Eddy-Train Encounters with a Continental Boundary: A South Atlantic Case Study

Abstract

Abstract Satellite altimetry suggests that large anticyclonic eddies (rings) originating from the Agulhas Current retroflection occasionally make their way across the entire South Atlantic Ocean. What happens when these rings encounter a western boundary current? In this work, interactions between a “train” of nonlinear lens-like eddies and a Southern Hemisphere continental boundary are investigated analytically and numerically on a β plane. The train of eddies is modeled as a steady double-frontal zonal current with the same vorticity and transport as the eddies themselves. The continental boundary is represented by a vertical wall, which is purely meridional in one case and is tilted with respect to the north in another case. It is demonstrated analytically that the eddy–wall encounter produces an equatorward flow parallel to the continental wall, thus suggesting a weakening of the transport of the associated (poleward flowing) western boundary current upstream of the encounter zone and unchanged transport downstream. A large stationary eddy is established in the contact zone because its β-induced force is necessary to balance the other forces along the wall. The size of this eddy is directly proportional to the transport of the eddy train and the meridional tilt of the wall. These scenarios are in good agreement with results obtained numerically using an isopycnal Bleck and Boudra model.