Assimilating FY-3E MWTS surface sensitive channels in CMA-GFS and its impact on the forecast of a heavy rainfall event

Fengyun-3E (FY-3E) Microwave Temperature Sounder-III (MWTS-III) provides critical early-morning-orbit observations for global numerical weather prediction (NWP). However, the assimilation of its surface-sensitive channels over land remains challenging due to the high uncertainty in characterizing land surface temperature and emissivity. This study investigates the impact of assimilating FY-3E MWTS surface-sensitive channels, with a particular focus over land using a physical land emissivity model. Three parallel experiments were conducted using the China Meteorological Administration Global Forecast System. It is shown that assimilating surface-sensitive channels effectively improves low-level atmospheric analyses. In addition, data assimilation over land shows overall positive global impacts on analyses. A case study shows that, in forecasting the heavy rainfall event associated with Typhoon Gaemi (2024), the assimilation of surface-sensitive channels over land improves spatial distributions of 24–hour accumulated precipitation and achieves higher equitable threat scores at high precipitation thresholds mainly for the 120-hour forecasts. The enhanced performance may be explained by the wetter increments and analyses of specific humidity at lower levels near the typhoon center. Overall, this study demonstrates that assimilating FY-3E MWTS surface-sensitive channels effectively improves the analysis fields and heavy rainfall forecasts, offering valuable insights for their future application in NWP.