Contrasting Regulation of Upper‐Ocean Temperature and Salinity Responses to Tropical Cyclones by the Barrier Layer

Abstract

This study investigates the role of the pre‐storm barrier layer (BL) in modulating the upper‐ocean response to tropical cyclones (TCs) from a global perspective. By synthesizing multi‐sensor satellite observations and in situ Argo profiles from 2003 to 2022, we show that the barrier layer thickness (BLT) exerts contrasting effects on the upper‐ocean temperature and salinity anomalies. For temperature, a thick BL acts as an effective thermal insulator that significantly weakens surface cooling and accelerates thermal recovery by restricting the deepening of the mixed layer and limiting entrainment of colder thermocline water. In contrast, surface salinification is amplified in regions with thick BLs. This enhancement arises from the strong vertical salinity gradient associated with thick BLs, where a fresh surface lens overlies a sharp and shallow halocline, allowing saltier subsurface water to be efficiently entrained into the mixed layer during TC passage. Subsurface composites from Argo floats further corroborate this mechanism, showing that thick BLs weaken the vertical thermal response while generating a pronounced salinity response, characterized by enhanced surface salinification and subsurface freshening. These findings underscore the BL as a critical regulator of vertical exchange during TC forcing, leading to a relatively warm and salty wake in freshwater‐influenced basins. Consequently, accurately representing this dual modulation is essential for coupled models to capture realistic upper‐ocean responses and associated air–sea fluxes.