Nonlinear processes generated by supercritical tidal flow in shallow straits

Abstract

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.

In Situ Observations of the Small‐Scale Dynamics at Camarinal Sill—Strait of Gibraltar

“…The generation of an ISB of higher modes strongly depends on the topographic length scale (see Figure 6 of Bordois et al. (2017)). As the sill width varies significantly meridionally, the generation of such mode could be very local.…”

3D phase-resolved wave modelling with a non-hydrostatic ocean circulation model

“…This property is essential for the accuracy of the non-hydrostatic behavior of the model. In practice, $ must remain larger than the phase speed of gravity waves (Bordois et al, 2017).…”

“…However, at the resolutions where these models are most often used, the consideration of non-hydrostatic effects may not be an essential issue (McKiver et al, 2016). The applications envisaged so far concern more the propagation of internal gravity waves (Bordois et al 2017) or the convective processes (Paluszkiewicz et al, 1994) than the high frequency surface waves. One of the obstacles to the deterministic modelling of waves over large domains is the cost of the non-hydrostatic solver (Klingbeil et al, 2018).…”

“…The alternative to the global approach is the local approach based on the direct resolution of non-hydrostatic pressure. Various methods have been proposed so far (Johns 1991, Klingbeil and Burchard, 2013, Bordois et al, 2017, Lee et al, 2006. Among them, Lee et al, 2006 (hereafter L06) ACM (artificial compressibility method) method has a reasonable numerical cost and its implementation in a model is easy.…”

The role of the free surface on interfacial solitary waves

“…They can be generated in a wide variety of ways, including by lee waves, tidal beams, resonance and river plumes [2][3][4][5][6] . However, ISWs of large amplitude are primarily generated by the action of tidal currents over bottom topography like sills, continental slopes, or sand banks [7][8][9] . ISWs generated in each tidal period tend to be grouped together into an ordered packets, with the largest wave in the lead 10 .…”