A brief review of the problem of lightning initiation and a hypothesis of initial lightning leader formation

Abstract

[1] A brief review of hypothesized mechanisms of lightning initiation is presented, with the suggestion that these mechanisms provide an incomplete picture of lightning initiation. This is followed by two ideas: (1) a combination of previously hypothesized lightning initiation mechanisms as a means for local intensification of the thundercloud electric field, and (2) a process for the formation of a hot lightning leader channel that is analogous to the space leader phase of the laboratory negative stepped leader. Thundercloud electric field observations have consistently yielded peak values that are an order of magnitude weaker than the dielectric strength of air. Various mechanisms have been proposed to explain how lightning can initiate in such weak electric fields, including hydrometeor-initiated positive streamers and cosmic ray-initiated runaway breakdown. The historically favored positive streamer mechanisms are problematic due to requiring electric fields two to three times larger than peak observed fields. The recently favored runaway breakdown mechanisms appear capable of developing in conditions comparable to peak observed fields although it is not clear how these diffuse discharges can lead to creation of a lightning leader. This paper proposes a solution whereby runaway breakdown and hydrometeor-initiated positive streamer systems serve to locally intensify the electric field. Following this local field intensification, it is hypothesized that formation of the initial lightning leader channel is analogous to the formation of a space leader in a laboratory negative stepped leader.

Variability of CONUS Lightning in 2003–12 and Associated Impacts

“…Price (2000) finds excellent agreement between lightning activity and upper-tropopheric water vapor, which is a more important greenhouse substance than boundary layer water vapor. In addition, laboratory results in Petersen et al (2008) suggest that the presence of ice can increase the probability of lightning initiation.…”

High-Energy Atmospheric Physics: Terrestrial Gamma-Ray Flashes and Related Phenomena

“…Figure 28 shows how RREAs can discharge the large scale field producing localized field enhancements (also see Petersen et al 2008). Dwyer (2005b) also showed that such discharges can push the field above the relativistic feedback threshold, providing a mechanism for generating TGFs.…”

“…However, this value is larger than the RREA threshold field. Indeed, in situ electric field measurements show that the electric field near the lightning initiation point sometimes exceeds the RREA threshold (Marshall et al 2005) It has been suggested that runaway electron avalanches seeded by cosmic-ray extensive air showers (EASs) could result in enough ionization to initiate lightning (Gurevich et al , 2003Solomon et al 2001Solomon et al , 2002Petersen et al 2008). This hypothesis has gained a great deal of attention in recent years, both from the scientific community and from the popular press (Dwyer 2005a;Gurevich and Zybin 2005).…”

Numerical simulations of local thundercloud field enhancements caused by runaway avalanches seeded by cosmic rays and their role in lightning initiation

“…[3] Among the ideas of the lightning initiation, some of which were reviewed by Petersen et al [2008], one of the most promising seems to be the very weakly elaborated hypotheses connecting the start of the lightning leader with relativistic runaway electron avalanches (RREAs) seeded by high-energy electrons of secondary space radiation [Gurevich et al, 1997]. According to this hypothesis, the RREAs, generating a considerable number of electron-ion pairs, produce an ionized domain, polarization of which in the thundercloud electric field leads to a local rise of the field at the edges of the domain up to the value required to "…initiate the spark type local electric breakdown…which services for the triggering of lightning" [Gurevich et al, 1997].…”