Simulated Influence of the Atlantic Multidecadal Oscillation on Summer Eurasian Nonuniform Warming since the Mid-1990s

Abstract

Based on ensemble experiments with three atmospheric general circulation models (AGCMs), this study investigates the role of the Atlantic Multidecadal Oscillation (AMO) in shaping the summer nonuniform warming over the Eurasian continent since the mid-1990s. The results validate that the positive-phase AMO can indeed cause nonuniform warming, with predominant amplified warming over Europe-West Asia and Northeast Asia, but with much weaker warming over Central Asia. The underlying mechanism is then diagnosed from the perspective that the boundary forcing modulates the intrinsic atmospheric variability. The results highlight the role of the Silk Road Pattern (SRP), an intrinsic teleconnection pattern across the subtropical Eurasian continent propagating along the Asian jet. The SRP can not only be identified from the AGCM control experiments with the climatological sea surface temperature (SST), but can also be simulated by the AMO-related SST anomaly (SSTA) forcing. Furthermore, diagnostic linear baroclinic model experiments are conducted, and the results suggest that the SRP can be triggered by the AMO-related tropical diabatic heating. The AMO-triggered SRP-like responses feature anticyclonic circulations over Europe-West Asia and Northeast Asia, but cyclonic circulation over Central Asia. These responses cause increased warm advection towards Europe-West Asia and Northeast Asia, reduced precipitation and cloud cover, and then increased downward shortwave radiation. This increased warm advection and increased downward shortwave radiation together cause amplified warming in Europe-West Asia and Northeast Asia. The situation is opposite for Central Asia.