Dust — and the microbes hitching rides on it — influences rain, climate

A press release from the American Chemical Society: Dusty air blowing across the Pacific from Asia and Africa plays a critical role in precipitation patterns throughout the drought-stricken western U.S. Today, a scientist will present new research suggesting that the exact chemical make-up of that dust, including microbes found in it, is the key to how much rain and snow falls from clouds throughout the region. This information could help better predict rain events, as well as explain how air pollution from a variety of sources influences regional climate in general.

...“We’ve learned that not all of the particles in the air at high altitudes have the same influence on clouds. We’re starting to think that these differences contribute to how rain gets distributed,” says Kim Prather, Ph.D.

Most of the dust that Prather’s team at the University of California, San Diego, detects in clouds and precipitation originates in Asian and Chinese deserts. It gets swept westward by the jet stream where it mixes with a variety of other airborne particles such as sea spray and smoke. Prather says that each of these types of particles — collectively known as aerosols — has its own, distinctive impact on clouds.

A major key to what turns ordinary clouds into rainmakers in the first place is their ability to form ice crystals around the microscopic particles that invade and “seed” them, Prather said. Without ice crystals as a catalyst, rain development inside clouds can be impaired.   “The standard belief is the more ice you have in a cloud, the more likely you will get precipitation out of it,” she says. “Our goal is to catch the first stages of ice forming and find out what exactly the chemical constituents are that the ice is forming on.”

...Prather speculates that the microbes hitch a ride on bits of sand, iron and other debris swept aloft from desert regions. Microbes and biological components could also become mixed with the dust as it is transported across the Pacific. She and her team are eager to learn just how important these bioparticles are in the rainmaking process.

...“Long term, our goal is to be able to predict how much precipitation we can expect to form when certain aerosols such as dust are coming toward us,” says Prather. “That’s a lofty goal but we’re making headway.”...

Via NASA, a satellite view of a dust cloud over Asia