Velocities of Positive Leaders in Intracloud and Negative Cloud‐to‐Ground Lightning Flashes

Abstract

We have performed a statistical study on velocities of positive leaders in 553 intracloud (IC) and 220 negative cloud-to-ground (−CG) flashes. It is found that velocities of positive leaders in IC and −CG flashes have very similar distributions, with the vast majority in the range of 1 to 3 × 10 4 m/s. Average velocities are 1.64 and 1.55 × 10 4 m/s, respectively, for positive leaders in IC and −CG flashes. Velocities of positive leaders in IC flashes show a clear negative correlation with initiation altitudes and leader propagation altitudes, similar to negative leaders in IC flashes. The negative correlation also exists for positive leaders in −CG flashes but is relatively weak. We also found that positive leaders in both IC and −CG flashes propagate with a stable velocity, contrary to downward positive leaders in +CG flashes and upward positive leaders in negative upward and triggered flashes, which were usually found to accelerate during propagations. These results suggest that positive leaders in IC and −CG flashes and those in +CG, upward and triggered flashes propagate with essentially different velocities. The differences and possible reasons are discussed.Plain Language Summary Positive leaders in lightning flashes are much less well known than negative leaders. It has long been thought that positive leaders are an order of magnitude slower than negative leaders, but recent observations of positive leaders in positive cloud-to-ground (+CG), upward and rocket-triggered lightning suggest that positive leaders can be as fast as, or even faster than, negative leaders. In this study, velocities of positive leaders in 553 intracloud (IC) and 220 −CG flashes are analyzed, and it is found that positive leaders in IC and −CG flashes are indeed an order of magnitude slower than negative leaders. The results also suggest that positive leaders in IC and −CG flashes are different from those in +CG, upward and triggered flashes in many respects. The differences and possible reasons are discussed.

Upward Negative Leaders in Positive Upward Lightning in Winter: Propagation Velocities, Electric Field Change Waveforms, and Triggering Mechanism

“…Values of V h show a decreasing trend with increasing altitudes with a correlation coefficient of −0.41. Similar correlation was also observed for initial negative leaders during the PB stage (Wu et al, 2015; Zheng, Shi, et al, 2019) and positive leaders in IC flashes (Wu, Wang, & Takagi, 2019), indicating that there may be a universal relationship between leader velocities and altitudes.…”

“…The 3‐D mapping results of the UNL are shown in Figures 2d–2f. The 3‐D velocities are estimated using a method similar to that described in section 3.2 in Wu, Wang, and Takagi (2019). Because the leader does not propagate in a straight line, several nodes (black diamonds in Figures 2d–2f) are added to divide the leader into roughly straight segments in 3‐D.…”

A Comparison on the E‐Change Pulses Occurring in the Bi‐Level Polarity‐Opposite Charge Regions of the Intracloud Lightning Flashes

“…All these features support that pulse trains are produced by negative dart‐stepped leaders as first suggested by Krider et al (1975). In MNCR, these dart‐stepped leaders are usually called recoil leaders which retrace the preexisting positive leader paths (e.g., Mazur et al, 2013; Wu et al, 2019b) and sometimes extend further along the PB channel to retrace the negative leaders in UPCR as well (e.g., Stock et al, 2014). We have estimated that about 7% of such recoil leaders in MNCR propagate through the PB vertical channel into UPCR as shown in Appendix .…”

Multiple‐Stroke Positive Cloud‐to‐Ground Lightning Observed by the FALMA in Winter Thunderstorms in Japan

“…In other words, for most MS +CG flashes, the in-cloud leader connecting sequential RS channels should have a velocity larger than 0.5 × 10 5 m/s. However, as demonstrated by Wu et al (2019), velocities of in-cloud positive leaders are mainly in the range of 1 to 3 × 10 4 m/s. Although Wu et al (2019) only analyzed positive leaders in intracloud (IC) and −CG flashes, it is likely that in-cloud horizontal positive leaders in +CG flashes are generally similar to those in IC and −CG flashes.…”

“…However, as demonstrated by Wu et al (2019), velocities of in-cloud positive leaders are mainly in the range of 1 to 3 × 10 4 m/s. Although Wu et al (2019) only analyzed positive leaders in intracloud (IC) and −CG flashes, it is likely that in-cloud horizontal positive leaders in +CG flashes are generally similar to those in IC and −CG flashes. Therefore, the scenario that multiple branches of a positive leader channel produce multiple positive RSs does not seem to be applicable to most of cases.…”