Direct radiative forcing and regional climatic effects of anthropogenic aerosols over East Asia: A regional coupled climate‐chemistry/aerosol model study

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Abstract
We present a series of simulations aimed at assessing the radiative forcing and surface climatic effects of anthropogenic sulfate and fossil fuel soot over east Asia. The simulations are carried out with a coupled regional climate‐chemistry/aerosol model for the 5‐year period of 1993–1997 using published estimates of sulfur emissions. Anthropogenic sulfate induces a negative top‐of‐the‐atmosphere (TOA) radiative forcing which varies spatially from −1 to −8 W m−2 in the winter to −1 to −15 W m−2 in the summer. The aerosol radiative forcing is maximum over the Sichuan Basin of southwest China and over some areas of east and northeast China. This forcing induces a surface cooling in the range of −0.1 to −0.7 K that is also maximum over the Sichuan Basin. Fossil fuel soot exerts a positive TOA radiative forcing of 0.5 to 2 W m−2 and enhances the surface cooling by a few tenths of Kelvins due to increased surface shielding from solar radiation. Doubling of the sulfur emission induces a substantial increase in negative radiative forcing (up to −7 to −8 W m−2) and associated surface cooling. With doubled sulfur emission, the surface cooling exceeds −1 K and is statistically significant at the 90% confidence level over various areas of China. The aerosol‐induced radiative forcing and surface cooling tend to inhibit precipitation over the region, although this effect is relatively small in the simulations. Some features of the simulated aerosol‐induced surface cooling are consistent with temperature trends observed in recent decades over different regions of China.

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