Nonlinear processes generated by supercritical tidal flow in shallow straits

Bordois, Lucie ; Auclair, Francis ; Paci, Alexandre ; Dossmann, Yvan ; Nguyen, Cyril

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Numerical experiments have been carried out using a nonhydrostatic and non-Boussinesq regional oceanic circulation model to investigate the nonlinear processes generated by supercritical tidal flow in shallow straits. Our approach relies on idealized direct numerical simulations inspired by oceanic observations. By analyzing a large set of simulations, a regime diagram is proposed for the nonlinear processes generated in the lee of these straits. The results show that the topography shape of the strait plays a crucial role in the formation of internal solitary waves (ISWs) and in the occurrence of local breaking events. Both of these nonlinear processes are important turbulence producing phenomena. The topographic control, observed in mode 1 ISW formation in previous studies [Y. Dossmann, F. Auclair, and A. Paci, 'Topographically induced internal solitary waves in a pycnocline: Primary generation and topographic control,' Phys. Fluids 25, 066601 (2013) and Y. Dossmann et al., 'Topographically induced internal solitary waves in a pycnocline: Ultrasonic probes and stereo-correlation measurements,' Phys. Fluids 26, 056601 (2014)], is clearly reproducible for mode-2 ISW above shallow straits. Strong plunging breaking events are observed above 'narrow' straits (straits with a width less than mode 1 wavelength) when the fluid velocity exceeds the local mode 1 wave speed. These results are a step towards future works on vertical mixing quantification and localization around complex strait areas.
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