JISAO data
North Atlantic Oscillation (NAO) Index

Lisbon minus Stykkisholmur Normalized December-March Average SLP Anomalies. Values ascribed to the year of the January.

Image shows significant decadal variability in the index, with positive values in 1903-14, 1920-37, and 1973-95; and negative values throughout the 1950s-60s.
PostScript | JPEG

This index was provided by Jim Hurrell ( jhurrell@ra.cgd.ucar.EDU ), and is an update of the time series published in Hurrell (1995). Jim provided seasonal means based on these calendar months as the centers-of-action of the NAO tend to move about or are not as well defined during the other calendar months. Updated values of this index, as well as monthly- and annual-mean indices are available at this link (NCAR climate and global dynamics division).

The U.S. National Centers for Environmental Prediction (NCEP) provides monthly NAO values (based on a rotated principal component analysis) and forecasts of daily NAO values.

Sea-level pressure and wind anomalies for positive values of the NAO (Mann and Drinkwater 1994).
Image shows SLP anomalies of one sign centered at 60N, 30W and of opposite sign centered at 36N, 20W, with friction-influenced geostrophic surface wind anomalies. The largest wind anomalies are along the SLP node-line and about the northern center-of-action. The pattern fills the north Atlantic.
Reference and further information:
  • Hurrell, J. W., 1995: Decadal trends in the North Atlantic Oscillation: regional temperatures and precipitation. Science, 269, 676-679.
  • a "white paper" on north Atlantic climate variabilty by John Marshall and collaborators.
  • David Stephenson's NAO WWW page
  • The Lamont-Doherty Earth Observatory NAO WWW page.
    Data:
    The following table and files contain normalized Lisbon minus Stykkisholmur normalized December-March average SLP anomalies. The index is standardized with respect to the years 1864-1983. [Jim Hurrell takes the difference of standardized time series, and I am providing the standardized difference of standardized time series.] Values are ascribed to the year of the January.
    The data is offered in 3 formats:
  • 2-column table (year and NAO value)
  • 1-column table (NAO values only)
  • A MATLAB ".mat" file ("load nao.mat" will load the data into the variable "nao."; there are values for 1860-2009; and "NaN"s for missing.).

     YEAR   +0   +1   +2   +3   +4   +5   +6   +7   +8   +9
 1860                      -56  -68   29  -75  153   93
 1870 -164  -55  -41  -27  127  -74   11    3   80 -121
 1880   49 -207  211  -13   79  -49  -61   25 -150   -1
 1890   97  -45 -110  -58  146 -217   61   59   56    2
 1900 -116  -18  -77  212   13  108  112  112   79    0
 1910  115   16   13  147   81  -11  -38 -207  -44  -44
 1920  173   89  101   94  -62  130    6   94   34  -56
 1930   50   -9  -27   14   47   53 -212   39   98   20
 1940 -156 -126  -30   81   33   89   15 -148   73  102
 1950   76  -69   45   10    7 -137  -94   83  -56  -20
 1960  -84   98 -130 -196 -156 -157  -92   70  -57 -267
 1970 -103  -52   19  137   67   89   75 -117    9 -123
 1980   31  112   44  187   87  -34   27  -41   39  277
 1990  216   56  179  146  165  216 -206  -11   39   93
 2000  153
    February 2002
    Todd Mitchell (mitchell@atmos.washington.edu)
    JISAO data