Individual and Combined Influences of ENSO and the Indian Ocean Dipole on the Indian Summer Monsoon

The relative influences of the ENSO and Indian Ocean Dipole (IOD) events on the Indian summer rainfall were studied using observational data and an atmospheric general circulation model (AGCM). The composite analysis of rainfall anomalies demonstrates that the IOD, while significantly influencing the Indian summer monsoon rainfall, also significantly reduces the impact of ENSO on the Indian summer rainfall whenever these events with the same phase co-occur. The AGCM experiments have shown that during an El Niño event, the Walker circulation over the tropical Indo–Pacific region is modulated; a low-level anomalous divergence center over the western Pacific and an anomalous convergence zone over the equatorial…