Dust from Africa affects snowfall in California

Dust from Africa affects snowfall in California
This 2011 image provided by the National Oceanic and Atmospheric Administration shows a field survey site in California's Sierra Nevada mountains. A new study published online Thursday, Feb. 28, 2013 in the journal Science found snowfall in the Sierras was influenced by dust and microbes from as far away as Africa. (AP Photo/Jessie Creamean/NOAA)

One of the driest spots on Earth—the Sahara desert—is increasingly responsible for snow and rain half a world away in the western U.S., a new study released Thursday found.

It's no secret that winds carrying dust, soot and even germs make transcontinental journeys through the upper atmosphere that can affect the weather thousands of miles (kilometers) away. Yet little is known about the impact of foreign pollutants on the West Coast, which relies on mountain snowmelt for its water needs.

Previous studies hinted these jet-setting particles may retard rainfall in the in Northern California by reducing the size of in clouds. But scientists who flew through in an aircraft, measured rain and snow and analyzed found the opposite: Far-flung dust and germs can help stimulate precipitation.

During the 2011 winter, a team from the University of California, San Diego and traced particles suspended in clouds over the Sierra to distant origins—from the skies over the arid Sahara that later mingled with other pollutants in China and Mongolia before crossing the Pacific.

The days with the most particles in the clouds were also "days when we see the most snow on the ground," said study leader Kimberly Prather, an professor at UC San Diego, whose study was published online Thursday in the journal Science.

Scientists believe wafting dust, grit and microbes—including bacteria and viruses—can spur the formation of ice crystals in clouds that in turn can influence how much rain or snow falls.

For years, governments and utilities in California and other Western states have used cloud seeding, in which a chemical vapor is sprayed into clouds, in a bid to increase rainfall.

The new study shows how "Mother Nature has figured out how to give us more precipitation" and that may lead to changes in cloud-seeding efforts, which can be hit-or-miss, Prather said.

David J. Smith at the NASA Kennedy Space Center said it was refreshing to see measurements from the ground, air and orbit to tackle how airborne particles affected Northern California snowfall.

"Such a comprehensive approach is the only way to thoroughly examine global transport" of particles, Smith, who had no role in the research, said in an email.


Explore further

Scientists to track impact of Asian dust and pollution on clouds, weather, climate change

More information: "Dust and Biological Aerosols from the Sahara and Asia Influence Precipitation in the Western U.S.," by J.M. Creamean et al., Science, 2013.

Press release: phys.org/wire-news/123594966/s … lobal-journey-i.html

Journal information: Science

Copyright 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

Citation: Dust from Africa affects snowfall in California (2013, February 28) retrieved 22 February 2020 from https://phys.org/news/2013-02-africa-affects-snowfall-california.html
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