Polar Vortex. Sounds scary, huh? Conjures up images of a giant gyre of ice that sucks in everything like a black hole. Or a Funnel of Doom.
Well, it isn’t that bad. The popular press is enamored of the phrase, given the invasion of arctic air into the heartland of the United States in January of 2014.
But the polar vortex is always in existence, customarily causing seasonally cold weather in Canada and Russia, and regularly bringing a modest chill farther south. Sometimes, however, the polar vortex gets frisky.
What Exactly is the Polar Vortex?
The polar vortex is simply a low pressure center in the middle of the atmosphere, located near the pole. The circulation around the polar vortex is commonly known as the jet stream.
In the southern hemisphere, the polar vortex is fairly uniform. In the northern hemisphere, the irregularity of the land masses leads to a circulation with a split personality — a bi-polar vortex as it were.
What Causes the Polar Vortex?
All weather on Earth owes its existence to the fact that the Earth is round and the poles receive less sunlight, and therefore less heat, than the equator. Cold air is denser than hot air, so if one goes up to a given height at the pole, there is more air below, and thus less air above, than at the equator. At a given altitude, the pressure is lower above the cold air of the poles than above the warm air of the tropics.
Air would like to flow from higher pressure to lower pressure, but there is the complication of the earth’s rotation. This introduces a ‘force’ (the Coriolis force) which turns the wind 90 degrees to the right. So air flows with low pressure on its left and high pressure on its right. Everyone is familiar with cyclonic (clockwise) and anticyclonic (counterclockwise) flow around low and high pressure systems. And that’s all the polar vortex is: A low pressure center in the mid-levels of the atmosphere, located near the pole.
The Position of the Polar Vortex in the Northern Hemisphere
The area around the north pole comprises water, ice, and land masses of various sizes. As a result, the polar vortex tends to have two centers; one over northern Canada and another over Siberia. Occasionally one of the vortices wanders to a location that proves inconvenient to those not used to frigid temperatures. That is what happened in the extreme arctic outbreak over the United States in January, 2014. The vortex over Canada became displaced to the south, and arctic air spilled into the central and eastern U.S.
What Does This Imply For the Future?
A single weather event can never be taken as evidence of a trend. Nevertheless, there is some indication that incursions of both warm and cold air into latitudes they normally avoid are becoming more frequent. Feedback mechanisms of climate change may cause unforeseen weather events; so prepare for extreme weather: Hot, cold, wet or dry — but don’t worry about getting sucked into the polar vortex.
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