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Inside the destructive forces at work in atmospheric river storms

The weather systems known as atmospheric rivers can bring much-needed rain and snow to drought-ridden regions, but they also mean destructive floods and winds.

Those extreme consequences are the focus of a new NASA study on atmospheric rivers, which have plagued the western U.S., especially California, in recent days and weeks.  

Atmospheric rivers are weather systems that move high concentrations of water vapor outside of the tropics. They can be big or small, but the biggest atmospheric rivers bring strong winds, moisture and lightning when they make landfall, often causing extreme rainfall and floods, according to the National Oceanic and Atmospheric Administration, or NOAA. 

Satellite observation shows this weather pattern in action:

atmospheric-river-feb2015-400.gif

Atmospheric rivers bring water vapor outside tropical regions.

NOAA

The study, published Monday in the journal Nature Geoscience, shows atmospheric rivers are associated with almost half of the most extreme mid-latitude windstorms of the past 20 years, causing billions of dollars in damage. 

Heavy precipitation is a well-known risk from atmospheric rivers, but the risks of extreme and hazardous winds are generally less understood. 

Researchers from the Jet Propulsion Laboratory and UCLA’s Joint Institute for Regional Earth System Science and Engineering collaborated on the study, examining weather records and NASA satellite data to better understand the real impact of atmospheric rivers. 

Atmospheric rivers have severe economic consequences, the researchers found. Examining the 19 most expensive European windstorms from 1997 to 2013, they found that atmospheric rivers were associated with about 75 percent of these events — accounting for more than $25 billion in losses. 

Those findings caught researchers by surprise. 

“We expected that there would be an association, but the degree of the connection exceeded our expectation,” researcher Bin Guan said.

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    Shanika Gunaratna covers science and technology for CBSNews.com