VHF lightning mapping observations of a triggered lightning flash

Abstract

[1] On 3 August 2010 an extensive lightning flash was triggered over Langmuir Laboratory in New Mexico. The upward positive leader propagated into the storm's midlevel negative charge region, extending over a horizontal area of 13 Â 13 km and 7.5 km altitude. The storm had a normalpolarity tripolar charge structure with upper positive charge over midlevel negative charge. Lightning Mapping Array (LMA) observations were used to estimate positive leader velocities along various branches, which were in the range of 1-3 Â 10 4 m s À1 , slower than in other studies. The upward positive leader initiated at 3.4 km altitude, but was mapped only above 4.0 km altitude after the onset of retrograde negative breakdown, indicating a change in leader propagation and VHF emissions. The observations suggest that both positive and negative breakdown produce VHF emissions that can be located by time-of-arrival systems, and that not all VHF emissions occurring along positive leader channels are associated with retrograde negative breakdown.

The physical concept of recoil leader formation

“…[14] and in Ref. [24], and also in observations with Lightning Mapping Array (LMA) (e.g., [5] and [3]). On the other hand, an unbranched upward positively charged leader that is initiated by a tall structure, and dies off without the ensuing dart leader to ground, exhibits the type of slowluminosity variation associated with changing ambient potential distribution in the cloud regions.…”

“…However, the term "streamer" misrepresented the nature of the phenomenon, and has been replaced by the physically correct term "recoil leader," that matches all the attributes of K-changes [13]. A new term, recently introduced [3] for this phenomenon, is "retrograde leader," i.e., going backwards, which does not change or add anything to the meaning of the term "recoil leader," but, in the author's view, only contributes to the existing confusion in lightning terminology.…”

Observations of the initial stage of a rocket‐and‐wire‐triggered lightning discharge

“…In natural lightning, positive polarity breakdown usually radiates weakly at VHF and is often masked by stronger radiation from simultaneously occurring negative breakdown [e.g., Edens et al, 2012]. In natural lightning, positive polarity breakdown usually radiates weakly at VHF and is often masked by stronger radiation from simultaneously occurring negative breakdown [e.g., Edens et al, 2012].…”

Asymmetries in bidirectional leader development of lightning flashes

“…[37] Positive leaders themselves radiate very weakly in the VHF band, and their detection [Edens et al, 2012] depends on the proximity of at least five LMA sensors, low background noise levels, and absence of stronger emitting lightning sources such as negative leaders. As the LMA records only the highest received power in 80 μs bins, weaker sources will not be registered.…”

“…While the term "recoil leader" is used frequently, the most fitting term is "retrograde negative leader" [Edens et al, 2012]. Observed with high-speed cameras, they look like luminous streaks occurring 3000-5000 times per second [Montanyà et al, 2012], revealing the locations of barely visible positive leader branches [Saba et al, 2008].…”