ELVES often appear as a dim, flattened, expanding glow around 400 km (250 mi) in diameter that lasts for, typically, just one millisecond. They occur in the ionosphere 100 km (62 mi) above the ground over thunderstorms. Their color was a puzzle for some time, but is now believed to be a red hue. ELVES were first recorded on another shuttle mission, this time recorded off French Guiana on October 7, 1990.
ELVES is a whimsical acronym for Emissions of Light and Very Low Frequency Perturbations due to 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 an underlying thunderstorm).
Read more about this topic: Upper-atmospheric Lightning
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