Elusive blue jet is caught on tape

Natural phenomenon thought to be electrical bridge to ionosphere

`This is amazing,' scientist says

March 24, 2002|By Bryn Nelson | Bryn Nelson,SPECIAL TO THE SUN

Scientists have recorded the clearest video image yet of the elusive blue jet, a spectacular flash sometimes observed zipping above thunderstorm clouds by airline passengers and pilots.

This brilliant phenomenon, scientists say, may provide a previously unrecognized electrical bridge between clouds and the charged layer of the upper atmosphere, or ionosphere.

After studying the phenomenon for seven years, Pennsylvania State University electrical engineer Victor Pasko said he was "very excited" finally to see one with his own eyes from the roof of an observatory in Puerto Rico in September.

"This is amazing, actually," he said. "To see it even from 200 kilometers [124 miles] away, it looked really like a gigantic event happening in front of us. The scale is enormous."

Half-second flash

Pasko and his research team used high-speed, low-light cameras to capture the fleeting image above a small thunderstorm system off the Puerto Rican coast.

Lasting a mere half-second, the flash extended upward and branched out like a tree before dissipating as it reached the ionosphere, 44 to 50 miles above the ground.

The highest altitude previously attributed to such a phenomenon was only half that distance.

Pasko said Earth and the ionosphere act like oppositely charged electrodes separated from each other by the weakly conducting atmosphere.

The net difference in electrical charge, some 300,000 volts, represents what is known as the potential difference.

"People believe that thunderstorms act as batteries to support these potential differences," Pasko said, by discharging large amounts of electrical energy.

Studies have estimated that as many as 40 or 50 typical flashes of lightning, from clouds to the ground, occur around the world every second.

But electrical phenomena above the clouds have proven far more elusive for scientific observation. Mushroom-shaped red sprites, for example, often appear in the upper atmosphere milliseconds after a lightning flash, but have been documented scientifically only since 1989.

The science of blue jets is newer yet, with the first scientific observation in 1994.

Starting in thunderclouds

Blue jets initiate from an electrical current shooting out of thunderclouds, ionizing molecules in the atmosphere and making them glow. The bluish color of a jet comes from ionized nitrogen molecules.

Gene Wescott, a professor emeritus of geophysics at the University of Alaska at Fairbanks who recorded the first blue jet observation, said the discharge of energy aids the formation of nitrogen-based chemicals.

Some of these chemicals may in turn interact with the ozone layer that shields Earth from ultraviolet radiation.

"It's probably been going on for billions of years," he said, "but nobody's known about it or paid much attention to it."

In the new study, published in a recent issue of the journal Nature, Pasko and his co-authors speculate that blue jets could prove more common than previously thought and thus also constitute a significant part of the global electric circuit by helping to bridge the gap between thunderclouds and the ionosphere.

Bryn Nelson is a reporter for Newsday, a Tribune Publishing newspaper.

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