Characteristics of the two active stages of lightning activity in two hailstorms

Abstract

Two hailstorms that occurred in Beijing and Tianjin, respectively, are investigated, based mainly on the total lightning data observed by the System d'Alerte Fondre par Interferometric Radioelecctrique (SAFIR3000), the cloud-to-ground (CG) lightning data of a CG lightning location system, and the echo data of a Doppler radar. Both hailstorms exhibited two lightning frequency peaks: the first was before the hailfall and the second was after the hailfall, with the second peak greater than the first. The dominant polarity of the CG lightning was positive in the stage around the first frequency peak, but changed to negative in the stage around the second frequency peak. The evolution of radar echoes and the height distribution of lightning radiation sources are explored, revealing that both hailstorms had stronger convection and the main positive charge occurred at mid levels during the stage around the first frequency peak. However, whilst the Beijing hailstorm experienced the enhancement of convection, with the main positive charge at upper levels around the second frequency peak, the Tianjin hailstorm generated its second frequency peak during the period when the convection kept weakening and the main positive charge dropped to mid-lower levels. Through evaluation of the radar parameters, we investigate the mechanisms responsible for the second stage of active lightning discharge. Furthermore, the lightning activity exhibited a close relationship with radar echo parameters and hailfall. Lightning jump signals were found before the hailfall and were associated with the change ratio of the 40-dBZ echo volume above the -15℃ level, which demonstrates the application value of lightning data in severe weather warning. Citation: Xu Shuang, Zheng Dong, Wang Yongqing, et al., 2016: Characteristics of the two active stages of lightning activity in two hailstorms.

Lightning Evolution in Hailstorms From the Geostationary Lightning Mapper Over the Contiguous United States

“…The two‐peak feature of lightning rate during hailfall was also found in the literature (Emersic et al., 2011; Xu et al., 2016). Nevertheless, there were some differences between our results and previous observations.…”

“…Not considering the spatial evolution and considering the storm as a whole, Xu et al. (2016) proposed that the downdraft during hailfall leads to a sharp decline in thunderstorm intensity and to a weakened charge region in the middle level. After the hailfall, the thunderstorm strengthened again.…”

“…In Figure 3, only lightning in the grid boxes with hail was counted, while Xu et al. (2016) included the regional lightning frequency. The occurrence time of the first peak was found to be advanced if the lightning rate in a broader area was used (not shown here).…”

“…Nevertheless, there were some differences between our results and previous observations. For example, in the two hailstorms reported by Xu et al (2016), the first peak occurred before hailfall occurred on the ground. One potential reason for this difference was due to the region in which the lightning frequency was considered.…”

“…For the decrease in the lightning rate after the first peak lightning rate, Emersic et al (2011) deduced that the wet growth of hail restrained the charge exchange between graupel and cloud ice. Not considering the spatial evolution and considering the storm as a whole, Xu et al (2016) proposed that the downdraft during hailfall leads to a sharp decline in thunderstorm intensity and to a weakened charge region in the middle level. After the hailfall, the thunderstorm strengthened again.…”