Baroclinic Eddy Interactions with Continental Slopes and Shelves

Abstract

The evolution and propagation of large anticyclonic eddies similar to the Loop Current eddies found in the Gulf of Mexico are studied in a two-layer intermediate equation numerical model. It is found that the propagation of these eddies is governed primarily by the ? effect, lower-layer flow driven by the surface eddies, and the image effect. As the eddies move westward under the influence of the ? effect, they drive deep circulation that typically includes a cyclone near the eddies' trailing edge. This cyclone accelerates the eddy southward, leading to a path substantially different from that found in reduced-gravity models of similar surface eddies. When the eddy encounters a continental slope, the lower-layer flow is dispersed by topographic Rossby waves, and the eddy loses its southward propagation component. If the continental slope is backed by a shelf that is wider than the eddy's radius, a deep anticyclone will form over the shelf as the eddy approaches the shelf break. This anticyclone will drive the surface eddy rapidly southward until it crosses the shelf break and encounters the boundary, where the eddy will turn northward under the influence of the image effect. Eddies initialized over a zonal slope, which cannot develop the deep circulation that accelerates the eddy southward because of topographic Rossby wave dispersion, propagate nearly zonally until they encounter the western boundary. Over a northern slope such as that found in the Gulf of Mexico, these eddies will retroflect and propagate westward under the influence of the image effect if the northwest corner shelf is narrow, but they will turn southward along the western boundary if the northwest corner shelf is wide.