Atmospheric driving forces for the Agulhas Current in the subtropics

Abstract

The Agulhas Current is the western boundary current of the South Indian Ocean and is thought to play an important role in the global overturning circulation. In this study, we investigate the contribution from the wind stress field over each ocean basin of the southern hemisphere to the variability of Agulhas Current transport. We ran a series of experiments using the Modular Ocean Model 2. The model grid extends from 20°S to 70°S and has a horizontal resolution of 1/2° with 25 levels in the vertical. The first experiment was forced with monthly means of the wind stress field from the project ERA 40 from ECMWF. In three other sensitivity experiments, the model was forced with the climatological mean over the whole domain plus the monthly wind stress anomalies (Jan/ 1979-Dec/2001) over one of the three ocean basins to whit: the South Atlantic, the South Indian and the South Pacific. The results show that inter-annual variations in the Agulhas Current transport are due largely to the wind field over the South Indian Ocean, whereas annual variations are driven by the wind field over both the South Atlantic and South Indian oceans. The annual signal from the South Atlantic is shown to move equatorward along the southeastern coast of Africa through coastally trapped waves. Copyright 2007 by the American Geophysical Union.