The Global Weather Research and Forecasting (GWRF) Model: Model Evaluation, Sensitivity Study, and Future Year Simulation

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Global WRF (GWRF) is an extension of the mesoscale Weather Research and Forecasting (WRF) model that was developed for global weather research and forecasting applications. GWRF is being expanded to simulate atmospheric chemistry and its interactions with meteorology on a global scale. In this work, the ability of GWRF to reproduce major boundary layer meteorological variables that affect the fate and transport of air pollutants is assessed using observations from surface networks and satellites. The model evaluation shows an overall good performance in simulating global shortwave and longwave radiation, temperature, and specific humidity, despite large biases at high latitudes and over-Arctic and Antarctic areas. Larger biases exist in wind speed and precipitation predictions. These results are generally consistent with the performance of most current general circulation models where accuracies are often limited by a coarse grid resolution and inadequacies in sub-filter-scale parameterizations and errors in the specification of external forcings. The sensitivity simulations show that a coarse grid resolution leads to worse predictions of surface temperature and precipitation. The combinations of schemes that include the Dudhia shortwave radiation scheme or the Purdue Lin microphysics module, or the Grell-Devenyi cumulus parameterization lead to a worse performance for predictions of downward shortwave radiation flux, temperature, and specific humidity, as compared with those with respective alternative schemes. The physical option with the Purdue Lin microphysics module leads to a worse performance for precipitation predictions. The projected climate in 2050 indicates a warmer and drier climate, which may have important impacts on the fate and lifetime of air pollutants.