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Stalking Arizona dust devils helps scientists understand electrical, atmospheric effects of dust storms on Mars
29 May 2002

By Robert Sanders, Media Relations

Berkeley - University of California, Berkeley, physicist Greg DeLory would rather be chasing dust storms across the fields of Mars, but until that becomes possible, he's stalking dust devils in the dry flats of Arizona.

With a grant from the National Aeronautics and Space Administration, he and a band of meteorologists and physicists have set up instruments on the Santa Cruz flats near Eloy, Ariz., to measure the atmospheric effects and electrical properties of dust devils - mini-tornadoes as common here as tumbleweeds - in preparation for studying their bigger cousins on Mars.

 
Mars Orbital Camera view of a Martian dust storm (above) and a terrestrial dust storm on the same photographic scale (below) which extends about 1100 miles off the coast of northwest Africa near the Earth's equator. Credit: NASA/JPL/Malin Space Science Systems
 

"They're everywhere," DeLory said via cell phone from Arizona. "You can look out at the horizon and see ten of them at a time."

Though 10 to 100 times smaller than dust storms on Mars, Arizona dust devils nevertheless will give the researchers an idea of the effect dust storms could have on sensitive instruments aboard future Mars landers, and how they might affect robots exploring the surface. The tests also will help identify what instruments are needed to study dust devils on Mars.

"We're studying terrestrial versions so that when we fly robotic instruments to Mars, which has tremendous dust devils all over the planet, we will be able to understand the observations," said DeLory, an assistant research physicist with UC Berkeley's Space Sciences Laboratory. He is one of the principle investigators with Project Matador, led by Nilton Renno and Peter Smith of the University of Arizona.

One of the main concerns is electrical discharges within dust devils, which could fry computers and electronic circuits and disable radio communications equipment aboard a lander or robot.

"Dust caught up in these vorticies undergoes frictional charging, like rubbing your hair with a balloon, generating voltages of many thousands of volts," DeLory said. Using special antennas and sensors, he and his collaborators are studying the DC (direct current) voltages generated within the twisters, as well as wind speeds and particle density.

Such data "would allow us to replay a large (dust devil) event with accurate, sub-second resolution of position, velocity, size, wind speed, dust concentration and radio noise," Renno said. "We should be able to completely characterize a dust devil as it moves over our sensors."

They also are looking at how dust gets airborne, and whether electrical charges make this easier or more difficult.

"If the electrical field is big enough, it could repel the dust and make it harder to get into the air," DeLory said.

The team began this year's tests on May 20 and plan to stay in Eloy for three and a half weeks to get sufficient data on dust devils. In their first tests last year, they chased dust devils around with a truck crammed with instruments and sensors. This year, they are placing the instruments in one spot and waiting for the ever-present dust devils to blow over.

"Last year was a lot of fun stalking dust devils, and we got great recordings," DeLory said. "But a metal truck can interfere with making sensitive electrical measurements."

The researchers also hope to learn about the effects dust devils have on our own atmosphere.

"The idea that dust devils and convective plumes play an important role in the vertical transport of heat and aerosols is novel and needs testing," Renno added. "It's also risky. No one has experience in measuring what convective plumes and dust devils contribute to heat and aerosols transport. This pilot study will be a learning experience for us."

Convective air and dust devils are a known hazard for aviation - up to 10 percent of accidents with light aircraft, sailplanes, helicopters and blimps are caused by gusts associated with these convective winds. Earth's dust devils may play an important role in climate change, atmospheric photochemistry and ocean biochemistry.

Smith, head of the Imager for Mars Pathfinder (IMP) camera on the hugely successful Pathfinder mission that landed on Mars in 1997, and Renno, an atmospheric scientist who is an expert on atmospheric convection, began collaborating in dust devil research in 1996. Their analysis of Mars Pathfinder meteorological data showed that dust devils blast over the Mars Pathfinder landing site with windspeeds greater than 140 mph and are an important source of dust in the martian atmosphere.

The 2002 field test expands on a Matador experiment that Smith and Renno organized last June at the same location. One surprising result from that four-day experiment was that even small terrestrial dust devils produce radio noise and electrical fields greater than 10,000 volts per meter. If they were on Mars, they would generate long-lived, charged particles powerful enough to trigger electrical discharges in the martian atmosphere.

Matador, funded by NASA's Human Exploration and Development of Space program and by the National Science Foundation, also involves collaborators from the Wageningen University in the Netherlands, and IMADES, or Instituto del Medio Ambiente y el Desarrollo Sustentable del Estade de Sonora, in Hermosillo, Sonora, Mexico.

Matador team scientists involved in the 2001 and 2002 experiments also include John Marshall of NASA Ames Research Center; William Farrell of NASA Goddard Space Flight Center; Allan Carswell of Optech, Ontario, Canads; and Barry Hillard of the NASA John Glenn Research Center.

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