity are investigated using a 30-yr coupled simulation by the high resolution GFDL CM2.5, which reproduces many observed TC statistics, such as the geographical distribution of genesis.

By means of composite analysis, we first characterize TC-induced ocean responses, including SST cooling and mixed layer deepening, and study their dependence on both TC (e.g., intensity and translation speed) and ocean (e.g., mesoscale eddies) features. We then proceed to understand how and to what extent the produced sea surface cooling affects TC intensification, and to link TC intensity to other TC characters as well as ocean states. Moreover, we compare this oceanic effect with the effect associated with atmospheric conditions (e.g., vertical shear of horizontal winds), and examine the dependence of their relative importance on basin and TC intensity.

The influence of SST cooling on TC activity is further highlighted by comparing the coupled simulation with an AMIP simulation that is forced by monthly SSTs output from the coupled simulation. Specifically, we compare the cyclogenesis pattern and frequency distribution of intensity in these two simulations, quantify differences in various intensity and related metrics (e.g., intensification rate and lifetime), and identify basins/regions where strong SST feedback exists. The implications of the results regarding TC intensification dynamics are also discussed.