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. The phenomena were named after the mischievous sprite (air spirit) Puck in William Shakespeare's A Midsummer Night's Dream. They normally are colored reddish-orange or greenish-blue, with hanging tendrils below and arcing branches above. They can also be preceded by a reddish halo. They often occur in clusters, lying 50 kilometres (31 mi) to 90 kilometres (56 mi) above the Earth's surface. Sprites have since been witnessed tens of thousands of times. Sprites have been held responsible for otherwise unexplained accidents involving high altitude vehicular operations above thunderstorms.
Read more about this topic: Upper-atmospheric Lightning