Strengthening cold wakes lead to decreasing trend of tropical cyclone rainfall rates relative to background environmental rainfall rates

Abstract

Tropical cyclone (TC) rainfall is an important component of global precipitation. Based on a 22-year satellite-based record of observed precipitation from 1998 to 2019, we find that composite rainfall rates averaged within 500 km of TCs have increased. However, the background precipitation rate in the TC-affected regions has also increased. Therefore we find, by subtracting the background increase in precipitation rate from the TC precipitation composite, that TC precipitation rates--relative to the background--have decreased, and that TC-related extreme precipitation rates near the TC center have also decreased. Besides TC intensity and environmental sea surface temperature, the TC-induced sea surface cooling, typically formed like a cold wake feature, is indicated to be a potentially important contributor to TC rainfall changes. The cold wake diminishes the upward transport of surface enthalpy flux and leads to a decrease of moisture in the boundary layer, being unfavorable for the rainfall. The relative decreasing rainfall trend of TCs to the background is therefore attributed to the strengthening sea surface cooling induced by TCs. The TC-ocean interaction is suggested to be fully resolved in state-of-the-art global and regional climate models in order to improve TC rainfall simulations and projections.