The Role of Precipitation in Modulating Upper-ocean Structure during Tropical Cyclone

Despite decades of research on typhoon-induced vertical mixing and upwelling, the role of typhoon precipitation on the upper ocean has remained sterile. This study identified a typhoon precipitation-driven temporal and spatial decoupling between simulated sea surface temperature (SST) and salinity (SSS) during Typhoon Hinnamnor (2022). To isolate the role of precipitation, sensitivity numerical experiments with varying rainfall rates were conducted. SST cooling was governed by horizontally advected cold surface water, suppressed by precipitation-enhanced stratification. Differently, vertical dissipation of SSS unexpectedly surged, despite salinity-induced stratification curtailing both horizontal and vertical transport (like its thermal counterpart). This thermohaline asymmetry exposed fundamentally distinct regulatory mechanisms. Diagnostic analysis further elucidated how precipitation-generated density gradients initiated baroclinic shear flows, disrupting rather than stabilizing stratification. These shear-driven instabilities enhanced vertical mixing, amplifying the SST cooling through dynamic feedback. These results underscored the critical role of precipitation-driven processes in reshaping upper-ocean dynamics during typhoons, contrary to the traditional view that enhanced stratification suppressed mixing and thereby reduced SST cooling.