Thermodynamic Diagnosis and Humidity Assimilation Using FY-4B GIIRS–Retrieved Temperature and Humidity Profiles for Early Warning and Forecasting of a Summer Thermal Convection Event

Accurate prediction of summertime thermal convective systems—including their initiation, intensity, and associated hazards—remains a major challenge in operational meteorology across China. This study evaluates the utility of high-resolution temperature and humidity profiles retrieved from the Fengyun-4B (FY-4B) Geostationary Interferometric Infrared Sounder (GIIRS) for analyzing and forecasting a representative thermal convection event in Zhejiang, a coastal province in Southeast China. With significantly higher temporal and spatial resolutions than conventional radiosondes, the retrieved profiles—characterized by strong convective available potential energy (CAPE), weak convective inhibition (CIN), and elevated equivalent potential temperature (θ_e)—exhibit critical diurnal variations in thermodynamic conditions and capture pronounced moisture accumulation and vertical expansion in pre-convection environments. On this basis, this study further investigates the impacts of GIIRS-retrieved humidity profile assimilation on summertime thermal convection simulations using the CMA-MESO model. Numerical experiments demonstrate that assimilating GIIRS-retrieved humidity profiles effectively adjust initial moisture and thermodynamic fields, leading to improved predictions of the location and intensity of convection initiation. Multi-case experiments reveal that the assimilation of GIIRS-retrieved humidity profiles yields a 44% higher average threat score (TS) for moderate rain and above compared with experiments without such assimilation, despite case-to-case variability. The results highlight the potential of FY-4B GIIRS data to enhance convective-scale forecasting and early warning systems.