Response and Feedback of Mesoscale Eddies to Tropical Cyclones Over the South China Sea

Abstract

Tropical cyclones (TCs) frequently encounter and interact with mesoscale eddies when moving over the ocean, affecting both of their subsequent evolutions. The South China Sea (SCS) suffers the most frequent TCs among global oceans and contains active eddies. On average, one TC encounters and interacts with at least one eddy during its lifespan in the SCS. Using 27-year satellite data and numerical simulations, we examined the response and feedback of mesoscale eddies to TCs over the SCS, based on TCs' interaction with 183 cyclonic ocean eddies (COEs) and 152 anticyclonic ocean eddies (AOEs). TCs induce a symmetric sea surface height reduction with maximum reduction (∼5 cm on average) appearing at the TC center. Pre-existing COEs (AOEs) are enhanced (weakened) by TCs with an average 24% increase (17% decrease) in amplitude and enlarged (shrunk) with an average 19% increase (13% decrease) in radius. Stronger or slower-moving TCs enhance COEs more significantly. Pre-TC existing COEs (AOEs) enhance (suppress) TC-induced sea surface cooling, and thus suppress (fuel) TC intensification, with the effect of COEs statistically stronger than AOEs. This modulating effect is more pronounced under stronger or slower-moving TCs. Eddy's location also influences the modulating effect, with pre-TC COEs located to the left (right) of TC track shifting the largest cooling leftwards (rightwards). Furthermore, the left-located COEs increase cooling amplitude by 61%, stronger than right-located COEs (26%). These results suggest that the combination of mesoscale eddies and TC attributes complicates TC-induced sea surface cooling, which potentially affects TC intensification, wind structure, and rainfall.