Lightning effects at high altitudes: sprites, elves, and terrestrial gamma ray flashes

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. To cite this article: U.S. Inan, C. R. Physique 3 (2002) 1411–1421.