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

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. Plain Language Summary Near‐inertial waves (NIWs) contain a pronounced portion of energy in the ocean interior and play an important role in maintaining the global meridional overturning circulations. However, sources of deep and abyssal NIWs are less known due to the lack of in‐situ observations. Here, we demonstrate that TC‐induced NIWs and parametric subharmonic instability (PSI) are conducive to generating deep near‐inertial kinetic energy (NIKE) based on a 3 year mooring measurement at 130°E/15°N. The warm core eddy (WCE) can facilitate the downward propagation of TC‐induced NIWs, which can be inferred from the positive correlation between eddy kinetic energy and vertical group velocity. Although the mooring location is poleward of the critical latitude for diurnal internal tides (DITs), the PSI of DITs can efficiently generate NIKE when the negative vorticity of WCE is presented. The linear regression analyses suggest that under WCE modulation, the downward propagating TC‐induced NIWs can explain more than 50% of the total variance of deep NIKE, while the PSI of DITs can only explain less than 30%. Key Points Mooring measurements reveal that downward propagating TC‐induced NIWs and PSI contribute to intensified near‐inertial energy below 1,000 m Deep warm core eddies improve NIW's vertical group velocity and PSI efficiency at site north of diurnal tidal critical latitude TC‐induced NIWs and PSI of internal tide explain more than 50% and les