Differential Influences Of El Niño Events On Indian Summer Monsoon Rainfall

Abstract:

The Indian Summer Monsoon (ISM) rainfall is largely influenced by El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) and the understating of the complex interaction between these modes of interannual variability with ISM is still a research challenge. In this study, an Intermediate Global Climate Model version 4 (IGCM4) is employed to examine the individual and combined influence of various types of ENSO and the IOD forcing on the ISM variability. To increase the scope of study, SST forcing from three different types of El Niño events categorically distinguished as Eastern Pacific (EP), Central Pacific (CP) and Mixed Pacific (MP) are analyzed. The role of IOD as well as the individual roles of warm (cold) anomalies over Western Indian Ocean (WIO) and South East Indian Ocean (SEIO) has been examined. The analysis of model output suggests that, the cooling over the western pacific (WP) largely explains the negative rainfall anomalies over India during the El Niño events. In addition, the negative rainfall anomalies over India are also induced by large-scale circulation changes in association with warm anomalies over central and eastern pacific. Despite the differences among the three El Niño events, warm anomalies over WIO are found to play an important role on ISM rainfall variability in the presence of El Niño forcing in the tropical Pacific. The results from IGCM are more interesting and needs to be further verified in both observations and fully coupled climate models to better understand ENSO-IOD relationships and their influence on ISM variability.