Wave spectra analysis on the spatiotemporal variability of sea states under distinct typhoon tracks in a semi-enclosed sea

The dynamics of typhoon-induced waves in semi-enclosed seas become an interesting topic with the increase of the typhoon intensity. Based on the calibrated Simulating Waves Nearshore (SWAN) model, wave dynamics were investigated under distinct typhoon tracks (e.g., Matmo (2014), Rumbia (2018), and Lekima (2019)) in the Bohai Sea. Distributions of significant wave heights (SWHs) are affected by the typhoon wind fields and are directly related to the typhoon tracks. The classical JONSWAP wave spectra were adopted for the analysis of sea states (e.g., wind-seas or swells) to further explain variations in wave heights. Results indicate that the dominant sea state with higher energy experiences significant spatiotemporal variability under distinct tracks. For typhoons passing through the central part of the Bohai Sea (e.g., Rumbia), high-energy waves are observed under swell-dominated and mixed sea states, which are subjected to the fetch limitation in the semi-enclosed sea and rapid changes in typhoon winds. The high energy waves induced by other typhoons passing along the edges of the Bohai Sea correspond to the wind-sea dominated sea state. Spatiotemporal variability of the sea state exhibits a high correlation with its position relative to the typhoon center. Therefore, a reference frame based on the radius of the maximum wind speed was established to discuss the sea states in this semi-enclosed sea. Further investigations reveal that swells (wind-seas) dominate the regions within the radius of the maximum wind speed (elsewhere), and the double-peaked wave spectra tend to appear in the left quadrants.