Modulation of SST Interannual Variability in the Agulhas Leakage Region Associated with ENSO

Abstract

Abstract The Agulhas leakage transports warm and saline water from the Indian Ocean into the South Atlantic Ocean, forming part of the upper returning arm of the meridional overturning circulation, which can influence climate. Ocean–atmosphere interactions and the strength of Agulhas leakage control sea surface temperature (SST) in the Agulhas leakage corridor, which may in turn affect regional climate variability. In a high-resolution run of the Community Climate System Model (version 3.5; CCSM3.5), it is found that the interannual variability of Agulhas leakage SST is linked to El Niño–Southern Oscillation (ENSO). Anomalous wind stress curl over the south Indian Ocean associated with ENSO excites westward-propagating oceanic Rossby waves that initiate southwestward-propagating anomalies along the coast of Africa. It takes approximately 2 years for this signal to reach the southern tip of South Africa and enter the South Atlantic, where it accounts for 20%–30% of the interannual SSH variability in the Agulhas leakage region. The authors find a similar propagation of anomalies with satellite observations. A similar ENSO cycle along with Rossby wave adjustment is detected in an analogous low-resolution CCSM3.5 run. However, the signal does not propagate all the way along the boundary to affect Agulhas leakage SST. Hence, it is found that high-resolution coupled climate models are necessary to resolve the tropical–subtropical oceanic teleconnection between ENSO and Agulhas leakage SST.