Assimilation and Impact of FY-4B GIIRS Radiances in CMA-BJ Numerical Weather Prediction System

The Geostationary Interferometric Infrared Sounder (GIIRS) on board the Fengyun 4B (FY-4B) satellite is the first hyperspectral interferometer flying in geostationary orbit. It can provide atmospheric information with high spatial and temporal resolution, which has significant potential for application in regional numerical weather prediction (NWP) models. Due to the high correlation between the infrared hyperspectral channels, it is critical to accurately characterize the inter-channel observational error correlation (IOEC) for assimilating the GIIRS radiance data effectively. This study firstly constructed an observation error covariance matrix for considering the inter-channel correlation of FY-4B GIIRS radiance data based on the NWP system developed by the China Meteorological Administration Beijing Urban Meteorological Institute (CMA-BJ). There was a strong error correlation between adjacent channels and channels with similar detection for the GIIRS radiances. Single-point observation assimilation experiments indicated that the IOEC had a significant impact on the magnitude and structure of temperature and humidity analysis increments. Two groups of assimilation experiments over a 10-day period were carried out and compared. The results showed that an average improvement of 1.5% could be obtained in the RMSE of the temperature and humidity forecasts within the first 12 hours incorporated the IOEC. With the IOEC, a positive impact was also achieved on the precipitation forecast skill, although it was not significant.