From: Editor, ENN
Published November 8, 2013 03:45 PM

Climate Linked to Atmospheric-River Storms

It's not every day that the weatherman reports on atmospheric river storms...but we may be hearing the term more frequently now as researchers have linked climate in the Pacific Ocean and West Coast mountains to these distinctive storms.

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An atmospheric river is a narrow stream of wind, about a mile high and sometimes of hurricane strength. Crossing the warm tropical Pacific in a few days, it becomes laden with water vapor. A moderate-sized atmospheric river carries as much water as the Mississippi River dumps into the Gulf of Mexico in an average week! When the river comes ashore and stalls over higher terrain, the water falls as snow or rain.

A new NASA-led study of atmospheric-river storms from the Pacific Ocean may help scientists better predict major winter snowfalls that hit West Coast mountains and lead to heavy spring runoff and sometimes flooding.

These atmospheric rivers are prolific producers of rain and snow on California's Sierra Nevada mountains. Consequently, the findings have major implications for water management in the West, where Sierra runoff is used for drinking water, agriculture and hydropower.

The research team studied how two of the most common atmospheric circulation patterns in the Northern Hemisphere interact with atmospheric rivers. They found when those patterns line up in a certain way, they create a virtual freeway that leads the moisture-laden winds straight to the Sierras.

Bin Guan of the Joint Institute for Regional Earth System Science and Engineering, a collaboration between NASA's Jet Propulsion Laboratory in Pasadena, Calif., and UCLA, led a team of scientists from NASA, UCLA and the National Oceanic and Atmospheric Administration (NOAA) on this research.

"Atmospheric rivers are the bridge between climate and West Coast snow," said Guan. "If scientists can predict these atmospheric patterns with reasonable lead times, we'll have a better understanding of water availability and flooding in the region." The benefit of improving flood prediction alone would be significant. A single California atmospheric-river storm in 1999 caused 15 deaths and $570 million in damage.

Guan's team used data from the JPL-developed Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua satellite, along with NOAA satellite data and snowpack data from the California Department of Water Resources. They looked at the extremely snowy winter of 2010-2011, when 20 atmospheric rivers made landfall. The team compared the dates of these events with the phases of the Arctic Oscillation (AO) and the Pacific/North American teleconnection (PNA).

Read more at NASA's Jet Propulsion Laboratory.

Earth image via NASA's Jet Propulsion Laboratory; Image credit: Bin Guan, MASA/JPL-Caltech and UCLA.

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