Modes of SST variability in the Indian Ocean: Interannual and interdecadal variability, connections with ENSO and East African coastal rainfall

An empirical orthogonal function (EOF) analysis of monthly SST within the Indian Ocean over the past 50 years is performed. The first principal componant (pc1) capturing 41% of the variance is composed primarily of a warming trend in the central equatorial Indian Ocean and is strongly correlated to the monthly Nino3 SST index. The strength of this correlation varies interdecadally, however, and the pc1 shows a strong shift to a warmer state in 1976. The second principal componant (pc2), with 10% of the variance, is a dipole pattern with one node in the Arabian Sea and the other node just NW of Australia. The pc2 is not strongly correlated with the Nino3 index, but is strongly correlated with October-November African rainfall from Kenya and Tanzania. The pc2 decorrelates from the ON African rainfall between 1983 and 1994. The ocean-atmosphere mechanisms giving rise to the dipole-rainfall relationship, as well as implications for prediction of rainfall extrema in Africa are discussed.