Interactions of Typhoon-Generated Near-Inertial Waves and Tidal Processes with a Mesoscale Warm Eddy during Typhoon Kalmaegi (2014)

Abstract

Using a high-resolution MITgcm simulation, together with mooring observations, satellite sea level anomaly (SLA) data, and tidal harmonic analysis, this study examines the interactions of typhoon-generated near-inertial waves and tidal processes with a mesoscale warm eddy in the northern South China Sea during Typhoon Kalmaegi (2014). Three sensitivity experiments are conducted to distinguish the roles of wind and tidal forcing. The results show that typhoon passage substantially weakens the target warm eddy, as evidenced by reduced sea surface height, eddy amplitude, effective radius, and low-frequency eddy kinetic energy. This weakening reflects a two-stage wind-forced adjustment: direct wind work dominates the initial typhoon-stage disturbance, whereas post-storm NIW–low-frequency kinetic energy exchange becomes more pronounced and sustains adjustment of the weakened warm eddy. In addition, the post-typhoon recovery of sea surface height is markedly slower within the eddy than in the surrounding waters, indicating that the anticyclonic eddy background prolongs the local adjustment time scale. In contrast, tidal-related processes exert a positive influence during the recovery stage: after the storm, the inclusion of tidal forcing is associated with a more favorable low-frequency APE tendency and a rebound of sea surface height within the warm eddy. Meanwhile, the eddy suppresses the surface expression of tide-induced periodic sea surface height variability. These results demonstrate a pronounced nonlinear coupling among typhoon-forced NIWs, tidal processes, and mesoscale eddies, and highlight their joint role in regulating post-typhoon energy redistribution and eddy adjustment in the northern South China Sea.