Modal content of typhoon-induced near-inertial waves around the East China Sea

Abstract

Recent studies show that typhoon-induced near-inertial waves (NIWs) exhibit different modal content in the shallow and deep regions, whereas the underlying mechanism has not been fully understood. Based on a three-dimensional numerical model, we simulate the NIWs induced by two typhoons (Songda and Meari in 2011) in the East China Sea and its adjacent deep waters in the northwest Pacific Ocean. Although the near-inertial kinetic energy induced by the two typhoons has different intensity and spatial distribution, the modal content of NIWs induced by them shares a common characteristic: In the shallow regions (water depth smaller than 200 m), the NIWs are mainly dominated by mode-1; whereas in the deep regions (water depth larger than 200 m), the NIWs are dominated by higher modes (mode-2 to mode-5). Different mechanisms are found to account for the different modal content in shallow and deep regions. The dominance of higher-mode wind forcing is the cause for the dominance of higher-mode NIWs in the deep regions. The two-layer-structure stratification is the cause for the dominance of mode-1 NIWs in the shallow regions.