Use of FY-3G PMR to analyze precipitation and microphysics of Typhoon Yagi (No. 2411) in rapid intensification

This study investigates the precipitation and cloud characteristics during the rapid intensification (RI) of Typhoon Yagi (No. 2411) using an observation at 11:00 UTC on September 4, 2024 from the Precipitation Measurement Radar (PMR) onboard Fengyun-3G (FY-3G) satellite. The results show that, precipitation during the RI of Typhoon Yagi is dominated by stratiform rainfall (82% of areal fraction), while convective precipitation, despite a smaller coverage (18%), contributes 54.7% to the total rain rates. The heaviest precipitation occurs in the eyewall, with composite reflectivity factors exceeding 45 dBZ and near-surface rain rates more than 100 mm/h. In stratiform precipitation, a typical bright band feature is observed at altitudes of 4-5 km, where reflectivity factors and droplet sizes experience a sharp increase. However, in stratiform precipitation, the droplet concentration is relatively low and its distribution is more uniformly vertically. Conversely, convective precipitation shows significant vertical variation. In the outer rainband, heavy convection leads to the generation of large ice-phase particles at 13 km, while convective precipitation in lower level is stronger and displays typical oceanic precipitation characteristics. Additionally, heavy convective precipitation is associated with a positive feedback mechanism involving strong upward motion, promoting particle growth and latent heat release, which further enhances the updrafts of the convective system. In contrast, the stratiform precipitation areas within the spiral rainbands are affected by the cooling effect of the melting, resulting in weaker vertical development of the cloud system, which limits particle growth and leads to the formation of low-concentration small raindrops. Overall, this study reveals the horizontal and vertical distribution characteristics of precipitation during Typhoon Yagi's RI phase, and discusses the associated dynamical-microphysical coupling mechanism. These findings offer critical insights for improving microphysical parameterization schemes in numerical models and typhoon forecasts.