Can tidal forcing alone generate a GM-like internal wave spectrum?

Zhiwu Chen1, Shaomin Chen2, Zhiyu Liu3, Jiexin Xu1, Jieshuo Xie1, Yinghui He1 and Shuqun Cai4, (1)South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China, (2)South China Sea Institute of Oceanology, Chinese Academy of Sciences, China, (3)Xiamen University, State Key Laboratory of Marine Environmental Science, and Department of Physical Oceanography, College of Ocean and Earth Sciences, Xiamen, China, (4)SCSIO South China Sea Institute of Oceanology, Chinese Acaademy of Sciences, Guangzhou, China
An idealized two-dimensional numerical model is utilized to study internal wave generation by tide-topography interaction. Previous studies suggested that the quasi-universal Garrett-Munk (GM) internal wave spectrum can be created and maintained only when energy is supplied from both the wind and the tides, while the present study shows that M2 tidal forcing alone is sufficient to generate a GM-like spectrum in a latitude band roughly from 17ºN to 29ºN, with the steepness parameter ε>1, N0h0/u0>1 (N0 is buoyancy frequency, h0 is topographic height, and u0 is tidal amplitude), and a finite excursion parameter. The key lies in the generation of near-inertial waves by breaking internal tides and triadic resonant interactions (TRI) around supercritical topography. Remarkably, internal tide breaking and TRI can contribute comparable amount of near-inertial energy as contributed by the wind in the northern South China Sea.