Airborne dust and particles from the Sahara desert and from Asia influences precipitation in the U.S., says a new study in Science magazine. As the scientists note, when they embarked on the study, they were certainly not expecting to find dust from Asia, Africa and elsewhere in the clouds over California, more than half a world away.
“Basically, we were able to show that dust and biological aerosols that were lofted from deserts all the way across the world in the Sahara and Asia were airlifted all the way across the world to make ice crystals in clouds in the western United States,” says study co-author Jessie Creamean, a postdoctoral associate at the National Oceanic and Atmospheric Administration’s Earth System Research Laboratory, in Scientific American. These aerosols help to form ice in the clouds, which could possibly lead to precipitation; other factors, such as storm winds and the availability of water vapor, may also play a part.
Tracking tiny airborne particles is no easy task. Cramean and study co-author Kaitlyn Suski, a graduate student at the University of California, San Diego, analyzed satellite images to do so. During storms, they also flew into the clouds in a research aircraft stocked with instruments that can identify the type of particle in a cloud and note whether it is dust or some other type of aerosol. In addition, they also looked at older data that tracked storm masses back across the Pacific and Asia, in order to figure out where the dust in the clouds they found had originated.
Besides dust, the scientists found a living organism in the clouds, bacteria. Such minute lifeforms can indeed be “lofted up high in the atmosphere and serve as nuclei for cloud formation,” notes the Smithsonian.
Earlier studies have found that dust from China’s Taklimakan desert could be blown far across the globe, says the Smithsonian. This desert and also the Gobi desert freeze for much of the year while the Sahara never freezes. Thus, dust blown from the Sahara could — and, according to Cramean’s and Suski’s study, is — seeding storms all around the world.
With some scientists warning about shortages of water to feed and power the world, the study offers some intriguing possibilities for how to capture more water and also reduce flooding, says another study author, Kimberly Prather, of the Scripps Institution of Oceanography. Currently the state of California (which helped to fund the research) relies on hydropower for about 15 percent of its electricity.
The Science magazine study has implications in understanding the effects of climate change on rainfall. Global warming has not only influenced the amount of rainfall in the Sierra Nevada but also on the amount of dust in the atmosphere. As temperatures rise, scientists expect that there will be more dust, aerosols and other particles in the air; these could indeed have an impact on the amount of precipitation that falls.
Without rain in the winter, California and Colorado face a serious risk of drought. Water from winter snows is directed to reservoirs, where it is stored for people to drink, for agriculture, power and other uses. Need it be said that what happens in one part of the world can have a deep-running, even life-changing, impact on another?
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