Trapped Atmospheric Waves May be Responsible for Recent Weather Extremes

Trapped atmospheric waves may be the overlooked explanation for the recent weather extremes plaguing the United States recently, according to a new study.

Extreme weather patterns like the heat wave that hit corn farmers and worsened US wildfires in 2012 have reached an exceptional number in the last 10 years. Most people blame human-made global warming, which can explain a gradual increase in periods of severe heat, but the observed change in the magnitude and duration of some events is not so easily accounted for.

A new data analysis now shows that more frequent wave-trapping events may be the answer.

"The large number of recent high-impact extreme weather events has struck and puzzled us," lead author Dim Coumou said in a press release. "Of course we are warming our atmosphere by emitting CO2 from fossil fuels, but the increase in devastating heat waves in regions like Europe or the United States seems disproportionate."

After analyzing large sets of global weather data, the researchers found that these types of waves become virtually stalled and greatly amplified during periods of extreme weather. Normally, these wandering waves, called Rossby Waves, swing north and then suck warm air from the tropics to Europe, Russia or the United States; when they swing south, they do the same thing with cold air from the Arctic.

"Evidence for actual changes in planetary wave activity was so far not clear. But by knowing what patterns to look for, we have now found strong evidence for an increase in these resonance events," added co-author Stefan Rahmstorf.

Researchers also determined from their findings that episodes of extreme weather have been almost twice as frequent as before the year 2000.

The team, from the Potsdam Institute for Climate Impact Research, suggests that these wave patterns are linked to warming temperatures in the Arctic. As the Arctic warms more rapidly, the temperature difference to other regions decreases. These discrepancies are main drivers of atmospheric circulation patterns that in turn rule our weather.

The study was published in the journal Proceedings of the National Academy of Sciences.