The assimilation of FY ‐ 4B Geostationary Interferometric Infrared Sounder long‐wave radiances in the China Meteorological Administration Global Forecast System

Abstract The Geostationary Interferometric Infrared Sounder (GIIRS) is the world's first hyperspectral infrared sounder to operate in geostationary orbit, carried on the FY‐4 series of satellites. This study aims to prepare and evaluate the assimilation of FY‐4B GIIRS long‐wave radiances in the China Meteorological Administration Global Forecast System (CMA‐GFS). A comparative assessment with the FY‐4A GIIRS shows that the O‐B (observations minus simulations) standard deviations of the FY‐4B GIIRS long‐wave channels are noticeably smaller than those of FY‐4A GIIRS. O‐B statistics from CMA‐GFS were used to evaluate and correct biases, with additional quality control procedures (including channel selection) implemented to ensure the observations conform to the basic assumptions of variational assimilation. An appropriate assumed observation error for FY‐4B GIIRS was obtained by inflating the diagnosed observation error. Nearly two months of cycle assimilation and forecast experiments were conducted to analyze the contribution of FY‐4B GIIRS long‐wave channels to numerical weather prediction. The results indicate that the assimilation of FY‐4B GIIRS has a positive effect on the CMA‐GFS analysis field, mainly in terms of temperature and geopotential height fields. And through the adjustment of the analysis field, there was a significant improvement in the 1–7‐day forecast skill scores of multiple elements of the thermal and dynamic fields in the middle and lower atmosphere of the Northern Hemisphere. This study reveals the potential of FY‐4B GIIRS data assimilation for improving numerical weather prediction, laying a technical foundation for its operational application in CMA‐GFS, and providing valuable experience and confidence for more research and application of FY‐4B GIIRS.