When Benjamin Franklin tied a key to a kite and flew it into a lightning storm, he briefly became an appliance plugged into the strongest power generator on Earth.
Franklin knew, as most people do, that thunderstorms are incredibly powerful. Researchers have tried to estimate precisely how powerful for more than a century, but have always come up short — even the most sophisticated airborne sensors are inadequate because thunderclouds are just too big and unpredictable to measure.
Now, in a paper published Mar. 15 in the journal Physical Review Letters, researchers in Ooty, India, have come up with a shocking new answer — thanks to a little help from some cosmic rays. [Electric Earth: Stunning Images of Lightning]
Using an array of sensors designed to measure electric fields and the intensity of muons — heavy particles that constantly rain down from Earth's upper atmosphere, decaying as they pass through matter — the team measured the voltage of a large thundercloud that rolled over Ooty for 18 minutes on Dec. 1, 2014. The researchers found that, on average, the cloud was charged with about 1.3 gigavolts of electricity, which is 1.3 times 10^9 volts — roughly 10 million times more voltage than is supplied by a typical power outlet in North America.
"This explains why thunderclouds are so destructive," study co-author Sunil Gupta, a cosmic ray researcher at India's Tata Institute of Fundamental Research, told Live Science. "If you dissipate this massive amount of energy through anything, it is going to cause severe devastation."
It's raining muons
Gupta and his colleagues primarily study muons — electron-like particles that are created when cosmic rays bash into various atoms in Earth's atmosphere. These particles have about half the spin of electrons but 200 times the weight, and are very good at penetrating matter. A muon raining down from the atmosphere can travel deep into the ocean or miles underground in just a fraction of a second, as long as it has enough energy.
Muons lose their energy when something gets in their way — say, a pyramid, for example. In early 2018, scientists discovered two previously unknown chambers inside the Great Pyramid of Giza by setting up muon detectors around the structure and measuring where the particles lost (and didn't lose) energy. Muons passing through the pyramid's stone walls lost more energy than muons passing through the large, empty chambers. The results allowed the researchers to create a new map of the pyramid's interior without setting foot inside of it.
Gupta and his colleagues used a similar method to map the energy inside the Ooty thundercloud. Instead of contending with stone, however, muons falling through the cloud faced a turbulent electric field.
"Thunderstorms have a positively charged layer on top and a negatively charged layer on bottom," Gupta said. "If a positively charged muon hits the cloud as it rains down from the upper atmosphere, it's going to be repelled and lose energy." [Infographic: How Lightning Works]
Using an array of muon-detecting sensors and four electric field monitors spread over several miles, the researchers measured the average drop in energy between muons that passed through the thundercloud and those that didn't pass through it. From this energy loss, the team was able to calculate how much electric potential the particles had passed through in the thunder cloud.
It was massive.
"Scientists estimated that thunderclouds could have gigavolt potential in the 1920s," Gupta said, "But it was never proven — until now."
Mapping the thunder
Once the researchers knew the cloud's electric potential, they wanted to go a step further and measure precisely how much power the thundercloud carried as it roared over Ooty.
Using the data from their widely dispersed electric field monitors, the team filled in some important details about the cloud — that is was traveling at roughly 40 mph (60 km/h) at an altitude of 7 miles (11.4 kilometers) above sea level, had an estimated area of 146 square miles (380 square km, an area about six times the size of Manhattan), and reached its maximum electrical potential just 6 minutes after appearing.
Armed with this knowledge, the researchers were finally able to calculate that the thunderstorm carried about 2 gigawatts of power, making this single cloud more powerful than the most powerful nuclear power plants in the world, Gupta said.
"The amount of energy stored here is enough to supply all the power needs of a city like New York City for 26 minutes," Gupta said. "If you could harness it."
With current technology, that's an unlikely prospect, Gupta noted: The amount of energy dissipated by such a storm is so high that it would probably melt any conductor.
Still, the violently powerful potential of thunderstorms could help settle a cosmic mystery that scientists like Gupta and his colleagues have asked for decades: Why do satellites sometimes detect high-energy gamma rays blasting out of Earth's atmosphere, when they should be raining down from space?
According to Gupta, if thunderstorms can indeed create an electric potential greater than one gigavolt, they could also accelerate electrons quickly enough to break apart other atoms in the atmosphere, producing gamma-ray flashes.
This explanation requires more research to verify its accuracy, Gupta said. In the meantime, be sure to marvel at the next thundercloud you see, for it is an unfathomably mighty force of nature — and, please, think twice before flying a kite.
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Originally published on Live Science.
