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

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.