The Modulation Effect of Sea Surface Cooling on the Eyewall Replacement Cycle in Typhoon Trami (2018).

The duration of the eyewall replacement cycle (ERC) in typhoons is determined by the rate of dissipation of the inner eyewall and intensification of the outer eyewall, which is an important indicator for predicting changes in the intensity and structure of typhoons. Previous studies on ERCs have focused on the internal storm dynamics associated with the interactions between the concentric eyewalls (CEs), but the impacts of the sea surface cooling (SSC) on ERCs remain not adequately investigated. The slow movement of Typhoon Trami results in remarkable SSC. Using a coupled atmosphere–ocean model, the simulation for Trami generates an ERC that matches observations, whereas an unrealistic long-lived ERC is produced in the uncoupled simulation. Numerical simulations suggest that the typhoon-induced nonuniform SSC cannot only weaken the typhoon, but can also modulate the duration of the ERCs. The SSC acts like a catalyst for triggering the negative feedback between the surface heat exchange and the circulations of Trami to reduce the energy supply to the inner eyewall more severely where the sea surface temperature (SST) dropped more sharply. The SSC works in concert with the interactions between the CEs to weaken the inner eyewall faster, thus terminating the ERC of Trami rapidly. The results indicate that a better understanding of the modulation effect of SSC is required for the accurate forecast of ERCs. Significance Statement: The duration of the eyewall replacement cycle in typhoons is determined by the rate of dissipation of the inner eyewall and intensification of the outer eyewall. While much is known about the cutoff effects of the outer eyewall on the dissipation of the inner eyewall, few studies have examined the dissipation induced by sea surface cooling. Using the coupled atmosphere–ocean model, the simulation for Trami generates an eyewall replacement cycle that matches observations, whereas an unrealistic long-lived one is produced in the uncoupled simulation. The results suggest that the typhoon-induced nonuniform sea surface cooling cannot only weaken the typhoon, but can also modulate the duration of the eyewall replacement cycle, which is essential for the accurate forecasting of eyewall replacement cycles. [ABSTRACT FROM AUTHOR]