Numerical simulation of spatial-temporal distribution of dust aerosol and its direct radiative effects on East Asian climate

The latest regional climate model version 4 (RegCM4) coupled with a dust module developed at the International Center for Theoretical Physics (ICTP, Italy) is used to simulate the spatial-temporal distribution of dust aerosol and its climatic impact through direct radiative forcing over East Asia. Dust coupled and uncoupled experiments are carried out for the past decade (2000-2009). Comparison with satellite observed aerosol optical depth (AOD) shows that the coupled RegCM4 better reproduces spatial distribution of Asian dust loading that has been poorly resolved by general circulation models (GCM), capturing three surface dust concentration (SDC) centers in the Taklimakan desert, western Inner Mongolia, and northern Xinjiang respectively, with maximum values greater than 1000 mu g m(-3) in spring. The negative surface shortwave (SW) irradiance is strongest in spring over East Asia. Its -20 W m(-2) forcing near dust source centers results in surface temperature cooling by 0.8 degrees C from spring through summer. SW irradiance at the top of the atmosphere (TOA) is also negative with a minimum value of up to -8 W m(-2) in North China. Dust aerosol induced cooling leads to the formation of a cyclonic circulation in the lower troposphere in Northwest China that further excites downstream an anticyclonic circulation (the Yellow River Loop) and a cyclonic circulation (East China Sea, ECS). The northeasterly flow in southern China straddled by the anticyclone and cyclone acts to weaken the southwest monsoon in southeastern China and the surrounding sea. Supported by the dust-induced circulations, precipitation increases in cyclonic regions in Northwest China and ECS and decreases in the anticyclonic north-central China.