A new model of current retroflection applied to the westward protrusion of the agulhas current

Abstract

The dynamics of current retroflection and rings shedding are not yet fully understood. In this paper, the authors develop an analyticalmodel of the Agulhas Current retroflection dynamics using three simple laws: conservation of volume, momentum balance, and Bernoulli's principle. This study shows that, for a retroflecting current with a small Rossby number, this theoretical model is in good agreement with numerical simulations of a reducedgravity isopycnal model. Otherwise, the retroflection position becomes unstable and quickly propagates upstream, leaving a chain of eddies in its path. On the basis of these findings, the authors hypothesize that the westward protrusion of the Agulhas retroflection and the local "zonalization" of the Agulhas Current after it passes the Agulhas Bank are stable only for small Rossby numbers. Otherwise, the retroflection shifts toward the eastern slope of theAgulhas Bank,where its position stabilizes due to the slanted configuration of the slope. This study shows that this scenario is in good agreement with several high-resolution numerical models.