Impact of the Detection Channels Added by Fengyun Satellite MWHS-II at 183 GHz on Global Numerical Weather Prediction

Fine spectral detection can basically solve the problem of low vertical resolution at the 183 GHz water-vapor absorption line, and it is expected to become one of the main methods for next-generation geostationary and polar-orbiting satellites. Here, using data from Microwave Humidity Sounder II (MWHS-II) onboard the Chinese Fengyun 3D (FY-3D) satellite in the Global/Regional Assimilation and Prediction System (GRAPES) Four-Dimensional Variational (4D-Var) system of the China Meteorological Administration (CMA), we explore the assimilation application of the water-vapor absorption line at 183.31 +/- 1 GHz, 183.31 +/- 3 GHz and 183.31 +/- 7 GHz, as well as 183.31 +/- 1.8 GHz and 183.31 +/- 4.5 GHz, two added channels, to assess the impact of adding the 183.31 +/- 1.8 GHz and 183.31 +/- 4.5 GHz sampling channels on data assimilation and numerical weather prediction. Our findings reveal a significant increase in the specific-humidity increment, which in the middle-upper troposphere is numerically much larger than in the lower troposphere. Specifically, the assimilation of 183.31 +/- 1.8 GHz observations, positioned near the center of the water-vapor absorption line, results in a pronounced adjustment compared with the 183.31 +/- 4.5 GHz observations. And under the strong constraint of the numerical model, the Root Mean Square Error (RMSE) of the wind field diminishes more significantly (by an average of 2-4%) after assimilating the water-vapor observations at greater heights.