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The Physics and Math of the Polar Vortex

This winter has been colder than anyone can remember. The term Polar Vortex has become part of our weather vernacular. But what is this weather phenomenon?

The Polar Vortex is a cyclone that can be found at either of the Earth’s poles. In fact, the cyclonic winds are a constant feature of these regions of the Earth. So why did these winds end up in the continental US?

The swirling winds of these cyclonic winds are held in place by the speed of the Jetstream and other winds that contain these cyclonic forces. Whenever there’s a swirl in an object’s motion, we’re talking about circular motion.

Whenever an object is moving in a circle, there is a centripetal force that keeps the object moving along that circle. The faster the circular speed, the more of a centripetal force. Here’s an example.

Suppose you want to jump off a moving merry-go-round. If it’s moving slowly, no big deal. But as the merry-go-round keeps moving faster and faster, it becomes more and more difficult (and dangerous) to jump off. The faster the merry-go-round goes, the stronger the centripetal force that keeps you in place. Faster speed means more force.

This is what usually happens with the Vortex. Normally, the fast winds of the Jetstream push the Vortex and create a large centripetal force. But as these winds slow down, the cyclonic forces are not held in check as they normally are. And this is what has happened this winter.

Mathematically, the speed of the wind that keeps the Vortex in check is inversely proportional to the mass of the air in the cyclone. A change in air pressure causes the cyclonic winds to get “heavier.” The heavier air mass needs a stronger force to keep it swirling at the same speed. When this doesn’t happen, the Polar Vortex is more difficult to keep in check.

The winds that normally keep the Polar Vortex in place have slowed down enough so that the Vortex has seeped out of the Arctic. What we’re experiencing in the Lower 48 is actual Arctic weather. This is why temperatures have plunged: Weather that is normally found in northern Canada is now on the US East Coast!

How long will this Arctic weather continue? Eventually the fast-moving winds that keep the Vortex in check will return and the Polar Vortex will return to its Arctic domain. In the meantime, we’ll be experiencing below-normal-weather conditions.

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