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Transient Luminous Events (TLEs)
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Revision as of 14:59, 5 August 2019 by Integration.Manager
Sometimes called upper atmospheric lightning or ionospheric lightning, transient luminous events (TLEs) are short-lived electrical-breakdown phenomena/electrically induced forms of luminous plasma, that occur well above the altitudes of normal lightning and Cumulonimbus (Cb) clouds.
Sprites are flashes of of bright red light that occur above storm systemsreach, 50 – 90 km in altitude and are triggered by positive discharges of lightning between a thundercloud and the ground. Sprite is also an acronym for Stratospheric/mesospheric Preturbations Resulting from Intense Thunderstorm Electrification. They are reddish-orange or greenish-blue in colour with hanging tendrils (sometimes referred to as "carrot sprites") and arcing branches above. Unlike tropospheric lightning, sprites are cold plasma, similar to fluorescent tube discharge. Based on their shape and visual appearance, we distinguish three types of sprites: jellyfish, column and carrot sprites.
Blue jets project directly from the top of the thunderstorm in a narrow cone jet up to approximately 50 km altitude. Unlike sprites, blue jets are, as the name implies, blue in color. A smaller variation of blue jets are blue starters, which are similar to blue jets, but only reach about 20 km high up and are thought to be ‘failed’ blue jets.
Blue jets are believed to be initiated as "normal" lightning discharges between the upper positive charge region in a thundercloud and a negative "screening layer" present above this charge region. The positive end of the leader network fills the negative charge region before the negative end fills the positive charge region, and the positive leader subsequently exits the cloud and propagates upward. The colour is believed to be due to a set of blue and near-ultraviolet emission lines from neutral and ionized molecular nitrogen.
Where blue jets are believed to initiate between the upper positive charge region and a negative screening layer directly above this region, Gigantic jets appear to initiate between the upper positive and lower negative charge regions in the thundercloud. In a similar process to how blue jets form, the higher charge region is discharged by the leader network before the same occurs in the lower charge region, and one end of the leader network propagates upward from the cloud toward the ionosphere. Gigantic jets reach higher altitudes than blue jets (up to 70km), and the upper portion of the jet changes colour from blue to red.
ELVES (Emission of Light and Very Low Frequency perturbations due to Electromagnetic Pulse Sources) are rare and indistinct types of TLE, producing large diffuse and expanding glows, up to 400 km in diameter. They occur in the ionosphere 100 km above the ground over thunderstorms. The light is generated by the excitation of nitrogen molecules due to electron collisions (the electrons possibly having been energized by the electromagnetic pulse caused by a discharge from an underlying thunderstorm).
Aviation safety concerns
It is possible that sprites and jets can cause electromagnetic pulses in flight electronics but evidence is limited.
- Lightning Detection Network
- Lightning Strike Risk to Engines
- Catatumbo Lightning
- Cumulonimbus (Cb)
- "Once Upon a Time in a Thunderstorm" ; an article from the NASA website concerning observations of TLEs from the International Space Station, 10 April 2018.
- [ "Full report on the uncontrolled free fall of a stratospheric balloon payload provoked by a Sprite"]; STRATOCAT website. Article describes investigation of an incident involving a scientific baloon on 5 June 1989.