Estimating global aerosol optical properties and their radiative forcings by a global model with 14 km grid spacing

We have estimated 14 km resolved spatial distributions of global aerosol optical properties, such as aerosol optical thickness (AOT) and direct aerosol radiative forcing (DARF), obtained from an aerosol-coupled global non-hydrostatic model (Suzuki et al., Geophys. Res. Lett., 2008). The dynamic model is Nonhydrostatic Icosahedral Atmospheric Model (NICAM; Tomita and Satoh, Fluid. Dyn. Res. 2004; Satoh et al., J. Comput. Phys. 2008), whereas the aerosol model is based on SPRINTARS (Takemura et al., J. Geophys. Res., 2005). In this study, we compared the simulated AOT with MODIS-derived and AERONET-derived AOT for one week of July 2006. We also calculated DARF using an offline radiative transfer model, MSTRN, developed by Nakajima et al. (Appl. Optics, 2000), Sekiguchi and Nakajima (J. Quant. Spectrosc. Radiat. Transfer, 2008), and openCLASTR (http://157.82.240.167/~clastr/). The global mean DARF obtained from NICAM under the clear-sky conditions was estimated to be -1.61 W/m2 (at the tropopause) and -2.91 W/m2 (at the surface), respectively. As for a reference, we also calculated DARF from the Model for Interdisciplinary Research on Climate (MIROC; Watanabe et al., J. Climate, 2010) with coarse grid spacing (approximately 2.8° by 2.8°) during the same period. The global mean DARF obtained from MIROC was estimated to be -1.70 W/m2 (at the tropopause) and -3.82 W/m2 (at the surface), respectively. The difference in the DARF between two simulations with different horizontal resolutions is mainly caused by a difference in modeled topography and simulated cloud-precipitation systems, which influence the transport of aerosols and their radiative forcings. In the presentation, we will also discuss aerosol chemical compounds in terms of AOT and DARF.