# Cold air mass from polar region. Replaced with anything?
**URL:** https://boards.straightdope.com/t/cold-air-mass-from-polar-region-replaced-with-anything/477444
**Category:** Factual Questions
**Created:** [December 16, 2008, 7:55pm UTC](https://boards.straightdope.com/t/cold-air-mass-from-polar-region-replaced-with-anything/477444 "2008-12-16T19:55:31Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@meanoldman](https://boards.straightdope.com/u/meanoldman)
#### Post date: [December 16, 2008, 7:55pm UTC](https://boards.straightdope.com/t/cold-air-mass-from-polar-region-replaced-with-anything/477444/1 "2008-12-16T19:55:31Z")
Much of northern North America is currently a bit chilly. I’ve heard it said that there is a polar air mass or Canadian air mass or an air mass from some place farther north than where the weather reporter happens to be at the time, that is responsible for the cold.
So, is there warmer (warmer for “up there” ) air displacing the cold air streaming down at us?
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### Author:  [@Napier](https://boards.straightdope.com/u/Napier)
#### Post date: [December 16, 2008, 8:38pm UTC](https://boards.straightdope.com/t/cold-air-mass-from-polar-region-replaced-with-anything/477444/2 "2008-12-16T20:38:09Z")
Of course. Air heats in the tropics and rises, moves toward the poles, gets cold there and sinks, and moves toward the tropics. There are more complications, but this is one of the big patterns.
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### Author:  [@The\_Flying\_Dutchman](https://boards.straightdope.com/u/The_Flying_Dutchman)
#### Post date: [December 16, 2008, 9:06pm UTC](https://boards.straightdope.com/t/cold-air-mass-from-polar-region-replaced-with-anything/477444/3 "2008-12-16T21:06:34Z")
> [@meanoldman](#):
>
> Much of northern North America is currently a bit chilly. I’ve heard it said that there is a polar air mass or Canadian air mass or an air mass from some place farther north than where the weather reporter happens to be at the time, that is responsible for the cold.
>
> So, is there warmer (warmer for “up there” ) air displacing the cold air streaming down at us?
Air is not a liquid though it is a fluid. It is compressible through temperature and gravity. The flow of air is due to relative pressures seeking equilibrium. This causes both vertical and horizontal flows.
Thus , for the time being all thats mostly going on with the air up north is a dropping of pressure.
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### Author:  [@RedSwinglineOne](https://boards.straightdope.com/u/RedSwinglineOne)
#### Post date: [December 16, 2008, 11:25pm UTC](https://boards.straightdope.com/t/cold-air-mass-from-polar-region-replaced-with-anything/477444/4 "2008-12-16T23:25:21Z")
Generally, the jet stream travels from the Pacific to the Atlantic close to the Canadian border. It is sometimes split, or deflected south by a high pressure area in Canada. This brings cold air from Canada to the U.S… It usually heads back north after passing the high pressure area.
So I think it is not so much cold air being displaced south, as it is easterly winds temporarily dipping south of the border.
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### Author:  [@dtilque](https://boards.straightdope.com/u/dtilque)
#### Post date: [December 17, 2008, 7:29am UTC](https://boards.straightdope.com/t/cold-air-mass-from-polar-region-replaced-with-anything/477444/5 "2008-12-17T07:29:32Z")
I asked essentially the same question last January and didn’t get a satisfactory answer: [Arctic outbreak](http://boards.straightdope.com/sdmb/showthread.php?t=453054)
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### Author:  [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)
#### Post date: [December 17, 2008, 1:54pm UTC](https://boards.straightdope.com/t/cold-air-mass-from-polar-region-replaced-with-anything/477444/6 "2008-12-17T13:54:24Z")
I’m not a met guy but I’ve had to study bits of it on occasion, unfortunately I’ve data dumped as much as I can.
**Napier** has the basics of it. There is a wiki article [here](http://en.wikipedia.org/wiki/Atmospheric_circulation) describing the main circulation patterns. The one of interest in terms of polar air masses moving south to bring cold weather to the warmer latitudes would probably be the “polar cell”.
> [@](#):
>
> The Polar cell is likewise a simple system. Though cool and dry relative to equatorial air, air masses at the 60th parallel are still sufficiently warm and moist to undergo convection and drive a thermal loop. Air circulates within the troposphere, limited vertically by the tropopause at about 8 km. Warm air rises at lower latitudes and moves poleward through the upper troposphere at both the north and south poles. When the air reaches the polar areas, it has cooled considerably, and descends as a cold, dry high pressure area, moving away from the pole along the surface but twisting westward as a result of the Coriolis effect to produce the Polar easterlies.
It should be noted that these patterns are nowhere near as neat and tidy as pictured. The variation in seasons causes substantial changes as well as the presence of landmasses or oceanic areas etc.
**dtilque** , your own thread contains an incorrect assumption. You picture warmer air replacing the cold air that has left the arctic because warmer air is all that is available, however there IS colder air available, it descends from higher altitudes. In fact it descends _because_ it is colder.