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| | | North Atlantic Oscillation |
Maintained by IOC
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| | The North Atlantic Oscillation (NAO) is a climate mode characterized by an oscillating pressure variability between the normally sub-tropical high pressure area located over the vicinity of the Azores (Portugal) and a sub-polar low pressure area over the vicinity of Iceland. This north-south dipole is a very dominant feature of natural climate variability that most notably impacts the winter weather patterns of Europe as well as fish stocks of the North Atlantic. In general terms, the high over the Azores and the low over Iceland are regular climatic features, however during winter they experience an intensification. Depending on the direction of the pressure intensification, an NAO event is considered either positive or negative. During the positive phase of the NAO, winters in northern Europe tend to be warmer and wetter, while the Meditteranean countries experience less precipitation; conversely, a negative phase of the NAO is generally associated with a colder winter across northern Europe and a wetter one in the Meditteranean. Moreover, an average of 2 or 3 NOA events occur per winter. However, in the last 30 years, the occurrance of NOA events have increased. Whether this increase is a natural part of the climate mode, or a result of anthropogenically induced changes to the chemical make-up of the atmosphere (ozone depletion, dramatically increasing levels of carbon dioxide) is currently one of the major questions researchers are trying to answer. |  | | | | A climate index is a tool scientists develop to map basic facts of climate modes in a manner that reveals the basic pattern of the climate mode. The NAO index is derived from the steepness of the pressure gradient between the high and the low pressure systems mentioned above. Graphic and source material courtesy of Martin Visbeck of the Lamont-Doherty Earth Observatory / | | | | |
 | | | | | Websites  CLIVAR Atlantic CLIVAR Atlantic seeks to understand and predict seasonal to decadal climate var...
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