Using a Sony digital camera on the roof of a laboratory at the Arecibo Observatory in Puerto Rico, researchers documented a strange instance of a thunderstorm's electricity tickling the fringes of outer space.
The scientists captured on film a phenomenon known as a blue jet, a lightning-like discharge, as it shot out the top of clouds in an offshore storm.
Other blue jets have been photographed. But this one soared twice as high as any previously recorded, nearly 50 miles (80 kilometers) above Earth. There, the electrical discharge apparently interacted with the base of the ionosphere, a region of the atmosphere where electrons roam freely after being split up by solar energy.
The finding supports a long-held suspicion that electricity makes its way from Earth all the way to the ionosphere during thunderstorms. Scientists knew that while Earth's surface packs a negative charge, the ionosphere is positive. The difference is 300,000 volts.
"Each thunderstorm acts like a battery," generating new electricity, explained Victor P. Pasko, a Penn State electrical engineer who led the study.
While one observation does not prove an Earth-to-space connection, Pasko told SPACE.com the blue jet involved a negative charge moving upward, and he suspects blue jets provide the circuit during a thunderstorm to get electricity from one "shell" to another -- Earth's surface to the base of the ionosphere.
Blue jets last less than a second. This one was observed last September above a thunderstorm that was about 125 miles out to sea. It began about 10 miles up, at the cloud tops, and branched out to develop into a cone-shaped structure something like a narrow oak tree.
Near the ionosphere, the blue jet developed hot spots and a fuzzy, diffused appearance, something not seen before.
Pasko said the newly observed aspects of the phenomenon may be confined to the tropics, which he said seem conducive to connecting Earth electrically to the ionosphere. More work will be needed to verify that, he said.
Images of the event are an eerie green due to the night-vision technology used to capture them. But the scientists say they distinctly saw, with their eyes, a characteristic blue flash. A false-color image, made to be blue, was designed to grace the cover of the March 14 issue of the journal Nature, where the results are published.
Reports of blue jets, and their cousins called red sprites, go back centuries. More recently, airline pilots reported seeing them. But scientists did not confirm their existence until 1989.
Pasko's colleagues included Penn State's John Mathews, Mark Stanley of New Mexico Tech, and Stanford's Troy Wood and Umran Inan. For Inan, it is not the first instance of monitoring a thunderstorm's interaction with space.
In separate research in 1999, Inan showed that lightning also generates "whistler waves," which streak thousands of miles above Earth's atmosphere into the magnetosphere. There, in space, the waves jiggle electrons into new paths, causing some to rain down on the planet thousands of miles away.
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