Transient luminous events (TLEs) are atmospheric optical phenomena that occur above thunderstorms. They are electrical discharges that take place in the upper atmosphere, typically between 40 and 90 kilometers (25 to 55 miles) above the Earth's surface. TLEs are characterized by their relatively short duration and distinctive luminous appearances. There are several types of TLEs, including sprites, blue jets, and elves:
Sprites: Sprites are large-scale electrical discharges that occur above thunderstorm systems. They are typically red, orange, or pink in color and appear as elongated, branching structures. Sprites can reach altitudes of 50 to 90 kilometers (31 to 56 miles) and have a width of several tens of kilometers. They are relatively brief, lasting only a few milliseconds. Sprites are associated with powerful lightning discharges in thunderstorms.
Blue Jets: Blue jets are less common than sprites and appear as cone-shaped, blue light emissions from the tops of thunderstorm clouds. They extend from the cloud tops to altitudes of around 40 to 50 kilometers (25 to 31 miles). Blue jets can last for several hundred milliseconds. They are thought to be related to strong lightning discharges and are named for their distinctive blue color.
Elves: Elves (Emissions of Light and Very Low-Frequency Perturbations due to Electromagnetic Pulse Sources) are rings or halos of light that appear in the upper atmosphere. They are usually located at altitudes of 90 to 100 kilometers (56 to 62 miles) and have a diameter of hundreds of kilometers. Elves are very brief, lasting only a few milliseconds. They are caused by the interaction of intense lightning-generated electromagnetic pulses with the upper atmosphere.
Transient luminous events are challenging to study because they occur high above the Earth's surface and are short-lived. They were first discovered in the late 1980s and early 1990s with the help of high-speed cameras and low-light detectors on high-altitude aircraft. Since then, satellites and ground-based observatories have been used to capture and study these phenomena in greater detail. TLEs provide valuable insights into the electrical and atmospheric processes occurring in thunderstorms and their effects on the upper atmosphere.