Impact of a New Three-Dimensional Cloud Detection Method of FY-4A GIIRS in the CMA-GFS

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To enhance the utilization and assimilation of the observations from the Geostationary Interferometric Infrared Sounder (GIIRS) into the China Meteorological Administration (CMA) Global Forecast System (CMA-GFS), a novel three-dimensional cloud detection (3DCD) method for GIIRS data has been recently developed. This study is an extension of the 3DCD method. In the original 3DCD (3DCD-OLD) method, the ideal atmosphere profile and observational error are used to construct a lookup table. In this study, the actual profiles and stricter threshold are used to improve the 3DCD method (3DCD-NEW). We aim to investigate the benefits of using the 3DCD-NEW and compare its impact on the analysis and forecasting through 1-month cycling and forecast experiments. Preliminary assessment results indicate that the number of assimilated GIIRS observations using the 3DCD-NEW is approximately double that of using completely clear-sky detection. The analysis fields of geopotential height, temperature, specific humidity, zonal wind, and meridional wind are neutral for the 3DCD-NEW when compared to the 3DCD-OLD. A neutral-to-positive impact is observed in the forecast fields of geopotential height, temperature, and vector winds over the Northern Hemisphere, tropics, and East Asia during the initial 7-day forecast period when compared to 3DCD-OLD. Significance Statement The three-dimensional cloud detection (3DCD) method of Geostationary Interferometric Infrared Sounder (GIIRS) has been developed recently; this study is an extension work of the 3DCD method. In the improved 3DCD method (3DCD-NEW), the actual profile is used instead of the lookup table derived from the ideal atmosphere profile in the original 3DCD method (3DCD-OLD). The number of assimilated GIIRS observation by using 3DCD method is about twice than that in the CTRL experiment (using the completely clear-sky cloud detection). Compared to 3DCD-OLD, a neutral-to-positive impact is observed in the forecast fields of geopotential height, temperature, and vector winds over the Northern Hemisphere, tropics, and East Asia during the initial 7-day forecast period.