Aug. 17, 2006 — It's not just wind that raises sands and dust devils, say physicists, powerful electrical fields created by wind, sand and dust also levitate more of the nose-tingling stuff into the air.
The first-of-its-kind discovery could have implications for global climate modeling and even help explain what makes Mars such a dusty world.
More than 100,000 volts per yard of natural, so called "static" electricity have been measured in desert dust storms and the mini-tornado-like dust devils. 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," said Kok of the power of electrical fields to raise dust and sand. He and his faculty advisor, 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 explained. 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," said Kok. In that case you are the smaller grain and the carpet is the larger grain.
Next, the negatively charged smaller grains are lofted 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 has shown in the lab, more grains can be lifted up by the electrical forces, making for even dustier conditions than wind speed alone could create.
