Direct radiative effect of aerosols over East Asia with a Regional coupled Climate/Chemistry model

Tropospheric chemistry and aerosol processes have recently been incorporated into a Regional Integrated Environmental Model System (RIEMS) to study direct radiative effect of aerosols (DRE) over East Asia where intense human activity and continuous economic growth occur. Five aerosol components (sulfate, black carbon, organic carbon, soil dust and sea salt) and their relevant processes affecting distribution (emission, transport, diffusion, deposition, chemistry etc.) are added into RIEMS, with gas phase chemistry represented by CB-IV mechanism. The study periods are March, July, October and December 2006, generally representing 4 typical seasons in East Asia. The modeled monthly average aerosol optical depth (AOD) is generally consistent with MISR retrievals, although the model tends to underpredict AOD in some regions. The AOD distribution was characterized by high values in eastern China and deserts of western China, and AOD in winter is apparently lower than that in other seasons. The DRE show apparent seasonal variation, with maximum surface cooling in March and minimum surface cooling in winter, but maximum Top Of the Atmosphere (TOA) cooling in July and minimum TOA cooling in winter. The light TOA heating in March under all-sky condition is due to both the abundant absorbing aerosol and the enhanced heating effect by cloud. The DRE averaged over the study domain and the four periods under all-sky condition are -6.2 W m(-2) at the surface and -0.2 W m(-2) at TOA, respectively, over East Asia.