Lightning - Related Phenomena - Upper-atmospheric Discharges

Upper-atmospheric Discharges

Sprites are large-scale electrical discharges that occur high above a thunderstorm cloud, giving rise to a range of visual shapes. They are triggered by the discharges of positive lightning between the thundercloud and the ground. The phenomena were named after the mischievous sprite (air spirit) Puck in Shakespeare's A Midsummer Night's Dream. They often occur in clusters, lying 50 to 90 kilometres (31 to 56 mi) above the Earth's surface. Sprites have been mentioned as a possible cause in otherwise unexplained accidents involving high altitude vehicular operations above thunderstorms.

Blue jets differ from sprites in that they project from the top of the cumulonimbus above a thunderstorm, typically in a narrow cone, to the lowest levels of the ionosphere 25 miles (40 km) to 50 miles (80 km) above the earth. They are also brighter than sprites and, as implied by their name, are blue in colour.

ELVES often appear as dim, flattened, circular in the horizontal plane, expanding glows around 250 miles (400 km) in diameter that last for, typically, just one millisecond. They occur in the ionosphere 60 miles (97 km) above the ground over thunderstorms. Their color was a puzzle for some time, but is now believed to be a red hue. Elves is an acronym for Emissions of Light and Very Low Frequency Perturbations from Electromagnetic Pulse Sources. This refers to the process by which the light is generated; the excitation of nitrogen molecules due to electron collisions (the electrons possibly having been energized by the electromagnetic pulse caused by a discharge from the Ionosphere).