Energy flux of nonlinear internal waves in northern South China Sea

Abstract

We analyze three sets of ADCP measurements taken on the Dongsha plateau, on the shallow continental shelf, and on the steep continental slope in the northern South China Sea (SCS). The data show strong divergences of energy and energy flux of nonlinear internal waves (NLIW) along and across waves' prevailing westward propagation path. The NLIW energy flux is 8.5 kW m−1 on the plateau, only 0.25 kW m−1 on the continental shelf 220 km westward along the propagation path, and only 1 kW m−1 on the continental slope 120 km northward across the propagation path. Along the wave path on the plateau, the average energy flux divergence of NLIW is ∼0.04 W m−2, which corresponds to a dissipation rate of O(10−7−10−6) W kg−1. Combining the present with previous observations and model results, a scenario of NLIW energy flux in the SCS emerges. NLIWs are generated east of the plateau, propagate predominantly westward across the plateau along a beam of ∼100 km width that is centered at ∼21°N, and dissipate nearly all their energy before reaching the continental shelf.