Mapping internal lee wave generation and dissipation in the deep South China sea

Abstract

Abyssal mixing induced by internal wave breaking has been proposed as an essential process that maintains and modulates the deep cyclonic circulation and meridional overturning circulation in the South China Sea (SCS). Previous studies have primarily focused on internal tides, leaving limited exploration on internal lee waves and their roles in mixing the SCS. This study represents the first basin-scale estimation of the lee-wave energy flux from the geostrophic flow and exploration of lee-wave-induced mixing in the SCS. Utilizing an improved spectra method with the synthetic full-scaled bathymetry, lee wave generation is estimated employing Bell theory with the outputs from the China Sea Multi-Scale Ocean Modeling System. The Luzon Strait (LS) features the strongest lee wave generation, reaching up to 19.7 GW. In the SCS interior, the total energy flux is estimated at 1.3 GW, with 70% occurring in the deep basin. In the basin area, energy flux from the mean flow surpasses that from eddy flow, whereas in the marginal area, the dominant energy flux is from eddy flow. This study reveals seasonal variation in lee wave generation, closely related to the seasonality of the deep-water overflow from the LS. The mixing driven by lee waves is found comparable with that driven by internal tides in the deep SCS basin. This study emphasizes the potentially significant lee wave energy and induced mixing in the deep SCS basin, which should be well-mapped and parameterized in ocean models for a better characterization of multiscale dynamics and energetics in the SCS.