Transient luminous event

Transient luminous events can be another source of ionization in the upper atmosphere.

During World War II (and probably before), high flying pilots were reported to have observed unexplained aerial phenomena (UAP), often now called transient luminous events (TLE’s), particularly in the vicinity of thunderstorms.

Known as Transient Luminous Events (TLEs), these unusual features were first spotted by accident in 1989.