[Phénomènes de haute altitude associés aux éclairs : sprites, elves et émissions gamma terrestres]
Un ensemble fascinant de phénomènes complexes étudiés lors de la dernière décennie indique que les orages troposphériques et les éclairs associés sont fortement couplés aux régions atmosphériques supérieures. Les éclairs formés à l'intérieur du nuage (à moins de 20 km d'altitude) ont des effets à plus de 40 km d'altitude via l'émission d'impulsions électromagnétiques intenses (EMP) et/ou la production de champs quasi-statiques (QE) élevés. Ces champs QE, dont l'amplitude atteint 1 kV/m, dirigés vers le bas pour des éclairs nuage-sol positifs, peuvent créer des avalanches d'électrons « runaway », d'énergie de l'ordre du MeV, accélérés vers la haute atmosphère, produisant des bouffées d'émission gamma de courte durée (environ 1 ms). Une manifestation spectaculaire de ces champs intenses est le phénomène de « Sprite », grande décharge lumineuse se développant entre 40 et 90 km, initiée par le chauffage d'électrons libres pendant quelques millisecondes suite à un éclair intense. Les phénomènes lumineux appelés « Elves », de durée beaucoup plus brève que les sprites (<1 ms), sont localisés entre 80 et 95 km d'altitude avec une extension latérale beaucoup plus grande (jusqu'à 600 km). Ils sont produits par les effets d'échauffement, d'ionisation et d'émission optique associés aux impulsions EMP rayonnés par les éclairs des deux polarités.
A fascinating set of newly discovered complex phenomena indicate that thunderstorms and lightning discharges are strongly coupled to the overlying upper atmospheric regions. Lightning discharges at cloud altitudes (<20 km) affect altitudes >40 km either via the release of intense electromagnetic pulses (EMPs) and/or the production of intense quasi-static electric (QE) fields. The intense transient QE fields of up to ∼1 kV·m−1, which for positive CG discharges is directed downwards, can avalanche accelerate upward-driven runaway MeV electron beams, producing brief (∼1 ms) flashes of gamma radiation. A spectacular manifestation of these intense fields is the so-called ‘Sprites’, large luminous discharges in the altitude range of ∼40 km to 90 km, which are produced by the heating of ambient electrons for a few to tens of milliseconds following intense lightning flashes. The so-called ‘Elves’ are optical flashes which last much shorter (<1 ms) than sprites, and are typically limited to 80–95 km altitudes with much larger (up to 600 km) lateral extent, being produced by the heating, ionization, and optical emissions due to the EMPs radiated by both positive and negative lightning discharges.
@article{CRPHYS_2002__3_10_1411_0,
author = {Umran S. Inan},
title = {Lightning effects at high altitudes: sprites, elves, and terrestrial gamma ray flashes},
journal = {Comptes Rendus. Physique},
pages = {1411--1421},
publisher = {Elsevier},
volume = {3},
number = {10},
year = {2002},
doi = {10.1016/S1631-0705(02)01418-4},
language = {en},
}
Umran S. Inan. Lightning effects at high altitudes: sprites, elves, and terrestrial gamma ray flashes. Comptes Rendus. Physique, Volume 3 (2002) no. 10, pp. 1411-1421. doi : 10.1016/S1631-0705(02)01418-4. https://comptes-rendus.academie-sciences.fr/physique/articles/10.1016/S1631-0705(02)01418-4/
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