Kinetic Energetic Exchange between Near-Inertial Waves and Mesoscale Eddy/Diurnal Tide during Typhoon Rai

Abstract Near-inertial waves (NIWs) in the oceans have multiple generation mechanisms. Typhoons with strong wind forcing are one of the major sources of NIWs; however, the kinetic energy (KE) exchange between NIWs and mesoscale eddies/internal tides during the typhoon remains unclear. In this study, we use 4 months of mooring data from the South China Sea to quantify the contributions of wind forcing, resonant wave–wave interactions (RWIs), and NIW–eddy interactions to the changing of near-inertial KE (NIKE) during Typhoon Rai. The contributions of the aforementioned mechanisms to the increase of NIKE decreased in the following order: wind forcing (7.1 kJ m −2 ) > RWI (5.59 kJ m −2 ) > NIW–eddy interactions (0.22 kJ m −2 ). Using three sensitivity analysis simulations based on the MITgcm, we confirm that the KE exchange between diurnal internal tides and NIWs is significantly enhanced during Typhoon Rai. However, in contrast to the enhanced surface KE exchange, the vertically integrated KE exchange between NIWs and mesoscale eddies changes little. According to our proposed tensor composition method, the high-mode geostrophic strain causes the direction of KE exchange to exhibit a high-mode structure, resulting in little vertically integrated KE exchange. This study extends our knowledge of the oceanic energy balances between mesoscale eddies/diurnal tides and NIWs during typhoon periods, which would be useful for global ocean numerical models. Significance Statement Near-inertial waves (NIWs), mainly generated by wind forcing, are the major contributors to ocean mixing. Recent studies have shown that mesoscale eddies and diurnal tides are also important sources of kinetic energy (KE) for NIWs. This study quantifies the KE exchange between NIWs and mesoscale eddies/diurnal tides during a typhoon: (i) During Typhoon Rai, the resonant wave–wave interaction between NIWs and diurnal tides is significantly enhanced. (ii) The direction of the energy exchange between NIWs and mesoscale eddies depends on the near-inertial frequency shift and the mesoscale geostrophic strain. A high-mode structure of the mesoscale geostrophic strain during typhoon can cause high-mode KE exchange. Therefore, the energy exchange between NIWs and mesoscale eddies/diurnal tides should be carefully considered during typhoon periods.