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Red Sprites
Fri Mar 12, 2004
Listen in RealAudio 
There are colored lights in the sky that dart and dance like the pixies in "A mid-summer
Nights Dream." Hi, I'm Bryan Yeaton and this is The Weather Notebook. The lights are called
Red Sprites and they were discovered just a few years ago as Alan Couckell reports.
Towers of pinkish light shooting twenty-five miles high above the tops of thunder clouds. Red
sprites were discovered by accident in 1989 when scientists pointed a low light video camera
at the horizon and left it to run overnight. No two sprites look exactly alike.
CR: Fundamentally they are generally vertical columns, so sometimes you'll see a small group
of columns like five or six. Often you'll see 40 columns all packed together like a bunch of
trees. But then there have been examples, like a classic one that looks like a gigantic
jellyfish just hanging in the sky.
Red sprites are thought to occur all over the world. Craig Rogers is a New Zealand physicist
who studies sprites in Australia. He says the lights seem to be caused by the discharge of an
electrical field that forms at the top of a thundercloud.
CR: You take the thundercloud charge away very suddenly and that's the lightning. All of the
shielding charge at high altitudes can't go away very fast, so you end up with a large
electric field and the light comes from the electric field exciting the molecules. Basically,
jiggling them around, they get excited and release light.
The flicker of a red sprite lasts only a fraction of a second, but it is possible to see one
with the naked eye. They can sometimes be seen from high flying airplanes at night or by
ground-based observers watching thunderstorms in which the preceding lightning flash is out of
sight beneath the distant horizon.
Alan Couckell comes to us from Auckland, New Zealand.
Today's Links
More on Sprites
http://science.nasa.gov/newhome/headlines/essd10jun99_1.htm
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