Chapter 2 - Interannual variation of the Indian summer monsoon, ENSO, IOD, and EQUINOO

Abstract

The most important factor determining the interannual variation of the Indian summer monsoon rainfall (ISMR) is El Niño Southern Oscillation (ENSO). The equatorial Indian Ocean oscillation (EQUINOO), which is considered to be the atmospheric component of the coupled Indian Ocean Dipole Mode, also plays an important role. However, the coupling between the oceanic component of Indian Ocean Dipole and EQUINOO is not strong and while the index of EQUINOO is well correlated with ISMR, the index of the oceanic component, Dipole Mode Index, is not. Climate models are now able to generate reasonable predictions of ENSO and can also simulate ENSO impact on the monsoon well. Hence, seasons in which the contribution of ENSO to ISMR dominates that of EQUINOO, the monsoon predictions generated by the models are reasonable. However, large errors occur in the prediction of ISMR when the EQUINOO contribution dominates because the models, in general, are not capable of simulating the link between EQUINOO and ISMR. For further progress, deeper understanding and improved prediction of EQUINOO and its link to ISMR is essential.