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Polar Vortex

Started by roadman65, December 31, 2024, 06:43:14 PM

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roadman65

I've been reading when one of them becomes weak, they unleash cold air to the south of the Arctic.

Normally the Vortex when strong, will keep the colder air in the polar regions. 

However, in physics, hot air is drawn to colder air and therefore in reality the warmer air is being drawn to the North Pole. The loss of warmth creates such colds here, and I'm guessing messes with the polar caps then?
Every day is a winding road, you just got to get used to it.

Sheryl Crowe


Road Hog

Late to the party here for sure, but the "polar vortex" is a misnomer that attempts to explain every cold snap that happens at any time of the year. Even in the glorious summer of 2014 that saw lows in the 60s in Texas for a few days in July.

When the polar vortex is strong, it stays put. When it weakens, what happens is the mid-latitude jet stream relaxes, and that lets cold air pour in from the north. At the same time the pole is invaded by subtropical air which can make Baffin balmy and Fairbanks friendly.

This particular air originated on the other side of the North Pole in Siberia, which can be even colder than polar air. (Exhibit A: February 2021.) But for most folks this time it won't result in anything other than low 20s or high teens, which is like, "meh." (As long is it don't snow!)

This is going to be more of an East Coast event.

wxfree

I've read that the technical definition of the polar vortex is stratospheric.  I don't know much about that.  Down here in the troposphere, it's a circulation that's both horizontal and vertical.  A vortex is a spinning fluid mass.  When it's strong, it's more stable.  The cold air piled up over the pole is heavy and wants to spread equatorward (for simplicity, let's say southward, discussing the North Pole).  This isn't because it wants to go south, but because it wants to sink, which results in spreading out at the ground.  It can just as easily spread northward if the coldest air is over Siberia rather than the pole.  A meteorology book I read compared it to a bucket full of sand upside-down on the beach.  If you pull the bucket off, the sand will sink, disappearing at higher levels and spreading out at the bottom.  This is simply because it's heavy and unstable, as a semi-fluid.  Cold air acts that way, although the difference in density is much smaller, so it's slower to sink.

The bucket, in a sense, is the vortex.  It confines the sand and keeps it from sinking.  The actual vortex is a spinning mass of air.  This spin is induced by the temperature gradient.  The physics is a little complex.  Air that's colder hugs the ground more, so as you go up, the pressure falls more rapidly.  Warmer air is less concentrated toward the ground, so the pressure falls more slowly with height.  (The differences are small, but since air overall is so light, it doesn't take much pressure to move it.)  At each level, 10,000 or 20,000 or 30,000 feet, the pressure over the colder air will be lower than it is over the warmer air.  This produces a pressure gradient that increases with height.  This is where jet streams happen, and why they happen over strong surface temperature gradients.

A spinning fluid mass is always unstable to some degree and will occasionally the spin will break down into a chaotic pattern.  If it's weaker, it's more unstable and more likely to break down, due in part to the conservation of angular momentum.  The polar regions are warming faster, I've read four times faster, than the rest of the planet.  The result is weaker temperature gradients and weaker pressure gradients in the upper levels above the poles.  This produces a weaker vortex that is more likely to break down into chaos, which releases the coldest air to sink and spread out at the ground.  This warms the upper levels of the troposphere over the poles because the sinking cold air is replaced with warmer air from the south.  That's where the warm southern air goes during a cold outbreak, 30,000 feet over the North Pole.  There's also a horizontal circulation, so the warm air can move at the surface far to the north.

The resulting pattern is more stable, with cold heavy air spread out over the ground and the warmer air in the upper levels where it wants to be.  The sun warms the ground in Georgia, which warms the air above it, while the same doesn't happen over Santaland, Siberia, or Greenland, and the vortex rebuilds itself.
I'd like to buy a vowel, Alex.  What is E?



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