A preliminary study of FY-4B AGRI all-sky assimilation by WRFDA for tropical cyclones

A new assimilation module for AGRI (Advanced Geostationary Radiation Imager) carried on Fengyun-4B (FY-4B) is developed within the WRFDA (Weather Research and Forecasting model's Data Assimilation) system. The impacts of assimilating FY-4B AGRI clear-sky and all-sky data are evaluated with cycling assimilation experiments for the typhoon Doksuri (2023) and Talim (2023) forecast. For typhoon Doksuri, compared with the benchmark experiment, AGRI assimilation brings a better analysis and forecast for atmospheric variables (wind, temperature and humidity). Meanwhile, clear error reductions for typhoon track and intensity forecasts are achieved with clear-sky and all-sky AGRI assimilation. The positive impact on landing precipitation prediction is also obtained by verifying with GPM (Global Precipitation Measurement) precipitation data. Moreover, AGRI all-sky assimilation yields better typhoon forecasts than clear-sky assimilation. In addition, the channel selection sensitivity for AGRI assimilation is also assessed with group experiments. It is suggested that with the assimilation of a new water vapor channel at 7.42 $\mathrm{\mu m}$, which is newly added in FY-4B, multiple-channel assimilation shows greater benefit for forecast than single-channel assimilation. The same positive impact of AGRI assimilation is also present in typhoon Talim (2023) forecast. Overall, the all-sky assimilation of FY-4B AGRI water vapor channels data is beneficial for the typhoon forecast.