J. Clim. http://doi.org/ckgt (2018)

The Agulhas Current (AC) — the western boundary current of the South Indian Ocean — flows south along the east coast of Africa. Model results suggest the AC has intensified in response to strengthened westerly winds, a manifestation of the positive trend in the Southern Annular Mode (SAM). However, observational support for this SAM-driven AC intensification is lacking. Using a satellite altimetry and in-situ-derived proxy for AC transport, Shane Elipot and Lisa Beal from the University of Miami, USA, investigate the atmospheric drivers of interannual AC variability and their relationship to longer-term trends.

On interannual timescales, AC transport is found to be most strongly related to climate forcings originating in the tropical Indo-Pacific, namely the El Niño–Southern Oscillation. By contrast, the SAM is shown to have a weak influence. Consequently, the positive trend in the SAM is expected to have a minor impact on longer-term AC variability. As the proxy time-series for AC transport also reveals insignificant trends, it is argued that the SAM is unlikely to have intensified the AC as models indicate. Thus, more work is required to resolve western boundary currents in climate models to minimize such discrepancies.