Internal Wave Breaking at Concave and Convex Continental Slopes*

Abstract

Internal wave reflection from a sloping topographic boundary may lead to enhanced shear if the topographic angle to the horizontal is close to that of the internal wave group velocity vector. Previous analytic studies have suggested that shear enhancement is reduced at concave slopes as compared with convex and planar slopes near the critical angle. Here the internal wave reflection from concave and convex slopes that pass through the critical angle is investigated numerically using the nonhydrostatic Massachusetts Institute of Technology General Circulation Model (MITgcm). Overturning, shear instability, and resultant mixing are examined. Results are compared with simulations of wave reflection from planar slopes with angles greater than, less than, and equal to the critical angle. In contrast to the analytic predictions, no reduction in mixing is found for the concave slope as compared with the other slopes. In all cases, stratification is eroded in a band above the slope, bounded at its outer edge by the internal wave characteristic. The difference between numerical and analytic results is caused by the nonlinearity of the numerical calculations, where the finite-amplitude flow leads to generation of upslope-propagating bores for a wide range of topographic slopes around the critical angle.