Photographic observations of streamers and steps in a cloud‐to‐air negative leader

Abstract

A color photograph has been obtained of a negative lightning leader in clear air at 10.3 km altitude. The individual leader steps are resolved as relatively straight segments of at least ~200 m in length, between sharp kinks (nodes) in the channel. Each node is accompanied by a group of streamers of ~100 m in length. One node has an unconnected secondary leader with streamers at both ends. Lightning Mapping Array observations show that the leader was part of an intracloud (IC) flash. The observation shows that steps of negative leaders near 10 km altitude are an order of magnitude longer than values reported in the literature for negative leaders near sea level. Since negative leaders propagate at comparable velocities at low and high altitudes, stepping occurs at a lower rate in IC flashes, which can explain why RF emissions from IC flashes are more intermittent than those from cloud‐to‐ground flashes.

Preliminary breakdown of intracloud lightning: Initiation altitude, propagation speed, pulse train characteristics, and step length estimation

“…Edens et al . [] observed cloud‐to‐air leaders in two IC flashes with a digital still camera and the LMA. They reported that the step lengths were at least 200 m and 264 m, respectively, in two leaders.…”

“…If this is true, the difference in the rate of radio emissions from IC and CG flashes cannot be simply attributed to the difference in step length in different altitudes as in Edens et al . []. Instead, we think that the ambient electric field is a more important factor, which will be discussed below along with other parameters in Table .…”

Abrupt Elongation (Stepping) of Negative and Positive Leaders Culminating in an Intense Corona Streamer Burst: Observations in Long Sparks and Implications for Lightning

“…This step was relatively straight and had a 2‐D length of about 1 km. (For comparison, Edens et al, , reported negative‐leader step lengths in excess of 200 m near 10‐km altitude and Pilkey, , Figures A‐1 and A‐2, reported what appeared to be a space leader initiated about 84 m from the positive leader channel near 3‐km altitude and 364 μs later connected to the lateral surface of that channel.) It appeared to occur in virgin air, propagated at a remarkably high effective speed of the order of 10 6 m/s, and produced a streamer corona burst at its far end.…”

“…The brush‐like streamer zone at the step tip was observed for upward negative leaders by Berger (), and a faint luminosity at the lower end of bright steps was reported by Schonland et al () for one downward stepped leader. Edens et al () presented optical records showing negative leader steps near 10‐km altitude. The step lengths were about 200 m or more; that is, considerably longer than at lower altitudes.…”

An unusual two-stroke negative cloud-to-ground flash showing profuse branching and corona-like formations

“…Berger [1967] [27] and Idone [1992] [28] presented photographic evidences of brush-like corona extending a few meters ahead of the tips of upward negative and upward positive leaders, respectively. Recently, Biagi [29] documented streamer zones (corona brushes) at negative leader tips with spatial extents of a few meters at some tens of meters AGL (altitude triggered lightning) and 100-200 m at 10 km AGL (cloud flash), respectively. The corona-like formations hypothesized in this paper, occurring at an altitude of 3.2 km AGL, were estimated to have 100-200 m spatial extent.…”