Science Says: Get used to polar vortex outbreaks

https://www.apnews.com/77d640ee81fa4890b689d39c6bea545d

By SETH BORENSTEIN
January 28, 2019

It might seem counterintuitive, but the dreaded polar vortex is bringing its icy grip to parts of the U.S. thanks to a sudden blast of warm air in the Arctic.

Get used to it. The polar vortex has been wandering more often in recent years.

It all started with misplaced Moroccan heat. Last month, the normally super chilly air temperatures 20 miles above the North Pole rapidly rose by about 125 degrees (70 degrees Celsius), thanks to air flowing in from the south. It’s called “sudden stratospheric warming.”

That warmth split the polar vortex, leaving the pieces to wander, said Judah Cohen, a winter storm expert for Atmospheric Environmental Research, a commercial firm outside Boston.

“Where the polar vortex goes, so goes the cold air,” Cohen said.

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When warm air invades the polar region, it can split the vortex or displace it, usually toward Siberia, Cohen said. Recently, there have been more splits, which increase the odds of other places getting ultra-cold, he said. Pieces of the polar vortex have chilled Europe, Siberia and North America this time. (It’s not right to call the frigid center of cold air the polar vortex because it is just a piece or a lobe, not the entire vortex, said University of Oklahoma meteorology professor Jason Furtado.)

When the forces penning the polar vortex in the Arctic are weak, it wanders, more often to Siberia than Michigan. And it’s happening more frequently in the last couple decades, Furtado said. A study a year ago in the Bulletin of the American Meteorological Society looked at decades of the Arctic system and found the polar vortex has shifted “toward more frequent weak states.”

When the polar vortex pieces wander, warmth invades the Arctic, Alaska, Greenland and Canada, Masters said. While the Midwest chills, Australia has been broiling to record-breaking heat. The world as a whole on Monday was 0.7 degrees (0.4 degrees Celsius) warmer than the 1979-2000 average, according to the University of Maine’s Climate Reanalyzer.

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