The polar vortex is a persistent, large-scale cyclone located near the Earth's poles, in the middle and upper troposphere and the stratosphere. It surrounds the polar highs and is part of the polar front.
Arctic and Antarctic variationEdit
The vortex is most powerful 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; 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 Arctic 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 catalyzes the photochemical destruction of ozone. Chlorine concentrations build up during the winter polar night, and the consequent ozone destruction is greatest when the sunlight returns in spring (September/October). These clouds can only form at temperatures below about -80°C. Since these temperatures are rarely reached in the Arctic, ozone depletion at the north pole is much less severe than at the south. Accordingly, the seasonal reduction of ozone levels over the Arctic is characterized as an "ozone dent," whereas the more severe ozone depletion over the Antarctic is considered an "ozone hole."
The Antarctic Polar Vortex forms during the polar winter. The ozone hole lasts from August to November.
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