Numerical Simulation and Characteristic Analysis of Wave Field Under the Influence of the Rapid Intensification of Typhoon Mekkhala

With the global climate changing, the number of rapidly intensifying typhoons has shown an increasing trend. Investigating the spatiotemporal evolution characteristics of wave fields during typhoon rapid intensification by numerical simulation has a significant influence on coastal disaster prevention and mitigation. In this paper, a coupled typhoon-wave numerical model for the northeastern South China Sea based on the coupled ocean-atmosphere-wave-sediment transport (COAWST) model was developed in order to analyze the characteristics of wave fields under the rapidly intensifying Typhoon Mekkhala (2020). Results indicate that, with Mekkhala rapidly intensifying, there is a positive correlation between the significant wave height and the change of local wind speed on the right side of the track, forming the about 5 m difference of the significant wave height compared to the other side. Additionally, significant wave height seems more sensitive to typhoon intensity than to typhoon size. Within five times of the radius of maximum wind speed away from the typhoon center, wave age moderately decreases, while the mean wave direction is weak in response to the rapidly increasing wind field, maintaining a 60°counterclockwise deflection relative to background wave direction. Further analysis of the wave spectrum shows that, ignoring the background wave field, wave spectral energy in the right-front quadrant increases during typhoon rapid intensification, while a bimodal wave spectral dominated by wind waves emerges in the left-rear quadrant. Notably, wind wave components with faster group velocity transmit from this quadrant to the right-rear quadrant, generating low-frequency swells.