An extremely short-lived optical phenomenon, first observed scientifically in the early 1990s, that occurs high above certain vigorous thunderstorms. Lasting approximately one millisecond, these transient flashes, invisible visually, occur at heights of 85–105 km, often in conjunction with sprites. They begin at a central point and expand (faster than the speed of light) as a torus, to diameters of several hundred kilometres. This agrees with the theory that elves occur when an electromagnetic pulse from a powerful lightning discharge reaches the ionosphere, where it accelerates electrons that collide with nitrogen molecules, which then radiate the faint red light.
Subjects: Meteorology and Climatology.