April 6, 1999

Storm Ribbons

O n Earth, springtime storms are often accompanied by electrical activity, of which lightning bolts are the most visible and dramatic sign.

But for most of this decade, scientists have been investigating another phenomenon of electrical storms -- wispy glowing ribbons that appear at high altitudes, above the clouds.

These red glows, known as sprites, accompany about one in every 200 lightning strikes. They are difficult to view from the ground (although airline pilots reported them for years before scientists determined what they were), and getting a reliable estimate of their number has been practically impossible.

Now, researchers at the University of Massachusetts and Stanford have determined that lightning bolts that have accompanying sprites have a distinct electrical signature. The scientists studied a 1996 storm in Kansas, videotaping the sprites and noting the duration of the electrical currents from the lightning. Bolts that were accompanied by a sprite lasted much longer than those that were not.

The researchers, who reported their results in the April issue of Geophysical Research Letters, say that with just four relatively low-cost receivers the number of sprites could be counted for the entire Western hemisphere. Determining their number may help determine what effect, if any, sprites have on the chemistry of the atmosphere.

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