Airborne dust settles like broken glass, concludes a new finding that could help improve climate models.
- The physics of breaking glass could govern the making of atmospheric dust.
- If true, the complicated ways scientists have to factor in dust to climate models could get a lot simpler.
- Dust is important to climate because it helps seed clouds, spawn hurricanes and can cool the planet.
Despite the old saying, there's nothing random or meaningless about the dust in the wind, according to a researcher who has discovered a strange mathematical principle ruling the airborne grime.
The discovery could help simplify the otherwise complex matter of including dust in climate models -- a critical variable in climate, since sometimes dust cools the Earth by reflecting sunlight into space and at other times can warm the atmosphere by absorbing sunlight and releasing it as heat.
The trick is knowing the amounts of dust particles of different sizes riding the wind.
"Basically what I found is that creating dust particles in a dust storm is kind of the same thing as dropping a glass on the floor," said Jasper Kok, a researcher at the National Center for Atmospheric Research.
Despite appearing chaotic, breaking glass actually cracks and falls apart in a mathematically predictable way that produces a predictable distribution of shard -- or particle -- sizes.
"The study of breaking glass has been done in great detail, but dust in dust storms -- it's very difficult."
To include dust storms in their models, climate modelers have been resorting to increasingly complex sets of equations, Kok explained. But that may not be necessary if dust production by storms can be described more simply -- like breaking glass.
"When these (dust) particles strike the soil they essentially break the soil," said Kok. They create cracks in soil aggregates in the same way that cracks are propagated through glass. "It's a very beautiful process that creates order out of chaos. The exact same relationship applies to dust."
And it's a far simpler relationship to add to an equation, he notes. "That allows us to get around all that complexity."
To test the idea, Kok looked at all the studies he could find that measure the distributions of dust particle sizes -- which is not very many. Still, in every case the dust follows the same particle distribution as breaking glass.
"It shows very good agreement," Kok said. His paper in the matter appears in the latest edition of the Proceedings of the National Academy of Science.
The work also suggests that climate modelers have been overestimating the fraction of very fine dust by a factor of two. That's pretty significant because it's the smallest particles that stay in the atmosphere longest and do important things like serve as seeds for cloud formation, help spawn cyclones and carry iron to the seas.
"Because they overestimate the fraction that is small, they overestimate its effects," said Kok. "There has been a lot of initial interest because it's a very easy thing to put into a climate model."
"His work is a different approach," agreed atmospheric researcher Shu-Hua Chen of the University of California at Davis.
One of the biggest advantages of Kok's approach, if it turns out to really work, is that it would apply to models regardless of the kinds of soils on the ground. Right now models have to factor in different soils.
"If it's true," said Chen, "it's great!"