A SciAm article outside their paywall .. and an excellent subject.
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At first, scientists wondered if the gamma rays could be related to another type of atmospheric marvel discovered only a few years earlier. Cameras trained above thunderclouds had photographed bright, brief flashes of red light, 50 miles above the ground and miles wide, that looked like giant jellyfish. These impressive electric discharges were whimsically named “sprites.” Because sprites almost reach the edge of space, it seemed plausible that they might shoot out gamma rays that an orbiting probe could see.
Soon theoretical physicists made the first attempts to explain how sprites could produce space-bound gamma rays. Sprites are thought to be side effects of ordinary lightning occurring in clouds far below. Lightning is an electrically conducting channel that temporarily opens through the air, which is otherwise an electric insulator. The bolt carries electrons between regions of the atmosphere or between the atmosphere and the ground. It is caused by an imbalance of electrostatic charge and is triggered by the resulting electric fields, whose potential differences may exceed 100 million volts.
The violent rush of electrons partially restores the electrostatic balance. Yet just as tamping down a bump in a rug often causes another bump to spring up elsewhere, a discharge inside a cloud often causes the field to spring up elsewhere, including on the ground—where it may later lead to upward lightning—or near the bottom of the ionosphere—where a sprite may result.
In 1992 Alexander V. Gurevich of the Lebedev Physical Institute in Moscow and his collaborators calculated that such secondary electric fields near the ionosphere might produce avalanches of energetic electrons, which, bumping into atoms, would unleash high-energy photons—x-rays and the even more energetic gamma rays—in addition to the sprites' characteristic red glow. The mechanism they proposed derived from a suggestion made by Nobel Prize–winning Scottish scientist C.T.R. Wilson back in the 1920s. At low energies, electrons being pushed by an electric field act like drunken sailors, bouncing from molecule to molecule and losing their energy with each collision. At high energies, however, the electrons travel in a straighter line, picking up even more energy from the electric field, which makes any collisions even less effective at disturbing their path, and so on—a self-reinforcing process. This sequence differs from our everyday experience, in which the faster we go, the more drag force we suffer, as any bicyclist can attest.
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hopefully that will drag you in...
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