Does a dipole mode really exist in the South Atlantic Ocean?

This study investigates the existence of a dipole mode in the sea surface temperatures (SST) over the South Atlantic Ocean (SAO), using observational and reanalysis data sets from 1950 to 2008. Our results demonstrate that an opposite SST mode, the SAO dipole (SAOD) occurs in the SAO as the anomalous surface waters in the northeastern part; that is, the Atlantic Nino sector and the southwestern part off the Argentina-Uruguay-Brazil coast are consistently anticorrelated in all months. A typical SAOD episode has a life cycle of about eight months, although the peak intensity in which the SST anomalies are evidently coupled to atmospheric circulation and precipitation anomaly fields lasts for four months during the austral winter (May-August). This coupled atmosphere-ocean interaction mechanism appears to be unique, distinct from the classical Atlantic Nino and independent of the direct influence of the Pacific Ocean-based El Nino or global SST variability. The SAOD may provide a useful framework for investigating climate variability and for improved predictions especially over parts of Africa and the Americas, and some preliminary results are already indicated, e.g., the SAOD is widely related to precipitation anomalies in these regions particularly during the austral winter.