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Re: [Phys-L] Polar Vortex



On 01/07/2014 09:20 AM, LaMontagne, Bob wrote:
The current buzzword used by the media is "polar vortex". It appears
to be a rather recent term, as no meteorology texts refer to it.

NASA explains that the polar vortex is a "whirling and persistent
large area of low pressure, found typically over both North and South
poles."

A quick perusal of introductory meteorology texts finds reference
instead to the Polar High.

At this point it pays to remember that the atmosphere is
three dimensional. There is a lot going on that cannot
easily be portrayed on a two-dimensional weather map.

Also -- as always -- it pays to focus attention on the best
available ideas, and not let one's knickers get twisted by
the worst available ideas. This is good practice in general,
and double-especially when dealing with a classroom full of
non-experts.

We can make an exception for misconceptions that are
particularly prevalent and particularly pernicious,
but even then it pays to get the correct idea out
there first, and then, quite a bit later, spiral back
and explain why the wrong idea is wrong.

In accordance with the usual ultra-simplified tricellular
model, there are giant convection rolls, three per
hemisphere, namely the Hadley cell, the Ferrell cell,
and the polar cell.
http://www.av8n.com/how/htm/atmo.html#fig-cells
For simplicity, let's talk about the northern hemisphere.
The southern hemisphere is the mirror image. If we could
neglect Coriolis forces, the polar-cell air would rise in
Canada, flow northward in the stratosphere, descend over
the pole, and then flow southward back to Canada.
http://www.av8n.com/how/htm/atmo.html#fig-prevailing

Mainly due to Coriolis and to some degree due to friction,
the atmosphere cannot "fill in" behind the rising air,
so rising air is associated with low pressure at the
surface. This is why amateur weather forecasters can
get good results by associating falling pressure
*AT THE SURFACE* with deteriorating weather.

The same logic applies in reverse in the stratosphere!!!!
Here's the situation:

vertical pressure at pressure
latitude flow SURFACE ALOFT circulation
-------- -------- ------------ ----------- -----------
60° rising low high CW
90° descending high low CCW


The low-pressure polar vortex is *not* at the surface.
It is a real thing, but it is not a surface thing.

Also beware: There is such a thing as an Arctic cyclone
aka arctic vortex, which is not the same thing as a polar
vortex. Not even close.

===========

Now, AFAICT it is incorrect to say the current weather pattern
is a polar vortex or even that it is directly caused by a polar
vortex. AFAICT that's completely backwards, and really what
we are seeing is a *weakening* of the polar vortex, leading to
a stronger negative Arctic Oscillation. This leads to a warmer
Arctic along with a colder winter along the US/Canada border.

I'm not an expert, but I can read the scientific literature.
Judah Cohen, Justin Jones, Jason C. Furtado, Eli Tziperman
"Warm Arctic, Cold Continents:
A Common Pattern Related to Arctic Sea Ice Melt,
Snow Advance, and Extreme Winter Weather"
Oceanography 26(4) (2013)
http://www.tos.org/oceanography/archive/26-4_cohen.html
http://www.tos.org/oceanography/archive/26-4_cohen.pdf