Shelf Flows Forced by Deep-Ocean Anticyclonic Eddies at the Shelf Break

Abstract

AbstractIsolated monopolar eddies in the ocean tend to move westward. Those shed by western boundary currents may then interact with the continental margin. This simple picture is complicated by the presence of other flow features, but satellite observations show that many western boundary continental shelves experience cross-shelfbreak exchange flows forced by mesoscale eddies translating near the shelf break. Here we extend our previous study of eddy interaction with a flat shelf to that with a sloping shelf. Using a set of primitive equation numerical simulations, we address the vertical structure of the onshore and offshore flows forced by the eddy, the origin of the exported shelf water, and the extent to which eddy water can penetrate onto the shelf. The simulations reveal an asymmetry in the vertical structure of cross-shelfbreak flows: the offshore flow is generally barotropic, whereas the onshore flow is always baroclinic. The exported shelf water is sourced from downstream of the eddy in the coastal-trapped wave direction and is supplied by a barotropic alongshore jet. This “supply jet” has a Rhines-like cross-shore length scale proportional to (eddy velocity scale/shelf topographic beta)1/2 measured from the shelf break. Eddy water is forced onto the shelf and is present up to a distance of one internal Rossby deformation radius, defined using shelf properties, from the shelf break. We rationalize these horizontal and vertical scales, connect them to existing observations, and extend our previous parameterization of eddy-forced offshore shelf-water flux to account for nonzero shelf slopes.