Runaway breakdown is a theory of lightning initiation proposed by Alex Gurevich in 1992.
Fast electrons which move at a large fraction of the speed of light have a mean free path up to 100 times longer.
This process, called the relativistic runaway electron avalanche, has been hypothesized to lead to electrical breakdown in thunderstorms, but only when a source of high-energy electrons from a cosmic ray is present to start the "runaway" process.
The resulting conductive plasma trail, many tens of meters long, is suggested to supply the "seed" which triggers a lightning flash.
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