What is the Polar Vortex? And Are we In One Now?

Teachable moment. Let’s get caught up again on the whole polar vortex thing. This post might be a good one to share with anyone who’s wondering what’s up with the cold snap we are seeing in North America.

Above: Nice video from Dr Mark Serreze of the National Snow and Ice Data Center.

ClimateProgress:

The Arctic Outbreak, an unseasonable bout of frigid air that’s sweeping across the U.S. this week, is not the same as last winter’s so-called “Polar Vortex” event. Though both gave Americans the rare experience of breathing crisp, cold Arctic air, both were caused by different things: last winter’s “Polar Vortex” event seemingly random, and the current Arctic Outbreak caused by Super Typhoon Nuri in the Western Pacific.

But the two events do have at least two things in common. One is that that they’re both due to deep dips in the jet stream. In both cases, Arctic air from the Polar Vortex has been displaced to the south by a wavy jet stream, which brings coldness down to the temperate United States and leaves Alaska and the Arctic relatively warm. Sure enough, right now it’s warmer in Alaska than it is in Texas, and next week the National Weather Service predicts temperatures in Alaska will be 70 percent higher than average, with temperatures in Texas about 50 percent below average.
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Though it may seem contradictory that extreme cold events could be linked to global warming, it’s been shown time and again that bizarre and unpredictable things can happen to the weather when heat accumulates in the atmosphere and ocean. A warmer atmosphere holds more water vapor, which in turn can make precipitation events — including snow — more extreme. And some scientists think a warmer ocean can make tropical storms more intense, which can drive big dips in the jet stream.The latter is why some scientists, like bioanthropologist Greg Laden, think that climate change helped make this year’s Arctic Outbreak more intense.

“We can’t rule out climate change here,” said Laden, who writes for National Geographic’s Scienceblog. “[Super Typhoon Nuri] was in the top 2 or 3 hurricanes, maybe the top 2 of the year, in terms of overall strength. That’s because the Pacific has been really warm, creating a lot of extra hurricanes and extra strong hurricanes.”

A growing body of research led by Jennifer Francis, a research professor at Rutgers University’s Institute of Marine and Coastal Science, suggests Arctic warming causes less drastic changes in temperatures between northern and southern climates, leading to weakened west-to-east winds, and ultimately, a wavier jet stream like the one that caused last year’s Polar Vortex event.

“This kind of pattern is going to be more likely, and has been more likely,” she said at the time. “Extremes on both ends are a symptom. Wild, unusual temperatures of both sides, both warmer and colder.”

NPR:

Jeff Masters, chief meteorologist at Weather Underground, wants people understand.

“This is just a regular old cold front,” Masters says. “The polar vortex has been around forever. It’s just the media happened to notice it last year, and it’s really not a very scientifically accurate thing to talk about.”

He says the recent popularity of the phrase is misleading. The polar vortex is a constant flow of arctic air circling in the upper atmosphere above the North and South Poles. The cold is usually corralled up there — but sometimes little bits of the arctic air escape.

“It’s just the ordinary sort of weather you expect in winter,” Masters says. “Every now and then you get a big trough of low pressure. It dips down from the pole and it allows arctic air to seep southwards.”

That’s not to say the polar vortex wasn’t involved in this bout of unseasonably cold weather. Masters says Typhoon Nuri, which hit Alaska last week, pushed one of those troughs of arctic air south across the eastern U.S.

Such temperature shifts serve a purpose, says Steven Nelson of the National Weather Service.

“These cold intrusions, cold fronts, are really restoring the balance in the temperature and moisture across the earth’s surface,” he says.

Below, I interviewed Dr. Serreze’ colleague, Dr. Walt Meier, formerly of the NSIDC, now of NASA Goddard, last year in San Francisco.

Below, the Weather Channel on the current arctic intrusion in North America:

I’ve posted several videos detailing changes in the jetstream thought to arise from global warming – last year’s polar vortex certainly fit the profile, and although in recent months, no one was predicting a repeat of that, our current configuration bears watching.