Stepped leader
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A stepped leader (possibly also referred to as a step leader) is a path of ionized air which extends downward from a thundercloud during the initial stages of atmospheric breakdown during a lightning strike. Often, there are multiple, branching stepped leaders. As the step leaders form, these branches of ionized air form in a stepwise fashion, followed by a short period of inactivity, until the final step leader reaches the ground, a tall object on the ground, or a positive streamer extending upward from a ground object. At this point, the lightning strike begins as an extremely large negative electric current that flows along the path defined by the stepped leaders from the thundercloud into to the ground. This flow of current is often referred to as the return stroke.
Stepped leaders appear to only move in quantized steps of approximately 50-100 feet at a time with a 20 to 50 microsecond pause between steps, and may either branch or proceed directly to ground.
