Theory of the Benguela Upwelling System

The paper gives a theoretical study of the Benguela upwelling system by means of a relatively simple conceptual model that allows an analytical treatment. The model consists of a stratified, flat-bottomed coastal ocean. The coast is idealized by a straight wall. The model ocean is forced by an alongshore wind band extending from the area near Cape Town to the border of Angola and Namibia. The wind varies alongshore and cross-shore (wind stress curl) and changes periodically in time. The response of the coastal ocean is governed by coastal jets, upwelling, and Kelvin waves, as well as by a current system driven by the wind stress curl. The model is able to reproduce several observed features such as the poleward undercurrent, the northward coastal currents in most of the wind band, and a southward coastal current near the northern edge of the wind band. Export of coastal jets out of the forcing area by coastal Kelvin waves provide a mechanism to guide energy into the area off Cape Town. The southward propagating Kelvin waves may bend around the southern tip of Africa and provide a dynamic linkage between the Benguela coastal current and the Agulhas Current.