AMIP6 Intermodel Spread analysis: Effects of precipitation deviation on circulation and its underlying mechanisms

Abstract While the ensemble mean of AMIP6 simulations reasonably reproduces the observed features of boreal summer precipitation, substantial intermodel spread persists. To investigate the mechanism underlying this spread, we apply empirical orthogonal function (EOF) analysis to identify the leading mode of global summer precipitation deviations and examine its dynamical impacts on atmospheric circulation. Our results reveal that the dominant mode features an out-of-phase precipitation pattern between the western North Pacific (WNP) and its surrounding regions, which modulates atmospheric circulation through two distinct pathways associated with key precipitation regions. First, enhanced precipitation over the WNP excites a Pacific–Japan (PJ) teleconnection pattern along the East Asian coast through the perturbations of the monsoon trough. Meanwhile, it also generates a meridional wave train extending from the South Indian Ocean to the Ross Sea through perturbations to the subtropical jet. Second, suppressed precipitation over North Africa - the Arabian Sea (NAF-AS), triggers two nearly equatorially symmetric zonal wave trains in the mid- to high latitudes of both hemispheres through disruptions of the North and South African subtropical jets. Sensitivity experiments using a linear baroclinic model (LBM) further support the distinct roles of WNP and NAF–AS diabatic heating in driving circulation variability, supporting the robustness of the proposed pathways. This study may provide a physical explanation for the ‘engine’ role of WNP precipitation deviations in shaping the global pattern of monsoon precipitation intermodel variability identified by Wen and Huan (2025).