Significance of direct and indirect radiative forcings of aerosols in the East China Sea region

Radiative forcings of aerosols and clouds in the East China Sea region are studied using data from surface radiation measurements, satellite remote sensing, and model simulation conducted in April 2001 as a study of Asian Atmospheric Particle Environmental Change Studies (APEX) cooperating with International Global Atmospheric Chemistry (IGAC)/ACE-Asia project. The monthly mean whole sky radiative forcing of the aerosol direct effect is derived from various methods as -5 to -8 W/M² at the top of atmosphere (TOA) and -10 to -23 W/m² at Earth's surface of Gosan (33.28N, 127.17E) and Amami-Oshima (28.15N, 129.30E) sites, though there is a large regional difference caused by changes in the aerosol optical thickness and single scattering albedo. The cloud forcing is estimated as -20 to -40 W/m², so that the aerosol direct forcing can be comparable to the cloud radiative forcing at surface. However, the estimate of the aerosol direct forcing thus obtained strongly depends on the estimation method of the aerosol properties, especially on the single scattering albedo, generating a method difference about 40%. The radiative forcing of the aerosol indirect effect is roughly estimated from satellite method and SPRINTARS model as -1 to -3 W/m² at both TOA and surface.