The polar vortex
is a persistent, large-scale cyclone centred near the Earth's poles, in the middle and upper troposphere and the stratosphere. The vortex is most pronounced in the hemisphere's winter, when the temperature gradient is steepest, and diminishes or can disappear in the summer. The Antarctic polar vortex is more pronounced and persistent than the Arctic one. The Arctic polar vortex is elongated in shape, with two centres, one roughly over Baffin Island in Canada
and the other over northeast Siberia.
Other planets are also known to have polar vortices, including Mars and Jupiter.