A thunderhead (not the one measured in this study) seen from the International Space Station over the Senegal-Mali border. Photo : NASA/ISS 16 ( Wikimedia Commons

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 o n 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 t he 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.




That voltage measurement i s 10 times higher than the previous most powerful observed storm on Earth. Storms with these strengths may be behind some of the other high-energy phenomena we’ve covered, like terrestrial gamma-ray flashes.

It’s important to point out that models aren’t always accurate , and require human assumptions. Michael Cherry, p hysics professor at Louisiana State University in Baton Rouge, told the science publication Physics that it was a unique but indirect way to measure the electric fields in thunderstorms, and the assumptions used in the analysis might not apply to every storm. He suggested that balloons or drones could be used to make measurements that refine the model.

But this mega measurement could help explain an important mystery. We’ve reported that satellites have measured terrestrial gamma ray flashes, or bolts of gamma rays. It’s assumed that storms cause these TGFs, but there haven’t been thunderstorms on record strong enough to generate the gamma rays observed by experiments like the AGILE satellite. But 1.3 billion volts would certainly be strong enough.

Provided the model is accurate, this would be the largest voltage ever measured in a thundercloud. And if the cloud were to discharge that electricity near you , well, you’d die in more ways than one.

