The Generation of Nonlinear Internal Waves in the South China Sea: A Three‐Dimensional, Nonhydrostatic Numerical Study

Abstract

AbstractThe generation of nonlinear internal waves (NLIWs) by stratified tidal flow over an isolated topography has been a subject of research for many years. However, the enhanced complexity of the dynamics as a consequence of flow over two topographical features has been less studied and understood. Here, we report results of the generation of type‐A and type‐B NLIWs in the South China Sea that originate from a double‐ridge system. Based on a realistic three‐dimensional nonhydrostatic simulation, it is found that type‐A NLIWs are generated at the western ridge through the mechanism of internal tide release, while the generation of type‐B NLIWs occurs at the eastern ridge as a consequence of internal wave interaction. Associated with the ridge height, separation distance, and modulated tidal forcing, the generation of type‐B NLIWs is strongly modified by the resonant process between the two ridges. As a result, type‐A and type‐B NLIWs appear in the observations with alternating large and small amplitudes. In addition, with a detailed knowledge of the generation, it is also found that the different arrival time of these waves could be due to their different generation times. Finally, the reflection/transmission of type‐B NLIWs at the subcritical western ridge is suggested as a key feature of resonance. However, it is governed by hydraulically controlled flow instead of the ratio of the local topographic slope to the internal wave beam angle.