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Polar vortex: The science behind the cold
_Elsa_
Posts: 37,047 
‘Atmospheric scientist Aditi Sheshadri discusses how the polar vortex works, what drives its behavior and why it seems to bring storms and bitter cold more frequently than in past decades.
The polar vortex forms every winter because of the temperature difference between the equator and the poles. In the polar stratosphere, sunlight basically gets cut off during the late fall and early winter – and that makes it really cold, while the equator remains quite warm.
A jet forms to balance this temperature difference. This jet is what we call the polar vortex or the polar night jet. It flows in a complete circle around the pole, 10 kilometers or a little over six miles above the Earth’s surface.
What drives the behavior of the polar vortex? - It's strongest in the middle of winter when the temperature difference is at the maximum. But at the same time, the polar vortex is this living creature. It’s affected by waves created at the surface of the Earth, which get excited by things like flow moving over mountains or flow moving over land and sea, which heat up to different extents. If Earth’s surface was completely flat – if you had an aqua planet with ocean all the way around – then the polar vortex wouldn’t break up.
These flows of air, known as Rossby waves, propagate upwards into the stratosphere, where they break just like waves break on a beach. You have this vortex that’s peacefully going around the pole. Every time a wave breaks, it imparts momentum to the vortex.
Sometimes a breaking wave can be strong enough to displace the vortex over the pole, or even reverse the direction of the vortex. When that happens, the temperature in the polar stratosphere can go up by 50 degrees in a week. It’s really an extreme event. These waves can also perturb the vortex enough that it splits into two segments, called daughter vortices.’ (Source)
“Maybe that’s why we are having such weird weather,” Elsa thinks to herself.
Let’s continue - What happens when the vortex splits?
Start at the beginning – The year that spring forgot
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