On the baroclinic response of supercritical topography to an oscillating tide: LES results

Steep topography on the ocean bottom, when underneath an oscillating tide, is not only associated with significant internal wave generation at the tidal frequency but also nonlinear flow features, large overturns and turbulent flow. Here, we investigate the internal wave dynamics and turbulence at an isolated steep obstacle using a three-dimensional, high-resolution large eddy simulation (LES). An obstacle with a smoothed triangular shape having a supercritical slope above a critical slope is considered as a laboratoryscale model of a two-dimensional ocean ridge. Downslope jets with intensified velocity from in the supercritical region. Later on, during the flow reversal phase, this jet encounters upward flow and creates a rebounding jet that distorts the density isopycnals as well as a transient lee wave above the obstacle. Primary mechanisms responsible for turbulence are shear in the jet and convective instabilities arising from steepened isopycnals followed by wave breaking. There is also turbulence generation from resonance in the near-critical boundary flow.