Topographic effects on the path and evolution of Loop Current Eddies

Abstract

Eddy‐topography (ET) interactions are important in determining the path and evolution of oceanic eddies, including Loop Current Eddies (LCE) in the Gulf of Mexico (GOM). We use the Hybrid Coordinate Ocean Model and satellite altimetry data to investigate the ET interactions and the impact on LCE pathway evolution in the GOM. Satellite altimetry reveals that LCEs translate dominantly westward in the central GOM and strongly collide and reflect against topography near the continental slope in the northern and western GOM. The result is the frequent generation of an anticyclone‐cyclone (AC) pair in conjunction with the LCEs. In the absence of lateral or surface boundary forcing but including realistic topography, simulations initialized with idealized eddies at various locations in the GOM reveal the following results. Southward eddy reflection from the northern slope occurs when a cyclone drastically strengthens east of the anticyclone because of the ET collision. The prevailing westward propagation in the central GOM occurs because the cyclone is very dispersive toward nearby topographic features, causing a reduced southward component of drift and/or moves to the south, forming a meridional AC pair, causing an enhanced westward component. ET collision is strongest over the northwestern slope (north of 24°N) because of the eddy colliding relatively normal to the steep slope, and the eddy typically tracks anticyclonic pathways during the collision/reflection process. Along the western slope, a strong ET collision produces a southeastward reflection, and the accompanying cyclone to the northeast strongly enhances the reflection. Near the southern GOM slope, eddy pathways tend to propagate alongslope with an onshore‐offshore oscillatory trajectory because of the competition between topographic and planetary β effects. In the southwestern GOM a bimodal pathway occurs, i.e., northward migration with an anticyclonic route for relatively stronger eddies and southward dissipative propagation along the shelf edge for weaker ones.