Toward a better regional ozone forecast over CONUS using rapid data assimilation of clouds and meteorology in WRF-Chem

This study assesses the benefits in surface O-3 predictions of using the Rapid Refresh (RAP) forecasting system that assimilates clouds as well as conventional meteorological variables at hourly time scales. We evaluate and compare the WRF-Chem simulations driven by RAP and the Global Forecast System (GFS) forecasts over the Contiguous United States (CONUS) for 2016 summer.

The day 1 forecasts of surface O-3 and temperature driven by RAP are in better agreements with observations. Reductions of 5 ppb in O-3 mean bias error and 2.4 ppb in O-3 root-mean-square-error are obtained on average over CONUS with RAP compared to those with GFS. The WRF-Chem simulation driven by GFS shows a higher probability of capturing O-3 exceedances but exhibits more frequent false alarms, resulting from its tendency to overpredict O-3.