Sprites are luminous flashes that occur high in the atmosphere, lasting a few tens of milliseconds, i.e. even shorter than the lightning flashes you see during thunderstorms.

They form at around 70-80 km altitude, where some sparks are generated and propagate rapidly down towards the cloud top at about 30-20 km, extending more than 40 km horizontally. The largest sprites can be as wide as 100 km. Looking at the horizon they will look much larger than mountains.

They form when a lightning flash alter the electrical properties of the atmosphere above a thunderstorm. Once this happens, the lightning flash is followed shortly by the sprite. You can see this by looking for a luminous area below the sprites in the pictures: that bright area is the cloud illuminated by the lightning flash.

Because of their attitude of appearing and disappearing quickly, you can barely feel you have spotted them. For this reason they have been called sprites, like the little spirits in the story tales.

Enrico and Anna