News in Science

Sprites may play role in Earth's climate

Elusive lightning 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 rumours of them," says geophysicist Dr 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."

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.

Their research was presented at the American Geophysical Union conference currently under way in San Francisco.

Using high-speed cameras mounted in two aeroplanes, 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, says 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," says Stenbaek-Nielson. "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 have global implications."

Affecting the Earth's atmosphere

"It may play an important role in solar activity and climate," says Professor Yukihiro Takahasi, a researcher 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," says Dr Geoffrey McHarg, director of the US 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."