Hurrell Wintertime SLP-based Northern Annular Mode (NAM) Index

The NAM (or Arctic Oscillation) is defined as the first EOF of NH (20°-90°N) winter SLP data. It explains 23% of the extended winter mean (December-March) variance, and it is clearly dominated by the NAO structure in the Atlantic sector. Although there are some subtle differences from the NAO regional pattern over the Atlantic and Arctic, the main difference is larger amplitude anomalies over the North Pacific of the same sign as those over the Atlantic. This feature gives the NAM a more annular (or zonally-symmetric) structure. Positive values of the NAM are associated with lower-than-normal sea level pressures over the Arctic and westerly wind anomalies along ~55º-60ºN.

To Access Resource:

Questions? Email Resource Support Contact:

  • Phillips, Adam
    asphilli@ucar.edu
    UCAR/NCAR - Climate and Global Dynamics Laboratory

Temporal Range

  • Begin:  1899-01-01
    End:  2016-03-31

Keywords

Resource Type dataset
Temporal Range Begin 1899-01-01
Temporal Range End 2016-03-31
Temporal Resolution Seasonal
Bounding Box North Lat 90
Bounding Box South Lat 20
Bounding Box West Long -180
Bounding Box East Long 180
Spatial Representation N/A
Spatial Resolution N/A
Related Links

Hurrell North Atlantic Oscillation (NAO) Index (Station-Based) : The NAO Index, and alternative to the NAM.
Additional Information N/A
Resource Format NETCDF
Standardized Resource Format NetCDF
Asset Size N/A
Legal Constraints

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Access Constraints citation: NAM Index Data provided by the Climate Analysis Section, NCAR, Boulder, USA. Updated regularly. Accessed DD Month YYYY [list date you accessed the data].
Software Implementation Language N/A

Resource Support Name Phillips, Adam
Resource Support Email asphilli@ucar.edu
Resource Support Organization UCAR/NCAR - Climate and Global Dynamics Laboratory
Distributor N/A
Metadata Contact Name Phillips, Adam
Metadata Contact Email asphilli@ucar.edu
Metadata Contact Organization UCAR/NCAR - Climate and Global Dynamics Laboratory

Author Hurrell, James
Publisher UCAR/NCAR - Climate and Global Dynamics Laboratory
Publication Date 1995-01-01
Digital Object Identifier (DOI) Not Assigned
Alternate Identifier N/A
Resource Version N/A
Topic Category climatologyMeteorologyAtmosphere
Progress onGoing
Metadata Date 2023-11-12T10:05:02
Metadata Record Identifier climatedataguide.ucar.edu::node.658
Metadata Language eng
Suggested Citation Hurrell, James. (1995). Hurrell Wintertime SLP-based Northern Annular Mode (NAM) Index. UCAR/NCAR - Climate and Global Dynamics Laboratory. https://climatedataguide.ucar.edu/node/658. Accessed 27 October 2025.

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