Interdecadal variability of the Indian Ocean dipole and its connection with precipitation

A dipole mode of SST variability in the Indian Ocean has recently been identified (Webster et al. 1999, Saji et al. 1999). We investigate the interannual and interdecadal variability of this mode and its relationship with ENSO and precipitation over the past 50 years. We find that between 1950 and 1970 the dipole has a strong biennial component. Between 1970 and 1990 the interannual variability has a predominantly 4-year period. We find that there is a strong correlation (0.8) between the dipole and the East African coastal rainfall, except during the decade between 1983 and 1994. We investigate the possible physical mechanisms giving rise to these interdecadal variations.