Turbulent aspects of a subsurface-recirculating core in a shoaling internal solitary wave of depression through high-resolution/accuracy three-dimensional simulations *

The three-dimensional convective breaking of an internal solitary wave (ISW) of depression, shoaling over a realistic gentle bathymetric slope and complex background stratification/current profiles sampled in the South China Sea, is examined via high-resolution/accuracy simulations. These massively parallel simulations are based on a hybrid high-order spectral-element-method/Fourier Galerkin flow solver which enables the reliable representation of the complex shoaling bathymetry, under the constraint of the ISW propagating in the normal-to-the-isobath direction. As the ISW shoals into shallower waters it undergoes a distinct convective instability: as the ISW continues to maintain its symmetric waveform, the plunging isopycnal originating from the rear of the wave produces a heavy-over-light configuration in the wave interior, effectively leading to the formation of a recirculating subsurface core. A subsequent secondary transverse instability follows, leading to turbulence transition and the resulting formation of finer-scale turbulence therein. Beyond outlining the structural features of the three-dimensional breaking process, the presentation also investigates the ISW-driven turbulent dissipation and its connection to the persistence of the recirculating core.