![]() But the results suggest that lightning is one of the most powerful natural particle accelerators that Earth-bound physicists can access. Most researchers in the community would have previously been skeptical that ultra-powerful cosmic rays could be affected by comparatively mundane lightning, he adds. “It’s an application that nobody has thought of before,” says Michael Cherry, who studies high-energy cosmic rays and gamma rays at Louisiana State University in Baton Rouge and was not involved in the recent work. “Because that’s what causes most of the damage.”įor now, the existing measurements have already impressed other researchers. “We want to look for the discharge,” he says. They would also like to study how quickly the voltage in a thunderstorm is dissipated through lightning strikes. Gupta says the team would like to include a gamma-ray detector in their instruments in future to help solidify the connection. Now, GRAPES-3’s gigavolt measurements are the first to suggest that such storms contain enough power to produce this enigmatic effect. ( Find out how thunderstorms can shoot antimatter into space.) ![]() Though lightning had been suspected to play a role, the thundercloud energies observed in previous experiments were not great enough to explain the terrestrial gamma-ray flashes. Nobody has since been able to give a full explanation for why our planet should produce events similar to some of the most powerful phenomena in the cosmos. In 1994, NASA’s Compton Gamma Ray Observatory, which was built to monitor powerful flashes of light occurring in distant galaxies called gamma-ray bursts, noticed a few high-energy eruptions coming from Earth’s atmosphere. This, in turn, might illuminate the origins of a long-standing head scratcher in atmospheric physics. That means prior data likely delivered underestimates, and many thunderstorms should have billions of volts of energy inside them. “But nature seems to know how to do it almost effortlessly.” Dangerous dischargeīecause the muon-based measurements can see large areas of the clouds, they are more accurate than plane- or balloon-borne experiments. “To achieve such high voltages on the ground is almost impossible,” he adds. That’s enough energy to run all of New York City for half an hour, Gupta says. The muons indicated that one particular leviathan, which appeared on December 1, 2014, briefly contained an electric potential of nearly 1.8 gigavolts. In the GRAPES-3 data, the researchers saw the electrical effects of 184 thunderstorms over the course of three years. ![]() Working backward, the team could then use their muon observations to estimate the electric field inside the clouds above the experiment. Study coauthor Balakrishnan Hariharan devised a model that determined how powerful an electric field would need to be to alter the number of muons detected in GRAPES-3. Airplane and balloon experiments, which have flown through thunderstorms taking readings at various locations, found electric potentials of tens of millions of volts, with the largest previously recorded event having 130 million volts. This implied that the storms, which can stretch for miles, should have enormous total electric potentials of around a gigavolt, or the equivalent of nearly a billion AA batteries.īut measuring voltage across an object usually requires placing two wires at either end, and nobody had figured out how to do that for a large and amorphous thing like a cloud. ![]() Gupta wondered if that property could be used to calculate how much energy the thunderclouds contained.īack in 1929, Nobel prize-winning physicist Charles Thomson Rees Wilson measured the electric field inside a thundercloud and found it to be a surprisingly large 12,700 volts per inch. Muons carry negative charge, meaning their paths are distorted by electric fields. “We were studying high-energy cosmic rays and interplanetary space, and not so much the thunderstorms.” Packing a punch “This was more of an amusing episode for us than anything serious,” says study coauthor Sunil Gupta, a high-energy physicist at the Tata Institute of Fundamental Research in Mumbai, India, whose team described their work last month in Physical Review Letters. ![]()
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