Climatic Research Unit : Data

North Atlantic Oscillation (NAO)


Please read the note in the File Format section regarding incorrect documentation of the format that may have caused you to incorrectly process this data.

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).

See also :

December 2000: The values for Gibraltar have been altered. New documentation will be in a paper currently in preparation by Jones, Briffa and Osborn.

File format (NAO)
for year = 1821 to 2000
  format(i5,12f7.2,f8.2) year, 12 * monthly value, annual value
Missing values represented by -99.99

March 2004 - Erratum: The format given above was previously incorrectly given as (i5,13f7.2)
If you used this fixed format to read the values you would suffer two errors:
  1. Loss of precision: second decimal place would not be read
  2. Bad missing data: missing values would be read as -99.9 so may not be detected as missing by your program
If you used free-format reading it should have worked correctly.
Please accept our apologies for incorrectly documenting this dataset

File format (Station 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 18 kilobytesNAO
nao_azo.dat 10 kilobytesPressure data for Ponta Delgada, Azores
nao_gib.dat 14 kilobytesPressure data for Gibraltar
nao_ice.dat 14 kilobytesPressure data for South-West Iceland


Last updated: March 2004, Mike Salmon

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