Dust from Africa affects snowfall in California

February 28, 2013 by Alicia Chang
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 reference: Science search and more info website


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2 / 5 (4) Feb 28, 2013
A couple of years ago in 6th grade science class, I learned that within every raindrop there is a small dust particle. Water in the form of gas cannot condense unless it touches something cooler than itself which is the function of the dust particle, & then it can condense to form a droplet of water. An ambient environment devoid of airborne particulates will never see rainfall no matter what the density of a cloud cover is. This is the reason your newly polished car looks so dirty after it has been left out in the rain, it'll have a dirty pock marked appearance to it.

If the planet we live on did not have volcanoes & forest fires routinely lofting particulates into the atmosphere, the entire planet would be a desert.

In 6th grade I still did not have my Engineering degree, but I understood the simple principle of water condensation, but when I read in the article that it was "governments & utilities in California" who are just learning about it.......then I understood.
5 / 5 (1) Mar 01, 2013
Wait. If this is a new study, how the heck do they know that that this is an accelerating trend?
Fact is, dust from everywhere goes everywhere else... in spite of some peoples best efforts.
5 / 5 (2) Mar 01, 2013
The dust from the Sahara, especially from the basin that holds Lake Chad, has a distinct chemical fingerprint (it's an old inland sea bed, full of nutrients derived from diatoms, algae, etc), so it's easy to tell it's from there, not, say the Taklamakan desert.
When the dust is blown westward across the Atlantic, it fertilizes the Amazon basin. In fact, it seems to be the main source of nutrients there.
I had been wondering if this dust made it to North America, now I know.
Watch the Earth from Space documentary on NOVA, which explains this and much more.
It would be worth taking some of this soil and seeing if it would increase plant growth in those parts of Africa where the soil is depleted.

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