East Asian summer monsoon response to anthropogenic aerosols redistribution: contrasting 1950-1980 and 1980-2010 to understand the role of non-Asian forcing

Anthropogenic aerosols (AA) induce pronounced East Asian summer monsoon (EASM) changes since the industrial revolution. However, the regional contribution from different AA emission sources is hard to quantify due to AA's heterogeneous spatial distribution and the nonmonotonic trend at decadal time scale. Using coupled climate models from Coupled Model Intercomparison Project Phase 6 (CMIP6) and Community Earth System Model 1 (CESM1) large ensemble simulations, we investigate EASM responses between 1950-1980 and 1980-2010, to understand how the remote influence of changes in the AA emissions from Europe modulates the EASM at decadal time scale. AA emissions from Europe increased early in the latter half of the twentieth century and then decreased rapidly after the 1980s. During 1950-1980, the increase of AA emissions from Europe, together with the localized increase of AA emissions from East Asia, weakens the EASM by generating the tropospheric cooling and shifting the East Asian subtropical jet equatorward. However, during 1980-2010, the declined AA emissions from Europe generate the tropospheric warming and induce an atmospheric teleconnection pattern that initiate at the heating anomaly and propagate downstream to northeast Asia following the westerly jet, leading to an enhanced EASM. This enhancement due to the remote influence of declined AA emissions from Europe explains why after the 1980s, despite the localized increase of AA emissions from East Asia, coupled climate models results show that the EASM is intensified by the anomalous southerlies and the precipitation increase in Northeast Asia. Our results imply that at the long-term change view, the local AA emissions dominate the EASM response, while the non-local European AA emissions play a more important role in shaping the decadal EASM changes.