Worldwide, lightning strikes the Earth an estimated 45 times a second.
The amount of energy released in one of those atmospheric electrical discharges can vary widely—from 100 megajoules to as high as 30,000 megajoules, says Don MacGorman, lightning expert with the U.S. National Oceanic and Atmospheric Administration. A typical range would be 1,000 to 5,000 megajoules, he says.
The wide range of estimates for lightning's energy is due to its complexity. A flash develops initially in the cloud, then a channel begins approaching the ground in steps. Once it connects with the ground, a large current surge moves back up the channel in a process called a return stroke—responsible for most of the energy transferred to ground. What the eyes perceive as a single lightning flash is actually made up of several strokes of lightning, enough to last nearly a half second. If the gap between strokes is long enough, the lightning flash appears to flicker.
While brief, the voltage is intense enough to quickly heat the air to nearly 50,000°F (30,000°C). (In contrast, the surface of the sun is about 10,000°F, or 5,500°C.) The rapid expansion of the heated air generates a shock wave that is heard as thunder.
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