Secret of 'Sprites'
A very low frequency radio antenna is helping researchers
distinguish between lightning strikes in thunderstorms that produce towering
luminous glows called sprites, and ones that don't, according to a new
A team of scientists from the Stanford University and
the University of Massachusetts reports in the most recent issue of Geophysical
Research Letters that they've added another piece to understanding this
mysterious phenomenon that accompanies thunderstorms.
Lightning that spawns sprites has two electrical signals,
whereas normal lightning has just one, says Umran Inan, a Stanford electrical
engineer. "It has a higher low frequency wave," he says, and it lasts longer
than lightning that doesn't generate a sprite.
Inan is excited because this signature will enable sprite
searchers to identify their quarry from great distances. "...We have a
signature in the electromagnetic signal that lightning releases that tells
us whether or not it will produce a sprite. And I can listen 12,000 kilometers
away and say if this signal is a sprite, " he says.
Sprites have only been studied for the past five years,
so researchers are hungry for every scrap of information they can uncover
Inan and his colleagues arrived at their findings by counting
sprites in a Kansas thunderstorm, tallying 98 in 90 minutes.
"So far sprites have been pretty much detected over America,
Australia and Japan. This way researchers can see whether or not they are
occurring over Europe and Africa. We think they are, but this way they
can prove it is actually happening," says Dana Moudry, a physics researcher
at the University of Alaska, Fairbanks.
What sprites do still isn't certain. Walter Lyons, an
atmospheric scientist at FMA research in Fort Collins Colorado, says sprites
may play a role in the generation of stratospheric ozone.
And in spite of the potential value of a radio signal,
Moudry says video recordings of sprites can offer something that a squiggle
on a computer screen doesn't.
"You still don't know about the structure of a sprite.
A radio signal doesn't tell you what they look like," she says.
By Harvey Black, Discovery Online News