The Preliminary Assimilation and Impacts of FY‐4B Geostationary Interferometric Infrared Sounder (GIIRS) Cloud‐Cleared Radiances

Abstract The Geostationary Interferometric Infrared Sounder (GIIRS) flying on Fengyun (FY)‐4B is the world's first operational geostationary hyperspectral infrared sounder, which can observe detailed atmospheric vertical structure with temporal continuity. It provides an unprecedented observational source for enhancing numerical weather prediction (NWP), especially for high‐impact weather events. Currently, GIIRS is limited to clear‐sky radiance assimilation in operational system, and a large amount of cloud‐affected data have not been effectively utilized. The cloud‐clearing technology can eliminate the cloud effects to obtain the cloud‐cleared radiances (CCRs), which is an alternative method to realize the assimilation of cloudy‐sky infrared observation. A high‐precision cloud mask retrieved from the Advanced Geostationary Radiation Imager (AGRI) is used to calculate the GIIRS CCRs in this study. A comparative analysis of the bias characteristics reveals that the CCRs exhibit larger standard deviation of O‐B than clear‐sky radiances. To evaluate the impact of GIIRS CCRs on NWP, a 1‐month cycle assimilation and forecast experiments are carried out based on China Meteorological Administration Global Forecast System (CMA‐GFS). The results show that CCRs increase the amount of assimilated GIIRS observations by nearly 50%. Compared with the control experiment, CCRs assimilation has a modest positive contribution to the analysis fields, including geopotential height, low‐level humidity, and wind fields. Additionally, it improves the forecast fields of geopotential height and precipitation skill scores, demonstrating better forecast potential in typhoon weather processes. This study provides valuable insights for the prospective operational application of FY‐4B GIIRS CCRs in NWP.