What Happens When Lightning Strikes?

There are few things in nature more awe inspiring that an intense electrical storm, complete with flashes of lightning so brilliant they can turn the night into day.

But those spectacular fireballs from Thor can also kill, claiming an average of 93 deaths and 300 injuries per year, according to the National Weather Service.

Considering the fact that lightning is one of the biggest weather-related killers in the country, it's a bit surprising that we are still rather ignorant about how it works.

Scientists have recently made new discoveries that should toss some long-held ideas out the window.

Multiple Strikes

In Florida, for example, a team of scientists led by Joe Dwyer, an assistant professor of physics at the Florida Institute of Technology, has found that lightning produces high-energy radiation, probably X-rays or gamma rays, despite the fact that most textbooks say that shouldn't be the case.

And across the country, atmospheric scientists William C. Valine and Philip Krider of the University of Arizona have found that one bolt of lightning frequently splits into separate strikes, hitting the ground in more than one place almost simultaneously. They say that means the odds of getting hit by a single bolt of lightning are probably 45 percent higher than had been thought because many thunderbolts hit in more than one place.

Dwyer's findings, reported in a recent issue of the journal Science, are especially significant because they fly in the face of conventional wisdom. It takes an extremely violent event, or an intensely powerful electric field, to produce high-energy radiation like X-rays or gamma rays, and few experts believed that lightning could provide either of those conditions, at least not close to the ground.

But that's just what the research shows.

"We got really big, obvious signals," says Dwyer, whose work is supported by a five year grant from the National Science Foundation. "In fact, the signals were so big and so obvious that it was a bit surprising to me."

That's partly because "almost all the current theories of how lightning works do not include this," he says. So those theories, he adds, "probably need to be revisited."

Homemade Lightning

To carry out his research Dwyer teamed up with scientists at the University of Florida and the International Center for Lightning Research and Testing at Camp Blanding, Fla. The center routinely launches small rockets into the thunderclouds that drift over Florida during the humid summer months to trigger lightning strikes for research purposes.

The rockets carry a large spool of copper wire which remains attached to the launch tower. As the rocket goes up, the wire continues to unspool, creating a direct link between the rocket, as it pierces the cloud, and the ground.

The copper wire soon vaporizes because of the high temperature of electric current that travels up from the ground to the cloud. That process creates a "conducting channel" for lightning.

If the conditions are just right, lightning in the form of a "dark leader" travels down the channel and strikes the launch tower. That is matched by a return strike traveling from the tower to the thundercloud, and that's the brilliant flash that can be seen during an electrical storm.

Although this is triggered lightning, it is identical to natural lightning, Dwyer says.

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