Loop Current Eddy Interaction with the Western Boundary in the Gulf of Mexico

Abstract

A two-layer, intermediate equations model that, uniquely, allows for the intersection of the bathymetry with the layer interface is used to study the interaction of isolated Loop Current Eddy (LCE)-type anticyclones with western-boundary topography. Two idealized topography configurations representative of the Gulf of Mexico (GoM) coastal topography at 25° and 23°N are studied; the 25°N topography configuration is characterized by a relatively wide shelf and a narrow continental slope, and the 23°N configuration is characterized by a relatively narrow shelf and a wide continental slope. The physical mechanism that has the most significant effect on the evolution of the LCE in both topographic configurations is the interaction of the LCE with cyclones formed directly to its north through the process of off-shelf advection of potential vorticity in the upper layer. The LCE interaction with those cyclones that are generated through this mechanism results in the LCE becoming elliptic and rotating clockwise with its center following a cyclic trajectory. The amplitude of the cyclic motion produced by LCE interactions with cyclones is controlled by a different physical mechanism. The mechanism consists of the LCE interacting with deep eddies that can be generated beneath the LCE over regions of flat topography adjacent to the continental slope. The deep eddies are generated by stretching and compression of the lower layer by a rotating elliptic LCE. The net effect of these eddies is to amplify significantly the cyclic motion of the LCE. The width of the continental slope is the critical parameter controlling the strength of the LCE interaction with deep eddies and, therefore, the amplitude of the cyclic motion. The characteristic pattern of LCE evolution seen in the numerical experiments can be identified in some observed cases of LCE interaction with the western boundary in the GoM.