The North Atlantic oscillation (NAO) is a complex climatic phenomenon in the North Atlantic Ocean (especially associated with fluctuations of climate between Iceland and the Azores). It is characterised predominantly by cyclical fluctuations of air pressure and changes in storm tracks across the North Atlantic. It is related to the Arctic oscillation. Flag of Azores Shaded relief map of the Azores from 1975 The Azores (Portuguese: Açores) are an archipelago of Portuguese islands in the middle of the Atlantic Ocean, about 1,500 km from Lisbon and about 3,900 km from the east coast of North America. ... Atmospheric pressure is the pressure caused by the weight of air above any area in the Earths atmosphere. ... The Arctic oscillation (AO) is the dominant pattern of non-seasonal sea-level pressure (SLP) variations north of 20N, and it is characterized by SLP anomalies of one sign in the Arctic and anomalies of opposite sign centered about 37-45N. The North Atlantic oscillation (NAO) is a close relative...

The NAO was discovered in the 1920s by Sir Gilbert Walker. Similar to the El Niño phenomenon in the Pacific Ocean, the NAO is one of the most important drivers of climate fluctuations in the North Atlantic, Europe, the Mediterranean Sea and as far east as northern sections of central Asia. Sir Gilbert Thomas Walker (1868-1958) was an English physicist and statistician of the 20th century. ... El Niño is also the nickname of Sergio García. ...

Especially during the months of November to April it explains a good deal of the variability of atmospheric disturbances in the North Atlantic region, and consequently wind speed and wind direction changes, changes in temperature and moisture distribution (within the region) and the intensity, number and track of storms. It is a key driver e.g. of whether winter storms track northward toward northern Europe, or more southerly toward the Mediterranean Sea. The Mediterranean Sea is a part of the Atlantic Ocean almost completely enclosed by land, on the north by Europe, on the south by Africa, and on the east by Asia. ...

A great deal however is not known, for example why the phase of the NAO fluctuations has reversed since the early 1980s with consequent widespread effects on North Atlantic and European weather that are difficult to disentangle from anthropogenic effects (the effects of man and the global economy).

Related material

• Atlantic Ocean
• Atmospheric pressure
• Anticyclone
• El Niño / SOI
• Global warming
• Pacific decadal oscillation

I hate related material diurnal (daily) rhythm of air pressure in northern Germany (black curve is air pressure) Atmospheric pressure is the pressure above any area in the Earths atmosphere caused by the weight of air. ... In meteorology, an anticyclone is a weather phenomenon associated with atmospheric high pressure. ... El Niño is also the nickname of Sergio García. ... Global mean surface temperatures 1856-2004 Global warming is a term used to describe an increase over time of the average temperature of Earths atmosphere and oceans. ... The Pacific Decadal Oscillation (PDO) is a 23-year pattern of Pacific climate variability, similar to the North Atlantic Oscillation (NAO). ...

External links

• UK Meteorological Office description of the North Atlantic Oscillation (http://www.met.rdg.ac.uk/cag/NAO/)
• UK's climatic research unit information sheet on the NAO (http://www.cru.uea.ac.uk/cru/info/nao/)
• Overview paper on the NAO from the USA's National Center for Atmospheric Research (http://www.cgd.ucar.edu/~jhurrell/PaperCopy/naobook.ch1.pdf)
• NAO (http://www.ldeo.columbia.edu/NAO/) by Martin Visbeck

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