Impacts of Momentum Fluxes Modulated by Surface Waves on Near-Inertial Motions in Tropical Cyclones

Surface waves play an essential role in modifying the momentum fluxes across the air-sea interface, especially under tropical cyclone (TC) conditions. A coupled wave-ocean circulation model system, taking into consideration the surface wave effects on momentum fluxes, is applied to investigate the generation of near-inertial motions (NIMs) under TC conditions. When surface waves are ignored, large overestimates in wind power input are obtained, about 10%-40%, occurring in the right and rear TC regions. Surprisingly, the modulation effects of surface waves on the momentum fluxes have impacts on NIMs that reach depths of similar to 100 m; the resulting reduction in the near-inertial velocity can exceed 0.1 m/s (up to 35%) and the reduction in the near-inertial energy (NIE) is up to 20%. The largest modifications to NIMs are located at two times the radius of the maximum wind speed, relative to the TC center. In the upper ocean, the mixed-layer NIE reductions due to surface waves are greater in medium-speed TCs (3-6 m/s) than in rapidly moving TCs, by about similar to 10%, because there are more young waves around the TC centers, and better overlapping between the regions with large wind stress changes and ocean current responses. Given that these effects are notable for surface waves impacts on NIMs, and thus on the currents and the resulting thermal redistribution under TCs, the feedbacks of these modified ocean properties must affect TC evolution and should be included in coupled atmosphere-ocean studies.