A Numerical Study of the Agulhas Retroflection: The Role of Bottom Topography

Abstract

The oceanic circulation near the eastern margin of the African continent is dominated by the poleward flow of the Agulhas Current. The Agulhas Current separates from the African coast near the southern tip of the continent, makes an abrupt turn to the east (known as the Agulhas Retroflection), and flows into the Indian Ocean as a meandering jet called the Agulhas return current. The object of this study is to investigate possible causes for the Agulhas Retroflection. A series of process-oriented experiments are conducted with the Princeton ocean model, a primitive equation numerical model in sigma coordinates. The model is started from rest, forced at its surface with different wind stress distributions, and run until dynamical equilibria are reached, after which the steady states of the model are analysed. In these experiments, the effects of inertia, wind stress distribution, and realistic bottom topography on the Agulhas Retroflection are analyzed. The results of these experiments indicate that bottom topography, rather than current inertia, is the main cause of the Agulhas Retroflection.