Direct Radiative Effect Of Dust And Anthropogenic Aerosols On The Asian Climate

A regional climate model RegCM4.0 coupled with a chemistry-aerosol model is used in this paper to investigate the direct radiation effect of dust and three anthropogenic aerosols(sulfate, black carbon and organic carbon) on the climate in Asia.For the East Asia and South Asia area, the sign of the short, long and total radiative forcings at the surface is substantially the same as that of the short, long and total radiative forcings at the top of the atmosphere, but the intensity of the short, long and total radiative forcings at the surface is larger than that of the short, long and total radiative forcings at the top of the atmosphere. For the surface and top of the atmosphere, aerosols lead to negative total radiative forcing mainly through the generation of negative short radiative forcing, while they have little effect on long radiative forcing.For the East Asia area, the intensity of optical thickness in winter is as large as that in summer, the intensity of total radiative forcing at the top of the atmosphere in summer is slightly larger than that in winter, the intensity of total radiative forcing at the surface in summer is much larger than that in winter. For the South Asia area, the intensity of optical thickness in summer is much lager than that in winter, the intensity of total radiative forcing at the top of the atmosphere in summer is much larger than that in winter, the intensity of total radiative forcing at the surface in summer is much larger than that in winter.For the East Asia area, in winter, aerosols decrease the low atmosphereic temperature in the south of 48°N,while increase the high atmospheric temperature slightly in the south of 48°N, so the stability increases, and aerosols induce downdraft basically over the south of 48°N， so the winter precipitation decrease in the south of 48°N. The summer precipitation in 2°N to 14°N,14°N to 16°N,16°N to 25°N and 25°N to 40°N respectively increase, decrease, increase and decrease because of upward motion, downward motion, upward motion and downward motion in 2°N to 14°N,14°N to 16°N,16°N to 25°N and 25°N to 40°N respectively.East Asian winter monsoon strengthen, East Asian tropical summer monsoon and East Asian subtropical summer monsoon in the north of 25°N respectively strengthen and weaken, the reasons for these maybe that dust and anthropogenic aerosols induce the change of surface pressure. In winter and summer, total precipitation decrease, but the amplitude of total precipitation’s increase in summer is larger than that of total precipitation’s decrease in winter, aerosols mainly lead to the reduction of stratiform precipitation while they have little effect on convective precipitation in winter, but aerosols mainly lead to the reduction of convective precipitation while they have little effect on stratiform precipitation in summer.For the South Asia area, in winter, aerosols induce updraft over 6°N to 16°N and 19°N to 26°N, so the winter precipitation increase in 6°N to 16°N and 19°N to 26°N, aerosols have little effect on vertical motion over 27°N to 32°N, but the temperature of the low atmosphere and high atmosphere respectively decrease and increase, the stability increases, so the winter precipitation decrease in 27°N to 32°N. The summer precipitation in 5°N to 16°N,17.5°N to 19°N and 28°N to 32°N increase because of upward motion in 5°N to 16°N,17.5°N to 19°N and 28°N to 32°N, aerosols induce downdraft over 20°N to 28°N, and the temperature of the low atmosphere and high atmosphere respectively decrease and increase, the stability increases, so the summer precipitation decrease in 20°N to 28°N.For the South Asia area, in winter, the surface pressure in the east and west sea area of the southern India decrease slightly, there is westerly wind in the south side of decompression area, so South Asia winter monsoon weaken. in summer, aerosols decrease surface pressure in the east Arabia sea, aerosols decrease surface pressure in northeast India, Bhutan and Bangladesh, there is westerly wind in the south side of above decompression areas, so South Asia summer monsoon strengthen. In winter, stratiform precipitation increase while convective precipitation decrease, but the amplitude of stratiform precipitation’s increase is larger than that of convective precipitation’s decrease, so the total precipitation increase slightly, in summer, aerosols lead to the reduction of total precipitation mainly through the reduction of convective precipitation.