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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.It appears that what Bob believes NASA defines as the locality of the polar vortices and what NASA defines as the locality of those vortices differ.
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. This refers to the fact that the coldness of the air over the poles, combined with the earth's general atmospheric circulation (rising air over the equator and descending air over the poles) gives rise to a generally high pressure region at the poles - not low pressure. The descending air over the poles flows southward at lower altitudes and turns somewhat to the west due to the Coriolis effect (momentum conservation basically). Eventually this air reaches warmer air to the south (Ferrell cell) and air rises where the air flow in the two air masses converge - giving a ring of generally low surface pressure at the latitude of the northern United States and Southern Canada - well south of the pole. At high altitudes (upper troposphere to stratosphere), the temperature difference between the two air masses produces a large density difference between the two air masses and a strong pressure gradi
ent directed from the warm air mass to the colder polar one. This strong gradient, in conjunction with the Coriolis effect, produces the jet stream - flowing generally from west to east. The polar air is unusually cold this year so the jet stream is very fast (180 knots in places right now). It also is dynamically unstable and wanders northward and southward along the boundary of the two air masses. As it changes direction from meandering toward the southeast to a flow to the northeast, there will be a low pressure to the north of the jet stream - associated with its turn to the left. This is quite visible in the upper air charts at the moment: http://weather.noaa.gov/pub/fax/QHUA15.TIF
There is nothing unusual or novel about these low pressure regions. They are present all the time around the jet stream - which is well south of the poles.
The reason I bring all this up is because of all the incorrect meteorology and physics that is being bantered about in the media and - wait for it - how it is supposedly connected to global warming. I have now twice seen graphics of a huge supposed "polar vortex" of low pressure that supposedly resides over the poles (remember the Polar High), followed by an explanation of how global warming has split the main vortex into two vortices that have wandered south over Southern Canada and the old Soviet Union, causing the extremely cold weather there.
This is just silliness. The low pressure flow we are seeing over Canada is often there- winter and summer. In colder winters than usual, the temperature gradient just intensifies these large scale lows producing what we all know in the US as "Alberta Clippers" or the "Montreal Express" - cold air coming in from over the Canadian plains. The media has simply repackaged these as the "Polar Vortex". As many have pointed out on this list, there is a difference between weather and climate. While global temperatures have risen over the past century, that has nothing to do with the weather we are currently experiencing.
Bob at PC
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