Contributions of Tropical Cyclones and Internal Tides To Deep Near-Inertial Kinetic Energy Under Eddy Modulation

Abstract

Near-inertial waves (NIWs) are essential energy sources for deep diapycnal mixing. However, the mechanisms for generating deep and abyssal NIWs are largely unknown. Here, using 3 year full-depth mooring data at 130°E/15°N, we demonstrate that downward propagating tropical cyclone (TC)-induced NIWs and parametric subharmonic instability (PSI) can contribute to the intensification of near-inertial kinetic energy (NIKE) over 1,000–3,000 m. The deep warm core eddy (WCE) is found to facilitate the downward propagation of TC-induced NIWs with fast vertical group velocity and the intensified PSI efficiency that improves the energy transfer from diurnal internal tides (DITs) to NIWs at the site poleward of critical latitude for DITs. Quantitative regression analysis suggests that compared to the PSI, downward penetrating TC-induced NIWs contribute more to the deep NIKE. Our study emphasizes that accurately representing deep eddy activities and TC's wind intensity in numerical models is crucial to simulating the deep NIKE.