Thunderstorms can reach voltages ten times greater than those previously recorded, a new measurement suggests.

Sunil Gupta at the Tata Institute of Fundamental Research in Mumbai, India, and his colleagues used an instrument called a muon telescope to measure storms’ electric potential — the voltage between the top and bottom of a thundercloud.

Muon particles are generated when cosmic rays smash into Earth’s atmosphere. As muons cross a storm’s electric potential, they lose energy, which causes some of the particles to fall below a muon telescope’s detection threshold. A storm with a higher voltage causes each muon traversing it to experience a greater energy drop. This means that a telescope’s detector sees a lower rate of incoming muons when storm voltage is greater.

Gupta’s team used the GRAPES-3 facility in Ooty, India, to record muons as they reached the ground during 184 thunderstorms. Using computer simulations, the researchers estimated that the electric potential of one storm in 2014 reached 1.3 billion volts, the largest value ever recorded.

This observation might explain the flashes of highly energetic γ-ray radiation observed during storms; scientists have theorized that only extreme voltages can produce such flashes.