Microphysical and cloud-to-ground lightning characteristics of three tornadoes in a squall line

Abstract

Convective weather events accompanied by multiple tornadoes are rare. However, on 29 August 2019, a typhoon-induced squall line produced three tornadoes on Hainan Island. This rare event provides a valuable opportunity to investigate the microphysical characteristics and cloud-to-ground (CG) lightning activity during tornado periods. This research employed data from S-band dual-polarimetric Doppler weather radar and a VLF/LF three-dimensional lightning location system. Results showed that during the first tornado (developing stage), hydrometeor particles were sparse and dispersed, resulting in minimal CG lightning activity. In contrast, during the second tornado (mature stage), hydrometeor particles were abundant and concentrated, leading to the most active CG lightning. During the third tornado (dissipating stage), hydrometeor particles began to dissipate, though CG lightning activity remained higher than during the first tornado. The characteristics of hydrometeor particles and CG lightning in tornadoes were consistent with the concurrent developmental phase of the squall line. The rapid rise in the top altitude of the 40 dBZ echoes was a significant indicator of tornado formation. Furthermore, dry graupel, wet graupel, and dry snow particles exhibited strong correlations with CG lightning activity. These findings enhance our understanding of the microphysical and electrification mechanisms associated with tornadoes and provide valuable insights for improving tornado prediction.