Sensitivity Experiments of Assimilating GIIRS Temperature and Humidity Retrieved Profiles on Three Typhoons Affecting Zhejiang

Assimilating satellite-retrieved profiles is an important approach to improving numerical model initial conditions and typhoon forecasting skill. This study uses temperature and humidity retrieved profile products from the Geostationary Interferometric Infrared Sounder (GIIRS) onboard Fengyun-4B for three typhoons that affected Zhejiang Province in July 2025 with different track types. Sensitivity experiments are conducted under clear-sky, cloudy-sky, and all-sky conditions. Vortex relocation experiments are designed to separate the contributions of typhoon vortex structure and environmental field to track forecasts. Results show that assimilation systematically adjusts temperature and humidity in the typhoon inner core, rainband, and outer environment. All schemes produce lower–middle tropospheric warming and upper tropospheric cooling. Humidity decreases in the low-level outer environment but increases around the typhoon vortex and along the Western Pacific Subtropical High edge. All-sky assimilation is optimal for track forecasts, whereas clear-sky or cloudy-sky assimilation alone can be adverse. For 72-h precipitation, all-sky assimilation increases the heavy rain threat score by 0.09 versus control and the torrential rain threat score by 0.09 versus cloudy-sky assimilation. This study reveals the comprehensive advantages of all-sky GIIRS profile assimilation for typhoon forecasting and supports the operational application of GIIRS-retrieved temperature and humidity profiles.