Regional ocean modelling around Southern Africa with SAfE (Southern Africa Experiments).

Penven, P. (1), Veitch, J. (2), Chang, N. (2),
Rouault, M. (2), Pohl (3) and Shillington, F. (2)

(1) Laboratoire de Physique des Oceans (UMR6523: CNRS, Ifremer,
IRD, UBO), France.

(2) Department of Oceanography, University of Cape Town,
South Africa.

(3) Centre de Recherches de Climatologie, Université de Bourgogne,
France.

The SAfE (Southern Africa Experiments) model configuration was designed to resolve the dynamics of the Agulhas Current from its sources around Madagascar to the Southern Atlantic where the Agulhas Rings dissipate. The grid extends from 2.5°W to 54.75°E and from 46.75°S to 4.8°S at 1/4° horizontal resolution. Several grid refinements are created using ROMS-AGRIF nesting capabilities to resolve the complex dynamics around Southern Africa.

One refinement, located along the west coast of Southern Africa, is used to compare the equilibrium dynamics of the Northern and Southern Benguela. The focus is to study the upwelling systems, signal cycles, and eddy dynamics. The impact of the Agulhas Current on the upwelling system is also addressed.

Another refinement, centered on the Agulhas Bank, is used to quantify the effects of the Agulhas Current on the Cool Ridge. The Cool Ridge is a tongue of colder water that is rich in nutriments and propagates along the southern coast of Africa.

On the larger scale, a recent increase in the Agulhas Current in response to an augmentation in wind stress curl in the South Indian Ocean is detected by our inter-annual regional simulation. This causes an intensification of the fluxes of salt and heat into the Atlantic Ocean. This, in turn, causes a transfer of energy from the ocean to the atmosphere. These changes could have far reaching consequences which could impact the climate and ecosystem.