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

摘要

The 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.