North Atlantic Oscillation (NAO)

Notes about these NAO index values:

1. These values are all from the Jones/CRU NAO index (Gibraltar minus Iceland). This is most useful during the winter half of the year when Gibraltar and Iceland sea level pressures (SLP) are strongly anti-correlated and the NAO index measures a coherent pattern of stronger/weaker atmospheric flow into NW Euope. Results are also shown for the summer, but these should be interpreted carefully due to more complex circulation regimes in summer that may not be well-described by this NAO index, not least because Gibraltar SLP is influenced by the Iberian thermal low during summer months.
2. The index was generated using a 1951-1980 reference period and therefore has a mean of zero during this period. It is inconvenient that this is a period of anomalous NAO index for most seasons, so the long-term mean of the index is not very close to zero when this reference period is used. See NAO visualisations to see a more representative baseline.

• When using the NAO data, cite "Updated from Jones et al. (1997)"

• Jones, P.D., Jónsson, T. and Wheeler, D., 1997: Extension to the North Atlantic Oscillation using early instrumental pre ssure observations from Gibraltar and South-West Iceland. Int. J. Climatol. 17, 1433-1450. doi: 10.1002/(SICI)1097-0088(19971115)17:1 3<1433::AID-JOC203>3.0.CO;2-P
• Osborn TJ (2011) Winter 2009/2010 temperatures and a record-breaking North Atlantic Oscillation index. Weather 66, 19-21. doi: 10.1002/wea.660

These datasets are made available under the Open Database License. Any rights in individual contents of the datasets are licensed under the Database Contents License under the conditions of Attribution and Share-Alike. Please use the attribution Climatic Research Unit, University of East Anglia