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Laboratory for Atmospheric and Space Physics

Polar Vortex

The polar vortex is a large circumpolar cyclone in the middle atmosphere that forms in the fall due to decreased solar insolation at polar latitudes. The vortex is present in both hemispheres during the winter and decays during the spring season. It is maintained radiatively by cold temperatures at the pole due to a lack of ozone heating during polar night. The vortex is occasionally disrupted by the upward propagation of planetary waves from the troposphere and the amplitude of these waves is larger in the Northern Hemisphere (NH) than in the Southern Hemisphere (SH). Extreme disruptions to the vortex are referred as sudden stratospheric warming events (see Sudden Stratospheric Warmings section). These disruptions result in the vortex being displaced off the pole and in some cases even split into two separate cyclones. When this occurs, significant changes in middle atmosphere chemistry and dynamics are observed and these changes are linked to tropospheric weather patterns.

See example below of the Arctic vortex in the Modern Era Retrospective-analysis for Research and Applications (MERRA) data on 1 December 1981. This figure shows the 3-D structure of the Arctic vortex (colored by temperature) from the tropopause to the middle mesosphere and planetary waves propagating up from the troposphere (black regions). The vortex size increases with height and wind speeds are largest around the edge of the vortex. Descent is largely confined to the region inside the vortex and thus the vortex is responsible for the transport of mesospheric air to the lower stratosphere during the winter.