Assimilation of Clear-sky FY-4A AGRI radiances within the WRFDA system for the prediction of a landfalling Typhoon Hagupit (2020)

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The capability of assimilating Advanced Geostationary Radiance Imager (AGRI) radiances of FengYun-4A (FY-4A) satellite is realized in the framework of the Weather Research and Forecasting model's Data Assimilation (WRFDA) system. Two experiments are carried out based on a landfalling Typhoon Hagupit to discuss the added values of assimilating the clear-sky radiances on typhoon's analysis and prediction. One experiment assimilates both the AGRI radiances and the Global Telecommunications System (GTS) conventional data, while another experiment only applies GTS conventional data. The results show that the errors of the analysis fields are reduced after the assimilation of AGRI radiances, which can be reflected by the vertical root mean square error (RMSE) profile of both dynamic and thermodynamic variables against the radiosonde observations. Besides, the final improvement of the track and rainfall prediction can possibly be accredited to the analyzed 500 hPa geopotential height increment and the vertically averaged horizontal water vapor flux to some degree. The area is enlarged with relative humidity exceeding 95% by the assimilation of AGRI radiances in the typhoon core, leading to the refinement of both the rainfall distribution and intensity in the prediction. With the improved dynamic and thermodynamic fields, the track of the AGRI experiment is more accurate with a mean error 37 km in the whole 36 h.