Characteristic of ocean surface wave across the mesoscale eddies during tropical cyclones in the South China Sea

This research aims to explore the response of sea surface wave fields across mesoscale eddies under the influence of tropical cyclones (TCs) in the South China Sea, utilizing numerical simulations from the Finite-Volume Community Ocean Model (FVCOM) one-way coupling with the Simulating WAves Nearshore (SWAN) model. Four types of vertical coordinates were tested in FVCOM to improve the representation of upper-ocean variability under rapidly changing depths. The high-resolution hindcast sea surface temperature data was used for validation, revealing that the general vertical coordinate in FVCOM exhibited the most accurate results, showing a correlation (COR) of 0.90 and a root mean square error (RMSE) reaching 0.29 °C. Wave simulations were conducted using the SWAN model, which incorporated wave breaking influenced by depth and complex nonlinear interactions between waves. Based on 51 mesoscale eddies detected during five TCs from 2022 to 2024, the results reveal distinct modulation patterns. Regression analysis indicates a significant coupling among wind, waves, currents, and Eddy Kinetic Energy (EKE) within the eddies. While significant wave height (SWH) increases with prolonged TC forcing duration, TC translation speed shows no significant impact on SWH or EKE, suggesting that internal geostrophic adjustment plays a dominant role in eddy dynamics. Structurally, intense TC forcing was observed to disrupt pre-existing eddies and trigger the ageostrophic cold eddies characterized by high Rossby numbers (> 0.5) and low Richardson numbers (< 0.25). Furthermore, the modulation of TC-induced waves is identified as a spatial process involving steepening-induced dissipation at the periphery and refraction-induced redistribution at the edge. The warm eddy periphery acts as a low-pass filter, dissipating high-frequency energy early due to opposing currents. Combined with refractive effects, this mechanism leads to wave energy convergence in cold eddies versus divergence in warm eddies.