Lightning activity and its associations with cloud structures in a rainstorm dominated by warm precipitation

Highlights

• Investigating electrical characteristics in a rainstorm dominated by warm cloud precipitation is novel.

• In this rainstorm, lightning discharges predominately occurred in areas featuring dry snow and relatively weak precipitation.

• The lightning discharges spatially deviate from the origin area of charging; the cause of this is discussed.

Abstract

Lightning activity and its associations with cloud structures during a rainstorm dominated by warm cloud precipitation were studied in Guangdong, China on May 7, 2017, using three-dimensional lightning location and polarimetric radar data. The overall convection and lightning activities of the rainstorm were weak. The rainstorm generally showed a typical tripolar charge structure with the main negative charge core located between the −15 and − 8 °C environmental isotherms in the first 4 h. The height of the charge regions clearly decreased after this period, with the main negative charge core being below the −8 °C isotherm. Lightning discharges were more concentrated in areas featuring relatively weak convection and relatively low precipitation intensity. Most of the locations with lightning discharges were dominated by dry aggregated snow and weak updrafts and downdrafts. This investigation demonstrated that the lightning discharges were spatially separated from the area of origin of charging in this rainstorm. It is proposed that, with weak convection in the rainstorm, the charging rate was lower than the speed of charge transfer from the area of origin, causing a relatively low charge density and a low frequency of lightning in the area of origin of charging. Meanwhile, the aggregation of small charged particles in regions away from the area of origin of charging might be conducive to the formation of a relatively high charge density and therefore relatively frequent lightning flashes. This situation is different from a typical thunderstorm with strong convection.

Introduction

Different weather systems often display variations in their lightning activities. For example, in typical thunderstorms and climate statistics, positive cloud-to-ground (PCG) lightning usually accounts for ~10% of the total cloud-to-ground (CG) lightning (Liu et al., 2011; Rudlosky and Fuelberg, 2010; Zheng et al., 2010), but the ratio of PCG lightning in severe thunderstorms is relatively high, even greater than 50% (MacGorman et al., 1989; Soula et al., 2004; Zheng and MacGorman, 2016). Winter thunderstorms may also produce high-proportion and large-current PCG lightning (Suzuki, 1992; Takeuti et al., 1976; Zheng et al., 2019a). Typical thunderstorms usually have tripolar charge structures (Williams, 1989), while some severe thunderstorms may have inverted charge structures (Rust et al., 2005; Zheng and MacGorman, 2016; Zheng et al., 2009). In typical or severe thunderstorms, the most active lightning discharges are usually distributed in or around the regions characterized by the strong kinematics, because of the dependence of charging process on the rebounding collisions between ice-phase particles under the influence of airflow; while in the regions away from convection, the lightning flashes are usually less frequent and spatially dispersed (Bruning and MacGorman, 2013; Carey et al., 2005; Feng et al., 2007; Liu et al., 2011; López et al., 1990; Ribaud et al., 2016; Zhang et al., 2017; Zheng and MacGorman, 2016; Zheng et al., 2010).

For storms yielding heavy rainfall (i.e., rainstorms), their precipitation characteristics and triggering and maintenance mechanisms are often the focus of research, but their electrical attributes and characteristics have received less attention. In this study, we investigated lightning activity in an extraordinary rainstorm that occurred near the Pearl River Delta in Guangdong, China on May 7, 2017 (Beijing time, the same below). The rainstorm yielded extreme rainfall in the Pearl River Delta, with a maximum recorded precipitation of 446.6 mm, but a relatively low lightning flash rate, which prompted us to explore the relationship between its lightning activity and precipitation structure.