Precipitation‐Driven Thickening and Wind‐Induced Erosion of the Ocean Barrier Layer Under Tropical Cyclones

Abstract Barrier layer (BL) thickness (BLT) modulates tropical cyclone (TC) intensity, yet its evolution mechanisms remain debated. While statistical studies attribute BL thickening to heavy precipitation in strong or slow‐moving TCs, numerical experiments suggest that enhanced wind‐driven mixing tends to erode it. Here, using reanalysis‐based statistical and composite analyses, we reconcile previously conflicting findings. Weak TCs predominantly thicken the BLT through precipitation‐driven surface freshening. In contrast, strong TCs tend to erode the BL owing to enhanced wind‐driven mixing and Ekman upwelling, which weaken salinity stratification and shoal the isothermal layer base, respectively. TC translation speed modulates these responses via the duration of forcings: fast‐moving TCs induce relatively weak BLT changes, whereas slow‐moving TCs generate stronger thickening and erosion. Across all translation speeds, however, precipitation effects dominate over wind‐driven processes, making thickening the prevailing response. These results clarify the competing mechanisms controlling BLT evolution and provide guidance for improving TC intensity forecasts.