New way to identify which El Ni?o events will have biggest impact on U.S. winter weather

Feb. 8, 2013 ? Weather forecasters have long known that El Ni?o events can throw seasonal climate patterns off kilter, particularly during winter months. Now, new research from NOAA and the University of Washington suggests that a different way to detect El Ni?o could help forecasters predict the unusual weather it causes.

A network of buoys that spans the Pacific, the TAO-Triton array, observes conditions in the upper ocean and is essential for forecasting El Ni?o months in advance, and for monitoring it as it grows and decays. A new study, just published in the February issue of the Journal of Climate, describes an atmospheric El Ni?o signal that is very strongly associated with U.S. winter weather impacts. Ed Harrison, Ph.D. of the NOAA Pacific Marine Environmental Laboratory in Seattle and Andrew Chiodi, Ph.D., of the NOAA Joint Institute for the Study of the Atmosphere and Ocean at the University of Washington, co-authored the paper.

"When it comes to El Ni?o's weather impacts, we are always looking for ways to improve our forecasting skill," said Harrison. "Our goal is to extract the most useful information to predict El Ni?o seasonal weather anomalies."

Harrison and Chiodi looked at all El Ni?o events that were identified by sea surface temperature measurements since 1979. They then examined satellite imagery for these events and found that a subset of the events showed a sharp dip in heat radiating from the tops of deep convective clouds, an indicator known as outgoing long-wave radiation or OLR. When comparing the El Ni?o events to historical weather records, the scientists found that the El Ni?o events with drops in OLR were the ones most likely to play havoc with winter weather.

They also found that El Ni?o events with no corresponding drop in OLR did not produce statistically significant anomalies in weather patterns. The dip in heat from deep convective clouds usually occurred before winter, so the timing of the signal could help forecasters improve winter seasonal outlooks, the scientists said.

"By sorting El Ni?o events into two categories, one with OLR changes and one without, forecasters may be able to produce winter seasonal outlooks with more confidence than previously thought possible," Harrison said.

El Ni?o refers to a warming of waters along the equator in the Eastern Pacific Ocean. Through its influence on the atmosphere, El Ni?o shifts tropical rainfall patterns which causes further shifts in weather around the globe, including milder winters in western Canada and parts of the northern United States and wetter winters in the some southern states.

Industry sectors from energy and construction to transportation and tourism are keenly interested in how El Ni?o will affect their costs. El Ni?o-influenced weather can affect fuel oil demand, travel delays, and retail sales. Better accuracy in El Ni?o predictions could help industry to prepare for its impacts more efficiently.

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The above story is reprinted from materials provided by NOAA.

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Journal Reference:

1. Andrew M. Chiodi, Don E. Harrison. El Ni?o Impacts on Seasonal U.S. Atmospheric Circulation, Temperature, and Precipitation Anomalies: The OLR-Event Perspective*. Journal of Climate, 2013; 26 (3): 822 DOI: 10.1175/JCLI-D-12-00097.1

Note: If no author is given, the source is cited instead.

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Source: http://feeds.sciencedaily.com/~r/sciencedaily/top_news/top_environment/~3/sWT7E3KNiVU/130208104927.htm

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