Assessment of aerosol effects on surface radiation in the north hemisphere using two-way WRF-CMAQ model

Climate change and global warming issues have been considered as one of the greatest threat to this planet. The importance of “global dimming or brightening” (the decrease or increase in surface solar radiation) in climate system has been well emphasized. Though the surface solar radiation suffers from both external and internal influences, many studies suggest that the anthropogenic aerosols play a dominant role in the “global dimming or brightening”. However, the simulations of Global Climate Models (GCMs) generally underestimate the decadal changes in surface solar radiation, compared to the observed trends during the 20th century. Therefore it is important to further reduce the uncertainties and to improve the model's ability of reproducing the decadal changes in surface radiation. A new two-way coupled meteorology and atmospheric chemistry model, i.e., Weather Research and Forecast (WRF) model coupled with the Community Multiscale Air Quality (CMAQ) model has been developed by U.S. Environmental Protection Agency. This model system can be applied as an integrated regional climate and chemistry model (RCCM) which is an important tool for downscaling future projections of global climate to higher resolution, and assessing the interactions between atmospheric chemistry and climate forcing and the effects of air pollutants on atmospheric radiation and secondary effects on meteorology and air concentrations. In this study, we extend the applicability of the two-way WRF-CMAQ model to hemispheric scales, by better representing the global dust emissions and tropopause ozone mixing ratio. The meteorological inputs for WRF simulations were derived from the NCEP/NCAR Reanalysis data with 2.5 degree spatial and 6-hour temporal resolution. The anthropogenic emissions were derived from EDGAR (Emission Database for Global Atmospheric Research) and biogenic VOC and lightning NOx emissions were derived from GEIA (Global Emission Inventory Activity). Temporal distribution was referred to EDGAR default profile. PM and VOC speciation was referred to SMOKE profile. Results of 20 years simulations in the north hemisphere from 1990-2010 where significant of change of emission and radiation was expected (e.g. dimming and brightening) will be thoroughly analyzed. Model performance on surface temperature, relative humidity, and wind speed was evaluated through the comparison with observations from NOAA's National Climatic Data Center (NCDC). Simulated vertical ozone mixing ratio was compared with ozone sonde observations provided by World Ozone and Ultraviolet Radiation Data Centre (WOUDC). Magnitude and spatial distribution of AOD and aerosol precursors generally agree with the MODIS satellite and surface observations from CASTNET. An examination of the capability of two-way coupled WRF-CMAQ model to represent the aerosol direct effects and to reproduce the observed changes in radiation was performed through comparison with CERES satellite retrieval and other long-term observations (incl. AERONET, SURFRAD). The aerosol direct impacts on meteorological variables and chemical species will be discussed. Our results suggest that the ground temperature, PBL height and surface solar radiation trends to be reduced over the whole domain, while PM2.5 will be enhanced in industrial regions, but reduced in windblown dust area.