What is a red sprite?

A red sprite is a brief, high-altitude electrical discharge that flashes above powerful thunderstorms, typically about 50 to 90 kilometers (roughly 30 to 55 miles) up in the mesosphere. Unlike ordinary lightning, it is a cold plasma event more like the glow of a fluorescent tube, driven by strong positive cloud-to-ground lightning that leaves an intense electric field above the storm; nitrogen emissions give the flash its red color, and the whole event lasts only milliseconds. Sprites were first photographed in 1989 and are often hard to see from the ground because storm clouds block the view, though cameras on mountains and spacecraft such as the International Space Station have captured clear examples.

Source: NASA Earth Observatory — Red Sprites Above the U.S. and Central America.

Image: Red sprite lightning seen from the ISS (ISS031-E-010712). NASA/Expedition 31, public domain, via Wikimedia Commons.