The demise of the polar vortex could spell weather surprises this spring

A plot of the stratospheric polar vortex showing where strong winds encircle a depression of frigid air. (Hannah Attard)

March 14

It was a weird winter in the Arctic, and even stranger in the United States and Europe, where wintry weather was mostly absent. A near-record strong polar vortex bottled up frigid air in polar regions, while mild weather frequently flooded the mid-latitudes. Europe posted its warmest winter on record.

As far removed as it is, the polar vortex had dramatic implications on our winter weather, and this could continue to heading into spring.

Some springs, abrupt changes in the polar vortex can favor wild temperature swings and severe weather over the Lower U.S. 48. Other years, a more gradual transition of the vortex from winter into springtime mode blends together the seasons more gingerly.

What’s in store this year? Scientists are unsure: After such a bizarre winter for the polar vortex, research scientists suggest to expect the unexpected.

What is the polar vortex?

A positive Arctic Oscillation (left) is associated with a strong, stable polar vortex whereas a negative Arctic Oscillation (right) is associated with weak, unstable vortex. (NOAA)

Each hemisphere has not one, but two polar vortexes: one in the troposphere, and one in the stratosphere.

The troposphere is the region of the atmosphere in which we live. It’s where our weather happens. At the equator, the troposphere might extend up to 60,000 feet high; in polar regions, sometimes less than 20,000 feet.

Above that lays the stratosphere. It’s a region of the atmosphere where temperatures warm with altitude — rather than decrease. That’s where a narrow, but more intense, polar vortex devilishly whirls round and round.

The polar vortex — in either section of the atmosphere — is caused by the frigid temperatures near the pole. Since cold air contracts and sinks, a sort of void is left in the upper troposphere and stratosphere. That void draws air spiraling inwards, where it too cools, and a vortex is born.

The tropospheric polar vortex is more meandering, wobbling north and south during different times of the year. It wears the jet stream as a necklace, the turbulent river of winds separating frigid air to the north and milder air south.

How the stratospheric polar vortex disintegrates at the end of the season has bearings on spring at the lower latitudes. Does the vortex go out with a bang? Or fade quietly into the ether? Experts say this season might fall somewhere in between, but emphasize the enormous predictive challenges we’re up against.

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