Lightning: Brief Bolts of Energy
Lightning bolts dance on the Colorado Plateau at Canyonlands National Park, Utah, in one of nature's most familiar energy displays.
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.
That would hardly be enough to transport anyone three decades across space-time, as the fictional Dr. Emmett Brown did when he harnessed a lightning bolt to fuel the time-traveling car he invented in the movie, Back to the Future. But it would be a blast sufficient to propel the average U.S. passenger car about 180 to 910 miles (290 to 1,450 kilometers), equivalent to the energy in about 8 to 38 gallons (30 to 144 liters) of gasoline.
The force that Dr. Brown called "1.21 jigawatts" was more like 280 to 1,390 kilowatt-hours, the amount used by the average U.S. household over about nine days at the low end to almost a month and a half at the high end.
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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Although lightning strikes certainly can be deadly, their energy output pales when considered against forces of nature that have leveled cities and altered coastlines. Japan's 9.0-magnitude Tohoku earthquake and tsunami on March 11, 2011, was one of the more fearsome displays of nature's power, but scientists have also sought to measure the energy in volcanoes, wildfires, hurricanes, and the waves lapping against the shore.
Their calculations show that society's successes in developing geothermal, wind, and solar energy have captured but a minuscule fraction of nature's energy.
—David Lagesse and Marianne Lavelle
Additional research: Julie C. Beer
This story is part of a special series that explores energy issues. For more, visit The Great Energy Challenge.
Pictures: Immense, Elusive Energy in the Forces of Nature
Japan's Tohoku earthquake and tsunami on March 11, 2011, displayed the fearsome power in nature. Only a small fraction of Earth's forces have been captured to fuel civilization.