Tide-Topography Interaction and Currents: Asymmetries in Internal Wave Breaking

Tide-topography interactions, the source of approximately half the internal wave energy and of most internal solitary waves in the oceans, have been the subject of many studies in recent decades. Many of these studies have considered the generation of internal waves over a two-dimensional symmetric ridge in the absence of steady background currents. In this situation waves propagating to the left and right of the ridge are the same. This symmetry is broken in the presence of steady background currents. In this talk the effects of a uni-directional steady background current confined to lie above a ridge will be discussed. Strong asymmetries in wave breaking can occur. Internal wave beams interacting with the background shear can result in overturning on the downstream side of the ridge. Lee waves on the upstream side of the ridge (with respect to the background current) are more prone to shear instabilities than those formed on the downstream side. Regions in parameter space where these types of asymmetric breaking occur will be discussed.