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

The anthropogenic aerosols play a dominant role in the global dimming or brightening (the decrease or increase in surface solar radiation). However, the simulations of Global Climate Models (GCMs) generally underestimate the decadal changes in surface solar radiation, compared to the observed dimming and brightening 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. 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 presented and discussed. The meteorological inputs needed for WRF simulations were obtained from the NCEP/NCAR Reanalysis data with 2.5 degree spatial and 6-hour temporal resolution. The anthropogenic emissions were provided by EDGAR (Emission Database for Global Atmospheric Research) and biogenic VOC and lightning NOx emissions were obtained from GEIA (Global Emission Inventory Activity). The capability of hemispheric WRF-CMAQ model to represent the effects of radiatively active gasses and aerosol and to reproduce the observed changes in radiation attributable to changes in atmospheric aerosol levels will be examined through comparison with available long-term observations.