The modulation of Tropical Cyclone Intensity by Subsurface Salinity Stratification: An Idealized Study Using Coupled General Circulation Model

Tropical cyclone (TC) intensification is strongly influenced by the oceanic thermal structure, shaped by both temperature and salinity stratification. However, the role of salinity stratification remains debated. We conducted idealized experiments using a fully coupled atmosphere–ocean model to systematically assess its impact on TC evolution. Generally, vertical advection dominates the thermal response. An intact barrier layer (BL) enhances vertical advection by intensifying vertical velocity gradients, whereas partial erosion suppresses it but inversion layer compensation emerges. Once the BL is fully eroded, the inversion layer vanishes, and the influence of salinity stratification on TC intensity is substantially diminished. These processes are modulated by TC translation speed. At the fastest translation speed (6 m s⁻¹), strong stratification maintains an intact BL that confines vertical velocity to the upper ocean. This enhances the contribution of the velocity gradient to vertical advection, allowing the TC to reach maximum intensity. Under moderate and weak stratification, partial erosion of the BL weakens vertical advection, leading to reduced TC intensity. At a moderate translation speed (3 m s⁻¹), BL erosion becomes more pronounced, weaker salinity stratification exerts less suppression on vertical advection and mixing, amplifies thermal compensation from the inversion layer, and favors TC intensification. For slow-moving TCs (1 m s⁻¹), the BL and inversion layer are fully eroded, salinity stratification plays a negligible role in modulating TC intensity. Overall, these findings highlight the non-negligible role of salinity stratification in regulating TC intensity and provide physical insights for improving intensity forecasts.