This 7,000 frame-per-second camera was being tested on cloud-to-ground lightning, but it will be used to study upper-atmosphere lightning called “jets.”
In this example, fingers of plasma emerge from the clouds and branch out, inching toward the ground. Eventually, one of the fingers meets the Earth and the frame erupts in a white-hot explosion.
These fingers are called “step-leaders,” which are channels of negatively-charged air. Scientists think they form as the negative charge builds up at the base of a thunderstorm cloud. When it gets close to the ground, it repels all of the other negatively charged particles — kind of like a magnet repels another of its own polarity — and attracts the positive charges.
The positive charges climb up from the ground and form streamers. They typically develop on the top of very tall things like radio towers or sky-scrapers, but can also form on the ground itself.
If a stepped leader makes contact with a streamer, an electrical discharge occurs — lightning!