Jumping sand helps climate models

Role of electric fields discovered in the formation of dust aerosols

Sand dunes © SXC
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Wandering sand dunes, erosion of rocks or the dust storm in the desert - the wind is generally regarded as the driving force behind these phenomena. But he is not alone. A model now published in the journal Physical Review Letters also includes the role of static electricity in these processes for the first time. The new findings could also help to improve existing climate models and models of aerosol release.

When the wind hits loose grains of sand on the ground, it whirls them up and drops them to the ground at some distance. This so-called saltation forms the basis of such diverse processes as the migration of a sand dune or the stirring and release of fine dust and aerosols into the atmosphere. As small as they are, these suspended particles are an important factor in the terrestrial climate system. Depending on their density and type, they can promote cloud formation, reflect or absorb sunlight, and thus heat or cool the temperature of the atmosphere.

Previous models of saltation insufficient

"The effect of aerosols is one of the most uncertain processes in modeling climate change, " explains Jasper Kok, a graduate student at the University of Michigan, and co-authored a study with Nilton Renno on saltation, the evolution of some aerosols. The impetus for their work was only recently taken field measurements of saltation, which seemed to contradict the classical model of this process, set up on the basis of wind tunnel tests.

Nothing but sand ... © SXC

The suspicion of the researchers: Possibly played next to the wind nor a force, namely the static electricity or charging of the particles involved an important role. Already in the study of the so-called "Dust Devils", a kind of dust dust in the desert of Arizona, the scientists had noticed that they had a strong electric field. Now they were able to physically describe the influence of electricity on the saltation and capture it in a model.

Electric field as a dust extractor

It turned out that the saltation creates an electric field that is so strong that it even more than doubles the concentration of bouncing sand particles over the pure wind effect. We discovered that the surface of the soil is positive, and that the particles develop a negative charge when the particles jump and collide and rub, Renn explains Renno. This electric field can become strong enough to lift sand directly from the surface. Display

"This represents a fundamental change in our understanding of saltation, " the researcher continues. Now we also know more about the physical laws that throw the dust aerosols into the atmosphere. We can now also improve the climate models for the release of aerosols.

(University of Michigan, 09.01.2008 - NPO)