The Weather Notebook: Red Sprites

Red Sprites
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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 forty 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 Physicists 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 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.