What Happens When Lightning Strikes?
By Lee Dye, ABC News - Feb 20, 2013
By Lee Dye, ABC News - Feb 20, 2013
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.
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."
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.
Dwyer and his colleagues set up sensors near the launch tower to see if they could capture high-energy radiation generated by lightning. It didn't take long to get results. The lightning did indeed produce high-energy radiation, either a powerful burst of X-rays, or possibly a single gamma ray, but the scientists don't know yet which. New sensors are being built to tackle that problem this summer. Of course, that will still leave the question of why a bolt of lightning should produce these intense, though short-lived, bursts of radiation.
The most likely explanation, Dwyer says, is that contrary to theory, the electric field that accompanies lightning is far more powerful than had been thought. It may be so powerful, in fact, that electrons are accelerated to nearly the speed of light, thus creating high-energy radiation whenever they strike an air molecule. Whatever the explanation, "there's something going on here that we don't understand, and we obviously need to figure it out," Dwyer says.
Meanwhile, in Arizona, researchers didn't need a rocket to figure out what was going on during their dazzling electrical storms. Two video cameras were put on top of a five-story building on the Tucson campus of the University of Arizona and recorded 386 lighting flashes. The recordings were made during the summer of 1997, but the results have only recently been announced in the Journal of Geophysical Research. By analyzing the tapes, the scientists found that 136 of the 386 thunderbolts, or 35 percent, struck in two or more places.
Krider and Valine figure that means someone on the ground has a lot better chance of getting struck by lightning because one bolt can get him or her in two, or even more, locations. Experts had thought that if you were two to three miles away from a previous flash, you were probably safe. But that has been changed to six to eight miles because the research shows lightning can strike twice, thus widening the danger zone. It might seem odd that it's taken so long to figure that out, but as Dwyer says, lightning happens so quickly that "it's all over in a flash."
At this point, it's not entirely clear where his research is leading. It's basic research, and in the end there may not be any practical applications. The X-rays, or gamma rays, that his sensors have detected aren't what will kill you if you get hit by lighting. They're over in a few milliseconds, so compared to the enormous electric charge and intense heat carried by lightning, they may prove insignificant. But maybe not.
"There's a lot of fundamental science questions that we are trying to answer here," he says. "Maybe some day there will be some applications that come out of it." At the least the research should enhance our understanding of one of the most dramatic events in nature.
Lee Dye's column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.