Simulating aerosol-radiation interactions in a desert environment

Global horizontal irradiance (GHI) is simulated using a three-dimensional atmospheric meteorology-chemistry model (WRF-Chem) and a triple-nesting configuration over the Middle East with a focus on the hot desert climate of Qatar. The model performance was assessed with measurement data of solar radiation from a ground monitoring station in Doha (Qatar) collected over a three-month period, of representative and distinct meteorological regimes. We examine the ability of the model to reproduce GHI values under two different shortwave downward radiation parameterizations, and assess the sensitivity of our results to the presence of aerosols. The introduction of an advanced treatment of aerosols greatly improves the model performance in predicting GHI. We suggest that explicitly including aerosol processes and its emissions in a 3-D numerical weather prediction (NWP) model can considerably decrease the model predicted relative bias of GHI (from up to 30 % to approximately 2 %) in the dust-rich environment of the Middle East. The introduction of a state-of-the-art treatment of aerosols greatly improves the model performance reducing the relative root mean square error for GHI from 25 % to 13 % in May and from 20 % to 12 % in August. The RRTM (Rapid Radiative Transfer Model) shortwave radiation scheme performs somewhat better than the Goddard scheme both with and without aerosols. We show that GHI predictions in regions that experience high aerosol loadings can benefit significantly from a detailed and explicit treatment of aerosols and their physicochemical processes. A novel approach to better manage the fluctuating nature of solar radiation originating from variable weather and air pollution conditions will be discussed.