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 40 to 50 km (25 to 30 miles) above the earth. They are also brighter than sprites and, as implied by their name, are blue in color. The color is believed to be due to a set of blue and near-ultraviolet emission lines from neutral and ionized molecular nitrogen. They were first recorded on October 21, 1989, on a monochrome video of a thunderstorm on the horizon taken from the space shuttle as it passed over Australia. Blue jets occur much less frequently than sprites; less than a hundred images have been obtained to date (2007). The majority of these images, which include the first color imagery, were obtained by researchers from the University of Alaska during a single aircraft flight in 1994 to study an intense Arkansas thunderstorm.

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