Skip to navigation | Skip to content

Dust storms are truly electric

Dust devil

Dust devils, or willy willies, can't be explained by wind alone, scientists say (Image: NASA)

It's not just wind that raises sand and dust devils, say physicists, powerful electrical fields created by wind, sand and dust also levitate more dust into the air.

The discovery could have implications for global climate modelling and even help explain what makes Mars such a dusty world.

More than 100,000 volts per metre of natural, 'static' electricity have been measured in desert dust storms and the mini-tornado-like dust devils or willy willies.

Now, under laboratory conditions, Jasper Kok, a graduate student at the University of Michigan in Ann Arbor, has reproduced the electrical fields found near the ground in desert wind storms and shown that they can also lift sand grains.

"We were very surprised," says Kok of the power of electrical fields to raise dust and sand.

He and his faculty advisor Associate Professor Nilton Renno are publishing their results in a coming edition of Geophysical Research Letters.

The process starts with a little dry wind in a dusty, arid place that kicks up small dust grains so they collide with larger sand grains, Kok explains.

When this happens the smaller grains steal electrons from the larger grains, giving the smaller grains a negative charge and the larger grains a positive charge.

"It's very similar to rubbing your feet on a carpet to become charged," says Kok. In that case you are the smaller grain and the carpet is the larger grain.

Next, the negatively charged smaller grains are lifted above the ground by breeze, creating a negatively charged region in the air above the positively charged ground. That separation of charges is an electrical field.

Once that field is in place, as Kok shows in the lab, more grains can be lifted up by the electrical forces, making for even dustier conditions than wind speed alone could create.

The phenomenon could have significant impacts on how much dust gets into the air worldwide, which means it's a matter that global climate modellers need to study more closely, says Dr Ron Miller of the NASA Goddard Institute for Space Studies in New York.

The many properties of dust

Dust is an 'aerosol', which can reflect sunlight back into space and cool the Earth's surface, as well as just influence the quality of the air.

"For a given wind that's already kicking up dust, you'd get more dust," says Miller.

It could also affect areas downwind of a dust source, he says, by transporting the electrical fields to other areas and also more readily mobilising dust there.

That matters a lot in places like China, where dust from the northern deserts whips south across industrial regions, picking up a lot of pollutants that can then be blown east as far as the European Alps.

Dust on Mars

Electrical fields may help explain how dust gets around on Mars, says Renno.

"On Mars the wind required to lift dust from the surface is very large," he says, because the atmosphere of Mars is very thin.

"Winds of the magnitude required have never been measured, but there's dust everywhere."

Kok says he's already working on a new laboratory experiment with Mars-like conditions to see if electrical fields may be at work on the Red Planet.

Tags: environment, astronomy-space, weather