John Baez on the science of red sprites: “Sprites are quite different from lightning. They’re not electric discharges moving through hot plasma. They involve cold plasma – more like a fluorescent light.”
Originally shared by John Baez
Red sprites
Far above a thunderstorm in the English Channel, red sprites are dancing in the upper atmosphere.
You can’t usually see them from the ground – they happen 50 to 90 kilometers up. People usually photograph them from satellites or high-flying planes. But this particular bunch was videotaped from a distant mountain range in France by Stephane Vetter, on May 28th.
Sprites are quite different from lightning. They’re not electric discharges moving through hot plasma. They involve cold plasma – more like a fluorescent light.
They’re quite mysterious. People with high speed cameras have found that a sprite consists of balls of cold plasma, 10 to 100 meters across, shooting downward at speeds up to 10% the speed of light… followed a few milliseconds later by a separate set of upward moving balls!
Sprites usually happen shortly after a lightning bolt. And about 1 millisecond before a sprite, people often see a sprite halo: a faint pancake-shaped burst of light approximately 50 kilometres across 10 kilometres thick.
Don’t mix up sprites and ELVES – those are something else, for another day:
https://en.wikipedia.org/wiki/Sprite_(lightning)
https://en.wikipedia.org/wiki/Upper-atmospheric_lightning#ELVES
You also shouldn’t confuse sprites with terrestrial gamma-ray flashes. Those are also associated to thunderstorms, but they actually involve antimatter:
https://en.wikipedia.org/wiki/Terrestrial_gamma-ray_flash
A lot of weird stuff is happening up there!
The photo is from here:
https://apod.nasa.gov/apod/ap170615.html
#physics
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