Polar vortex
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. The chemistry of the Antarctic polar vortex has created severe ozone depletion. The nitric acid in polar stratospheric clouds reacts with CFCs to form chlorine, which destroys ozone. These clouds can only form at temperatures below about -80°C, so the warmer Arctic region does not have a ozone hole. Other planets are also known to have polar vortices, including Mars and Jupiter.
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