[A-OS11] Ocean Mixing Frontiers

[AOS11-P12] Can tidal forcing alone generate a GM-like internal wave spectrum?

*Zhiwu Chen¹, Shaomin Chen¹, Zhiyu Liu², Jiexin Xu¹, Jieshuo Xie¹, Yinghui He¹, Shuqun Cai¹ (1.South China Sea Institute of Oceanology, Chinese Academy of Sciences, 2.Department of Physical Oceanography, College of Ocean and Earth Sciences, Xiamen University)

Keywords:Internal waves, Garrett-Munk spectrum, Near-inertial waves, Parametruc Subharmonic Instability

An idealized two-dimensional numerical model is utilized to study internal wave generation by tide-topography interaction and wind forcing. Previous studies suggest that the quasi-universal Garrett-Munk (GM) internal wave spectrum can be generated 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 between 17° and 29°, with the steepness parameter ε >1, N₀h₀/u₀>1 (N₀ is buoyancy frequency, h₀ topographic height, and u₀ tidal amplitude), and a finite excursion parameter. The key lies in the generation of near-inertial waves (NIWs) by breaking internal tides and triadic resonant interactions around supercritical topography. Remarkably, in the northern South China Sea, tidal forcing can contribute a comparable amount of near-inertial energy as that contributed by the summer wind and thus is an important NIW generation mechanism.