March 6, 2006—Snapping 5,000 frames per second, a high-speed camera has captured the best images ever of elusive sprites, flashes of light associated with intense thunderstorms.

The findings, published by Steven Cummer of Duke University and his team in a recent online edition of Geophysical Research Letters, show how sprites develop.

They could also help scientists get a better handle on the chemical make up of the upper atmosphere, a region that is too high to analyze with planes and too low for satellites.

"They substantially improved the time resolution of the observation of sprite events," said Victor Pasko, associate professor of electrical engineering at the Pennsylvania State University.

"That immediately brought some very interesting results in comparison to previous studies," said Pasko, who is not involved in the research.

To date, the fastest images ever taken of sprites have been at a speed of 1,000 frames per second. From those and previous studies, scientists had some insights into these so-called transient luminous events that burst and fade out faster than the blink of a human eye.

For example, they knew that sprites occurred 20 to 50 miles above powerful thunderstorms; that they happened after unusually strong lightning strikes; that they had a branching structure; and that they were often characterized by intense bright spots that persisted seconds after the sprite disappeared.

Cummer and his team rented a camera typically used to film such high-speed action as crash tests, rocket launches, and explosions. They turned its lens on several thunderstorms in Fort Collins, Colo., over a six-week period in the summer of 2005.

Team members watched monitors that displayed live video from the conventional cameras. When intense lighting flashes indicative of sprites occurred, a scientist would press a trigger that remotely opened the shutter on the high-speed camera.

After reviewing the images, the scientists determined what caused about half of the bright spots.

According to Cummer, the tips of some of the branches of some of the sprites are attracted by electromagnetic forces to the channels left behind by branching that occurred just milliseconds earlier.

The intense brightness indicates some kind of interesting chemistry that is still unknown.

"And because we can't get to that region (of the atmosphere), the only way we have to say anything reasonable is to take those processes and translate them into models," said Cummer.

Such models might tell scientists whether the chemical reactions occurring 50 miles above the earth could be having an effect on chemicals in the atmosphere much closer to Earth's surface.

"If the streamers are changing ozone concentrations in the atmosphere, there might be some long term effects," said Pasko.

To know for sure could require an even faster camera, said Pasko, one that can capture 25,000 to 50,000 frames per second.