Impacts of Precipitation on Upper‐Ocean Responses: A COAWST Modeling Study

Abstract This study investigates how precipitation‐induced freshwater flux affects the upper‐ocean structure during Typhoon Mangkhut (2018) using an atmosphere‐ocean coupled model (COAWST). It was found that accounting for precipitation forcing can modulate the simulated intensity of tropical cyclones (TCs). At a buoy near the TC center, freshwater input from precipitation induces a warmer (+0.3°C), fresher (−0.2 psu) and shallower mixed layer. Spatially, analysis found a heterogeneous sea surface temperature (SST) responses but homogeneous freshening sea surface salinity responses. Quantitatively, precipitation enhances inner‐core (within 125 km) SST cooling by 0.006°C (1.75%) while suppressing outer‐region (within 250 km) cooling by 0.014°C (6.3%). This signal reversal marks a regime shift from shear‐dominated mixing inside the radius of maximum winds to stratification‐dominated suppression farther outward. Although precipitation‐driven stratification and current shear are strongly positive correlated ( r = 0.81 ∼ 0.91) in both the inner‐core and outer regions, neither variables correlates strongly with SST anomalies ( r < 0.3). This indicates that freshwater flux alters ocean thermal structure via competing mechanisms between stabilizing the mixed layer while enhancing turbulence mixing. These results underscore the necessity of incorporating precipitation effects in coupled TC models, particularly for improved representation of subsurface processes and their potential impact on TC intensity.