A "polar vortex" or "Arctic cyclone"

A polar vortex (also known as an Arctic cyclone, sub-polar cyclone, and a circumpolar whirl) is a persistent, large-scale cyclone located near one or both of a planet's geographical poles. On Earth, the polar vortices are located in the middle and upper troposphere and the stratosphere. They surround the polar highs and lie in the wake of the polar front. These cold-core low-pressure areas strengthen in the winter and weaken in the summer. They usually span 1,000–2,000 kilometers (620–1,240 miles) in which the air is circulating in a counter-clockwise fashion (in the northern hemisphere). As with other cyclones, their rotation is caused by the Coriolis effect.

The Arctic vortex in the Northern Hemisphere has two centres, one near Baffin Island and the other over northeast Siberia. In the southern hemisphere, it tends to be located near the edge of the Ross ice shelf near 160 west longitude. When the polar vortex is strong, the Westerlies increase in strength. When the polar cyclone is weak, the general flow pattern across mid-latitudes buckles and significant cold outbreaks occur.

Ozone depletion occurs within the polar vortex, particularly over the southern hemisphere, which reaches a maximum in the spring.
Duration and Power
Polar cyclones are climatological features which hover near the poles year-round. They are weaker during summer and strongest during winter. Extratropical cyclones which occlude and migrate into higher latitudes create cold-core lows within the polar vortex. Volcanic eruptions in the tropics lead to a stronger polar vortex during the winter for as long as two years afterwards. The strength and position of the cyclone shapes the flow pattern across the hemisphere of its influence. An index which is used in the northern hemisphere to gauge its magnitude is the Arctic oscillation.

The Arctic vortex is elongated in shape, with two centres, one normally located over Baffin Island in Canada and the other over northeast Siberia. In rare events, when the general flow pattern is amplified (or meridional), the vortex can push further south as a result of axis interruption, such as during the Winter 1985 Arctic outbreak. The Antarctic polar vortex is more pronounced and persistent than the Arctic one; this is because the distribution of land masses at high latitudes in the northern hemisphere gives rise to Rossby waves which contribute to the breakdown of the vortex, whereas in the southern hemisphere the vortex remains less disturbed. The breakdown of the polar vortex is an extreme event known as a sudden stratospheric warming, here the vortex completely breaks down and an associated warming of 30-50 degrees Celsius over a few days can occur.

Sudden stratospheric warming events, when temperatures within the stratosphere warm dramatically over a short time frame, are associated with weaker polar vortices. These changes aloft force changes down below in the troposphere. Strengthening storm systems within the troposphere can act to intensify the polar vortex by significantly cooling the poles. La Nina-related climate anomalies tend to favor significant strengthening of the polar vortex.

Outside Earth
Other astronomical bodies are also known to have polar vortices, including Venus (double vortex - that is, two polar vortices at a pole ), Mars, Jupiter, Saturn and Saturn's moon Titan.

http://en.wikipedia.org/wiki/Polar_vortex