Sahara dust linked to rain and snow in California
Desert dust carried thousands of miles across the Pacific Ocean can increase California precipitation, study finds.
Fri, Mar 01 2013 at 11:36 AM
Photo: Marsu Mic/Flickr
Dust from the Sahara Desert, which has previously been known to travel across the Atlantic Ocean and influence weather in Florida and other eastern states, also affects precipitation levels all the way in California, according to research published this week in the journal Science.
The research, by scientists from eight universities and other institutions, found that "dust and biological aerosols transported from as far as the Sahara were present in glaciated high-altitude clouds" around California's Sierra Nevada Mountains. When dust from the Sahara and similar deserts in Asia were present at elevated levels, there were increased levels of rain and snow in the region. Dust, bacteria and other microparticles function as condensation nuclei around which cloud water vapor can coalesce, creating snow or rain.
The authors say understanding of this mechanism is critical to understanding California's water resources, since melting snowpack from the Sierra Nevada Mountains feed into much of the state's water resources.
"The fact that something happening on another continent in terms of dust generation could influence precipitation patterns in the U.S — that's a challenging problem," one of the paper's authors told the Los Angeles Times.
The authors were inspired to conduct their study by two storms in 2009. Both winter storms contained the same amount of water vapor but one of them produced significantly more levels of rain and snow – 40% more, in fact. They tested the precipitation at ground level and found that it contained high levels of Asian desert dust after the second storm.
They followed this up in 2011 by flying through storm clouds above the Sierra Nevada and testing both samples they collected from the air and concurrently on the ground. Samples showed more desert dust coincided with periods of greater precipitation.
The source of the dust was identified by testing it for specific chemical "fingerprints" that linked it to deserts in Africa, China and Mongolia. They also looked at weather models which showed that wind could have carried dust across the Pacific prior to the storms.
Dust clouds from the Sahara are often big enough to be seen from space and can take about a week to cross the Atlantic Ocean before arriving in North America, where the dust has been linked to coral disease, allergic reactions in humans, and red tides, according to NASA. The dust that reaches the Western portion of America and Canada more commonly comes from Asia, although not exclusively. The first documented case of Saharan dust reaching North America after traveling over the Pacific Ocean was observed in 2005 (pdf).
NASA has an online animation of dust aerosol patterns from both Africa and Asia, which you can view here.
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