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Interdecadal modulation of interannual ENSO‐Indian summer monsoon rainfall teleconnections in observations and CMIP6 models: Regional patterns

This study examined the Inter‐decadal modulations of interannual El Niño‐Southern Oscillation (ENSO)‐Indian Summer Monsoon (ISM) rainfall regional teleconnection patterns in the observations and Coupled Model Intercomparison Project Phase 6 (CMIP6) models. Observations show strong epochal changes of the relationship between ENSO and all‐India summer rainfall (AISR) with weak teleconnections in epoch‐1 (centred around 1915) and epoch‐4 (recent epoch) and strong teleconnections in epoch‐2 (centred around 1940) and epoch‐3 (centred around 1970) during the study period of 1901–2014. While on the regional point of view, it is found that epochal/decadal ENSO teleconnections to rainfall over northern central India and southern peninsular India are stronger and stable in all epochs. Whereas the rainfalls over the regions like Central India and Eastern Central India (ECI) displayed strong epochal changes in teleconnections, similar to that of AISR. This suggests that changes in ENSO‐ISM rainfall teleconnections are highly influenced by regional rainfall response. Anomalous upward motion over the head Bay of Bengal (BOB) and ECI regions related to Indian Ocean Dipole (IOD) and the westward extension of low‐level cyclonic circulation from the Western‐North Pacific (WNP) region are mainly responsible for the epochal changes in regional rainfall patterns over India associated with ENSO. We have assessed the fidelity of 29 CMIP6 models in representing the epochal changes in ENSO‐monsoon teleconnections. Nearly, 35% of models simulate epochal changes in teleconnections reasonably well. In most of the models, epochal changes in teleconnections are influenced by the strength and location of large‐scale subsidence coupled to the strength of Walker circulation associated with ENSO. It is noted that the drivers of epochal changes in ENSO‐monsoon teleconnections vary from model to model. Whereas, in the observations, the variance of ENSO itself in summer could influence modulations in the ENSO‐ISM teleconnections apart from IOD and WNP forcing.