Association between the meridional displacement of the Asian jet and Indian summer monsoon rainfall in <scp>CMIP6</scp> models: Impact of El Niño and <scp>Pacific decadal oscillation</scp>

Abstract The relationship between meridional displacement of the Asian jet and Indian summer monsoon (ISM) is examined in the observations and 40 state‐of‐the‐art Coupled Model Intercomparison Project, phase 6 (CMIP6) historical simulations. The southward displacement of the Asian jet (SWDAJ) is found to be linked with reduced rainfall over central and north India including monsoon trough region in both the observations and most of the CMIP6 models. In general, models are able to simulate the characteristics of the SWDAJ during summer with some differences in zonal asymmetry. Detailed analysis elucidated two observed pathways that connect the SWDAJ with ISM rainfall variability. The first is the west Asian jet–easterly jet pathway, where the SWDAJ is linked with the southeastward shift of the South Asian high, contributing to the weakening of tropical easterly jet. This pattern aligns with changes in low‐level ISM circulation and contributed to reduced rainfall over India. The west Asian jet–easterly jet pathway is well represented by most of the CMIP6 models. The second pathway involves the East Asian jet–Pacific Japan pattern, in which the SWDAJ over East Asia strengthens the western North Pacific anticyclone through the barotropic–baroclinic coupling. The anomalous westward extended easterlies originating from the western North Pacific anticyclone hinder the southwesterly monsoon flow and suppress the rainfall. It is found that CMIP6 models largely failed to capture the East Asian jet–Pacific Japan pathway, likely due to the models' tendency to overestimate the simulation of the Indian Ocean dipole, and westward extension of El Niño‐related sea‐surface temperature anomalies in most of the models. Further, the combined influence of El Niño and the Pacific decadal oscillation and El Niño alone on the SWDAJ and ISM rainfall is also discussed in detail. Results obtained in this study are useful to understand the ability of CMIP6 models in representing the midlatitude circulation associated with ISM rainfall variability.