Upper-atmospheric lightning
Representation of upper-atmospheric lightning and electrical-discharge phenomena
Main article: Upper-atmospheric lightning
Reports by scientists of strange lightning phenomena about storms date back to at least 1886. However, it is only in recent years that fuller investigations have been made. This has sometimes been called megalightning.[49][50]
[edit] Sprites
Main article: Sprite (lightning)
Sprites are large scale electrical discharges which occur high above a thunderstorm cloud, or cumulonimbus, giving rise to a quite varied range of visual shapes. They are triggered by the discharges of positive lightning between the thundercloud and the ground.[37] The phenomena were named after the mischievous sprite (air spirit) Puck in Shakespeare's Midsummer Night's Dream. They normally are colored reddish-orange or greenish-blue, with hanging tendrils below, and arcing branches above, their location, and can be preceded by a reddish halo.[49] They often occur in clusters, lying 50 miles (80 km) to 90 miles (145 km) above the Earth's surface. Sprites were first photographed on July 6, 1989 by scientists from the University of Minnesota and have since been witnessed tens of thousands of times.[51] Sprites have erroneously been held responsible for otherwise unexplained accidents involving high altitude vehicular operations above thunderstorms.[52]
[edit] Blue jets
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 30 miles (48 km) above the earth.[citation needed] They are also brighter than sprites and, as implied by their name, are blue in colour. They were first recorded on October 21, 1989, on a video taken from the space shuttle as it passed over Australia, and subsequently extensively documented in 1994 during aircraft research flights by the University of Alaska.[53][50]
On September 14, 2001, scientists at the Arecibo Observatory photographed a huge jet double the height of those previously observed, reaching around 50 miles (80 km) into the atmosphere. The jet was located above a thunderstorm over the ocean, and lasted under a second. Lightning was initially observed traveling up at around 50,000 m/s in a similar way to a typical blue jet, but then divided in two and sped at 250,000 m/s to the ionosphere, where they spread out in a bright burst of light.[54] On July 22, 2002, five gigantic jets between 60 and 70 km (35 to 45 miles) in length were observed over the South China Sea from Taiwan, reported in Nature.[53] The jets lasted under a second, with shapes likened by the researchers to giant trees and carrots.[citation needed]
[edit] Elves
Elves often appear as dim, flattened, expanding glows around 250 miles (402 km) in diameter that last for, typically, just one millisecond.[55] 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 were first recorded on another shuttle mission, this time recorded off French Guiana on October 7, 1990. Elves is a frivolous acronym for Emissions of Light and Very Low Frequency Perturbations from Electromagnetic Pulse Sources.[56] 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).[50]
