Dynamic Feedback of Aerosol Effects on the East Asian Summer Monsoon

The influence of present-day anthropogenic aerosols on the summer monsoon over the East Asia region was simulated using the Community Earth System Model coupled with a slab ocean model. The simulations revealed significant radiative forcing from anthropogenic aerosols and associated changes in clouds over East Asia and the northwestern Pacific; however, their spatial patterns differed from the exhibited surface temperature and precipitation responses. Two major dynamic feedback mechanisms were identified to explain such discrepancies. The wind-evaporation-sea surface temperature (WES) feedback, triggered by an initial cooling over the midlatitude sea surface, induced an equatorward expansion of ocean cooling through strengthened trade winds. The sea surface cooling excited a meridional wave pattern similar to the Pacific Japan teleconnection pattern. Although the aerosol effect generally caused weakening in summer monsoon strength and regional precipitation over East Asia, precipitation increases were seen over the locations of the midlatitude mei-yu front and around the tropics. These precipitation increases are primarily associated with the WES feedback and teleconnection patterns. The aerosol effect also reached the upper troposphere, causing an equatorward shift of the jet stream over East Asia and the northwestern Pacific, indicating a much broader scale of teleconnection.