Long-range transport of South and East Asian anthropogenic aerosols counteracting Arctic warming

The large-scale convection during the Asian summer monsoon plays an important role in the rapid transport of boundary layer aerosols into the Asian summer monsoon anticyclone. Using the ECHAM6-HAMMOZ aerosol-chemistry-climate model, we show that these aerosols are further transported to the Arctic along isentropic surfaces by the Brewer-Dobson Circulation during the monsoon season. Model simulations show that East and South Asian anthropogenic emissions contribute significantly to the aerosol transported to the Arctic, causing higher negative net aerosol radiative forcing at the surface (dimming) of -0.09 ± 0.02 W m^-2 and -0.07 ± 0.02 W m^-2, respectively. Over the Arctic, East Asian anthropogenic aerosols including large amounts of sulfate cause a seasonal mean net radiative forcing at the top of the atmosphere (TOA) of -0.003 ± 0.001 W m^-2 and a surface cooling of -0.56 K, while black-carbon-dominated aerosol from South Asia shows a positive TOA forcing of +0.004 ± 0.001 W m^-2 with an only minor surface cooling of -0.043 K. Overall, long-range transport of South Asian aerosols results in notable warming throughout the atmospheric column but minimal Arctic surface temperature response, whereas East Asian aerosols cool the troposphere and heat the lower stratosphere in the Arctic. Asian aerosols thus play an ambivalent role, with East Asian sources in particular having the potential to counteract the rapid rise in Arctic temperatures and associated snow and ice melt.