Polar Vortex Behind U.S. Cold Blast

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An image captured by a NOAA satellite on Jan. 6 shows an area of low pressure from the polar vortex over North America.
NOAA

The latest public enemy No. 1 comes complete with an ominous, super-villain name and a tendency to waver drunkenly around the Northern Hemisphere, leaking great, vast gasps of frigid Arctic air into normally more temperate latitudes.

But what is the polar vortex, and why has it been making so much trouble over the last few winters?

First off, there's the scary name. It comes from the fact that when viewed from above the North Pole, the polar vortex forms a river of air that spins in a rough circle, around the hemisphere from west to east. It's always been there, but most of the time it minds its own business and serves as a wall of wind to hold wintry Arctic air where it belongs -- in the Arctic. But this week it's not doing that.

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Yoon S. Byun/The Boston Globe via Getty Images

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“That wind can look like an ellipse or it can be wavier,” explained James Overland, a senior scientist at the NOAA/Pacific Marine Environmental Laboratory in Seattle. “That wavy pattern is what we are seeing today.”

The waviness is usually bad news for the Eastern United States because that region is already on the edge of a back up and turn in the vortex's river of air, caused by the obstruction of the Greenland's mountains, Overland said.

The wavier the vortex, the more likely it will swerve even more as it veers over and around Greenland, sending a lobe of Arctic air down the center of North America and over the East Coast like a blast straight from the hyperborean lungs of Jack Frost. The past four out of five winters have seen seen more of these blasts, Overland said. Which naturally prompts the question: Why?

“The atmosphere will often repeat itself,” said forecaster Bob Oravec with the National Weather Service in Maryland.

Historic cold events in January 1994, 1985 and during the 2009 first inauguration of President Barack Obama, for instance, happened when the atmospheric patterns looked similar to what we are seeing this week. But that doesn't explain why extreme winter weather may be on the rise.

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“We can't really explain why we tend to have more extreme events,” said Overland. “But it's clear that we are.”

And while some non-scientists and lobbyists argue the cold waves disprove tomes of peer reviewed science on global warming, the scientists themselves are not suggesting this at all -- although they have a range of opinions on the cause of the events.

On one hand some researchers put it down to dumb luck, Overland said. After all, four out of five winters isn't a lot to go on. On the other hand, there have already been connections found between Arctic warming changes in the northern jet stream which cause weather patterns to slow and increase the changes of heat waves and droughts. Perhaps the dramatic warming of the Arctic is changing the wintertime behavior of the polar vortex as well.

Whatever the cause, Overland points out that the waviness of the polar vortex is not permanent, and can switch back and forth, from wavy to a nice, tight circular pattern in a matter of weeks, as has happened already a few times this fall and winter.

“It's not a prolonged event,” agreed Oravec. By the end of the week the worst of the cold will have moderated, he said.

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