Estimating Hourly Surface Shortwave Radiation over the Tibetan Plateau by Assimilating Himawari-8 Cloud Optical Thickness

Abstract In order to reduce uncertainty in the estimation of surface shortwave radiation (SSR) in the presence of clouds over the Tibetan Plateau, a new cloud assimilation system is proposed which is the first attempt to directly apply the four-dimensional local ensemble transform Kalman filter method to assimilate the cloud optical thickness (COT). The high-resolution spatial and temporal data assimilated from the next-generation geostationary satellite Himawari-8, with the high-assimilation frequency, realized an accurate estimation of the clouds and radiation. The COT and SSR were significantly improved after the assimilation. The correlation coefficient (CORR) of the SSR was increased by 11.3%, and the root-mean-square error (RMSE) and mean bias error (MBE) were decreased by 28.5% and 58.9%, respectively. These findings demonstrate the high impact and innovative application of this assimilation technique in numerical weather prediction.