The Evolution of Microphysical Structures and Cloud-to-Ground Lightning in a Deep Compact Thunderstorm over the Nanjing Area

In this study, we examine the dynamics and microphysical structures of a deep compact thunderstorm event driving cloud-to-ground (CG) lightning over the Nanjing area located within the Yangtze-Huai River Basin (YHRB) during the monsoon break period. The microphysical structures combined with the dynamics in the glaciated, mixed-phase, and warm-phase layers during the formative, intensifying, and mature stages of the thunderstorm were first investigated using C-band polarimetric radar and CG lightning observations. The results show that the mature phase of the thunderstorm produced a local cold pool, which collided with a southerly warm wind, resulting in a strong updraft. The strong updraft favored the lifting of raindrops to the mixed-phase region to form abundant supercooled liquid water and graupel. From the formative stage to the developing stage and further to the mature stage, increased Z_H- and reduced Z_DR-values within the mixed-phase region are found, especially within the strong updraft region (> 5 m s⁻¹). This phenomenon suggests that supercooled raindrops evolved into large hydrometeors (graupel and hail), indicative of a strong riming process. The signatures within this region are consistent with a favorable environment for thunderstorm electrification and generate the most frequent lightning during the thunderstorm life cycle.