Science

The birth of a lightning bolt was caught on video

A new slow-motion video offers the best view yet of the split-second collision of electric currents that creates a flash of lightning.

The video captures a thread of electric current, or lightning leader, zipping down from a thundercloud to meet another leader reaching up from the ground. When the two touch, it triggers a much stronger current to surge between the cloud and ground, and lightning flashes.

A single strand of electricity, or streamer, at the frayed tip of each lightning leader is enough to forge the connection between the two currents, researchers report online February 1 in Geophysical Research Letters. Understanding this cloud-to-ground connection is important because it determines where lightning strikes (SN: 6/25/20).

Streamers at the tips of lightning leaders were known to link these currents together. But because streamers are so faint and lightning leaders merge in mere millionths of a second, it was unclear exactly how they fused together. The link could be forged by many overlapping streamers coalescing into a single channel of electric current, or by contact between single streamers from each leader.

images of lightning formation over time
Lightning is fast, but high-speed cameras are faster — allowing scientists to view the play-by-play of how lightning flashes form (shown left to right, each frame 2.6 millionths of a second apart). When an electric current traveling down from a cloud meets one reaching up from the ground, a single thin strand of electricity bridges the gap (red box), triggering a flash of lightning.R. Jiang et al/Geophysical Research Letters 2021

Rubin Jiang, an atmospheric scientist at the Chinese Academy of Sciences in Beijing, and colleagues caught two lightning leaders on tape in 2017, during a lightning storm. Using a high-speed camera that snapped a picture of the lightning bolt every 2.6 microseconds, Jiang and colleagues saw a play-by-play of what happened when the fringe of streamers at the tip of each lightning leader met.

A single glowing filament of electricity appeared between the leaders right before the flash of lightning. That suggests that the hairline connection between the first two streamers to touch channeled the torrent of electric current that formed the lightning flash, while the other streamers fizzled out (SN: 2/15/19).

Behold: the split-second collision of electric currents that creates a flash of lightning. A current reaches down from a cloud. It meets another reaching up from the ground. When a single tenuous thread of electricity bridges the gap between them, lightning flashes.