Assimilation of data from the MWHS‐II onboard the first early morning satellite FY‐3E into the CMA global 4D‐Var system

Abstract

AbstractRadiance data from satellite microwave radiometers are becoming increasingly important in the assimilation of numerical prediction systems. FengYun‐3E (FY‐3E), which was launched in July 2021, as the first early morning orbital satellite among FY‐3 polar‐orbiting meteorological satellite series, can greatly enhance the atmospheric sounding capacity in three orbits compared with the two‐orbit system that is distributed in morning or afternoon orbit. Focusing on MicroWave Humidity Sounder‐2 (MWHS‐II) onboard it, the schemes for thinning, quality control, bias correction and observational error calculation are developed. The scan‐position‐dependent biases are assessed in each channel and increasing biases near the edges of scanline are found in several temperature‐sounding channels. The data quality is compared with four analogous instruments used in Global/Regional Assimilation and Prediction System–Global Forecast System (CMA_GFS), and the performance improvements are confirmed relative to the previous FY‐3C/D MWHS‐II. Three batch experiments were implemented in CMA_GFS with four‐dimensional variational (4D‐Var) system—assimilating only the humidity‐sounding channels, the temperature‐sounding channels and the combined channels—to reveal the impact of assimilation by different channel groupings. Analysis results conclude that FY‐3E MWHS‐II radiances are beneficial to the humidity and temperature analysis fields. These results emphasize the advantage of simultaneously assimilating the humidity/temperature‐sounding channels, in which the former dominates the improvement above 700 hPa while the latter have a positive impact below 700 hPa. The forecast results also show that assimilating both the 183‐ and 118‐GHz channels further improves the forecast skills, especially short‐ to medium‐term forecasts in both hemispheres. FY‐3E MWHS‐II also improves the short‐term prediction of heavy rain, which is always weakly predicted in global forecast systems. This study shows that a three polar orbits system that FY‐3E began can produce marked effects in the numerical prediction system. This study also shines light on the application potential of the distinctive 118‐GHz channels of MWHS‐II.