Climatic Research Unit : Data

North Atlantic Oscillation (NAO)


Latest update (see below for earlier updates) 3 Jul 2017:

The NAO is traditionally defined as the normalized pressure difference between a station on the Azores and one on Iceland. An extended version of the index can be derived for the winter half of the year by using a station in the southwestern part of the Iberian Peninsula (Hurrell, 1995). Here we give data for SW Iceland (Reykjavik), Gibraltar and Ponta Delgada (Azores). The NAO calculated from Gibraltar and SW Iceland is also given (Jones et al., 1997).

The standard NAO index data file has been provided in the same format since 1998. This was supplemented by a version stored with 3 decimal places in 2017. The extra precision is provided for users who are making further calculations where rounding to the appropriate precision is best done at the end of the calculations.

See also :

File format (NAO index)
for year = 1821 to endyear
  format(i5,12f7.2,f8.2) year, 12 * monthly value, annual value
Missing values represented by -99.99

File format (NAO index with 3 decimal places)
for year = 1821 to endyear
  format(i5,12f8.3,f8.3) year, 12 * monthly value, annual value
Missing values represented by -99.99

File format (Station sea-level pressure)
format(i1,i5,i5,a) ?,startyear,endyear,name
for year = startyear to endyear
  format(i5,12i6) year, 12 * monthly value
Missing values represented by -10
Divide by 10 for millibars

Filename SizeDescription
nao.dat 19 kilobytesNAO index
nao_3dp.dat 22 kilobytesNAO index (stored with 3 decimal places)
nao_azo.dat 10 kilobytesSea-level pressure data for Ponta Delgada, Azores
nao_gib.dat 15 kilobytesSea-level pressure data for Gibraltar
nao_ice.dat 15 kilobytesSea-level pressure data for South-West Iceland

Change log


Last updated: April 2017, Tim Osborn

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