Transient luminous event
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A transient luminous event (TLE) is a short-lived electrical phenomenon that occurs above storm clouds. Less commonly called upper-atmospheric lightning, transient luminous events are believed to be electrically induced forms of optical fluorescence.
There are several types of TLEs, the most common being sprites. Sprites are flashes of bright red light that occur above storm systems. C-sprites (short for "columniform sprites") is the name given to vertical columns of red light. C-sprites exhibiting tendrils are sometimes called carrot sprites. Other types of TLEs include gnomes, blue jets, gigantic jets, blue starters, and elves, the latter being the plural of "ELVE," a somewhat forced acronym for "e(mission of) l(ight and) v(ery low-frequency perturbations from) e(lectromagnetic pulse sources)". TLEs are secondary phenomena that occur in the upper atmosphere in association with underlying thunderstorm lightning.
TLEs generally last anywhere from less than a millisecond to more than 2 seconds. The first TLE was captured accidentally in a video recording in 1989. University of Minnesota researchers were waiting to record a rocket launch and pointed the camera at a distant thunderstorm. A TLE was later identified, appearing in only two frames of the film. TLEs have been captured by a variety of optical recording systems, with the total number of recorded events currently (early 2009) estimated at many tens-of-thousands. The global rate of TLE occurrence has been estimated from satellite (FORMOSAT-2) observations to be several million events per year.
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