New Beasts in the High-Sky Menagerie

The list of mysterious lights in the high sky above thunderstorms adds gnomes and pixies.

Each year brings more discoveries from the charged atmosphere high above large thunderstorms. Now there are some new members of the whimsically named troupe that includes sprites, elves, trolls, and blue jets.

The whole field of upper-atmosphere lights has depended on lucky breaks. Sprites, for instance, were first recorded in 1989 when a group of University of Minnesota scientists were using a brand-new video setup to film a rocket launch. While they were waiting around, they pointed the camera toward a distant thunderstorm. One of them checked the wiring, which they had rigged up in the dark to save their night vision, and fixed a loose cord. Just minutes later, the tape caught a flash so brief that it occupied only two frames. But those two frames of video launched a worldwide research effort and a whole new branch of Earth science.

The first sprites ever captured on video, 6 July 1989 at 10:14 pm. The associated thunderstorm was 250 km away, below the horizon. Later that year, sprites were imaged from the Space Shuttle. Image from the Global Hydrology and Climate Center.

That kind of serendipity continues. On July 22, 2000, Walter Lyons of FMA Research was at his firm's Yucca Ridge Field Station in northern Colorado, shooting high-speed video of distant thunderstorms. The huge "mesoscale" storm complex wasn't doing much in the way of sprites when a smaller isolated "supercell" thunderstorm drifted northward, blocking the view. Supercells-the typical anvil-shaped cumulonimbus thunderstorms-do not produce sprites, but Lyons let the cameras roll anyway. To his surprise, the tapes showed two new kinds of lights at the top of the supercell, which Lyons has named gnomes and pixies.

Gnomes are relatively small, very brief white spikes of light that point upward from the top of the supercell's anvil top, specifically the "overshoot dome" caused as strong updrafts push rising moist air slightly above the anvil. They appear about 150 meters wide and about a kilometer high, and they last a few microseconds.

Pixies are so small that they appear as points, making them less than 100 meters across. In the July 22 video they appear scattered across the overshoot dome, flashing seemingly at random. Pixies and gnomes appear to be a pure white color, like ordinary lightning, and unlike sprites or elves they do not accompany lightning strokes.

Besides hoping for more sightings of gnomes and pixies, Lyons is still looking for new lights. The scientific literature has eyewitness descriptions of lights in the high atmosphere that date back more than a century, and most of them correspond to sprites and blue jets. The tantalizing handful of exceptions are accounts of bright white streaks rising from thunderstorm tops. Unlike lightning, these are described as straight and unbranched. A few rare photos exist, giving the further detail that the tops of these lights shade to blue.

Researchers once believed that these spikes were somehow related to blue jets, but the growing evidence suggests that they are a different phenomenon, as yet unrecorded. But some day we will certainly capture them on tape, analyze their spectra, and give them a name. Like sprites, elves, and trolls, they have always been here, but we never had eyes to see them with.

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