Sprite (lightning)

Sprites are large-scale electrical discharges that occur high above thunderstorm clouds, or cumulonimbus, giving rise to a quite varied range of visual shapes flickering in the night sky. They are triggered by the discharges of positive lightning between an underlying thundercloud and the ground.

Sprites appear as luminous reddish-orange flashes. They often occur in clusters within atmosphere above the troposphere at an altitude range of 50–90 km (31–56 mi). Sporadic visual reports of sprites go back at least to 1886, but they were first photographed on July 6, 1989 by scientists from the University of Minnesota and have subsequently been captured in video recordings many thousands of times.

Sprites are sometimes inaccurately called upper-atmospheric lightning. However, sprites are cold plasma phenomena that lack the hot channel temperatures of tropospheric lightning, so they are more akin to fluorescent tube discharges than to lightning discharges.

Allusions to transient optical phenomena above thunderclouds can be found in anecdotal reports from as early as 1730 (see Johann Georg Estor). Nobel laureate C. T. R. Wilson had suggested in 1925, on theoretical grounds, that electrical breakdown could occur in the upper atmosphere, and in 1956 witnessed what possibly could have been a sprite. They were first documented photographically on July 6, 1989 when scientists from the University of Minnesota, using a low-light video camera, accidentally captured the first image of what would subsequently become known as a sprite. Several years after their discovery they were named sprites (air spirits) after their elusive nature. Since their 1989 discovery, sprites have been imaged tens of thousands of times, from the ground, from aircraft and from space, and have become the subject of intensive investigations.

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Wikipedia