Jim Hurrell, Senior Scientist
NAO/NAM Climate Indices
Introduction to NAO Indices
Reference Information
To learn more about how the spatial structure and time series of the NAO are defined, please see Hurrell et al. (2003)
Observational data is subject to corrections after it has been published and used in our indices. Once noted, these corrections are applied to our input data, and the corresponding climate indices may change. It is thus recommended that one downloads an entire climate index each time they wish to update their holdings.
| Index | Description | Updated Thru | Next Update | Format |
| NAO Station Based (DJFM) | Winter (December through March) index of the NAO based on the difference of normalized
sea level pressure (SLP) between Lisbon, Portugal and Stykkisholmur/Reykjavik, Iceland since 1864. Detailed Description, Timeseries Plot | DJFM 2009 | June 2010 | HTML Table / ascii / Microsoft Excel File (.xls) |
| NAO Station Based (Monthly) | Monthly index of the NAO based on the difference of normalized sea level pressures (SLP) between Ponta Delgada, Azores and Stykkisholmur/Reykjavik, Iceland since 1865. The nearest NCEP/NCAR Reanalysis grid point is used as a substitute for Ponta Delgada observational data from April 2003 to present. See note above the HTML Table for more details. | August 2009 | June 2010 | HTML Table |
| NAO Station Based (3 month seasons) | Seasonal (DJF,MAM,JJA,SON) indices of the NAO are based on the difference of normalized sea level pressure (SLP) between Ponta Delgada, Azores and Stykkisholmur/Reykjavik, Iceland since 1865. The nearest NCEP/NCAR Reanalysis grid point is used as a substitute for Ponta Delgada observational data from April 2003 to present. See the Detailed Description for more details. | JAS 2009 | June 2010 | HTML Table |
| NAO Station Based (Annual) | The annual index of the NAO is based on the difference of normalized sea level pressure (SLP) between Ponta Delgada, Azores and Stykkisholmur/Reykjavik, Iceland since 1865. The nearest NCEP/NCAR Reanalysis grid point is used as a substitute for Ponta Delgada observational data from April 2003 to present. See the Detailed Description for more details. | 2008 | June 2010 | HTML Table |
| CPC NAO Projection Based (Daily) | The daily NAO index is constructed by projecting the daily (00Z) 500mb height anomalies over the Northern Hemsiphere onto the loading pattern of the NAO since 1950. Detailed Description | Today | Tomorrow | ascii (Last 120 days) / ascii (1950-Current) / Teleconnections Data Archive |
| CRU NAO Station Data (Monthly) | Sea level pressure (SLP) data from the Azores (1865-2002), Gibraltar (1821-2007), and Reykjavik, Iceland (1821-2007). | Jul. 2008 | Unknown | CRU NAO Data Updated CRU NAO Data |
| NAO PC Based (DJFM) | The principal component (PC) time series of the leading EOF of seasonal
(December through March) SLP anomalies over the Atlantic sector (20-80N, 90W-40E), available since 1899. Detailed Description, Timeseries Plot | DJFM 2009 | May 2010 | HTML Table |
| NAO PC Based (Monthly) | The principal component (PC) time series of the leading EOF of monthly
SLP anomalies over the Atlantic sector (20-80N, 90W-40E), available since 1899. Plot of Spatial Pattern, Timeseries | Dec 2009 | May 2010 | HTML Table |
| NAO PC Based (DJF) | The principal component (PC) time series of the leading EOF of DJF
(December through February) SLP anomalies over the Atlantic sector (20-80N, 90W-40E), available since 1899. Plot of Spatial Pattern, Timeseries | DJF 2009 | May 2010 | HTML Table |
| NAO PC Based (MAM) | The principal component (PC) time series of the leading EOF of MAM
(March through May) SLP anomalies over the Atlantic sector (20-80N, 90W-40E), available since 1899. Plot of Spatial Pattern, Timeseries | MAM 2009 | May 2011 or as requested | HTML Table |
| NAO PC Based (JJA) | The principal component (PC) time series of the leading EOF of JJA
(June through August) SLP anomalies over the Atlantic sector (20-80N, 90W-40E), available since 1899. Plot of Spatial Pattern, Timeseries | JJA 2009 | May 2011 or as requested | HTML Table |
| NAO PC Based (SON) | The principal component (PC) time series of the leading EOF of SON
(September through November) SLP anomalies over the Atlantic sector (20-80N, 90W-40E), available since 1899. Plot of Spatial Pattern, Timeseries | SON 2008 | May 2010 or as requested | HTML Table |
| NAO PC Based (Annual) | The principal component (PC) time series of the leading EOF of annual
SLP anomalies over the Atlantic sector (20-80N, 90W-40E), available since 1899. Plot of Spatial Pattern, Timeseries | 2008 | May 2010 | HTML Table |
| Northern Annular Mode (DJFM) |
The NAM (or Arctic Oscillation) is defined as the first EOF of NH (20-90N) winter SLP data. The normalized PC values are available since
1899.
Detailed Description, Plots | DJFM 2009 | May 2010 | HTML Table |
Reference Information
Correct reference for all NAO/NAM timeseries taken directly from this webpage:
NAO Index Data provided by the Climate Analysis Section, NCAR, Boulder, USA, Hurrell (1995).