Microphysical Structure of Thunderstorms and Their Lightning Activity during the Mei-Yu and Post-Mei-Yu Periods over Nanjing, Yangtze River Delta

Using polarimetric radar, cloud-to-ground (CG) lightning, and reanalysis data, this study examined the microphysical structures of thunderstorm and their environmental impact during two active monsoon periods over Nanjing, Yangtze River Delta. The results show that the mei-yu thunderstorm presented a large area of radar echo and many graupels between 0 and -10 ℃ levels; these were accompanied by large vertical wind shear, which was favorite for the organization of thunderstorm. Broad updrafts within the mei-yu thunderstorms were hypothesized, causing lower amount of dilution and entrainment, facilitating transportation of supercooled liquid water to the mixed-phase region and producing CG lightning. Due to large atmospheric instability, strong updrafts within the post-mei-yu thunderstorm were expected to supply supercooled liquid water for the riming process to form more graupel above -10 ℃ level. These provided favorable conditions for electrification, resulting in more CG lightning during the post-mei-yu period than during the mei-yu period.