On Dipolelike Variability of Sea Surface Temperature in the Tropical Indian Ocean

The interannual variability of the tropical Indian Ocean sea surface temperature (SST) is studied with observational data and a hierarchy of coupled general circulation models (CGCMs). Special attention is given to the question of whether an oscillatory dipole mode exists in the tropical Indian Ocean region with centers east and west of 80°E. These results indicate that dipolelike variability can be explained as an oscillatory mode only in the context of El Niño–Southern Oscillation (ENSO). A dipolelike structure in the SST anomalies independent of ENSO was found also. This series of coupled model experiments shows that ocean dynamics is not necessary to this type of dipolelike SST variability. It is forced by surface heat flux anomalies that are integrated by the thermal inertia of the oceanic mixed layer, which reddens the SST spectrum.