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"Maps" Help Reveal How Lightning Strikes

Craig Miller
National Geographic Channel
September 25, 2002
 
During the late New Mexico summer and early fall, afternoon clouds gather over the mountain peaks. The rising desert heat pushes them into vertical towers until they burst forth into storms that produce fleeting, torrential rains, flash floods and remarkable displays of lightning. This is when Bill Rison, a lightning researcher, heads for the hills.

For the past 18 years Rison, a professor of electrical engineering at New Mexico Tech, Socorro, has been chasing his elusive subject as part of the lightning research team.



"There is much that we still don't know about lightning," says Rison. "We just don't understand what it is that initiates lightning in thunderstorms." Lightning also occurs without thunderstorms, adds Rison, such as during volcanic eruptions and in the smoke-laden air above wildfires.

High-speed video reveals that lightning begins with a dim light coming down from the cloud, then when the light has almost reached the ground a luminous spark seems to travel from the ground up. "We have no idea what features on the ground initiate the 'spark' that causes lightning to strike at that particular spot."

Researchers also do not know what causes the jagged structure of lightning.

Lightning Fatalities

The almost daily light shows above New Mexico are as dangerous as they are dazzling. Per capita, the state has the highest incidence of lightning fatalities in the nation. Highway workers are especially vulnerable.

But Patricia Stribling wasn't paving a highway. She had just come out of the Post Office in Corrales, on a spring day in 1986, and returned to her car, which was parked right next to the flagpole.

"Then, just all of a sudden was…this light that was like being in an arc welder's light and…this horrendous sound," says Patricia Stribling.

Stribling was probably caught in the periphery of a bolt that hit the aluminum flagpole. She'll never be certain exactly what happened. "But mostly I remember that light because I had seen arc welder light and it was the most blue, white intense light that I'd ever seen," she said.

Rison has seen that light many times over the years and aspects of it remain mysterious, even to the experts. After 45 years, Rison's colleague Charles Moore is still surprised by new findings.

"The more you know, the more loose ends you find," says Moore, an emeritus professor of atmospheric physics at New Mexico Tech. Within the last year, the team found that the leader coming down from a thundercloud radiates x-rays.

Lightning Mapping

One piece of knowledge that still eludes scientists is one of the most basic: how storm clouds become electrically charged in the first place.

Seeking the answer, Rison climbs high into the Magdalena Mountains, where New Mexico Tech maintains one of the world's premier lightning research facilities, Langmuir Lab. At 11,000 feet, it's right where the action is.

"We can put our instruments right on top of the mountain, knowing that the storm should be formed there, so we can study a thunderstorm from its birth, through its mature stages, to its death," says Rison.

What Rison is doing is called lightning "mapping" and it is done by strategically placing an array of detectors on the mountain around Langmuir.

The detectors that make up the mapping array pick up radio impulses given off by lightning. Those impulses are picked up by an antenna, and travel through a cable to a recorder.

Using computer imaging, Rison and his colleagues at Langmuir can translate the array data into moving images that show the anatomy of a strike.

Bolt from the Blue

The mapping may help to explain some of lightning's most bizarre behavior. Tracking one bolt on the monitor, it seems to be a typical cloud-to-cloud discharge. But then, something startling happens: It abruptly changes direction and arcs upward and outward, striking the ground miles from where it began. Lightning researchers call this a "bolt from the blue," which, scientists are discovering, are not all that rare.

It seems possible that just such a bolt "from the blue" struck Patricia Stribling.

"It wasn't a stormy day," says Stribling, "it was in May, drizzly, overcast—it wasn't a day that you'd think there'd be lightning."

Stribling's only visible injury was a mild burn on the top of her head. And though she now has an acute sensitivity to light that she can't explain, she's lucky to be alive.

"You really do need to be careful when there's a thunderstorm in the area, even five or ten miles away—the lightning can travel that far from the center of a storm and come to ground where you may be," says Rison.
 

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