Polar vortex

A polar vortex is a persistent, large-scale cyclone located near one or both of a planet's geographical poles. On Earth, the polar vortices are located in the middle and upper troposphere and the stratosphere. They surround the polar highs and are part of the polar front.

Arctic and Antarctic variation

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 breakdown of the polar vortex is an extreme event known as a sudden stratospheric warming, here the vortex completely breaks down and an associated warming of 30-50 degrees Celsius over a few days can occur. The Arctic vortex is elongated in shape, with two centres, one roughly over Baffin Island in Canada and the other over northeast Siberia. In rare events, the vortex can push further south as a result of axis interruption, see January 1985 Arctic outbreak.

Ozone depletion

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 polar winter, 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 usually characterized as an "ozone dent," whereas the more severe ozone depletion over the Antarctic is considered an "ozone hole." This said, chemical ozone destruction in the 2011 Arctic polar vortex attained, for the first time, a level clearly identifiable as an Arctic "ozone hole".

Duration

The Antarctic Polar Vortex forms during the polar winter. The ozone hole lasts from August to November.

Outside earth

Other astronomical bodies are also known to have polar vortices, including Venus (double vortex - that is, two polar vortices at a pole [1]), Mars, Jupiter, Saturn and Saturn's moon Titan.

References

• "Polar vortex". European Environment Agency multilingual environmental glossary. http://glossary.eea.europa.eu/EEAGlossary/P/polar_vortex. Retrieved January 29, 2005. 
• "Polar vortex". Glossary of Meteorology. http://amsglossary.allenpress.com/glossary/search?id=polar-vortex1. Retrieved January 29, 2005. 
• "World temperature gradient". Integrated Publishing: Aerographer/Meteorology. http://www.tpub.com/weather2/3-2.htm. Retrieved January 29, 2005. 
• "What is the polar vortex?". The Weather Prediction.com. http://www.theweatherprediction.com/habyhints/327/. Retrieved January 29, 2005. 
• "The Antarctic Polar Vortex". Dynamics in the Ocean and Atmosphere. http://www.cfm.brown.edu/people/sean/Vortex/. Retrieved January 29, 2005. 
• "The Polar Vortex and Arctic Weather Patterns". Arctic Climatology and Meteorology. http://nsidc.org/arcticmet/patterns/polar_vortex.html. Retrieved January 29, 2005. 
• "NASA Sees into the Eye of a Monster Storm on Saturn". Cassini-Huygens: News-Press Releases-2006. http://www.jpl.nasa.gov/news/news.cfm?release=2006-137. Retrieved November 12, 2006.