Monday, 3 June 2002
Global distributions of aerosol optical properties simulated with the SPRINTARS
To understand global aerosol distributions and effects of aerosols on the climate system, the SPRINTARS (Spectral Radiation-Transport Model for Aerosol Species) is developed. It is coupled with the CCSR (Center for Climate System Research, University of Tokyo, Japan)/NIES (National Institute for Environmental Studies, Japan) atmospheric general circulation model, and treats main tropospheric aerosols, that is, carbonaceous (black carbon and organic carbon), sulfate, soil dust, and sea salt. The meteorological field can be nudged by reanalysis data for specific-year simulations. The aerosol transport processes include emission, advection, diffusion, sulfur chemistry, sub-cloud scavenging, in-cloud scavenging, dry deposition, and gravitational settling. The SPRINTARS calculates global distributions of not only aerosol concentrations but also optical properties, that is, optical thickness, Angstrom exponent, single scattering albedo, and radiative forcing. The refractive index depending on wavelengths, size distribution, and hygroscopic growth of each aerosol species are considered for the radiative flux calculation using the two-stream discrete ordinate/adding method. The simulated optical properties are compared with retrieved data of remote sensing from satellites (e.g., AVHRR) and ground (e.g., AERONET). Simulated and observed seasonal and quantitative variations of aerosol optical properties are in reasonable agreement at dozens of regions and locations. The present global annual mean radiative forcings of anthropogenic aerosols at the tropopause are calculated to be -0.19 W m-2 for the direct effect and -0.98 W m-2 for the first plus second indirect effects. The simulation during the ACE-Asia experiment is also performed, and dust storms transported from Chinese deserts to the Pacific Ocean are reproduced well.