Near-Space Lightning May Play Role in Climate

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A sprite captured on video over a thunderstorm above the U.S. midwest on July 3, 1995. The top of the sprite is 280,000 feet (85 km) above the Earth.
Geophysical Institute, University of Alaska Fairbanks

THE GIST

— Super-fast, extremely bright lightning in the upper-atmosphere may be impacting climate.

— Research shows the flashes, known as sprites, end in streamers that seem to connect directly to the lower atmosphere.

— Sprites radiate most of their visible light in deep red, which the human eye is not very sensitive to.

For the longest time, scientists didn't even know that extremely bright, split-second bursts of lightning called sprites were happening in Earth's upper atmosphere.

"There were some rumors of them," said geophysicist Hans Stenbaek-Nielson, with the University of Alaska in Fairbanks. "Pilots had seen them, but back in the early '90s no pilot was willing to acknowledge that they saw something up there because that would result (in questions about) their mental state."

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Now scientists not only know sprites exist, they've caught them and a host of related phenomena flashing in the skies above the Midwestern United States this summer.

Using high-speed cameras mounted in two airplanes, researchers were able to get the first three-dimensional views of sprites, which last for about 10 milliseconds and disappear.

What sprites lack in staying-power, they make up for in brightness. The flashes, which are associated with parent lightning storms lower in the atmosphere, momentarily will outshine Venus, the third brightest object in the sky after the sun and moon, said Stenbaek-Nielson.

Most of sprites' visible energy radiates in deep red, which is not particularly visible to the human eye. But the impacts of sprites could be far-reaching. Sprites trigger secondary lightning events known as streamers which appear to connect directly to the lower atmosphere.

"We don't understand what's going on here," Stenbaek-Nielson said. "When you look at sprites, there's a lot of energy involved and there may be actual contact between the low-level cloud cover in the atmosphere, which would would have global implications."

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"It may play an important role in solar activity and climate," added Yukihiro Takahasi, a professor at the Department of Cosmosciences at Japan's Hokkaido University.

Aside from impacting the motion of air, sprites have enough energy to trigger chemical changes in the atmosphere, such as the production of ozone-eating nitrogen oxides.

"Traditionally, the weather here on the ground has been thought to be separated physically from the weather going on in space," said Geoffrey McHarg, director of the U.S. Air Force's Space Physics and Atmospheric Research Center in Colorado. "It turns out that there might be something fundamental different going on in the middle."

The research was presented at the American Geophysical Union conference under way in San Francisco this week.