Analysis of anomalous cloud-to-ground lightning in a Wuhan tornadic supercell on 14 May 2021

Abstract

Data primarily from the China Lightning Detection Network and dual-polarization radars were analyzed to investigate the cloud-to-ground lightning activity and its relationship with the thunderstorm structure in a supercell in Wuhan, Hubei, China, on May 14, 2021. This storm produced an EF3-scale (Enhanced Fujita Scale) tornado and exhibited complex variations in cloud-to-ground lightning activity. The dominant polarity of cloud-to-ground lightning transitioned from negative to positive and back to negative, with each polarity reversal accompanied by a decrease in cloud-to-ground lightning frequency. During a period when positive cloud-to-ground flashes accounted for 92.7 % of all cloud-to-ground flashes, the mean peak current reached an extraordinary 96.1 kA, significantly higher than during other periods or for negative cloud-to-ground lightning throughout the thunderstorm's lifetime. The tornado occurred near the peak of positive cloud-to-ground lightning activity. Based on an analysis of the relationship between cloud-to-ground lightning activity and the dynamic and microphysical parameters derived from radar data, it is deduced that the storm's charge structure likely evolved through the following sequence: an initial normal tripolar structure with predominant negative cloud-to-ground lightning, transitioning to an inverted tripolar structure during the dominance of positive cloud-to-ground lightning, followed by an inverted dipolar structure with a temporary increase and predominance of negative cloud-to-ground frequency, and finally returning to a normal tripolar structure characterized by high-frequency, predominantly negative cloud-to-ground lightning. The high peak current of positive cloud-to-ground lightning may be attributed to increased charge density from intense convection and a strong environmental electric field, particularly at lower lightning initiation altitudes.