On the physics of the Agulhas Current: steady retroflection regimes

Abstract

From previous model studies,it has become clear that several physical mech- anisms may be at work in the retroflection of the Agulhas current.Here,a sys- tematic study of steady barotropic flows connecting the Indian Ocean and South Atlantic Ocean in several idealized set-ups is performed.By solving directly for the steady circulation with continuation methods,the connection between differ- ent retroflection regimes can be monitored as external conditions,such as the wind forcing,bottom topography as well as parameters,for example the lateral friction and layer depth,are changed.To distinguish the different steady retroflecting flows,an objective measure of the degree of retroflection,a retroflection index R ,is introduced.By monitoring R along a branch of steady solutions,using the horizontal friction as control parameter,several steady retroflecting regimes are found.At large friction there exist stable steady states with viscously dominated retroflection.When friction is decreased,inertial effects become more dominant and eventually unstable steady states with strong retroflection characteristics ex- ist.Within this framework,different results from earlier studies can be reconciled.