Scientists have discovered a startling secret in the sky: gigantic jets of lightning that shoot upward from cloud tops to nearly 60 miles into the upper atmosphere.
Unlike the familiar lightning bolts, these brilliant jets spread out in extremely thin air to form shapes resembling giant trees or carrots some 50 miles tall, according to a study by researchers in Taiwan.
"These things are so spectacular, and so startling, and we're just finding it this late in the game,'' said Walt Lyons of FMA Research in Fort Collins, Colo., an atmospheric scientist who specializes in lightning research.
"It's sort of like biologists announcing we've discovered a new human body part,'' Lyons said. ``We thought we knew everything that was up there and, lo and behold, we don't.''
The study, led by Han-Tzong Su of the National Cheng Kung University in Taiwan, used low-light cameras on the southern tip of the island to capture images of five gigantic lightning jets streaming upward from thunder clouds over the South China Sea in July 2002.
The enormous jets typically disappear in less than a second and are very difficult to see with the naked eye, researchers said.
The study, which appears Thursday in the journal Nature, also found that four jets generated extremely low frequency radio waves that could interfere with global radio communications, said Victor Pasko, a Penn State electrical engineer.
"So we know now that these kinds of events can produce some perturbation in those radio signals,'' said Pasko, who wrote a Nature commentary on the study.
In the 1990s, Pasko documented another form of lightning, blue jets, that also stream upward but do not reach as high or spread out as far as the jets reported in the new study.
Still another form of high-altitude lightning, called sprites, were discovered in 1989. Unlike the newly reported jets, sprites travel downward toward clouds and do not stretch as far, averaging about 25 to 30 miles before they dissipate far above the cloud tops, according to Umran Inan of Stanford University, who was not part of the latest study.
"Unlike sprites, these lightning jets the Taiwan group observed are more intense and show a clear connectivity between thunder clouds and the far upper atmosphere,'' Inan said.
Scientists had found plenty of evidence of sprites in the 1990s, but the larger, upward streaming lightning jets had escaped detection _ possibly because they may only occur over oceans, Inan said.
The various forms of high-altitude lightning are not expected to pose any danger to aircraft because they spread out over such a wide area of the upper atmosphere, called the ionosphere, researchers said. Since space shuttles travel through the ionosphere, Lyons said NASA might do well to study these phenomena, although they probably pose little threat to spacecraft.
While no studies have been done to see if the various forms of high-altitude lightning affect the chemistry of the upper atmosphere, scientists suspect they may play a role in ozone formation.
Researchers said the discovery of the new form of high-altitude lightning jets will change computer models of the atmosphere. It also may help military satellites avoid confusing manmade explosions with natural phenomena.
"There are issues like, are certain sensors in space being fooled by this?" Lyons said.
