Scientists in the US say they have found a dramatic new electrical-discharge mechanism that could explain how thunderstorms can produce flashes of gamma radiation. Called "dark lightning", the effect is silent, invisible to the eye and a potential threat to aeroplane passengers – at least according to the researchers' models.
The explosive cascade produces around 10(17) electrons in just a few tenths of a millisecond – spewing out gamma rays all the while – at which point the number of charged particles is so great that the thunderstorm's electrical field collapses and it discharges rapidly and invisibly. The electrical currents produced by these beams of high-energy electrons are comparable to those produced by conventional lightning – tens of thousands of amps in magnitude.
Dark lightning sheds light on gamma-ray mystery
Dark lightning is a process similar to ordinary lightning that creates pairs of electrons and antielectrons (or positrons), and that produces gamma rays and relatively little (visible) light. Since the amount of light created is so small, dark lightning is practically invisible to the human eye.