Oceanic response to super typhoon based on simulation by FVCOM and SWAN

The South China Sea is a region frequently impacted by intense tropical cyclones (TCs). Recent super typhoons such as Yagi (2024), Haikui (2023), Saola (2023), Doksuri (2023), and Koinu (2023) have caused catastrophic damage. This study primarily investigates the oceanic response to westward-moving super typhoons. The cyclonic wind field is reconstructed based on reanalysis from the European Centre for Medium-Range Weather Forecasts (ECMWF), and the TC wind speed derived from measurements of five moored buoys shows a 4.01 m/s root mean squared error (RMSE), a 0.90 Pearson’s correlation (Cor), and a 0.48 scatter index (SI). A triangular-grid-based numerical circulation mode, namely the Finite-Volume Community Ocean Model (FVCOM), is employed to simulate sea surface currents and sea levels. The reconstructed TC winds act as the forcing field, and the FVCOM-simulated sea surface currents and sea levels are then incorporated into wave simulations conducted with the Simulating WAves Nearshore (SWAN) model. It is found that the hindcasting significant wave heights (SWHs) are most consistent with measurements from moored buoys when current and sea level are included, and this phenomenon is particularly significant around the Taiwan Strait. Two parameterizations of the drag coefficient 𝐶𝑑, i.e., the 𝐶𝑑 by Wu (1982) and the 𝐶𝑑 by Hu et al. (2024), are used in SWAN. The improved 𝐶𝑑 shows a clear advantage when SWH > 3 m, resulting in a reduction of over-estimation and an increase in SWH accuracy by 0.6 m. Wind and SWH exhibit opposing asymmetry trends due to swell influence. Along super typhoon tracks, sea surface temperature (SST) cooling reaches a maximum of 4°C; however, the Kuroshio Current and Zhejiang-Fujian Coastal Current mitigate this cooling, reducing it by approximately 1°C. These findings offer significant implications for understanding super typhoon responses to ocean dynamics and provide critical insights for enhancing disaster resilience strategies during extreme wheather events.