Lightning Facts

Some Lightning Facts

A typical lightning flash lasts about a quarter of a second and consists of 3 or 4 individual discharges called strokes. Each stroke lasts a few ten thousandths of a second, although the visual appearance is longer. The “flicker” sometimes observed in lightning is due to seeing the actual strokes making up the flash.

A lightning stroke begins with a faint predischarge, called the leader, which goes from the cloud to the ground. The leader establishes a path for the highly luminous return stroke (what you really see) which propagates from the ground up to the cloud. The first stroke of a flash is usually preceded by a “stepped leader”, so called because it appears to progress in discrete steps (about 100 segments, each 50 m long) from cloud to ground. The subsequent strokes are preceded by a “dart leader” which smoothly follows the path of the previous return stroke (and is about 10 times faster).

Thunder is formed from the shock wave formed by the rapid heating of the air along the path of the return stroke, which reaches some 30,000 degrees K. The sound of thunder varies depending on how far you are from the various parts of the stroke. The sound from a part of the stroke farther away will get to you later and be fainter. {more}

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