A polar vortex is a large-scale cyclone located near either of the geographical poles. Located in the middle and upper troposphere and the stratosphere, they surround the polar highs and lie in the wake of the polar front.
Typical polar vortex configuration (source:NOAA)
The polar vortices are cold-core low-pressure areas that strengthen in the winter and weaken in the summer due to their reliance upon the temperature differential between the equator and the poles. They usually span less than 1,000 kilometres (620 miles) in which the air circulates in a counter-clockwise fashion (in the Northern Hemisphere) due to the Coriolis effect.
The Northern Hemisphere vortex often has two centres, one near Baffin Island and the other over north-east Siberia. The Antarctic vortex in the Southern Hemisphere tends to be located near the edge of the Ross Ice Shelf near 160 west longitude.
The breakup of the polar vortex is one of the main factors that determine the season transition (end of winter and beginning of spring).
The polar vortex can cause snowstorms and blizzards that affect large areas.
Ozone depletion occurs within the polar vortex, particularly over the Southern Hemisphere, and reaches a maximum in the spring.
Specific impact on aviation operations include very cold ground temperatures, necessitating significant corrections to approach and safety altitudes, as well as greater than average amounts of winter precipitation which could occur as snow or, in some cases, as freezing rain.