An anonymous reader shares a report: Scientists in India observed the highest-voltage thunderstorm ever documented with the help of a subatomic particle you might not hear much about: the muon. The researchers operate the GRAPES-3 telescope, which measures muons, particles that are similar to electrons but heavier. Specifically, the Gamma Ray Astronomy at PeV EnergieS Phase-3 (GRAPES-3) muon telescope measures high-energy particles from outer space called cosmic rays. It typically picks up 2.5 million muons each minute, mapped on a 13-by-13 grid across the sky. But during thunderstorms, it experiences quick changes to the amount of muons it receives. The GRAPES-3 researchers added electric field monitors to the experiment, and devised a way to turn these muon fluctuations into measurements of the voltage of passing storms.
A storm on December 1, 2014, led to a relatively enormous 2 percent decrease in the amount of muons that the experiment received. According to their methods, published in Physical Review Letters, this would be equivalent to a 1.3-billion-volt electric potential in the thunderhead. This doesn’t refer to a single lightning bolt, but rather the strength of the electric field caused by positively charged water molecules carried by convection to the top of the cloud while negatively charged ice remains lower down. For comparison, most lightning bolts have 100 million volts of electric potential between their ends. Subway tracks carry less than 1,000 volts.