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Martian Dust Devils
Wed Sep 28, 2005
Listen in RealAudio 
Dust devils, the whirling swirls of wind and dust you see in parking lots, fields and deserts, have been found to carry electrical charges. And sometimes, pretty big ones. And the giant dust devils seen on Mars may drive the lightning and dust storms of the Red Planet. Hi, I'm Bryan Yeaton, and this is The Weather Notebook.
Dust devils are created when a difference in temperature, like that between a hot asphalt road and a cooler stretch of sand, sets the air rising and swirling in a funnel. Large dust devils can be 200 yards high and 100 yards wide, and last for an hour or two, with winds up to 40 miles per hour. Most dust devils die out after a few minutes.
In a surprising new discovery, researchers at NASA found that dust devils carry surprisingly large voltages, up to 4 kilovolts per meter. These voltages build up because lighter dust particles, which tend to be negatively charged, get blown up into the top of the funnel, while heavier, positively charged particles sink to the bottom of the funnel.
That's not enough to cause any damage on Earth -- which the researchers verified by driving a truck into a dust devil -- but on Mars it's a different story. There, dust devils can be enormous, as much as 10 kilometers tall, about the size of a thunderstorm on Earth. There, the voltage in dust devils is near the threshold for atmospheric breakdown, about 20 kilovolts per meter, and can, according to researchers, ionize the thin atmosphere and cause lightning storms. You’ve got to hope the Martians have invented lightning rods.
Thanks to David Appell for today’s story. All The Weather Notebook’s past shows are online at www.weathernotebook.org. We are supported by Subaru of America and the National Science Foundation. Thanks to Trish Anderton for putting the show together.
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