Lightning: Brief Bolts of Energy
Photograph by Markus Mauthe, Iaif/Redux
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
Published March 8, 2012
Volcanoes: Too Hot to Capture
Photograph by Brynjar Gauti, AP
An ash cloud billows from southern Iceland's sub-glacial Eyjafjallajökull volcano on April 16, 2010, signaling an escape of the heat inside the Earth that is drawing renewed interest worldwide as an energy source.
Almost all of Iceland's building and water heating comes from geothermal energy, which also provides about a third of the nation's electricity. But nobody has figured out how to harness that energy safely when it breaks through the surface as an active volcano. That's too bad, because thermal emissions coming from Iceland's Eyjafjallajökull volcano in March 2010, during the first of two eruptions, quickly reached 1 gigawatt , and later peaked at 6 gigawatts, says Ashley Davies, a volcanologist at NASA's Jet Propulsion Laboratory in Pasadena, California.
One gigawatt is the capacity of a large power plant, like the Hudson Generating Station across the Hudson River from Manhattan in Jersey City, New Jersey, which serves 750,000 households with a mix of coal, natural gas, and oil. Six gigawatts is greater than the capacity of any U.S. electric plant except for the huge Grand Coulee hydroelectric plant.
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And that's just a small portion of the total thermal output in the volcano's 2010 eruption. It does not account for mechanical energy—the accompanying earthquakes and explosive blasts—or additional heat in the erupting lava. NASA measured the volcano's thermal output using satellite imagery, which it also employs to gauge volcanoes elsewhere in the solar system. Some of those other-world volcanoes dwarf those on Earth, Davies adds, including one on the Jupiter moon Io whose 2001 eruption radiated 78 terawatts of heat. Think of that as 78 times the total capacity of all the power plants in the United States.
Over an hour, that would be equivalent to the energy in about 46 million barrels of oil— about half the amount consumed around the world every day.
Back at Iceland's Eyjafjallajökull, another part of the volcano underwent a much larger eruption in April 2010. That eruption occurred under an ice cap that hid much of its power from the NASA satellite, which still measured 60 megawatts of radiated power. Over the course of an hour, that would be equivalent to the energy output of 1,648 gallons (6,238 liters) of gasoline—the amount that an average U.S. motorist would have to buy over four years to fuel a car that drives 10,000 miles annually.
That eruption's interaction of lava with ice generated clouds of steam and ash that grounded flights in Europe. It was, Davies says, "the ash plume that ate Europe."
Published March 8, 2012
Earthquakes: Energy in Motion
Photograph from Kyodo/Reuters
Rescue workers, appearing small against the rubble in red and orange uniforms, search through the remains of Noda-mura village, in the Iwate Prefecture in northern Japan, on March 14, 2011.
To cause the tsunami that wreaked devastation here and along the east coast of Japan, the earthquake three days earlier in the northwest Pacific Ocean had to have produced, at minimum, energy that was equivalent to 475 megatons of TNT, according to the estimates that scientists at the U.S. Geological Survey have developed.
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That's equivalent to the energy content of 326 million barrels of crude oil, close to the amount the world consumes in four days.
The energy in an earthquake is one of the few forces of nature that is closely measured by scientific instruments. Seismograph readings enable scientists to estimate the energy that an earthquake radiates through the earth, shaking buildings near and far. Even so, the instruments do not capture the whole picture, for example, the energy dissipated as heat through friction.
With a magnitude of 9.0, last year's earthquake was the largest to rock Japan and among the largest ever measured.
Published March 8, 2012
Hurricanes: Force From the Sea
Photograph by Irwin Thompson, Dallas Morning News/AP
The winds of Hurricane Katrina blow the roof off a restaurant in Kenner, Louisiana, on August 29, 2005.
A hurricane can be viewed as an engine that gathers energy from warm, humid tropical water and releases it in swirling winds. And its massive size makes for a massive release of power.
Hurricane Katrina at its peak—about 17 hours before its destructive August 2005 landfall in Louisiana—had hurricane-force winds that extended as far as 105 miles (169 kilometers) from its center. Those winds also blew at sustained speeds of 175 miles per hour (282 kilometers per hour).
That means Katrina was producing about 20 trillion watts of power, or 20 million megawatts, calculates Kerry Emanuel, a professor of atmospheric science at the Massachusetts Institute of Technology.
That approaches 1,000 times the capacity of Louisiana's entire fleet of power plants (26,000 megawatts, as measured during peak summer months.)
Calculating the energy in a hurricane's winds is more than an academic pursuit. Federal scientists are studying a new rating system that strives to better measure a hurricane's destructive potential. At the heart of the new system is a broader measure of a hurricane's winds, expressed as "integrated kinetic energy."
Proponents of the new system argue that it can better predict storm surge, the swell of water that is pushed ashore by a storm's winds. It is the storm surge that causes most deaths in hurricanes, including in Hurricane Katrina, which claimed nearly 1,000 lives.
Published March 8, 2012
Tornadoes: Funneling Power
Photograph by Whitney Curtis, Getty Images
A man surveys the debris of the home where his mother-in-law died in Harrisburg, Illinois. The wrecked dwelling was hit by one of dozens of tornadoes that sliced through the U.S. Midwest and South last week. At least 39 people in five states lost their lives.
The 180 mile-per-hour (290 kilometer-per-hour) twister, about 275 yards (250 meters) wide, that touched down in Harrisburg was rated an F-4 tornado on the five-level enhanced Fujita scale of intensity. The power it packed was the equivalent of 160,000 kilowatt-hours, says Dr. Joseph Schaefer, director emeritus of the Storm Prediction Center, part of the U.S. National Oceanic and Atmospheric Administration, based in Norman, Oklahoma. That's the amount used by 5,000 average U.S. homes over the course of a day.
And tornadoes can generate even more destructive energy. The unusually monstrous F-5 funnel that devastated Joplin, Missouri, on May 22, 2011, may have exceeded 200 mph (320 km/hour). Its energy could be estimated at double that of the tornado at Harrisburg, says Schaefer.
A tornado's intensity comes from packing its wallop into a small space. The average tornado over the past 20 years has been only 100 yards (91 meters) wide, says Greg Carbin, the storm center's warning coordination meteorologist. An example, Carbin says, is a tornado that touched down outside Tampico, Texas, in 1999. Nobody was hurt and little damage was done.
In contrast, a typical hurricane is 300 miles (483 km) across.
Published March 8, 2012
Tsunami: Awash With Intensity
Photograph from Mainichi Shimbun/Reuters
A wall of water advances on Miyako, in northeastern Japan's Iwate Prefecture, on March 11, 2011.
The massive tsunami unleashed by the earthquake about 80 miles (129 km) east of the city of Sendai in northern Japan utterly destroyed cities along the island nation's east coast. Comparisons to the destruction of the atomic bombs visited upon Japan at the end of World War II were common, especially given that the flooding, which knocked out crucial backup cooling power at the Fukushima Daiichi nuclear power plant, triggered a nuclear crisis second only to the 1986 Chernobyl accident in Ukraine.
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The energy released by the tsunami in fact greatly exceeded the destructive power of the atom bombs that hit Hiroshima and Nagasaki in 1945, estimates University of Illinois geologist Susan Kieffer, an expert on geological fluid dynamics. The tsunami's energy likely exceeded the explosive power of a megaton of TNT, or about 28 times the combined power of the two atomic bombs that hit Japan, she wrote on her blog, Geology in Motion. But Kieffer says the destructive power may have been much greater, perhaps 10 megatons, or 280 times the force of the atomic bombs. The difference depends primarily on how long the tsunami lasted, with her estimate ranging from 100 to 1,000 seconds.
At the upper end, that's the energy equivalent of 6.9 million barrels of crude oil, or 50 percent more than all of the oil Japan consumes each day.
The calculation also considers the velocity of the wave, which Kieffer estimated was about 220 meters (722 feet) per second based on the 30 minutes or so that it took to reach shoreline. Also, Kieffer used the wave's estimated open-ocean height at 7 meters (23 feet), and calculated that the wave was about 800 miles (1,300 kilometers) long, or about half as long as the coastline of Honshu, the island it struck.
Published March 8, 2012
Ocean Waves: Pounding Power of Surf
Photograph from Alaska Stock Images/National Geographic
Waves crashing at the edge of the continental shelf off Alaska's Pacific coast pack the power of 1,360 terawatt-hours of energy each year, an analysis led by the U.S. Electric Power Research Institute (EPRI) found. That's about 40 percent more than Japan's total annual electricity output, and equivalent to about one-third of United States' electricity demand.
Alaska's Pacific shoreline has more available wave energy than all of the other coasts of the United States combined. That's partly because it is the longest U.S. coastline, from the Aleutian Islands to Prince of Wales Island and the panhandle. But the seas off Alaska also gain power because of what oceanographers call their "fetch," the vast area of open water over which the wind works to create the waves that break on the shores of The Last Frontier.
Buoys that measured wave power density in the EPRI study (to validate the scientists' models) delivered averages as high as 52 kilowatts per meter off Alaska, about seven times greater than the maximum readings off the South Atlantic coast of the United States.
Of course, it's not so easy to capture all of that power. EPRI, an independent, nonprofit organization that conducts research on the electric power industry, analyzed how much of that energy was technically recoverable with the state of design science today. Wave power is not a widely deployed commercial technology today, although there are some commercial prototype wave energy conversion devices deployed. They work by various methods, including floats or buoy systems that use the rise and fall of ocean swells to drive hydraulic pumps. These devices won't work if the waves are too intense nor if they are too mild, and they need to be optimized for the location where they are being deployed. In other words, the wave energy converters that would work best off Alaska would be different—optimized to capture stronger waves—than devices that would work best off the coast of Georgia.
Taking the limitations of the technology into account, EPRI's scientists concluded that only about 29 percent of the wave energy of the outer continental shelf and 46 percent of the wave energy of the inner continental shelf of Alaska is technically recoverable. In contrast, on the southern U.S. East Coast, about 67 percent of the wave energy on the inner shelf and 78 percent on the outer shelf could be captured with current technology. Even so, Alaska's wave resource is so vast that the technically recoverable energy is gauged to be 15 times greater than that off the south Atlantic coast.
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But what is technically recoverable is not necessarily what is "practically" recoverable, points out Paul Jacobson, waterpower program manager for EPRI. Many areas will be off limits to future wave energy projects, whether due to shipping lanes, fishing areas, or environmentally sensitive or protected stretches of the ocean where marine life could be disrupted by wave energy devices or their moorings.
Also important: How practical will it be to get power from the ocean to people by submerging and installing transmission lines?
That's why the United States confronts an irony as it contemplates drawing future energy from the seas. Its greatest ocean wave resource is swelling and breaking off the coast of its least densely populated state.
Published March 8, 2012
Wildfire: Energy That’s Tough To Control
Photograph by Jonathan Blair, Corbis
Smoke and flames enveloped Yellowstone National Park in 1988. A number of smaller fires merged into flames that burned or partially burned about 800,000 acres, affecting more than one third of the park and closing portions from visitors at times.
That much destruction involves massive energy—about 77.9 billion megajoules over the fire's life of 71 days, according to a calculation by Bob Kremens, a research associate professor at the Rochester Institute of Technology who studies wildfires.
That's 22 million megawatt-hours, as much as all of the electricity generated in all of California and Oregon over the course of a month.
Kremens worked in cooperation with the Missoula Fire Sciences Laboratory, a part of the U.S. Forest Service's Research and Development branch., which has developed data and formulas for calculating rates of spread and energy released in forest fires.
The lab has studied and mapped the nation's wild lands, their ecology, and their relationships to wildland fire, as well as their potential to burn. Scientists also conduct experiments to measure the energy produced by burning different types of vegetation and other fuels, using the world's largest suite of controlled wind tunnels and burn chamber, says Colin Hardy, the lab's program manager.
The data help guide "fire behavior analysts" who, as part of efforts to contain wild land fires, project how fast and in what direction they might burn, and what resources are at risk. The same data contribute to the rating system that alerts land managers and visitors to the local risk of forest fires with Smokey Bear signs and colors from green (low) to red (high).
Published March 8, 2012
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