Elusive beasts dance high in the night sky.

Once considered a sleepy part of the sky, the middle atmosphere has recently gained a reputation as the home of Earth's most exotic fireworks. Peering high above the tops of thunderstorms, researchers are discovering new forms of lightning that flash red and blue in the shapes of giant jellyfish, carrots, doughnuts, and trumpets.

Though rumors of lofty lights had circulated for years among pilots and weather watchers, atmospheric scientists first observed these flares in the early 1990s. This summer, 50 researchers from the United States, Japan, and New Zealand gathered at mountaintop observation stations in the Rocky Mountains to capture the most detailed pictures yet of the electric beasts. The scientists unveiled their results this week at a meeting of the American Geophysical Union in San Francisco.

The recent discoveries have electrified a formerly quiet, obscure branch of atmospheric physics. "Four or 5 years ago, I would go to [these] sessions, and there were maybe 10 people in the audience at most. Within the last 2 years, these meetings have become packed, and it's getting worse and worse," says Robert Roussel-Dupre of Los Alamos (N.M.) National Laboratory.

Whereas normal lightning streaks through the lower atmosphere, the high-altitude flares occur in the stratosphere and mesosphere-from 17 to 105 kilometers above ground. Because they lie above storm clouds, the flares are normally hidden from people directly beneath them. Adding to their reclusive nature, these flickerings last for just a few thousandths of a second. Lower-altitude lightning can persist for seconds (SN: 12/23&30/95, p. 421).

Like biologists tracking new animal species on an uncharted island, atmospheric researchers are still simply trying to document the various phenomena above clouds. They have identified three categories. Bloodred features known as sprites appear between 50 and 90 km in altitude and can last long enough to be seen by observers to the side of a storm. Doughnutlike bursts called elves, which often occur with sprites, flicker for less than a millisecond at 85 to 105 km. Indirect evidence suggests that they are red. The rarest and lowest flashes, called blue jets, shoot from the tops of storms and flare out like the bell of a trumpet.

From a station on Yucca Ridge, Colo., scientists this summer detected 1,127 sprites and elves during 21 nights of watching storms brew on the high plains, reports Walter A. Lyons of Forensic Meteorology Associates. Lyons' home on the ridge served as the central research facility; teams also stationed themselves on other mountains in Colorado, Wyoming, and New Mexico.

The scientists detected a new form of sprite that differs from the traditional jellyfish shape, with its downward-pointing tendrils. The subspecies has a thin body and branches upward and out, like the leaves on a carrot. "We found that sprites are vastly more complicated than we had thought," says Lyons.

To study elves, researchers from Stanford University built a special instrument with 12 light-capturing tubes. Their observations indicate that elves start at a central point and expand in a circle until they reach several hundred kilometers across.

This style of growth matches predictions made previously by Umran Inan of Stanford and his colleagues. They had proposed that elves stem from extra electromagnetic pulses triggered by lightning. The pulses race upward, generating light when they reach the ionosphere. The theory predicts that elves should start right above the lightning and then spread as the pulses reach more distant parts of the ionospheric layer.

Roussel-Dupre agrees that the pulse model fits the new observations but suggests that the pulses could come from sprites rather than from regular lightning. As for sprites, there is even less agreement on what causes these flares and how they assume such a variety of shapes.