Stepped leader

Stepped leader

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 along the path defined by the stepped leaders, but in the opposite direction: from ground to cloud. This 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.

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