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EARTH SCIENCE > CLIMATE INDICATORS > ATMOSPHERIC/OCEAN INDICATORS > TELECONNECTIONS > NORTH ATLANTIC OSCILLATION

Definition:
The North Atlantic Oscillation (NAO) index is often defined as the
difference of sea-level pressure between 2 stations situated close to
the "centres of action" over Iceland and the Azores. Stykkisholmur
(Iceland) is invariably used as the northern station, whereas either;
Ponta Delgada (Azores) Lisbon (Portugal) Gibraltar are used as the
southern station.
Strong positive phases of the NAO tend to be associated with
above-normal temperatures in the eastern United States and across
northern Europe and below-normal temperatures in Greenland and
oftentimes across southern Europe and the Middle East. They are also
associated with above-normal precipitation over northern Europe and
Scandinavia and below-normal precipitation over southern and central
Europe. Opposite patterns of temperature and precipitation anomalies
are typically observed during strong negative phases of the
NAO. During particularly prolonged periods dominated by one particular
phase of the NAO, abnormal height and temperature patterns are also
often seen extending well into central Russia and north-central
Siberia.


Reference:
From NOAA/NWS:
http://ww2.wrh.noaa.gov/climate_info/Arctic_N_Atlantic_Oscillation....
See also: "http://horizon.atmos.colostate.edu/ao/