Gamma ray and x-ray bursts may be associated with lightning Credit: © GettyImages

The conventional view of how lightning is produced is wrong, according to a Florida-based physicist.

Electrical fields in the atmosphere simply cannot grow large enough to trigger lightning, calculates Joseph Dwyer of the Florida Institute of Technology in Melbourne1. "This means back to the drawing board," he says.

Dwyer mainly studies high-energy particles in space. But two years ago, after moving to central Florida, one of the most lightning-prone areas of the world, he became intrigued by reports of huge gamma-ray and X-ray bursts associated with lightning. Such high-energy radiation tends to be seen only in outer space, as moving through Earth's atmosphere slows it down.

Most scientists believe lightning is generated when a giant electric field builds up in the atmosphere. Although no one has actually seen such a field, researchers assumed that this was simply because they hadn't looked hard enough.

When Dwyer factored the production of high-energy radiation into a model describing the build-up of electrical fields in thunderstorms, he got a shock. He found that the release of gamma-rays and X-rays diffuses the electric field, preventing it from becoming large enough to spark lightning.

"This may be a significant theoretical breakthrough," says Martin Uman who studies lightning at the University of Florida in Gainesville. "It shows how large doses of x-rays and gamma rays can be formed in small volumes," he says.

The true origin of lightning remains a mystery. Dwyer suspects that the same process that limits fields could actually concentrate charge in some areas just long enough to trigger lightning.

Limiting factor

Electric fields grow inside thunderstorms when updrafts and downdrafts push water molecules past each other causing them to shed electrons. These electrons can eventually overcome the drag associated with travelling through air and speed up. "Some electrons accelerate to close to the speed of light," says Dwyer.

This may be a significant theoretical breakthrough Martin Uman , University of Florida

According to his model, these high-speed electrons bump into other particles, knocking off more electrons until a burst of gamma or X-rays releases the energy from the electric field, reducing its charge. "This really is a fundamental limit on how much voltage can exist in electric fields," says Dwyer.