A Mechanism for Observed Interannual Variabilities over the Equatorial Indian Ocean

Abstract A mechanism is proposed that can give rise to a sustained interannual variability of sea surface temperature (SST) and other variables even over an ocean basin of small zonal extent such as the Indian Ocean, as observed. A simple one-dimensional ocean–atmosphere coupled climate model with “minimal” dynamics is considered to isolate and emphasize the basic physical mechanism. In particular, unlike in the conventional scenario of the El Nino–Southern Oscillation, the equatorial Rossby waves are not included in the dynamics of the model. However, although the dynamics is minimal, the model as a whole is nonlinear due to the nonlinear parameterization of the atmospheric heating. It is shown that even with this minimal dynamics the model exhibits interannual variabilities for appropriate air–sea interaction. Further, in the one-dimensional case a basic factor that suppresses variability over the smaller basins is the zonal extent of the ocean basin. For an ocean-covered globe and for two basins of equ...