The Generation of Nonlinear Internal Waves in the South China Sea: A Three‐Dimensional, Nonhydrostatic Numerical Study. Issue 12 (12th December 2019)

• Record Type: Journal Article
• Authors: Lai, Zhigang; Jin, Guangzhen; Huang, Yongmao; Chen, Haiyun; Shang, Xiaodong; Xiong, Xuejun
• Is Part Of: Journal of geophysical research. Volume 124:Issue 12(2019)
• Page Start: 8949
• Page End: 8968
• Publication Date: 2019-12-12
• Subjects: Nonlinear internal waves -- Generation mechanism -- Double‐ridge system -- Resonance -- Nonhydrostatic simulation -- Luzon Strait; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2019JC015283
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: 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. Plain Language Summary: Internal waves are fascinating phenomena of considerable interest to a variety of fields related to the ocean, and the South China Sea (SCS) is a popular area for researching strong nonlinear internal waves (NLIWs) worldwide. In the past decade, significant progress has been achieved regarding these waves in terms of their propagation and interactions with the Chinese continental shelf. However, the mechanism of wave generation is still unclear, and the detailed generation process remains ambiguous from previous idealized numerical investigations. Recently, a three‐dimensional, nonhydrostatic model was established to examine the internal wave dynamics in the SCS using realistic model configurations. The results showed that type‐A and type‐B NLIWs in the SCS are generated from the western and eastern ridges, respectively, in the Luzon Strait and under different dynamics. In particular, the generation of type‐B NLIWs involves a complex three‐dimensional process that is strongly modified by the double‐ridge internal tide resonance in the strait. These findings thus provide new insights into the generation mechanism of type‐A and type‐B NLIWs in the SCS. Key Points: The A NLIWs are generated at the western ridge by a release mechanism, and the B NLIWs are generated at the eastern ridge under resonance Three‐stage resonance includes the interaction of local and remote waves at ridges and the transmission of B NLIWs over the western ridge The reflection/transmission of the B NLIWs is governed by a hydraulically controlled flow on the subcritical western ridge