What is the polar vortex and why is it so cold?

CHICAGO • Meteorologists have blamed a phenomenon called the polar vortex for the bitter cold that has descended on much of the central and eastern United States this week, forcing residents to huddle indoors, closing schools and businesses and cancelling flights.

As ominous as the term "polar vortex" sounds, meteorologists say the phenomenon is not new, nor, despite its sound, does it refer to a cyclone of cold or a freakishly dangerous storm.

"The term 'polar vortex' has become more commonly used in the past couple of years but the phenomenon has been around forever," National Weather Service meteorologist Mark Chenard said.

There is some debate among scientists about whether polar vortexes have become more frequent and, if so, what effect climate change might be having on them.

Mr Chenard said a polar vortex refers to the upper-level jet stream that typically circulates around both the North and South Poles, keeping the coldest air there.

When that jet stream occasionally weakens and buckles, he said, it disrupts weather patterns - bumping warmer air into Alaska and pushing cold winds down into the US Midwest and East Coast. "This (winter) happens to be a pretty extreme example of some of that cold arctic air making it down to us," he said.


Though the potentially record-shattering low temperatures descending on a large swathe of the country may touch off a political debate over global warming, Mr Chenard said, the phenomenon is not related to climate change.

Dr Jennifer Francis, senior scientist and Arctic expert at the Woods Hole Research Centre, said that while the latest move in the polar vortex "may unleash claims that global warming is a hoax", the mass of frigid air over North America is far outweighed by areas elsewhere that are warmer than usual.

She said modelling studies offer evidence that the stratosphere over the Arctic is changing and so disruptions to polar vortexes are increasing. "We are seeing this more often and there are a few studies suggesting that the melting and warming of the Arctic make these disruptions more likely than they used to be,"she said.


A version of this article appeared in the print edition of The Straits Times on January 31, 2019, with the headline 'What is the polar vortex and why is it so cold?'. Subscribe