Separation of a Density Current from the Bottom of a Continental Slope

Abstract

Separation from the continental slope of stratified jets like the Gulf Stream involves the sliding of successive isopycnal layers from a nearly horizontal bottom to the adjacent offshore isopycnal in the deep ocean. One mechanism for producing such an effect is due to a downstream convergence of slope isobaths, as shown herein for a 1-layer density model. Upstream of the convergence, a geostrophically balanced jet is assumed with an inshore region of cyclonic vorticity resting on the continental slope and an offshore anticyclonic region resting on the isopycnal interface above heavier water. For O(1) Rossby number and cross-stream topographic variation, the steady transverse current displacements forced by slowly varying downstream topography are computed. For ?supercritical? upstream flow (i.e., fast compared to free topographic waves) offslope displacements are produced by converging isobaths; extrapolation of the small amplitude result suggests that the mechanism is quantitatively important for the explanation of the full separation of the Gulf Stream from the bottom of the continental slope. The kinematics involved in this process should apply to a continuously stratified jet, as well as to other forcing mechanisms known to be of importance in continental boundary current separation.