Monday, February 25, 2013

Extreme weather linked to giant waves in atmosphere

Tanya Lewis in Live Science: Extreme weather events have been on the rise in the last few decades, and man-made climate change may be causing them by interfering with global air-flow patterns, according to new research.

The Northern Hemisphere has taken a beating from extreme weather in recent years — the 2003 European heat wave, the 2010 Pakistan flood and the 2011 heat wave in the United States, for example. These events, in a general sense, are the result of the global movement of air.

Giant waves of air in the atmosphere normally even out the climate, by bringing warm air north from the tropics and cold air south from the Arctic. But a new study suggests these colossal waves have gotten stuck in place during extreme weather events.

"What we found is that during several recent extreme weather events these planetary waves almost freeze in their tracks for weeks," lead author Vladimir Petoukhov, of the Potsdam Institute for Climate Impact Research (PIK) in Germany, said in a statement. "So instead of bringing in cool air after having brought warm air in before, the heat just stays."

How long these weather extremes last is critical, the researchers say. While two or three days of 86 degrees Fahrenheit (30 degrees Celsius) pose little threat, 20 days or more can lead to extreme heat stress, which can trigger deaths, forest fires and lost harvests

...The researchers created equations to model the motion of the massive air waves, determining what it takes to make the waves plough to a stop and build up. The team then used these models to crunch daily weather data from the U.S. National Centers for Environmental Prediction. During extreme weather events, the waves were indeed trapped and amplified, the scientists found. They also saw a significant increase in the occurrence of these trapped waves...

A shelf cloud, shot by NOAA

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