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Martian Dust Devils
Tue Aug 24, 2004
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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