Evaluation and Assimilation of FY-3E Microwave Instruments in the Yinhe Four-Dimensional Variational Assimilation System

Abstract The world’s first operational early morning-orbit meteorological satellite, Fengyun-3E (FY-3E), launched on 5 July 2021, and has expanded global data coverage for numerical weather prediction (NWP) of 6-h assimilation windows. To determine whether the early morning orbit affects microwave observations and the benefits to NWP, radiance from FY-3E microwave instruments was assimilated into the operational global Yinhe four-dimensional variational assimilation (YH4DVAR) system. The performance of the microwave instruments was first assessed based on the statistics of background departure. The sunlight conditions have little effect on FY-3E microwave observations, and ascending and descending pass observations could be uniformly assimilated for both the Microwave Humidity Sounder-2 (MWHS-2) and the Microwave Temperature Sounder-3 (MWTS-3). The standard deviation of observation minus background (OmB) after variational bias correction increased, indicating slightly reduced performance of MWTS-3 compared with equivalent Advanced Technology Microwave Sounder (ATMS) channels on SNPP/NOAA-20. Based on reduced OmB mean and standard deviation values, FY-3E MWHS-2 performs better than MWHS-2 on predecessor satellites. To test the impact of FY-3E microwave observations on the operational YH4DVAR system, three NWP experiments were performed from June to August 2022. All-sky assimilation of FY-3E MWHS-2 observations in the YH4DVAR system has a neutral to positive impact on forecast skill. Assimilation of FY-3E MWTS-3 under clear-sky conditions provides little benefit to the YH4DVAR system in longer-range forecasts but improves the fit to the background of stratospheric temperature-sounding channels of ATMS and Advanced Microwave Sounding Unit-A (AMSUA) and radiosonde temperature observations over 150–400 hPa in the Northern Hemisphere and humidity observations over 100–850 hPa.