Development and evolution of turbulence in convectively breaking internal solitary waves of depression shoaling over gentle slopes in the South China Sea.

This presentation discusses three-dimensional high accuracy/resolution simulations of convectively-breaking internal solitary waves (ISWs) shoaling over realistic gentle bathymetric slopes in the South China Sea. The shoaling ISWs, consistently observed by Lien et al. (Journal of Physical Oceanography 2012 & 2014) and Chang et al. (Communications Earth & Environment 2021), are subject to convective breaking (Umax/c > 1) and, by virtue of the near-surface shear structure of the background current, develop a turbulent subsurface recirculating core. A high-accuracy/resolution massively parallel 3D non-linear non-hydrostatic flow solver (Diamantopoulos et al. (Ocean Modelling, 2022)) is used to explore the fundamental physics governing the wave-induced flow structure, the convective breaking and the associated turbulence inside the shoaling ISWs. Particular attention is devoted to examining the potential for marginal instability (Umax/c ≃ 1), the generated shear instability, and the corresponding wake on the continental shelf. In addition, an investigation of the highly active regions where mixing occurs and the examination of the turbulence that emerges, is included. Finally, results are presented and compared for three production runs with ISWs of varying initial amplitude (defined as the maximum isopycnal displacement).