The start of lightning: Evidence of bidirectional lightning initiation

Abstract

Lightning flashes are known to initiate in regions of strong electric fields inside thunderstorms, between layers of positively and negatively charged precipitation particles. For that reason, lightning inception is typically hidden from sight of camera systems used in research. Other technology such as lightning mapping systems based on radio waves can typically detect only some aspects of the lightning initiation process and subsequent development of positive and negative leaders. We report here a serendipitous recording of bidirectional lightning initiation in virgin air under the cloud base at ~11,000 images per second, and the differences in characteristics of opposite polarity leader sections during the earliest stages of the discharge. This case reveals natural lightning initiation, propagation and a return stroke as in negative cloud-to-ground flashes, upon connection to another lightning channel – without any masking by cloud.

Initiation and propagation of cloud-to-ground lightning observed with a high-speed video camera

“…2g. That point was repeatedly traversed by fast luminosity waves, which is in contrast with the event reported by Montanya et al 2,. who inferred from their high-speed video record that the neutral point was stationary.…”

“…who inferred from their high-speed video record that the neutral point was stationary. It is important to note that the two leader ends in Montanya et al .’s2 case started their extension at the same time from a single point in virgin air. In contrast, in our case, a decayed channel section was involved.…”

“…In contrast, in our case, a decayed channel section was involved. Additional comparison with Montanya et al .’s2 event is found in Supplementary Section S3.…”

“…The dynamics of positive and negative leader ends in terms of the extension speed and branching can be very different either for the same bidirectional leader or for leaders following different scenarios. Positive end can extend faster2224 or slower23 than the negative end, or the two ends can extend at similar speeds10. In the present study, we observed a pulsating behavior of the positive end, while the negative end extended normally.…”

“…Most of the time, bidirectional leaders are completely or in part hidden inside the cloud, which makes their optical imaging impossible. This is why, as of today, there are only a few optical observations of bidirectional leaders in virgin air found in the literature [Montanya et al 2,. Warner et al 3…”