Connections and causes of inter-model spread in boreal summer precipitation across monsoon regions in AMIP6 simulations

This study investigates the interconnections and underlying causes of the inter-model variability in boreal summer precipitation across global monsoon regions, based on historical AMIP6 simulations. The results reveal significant connections among the leading modes of precipitation inter-model deviations in different monsoon domains, with the western North Pacific (WNP) emerging as a key driver. Deviations over the WNP modulate adjacent monsoon systems -- including the South Asian, North African, and Australian monsoons -- primarily through the Walker and Hadley circulations. In addition, WNP precipitation anomalies, via jet stream disturbances originating from the tropical Indian Ocean, indirectly generate zonal wave trains in the mid-to-high latitudes of both hemispheres, influencing the Somali and South American monsoon. The WNP also affects East Asian monsoon precipitation mainly through meridional wave trains along the East Asian coast, triggered by perturbations in the monsoon trough. These findings underscore the 'engine' role of WNP precipitation deviations -- via atmospheric dynamic process -- in shaping the global pattern of monsoon precipitation inter-model variability in AMIP6, and highlight the need for improved model performance over this region to enhance global monsoon simulation fidelity.