North Pacific (NP) Index by Trenberth and Hurrell; monthly and winter

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NP Index
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The North Pacific Index (NP index or NPI) is the area-weighted sea level pressure over the region 30°N-65°N, 160°E-140°W. The NP index is defined to measure interannual to decadal variations in the atmospheric circulation. The dominant atmosphere-ocean relation in the North Pacific is one where atmospheric changes lead changes in sea surface temperatures by one to two months. However, strong ties exist with events in the tropical Pacific, with changes in tropical Pacific SSTs leading SSTs in the north Pacific by three months.

Key Strengths

Key Strengths

Long timeseries running from 1899 to present.

Depicts changes in the intensity of the Aleutian low, and is highly correlated with the 500hPa PNA index from Wallace and Gutzler (1981).

Official North Pacific Index cited in Trenberth & Hurrell (1994).

Please cite data sources, following the data providers' instructions
Dataset DOIs
None
Hosted Climate Index Files
  1. North Pacific Index (monthly)

    Missing Value
    -999

    Units
    hPa

    Updated Through
    2024-03-31

    Next Update
    2025-05-01

    Start Date
    1899-01-01

    File Notes

    CAS Citation
    NP Index Data provided by the Climate Analysis Section, NCAR, Boulder, USA, Trenberth and Hurrell (1994). Updated Regularly. Accessed DD Month YYYY [list date you accessed the data].

  2. North Pacific Index (NDJFM)

    Missing Value
    -999

    Units
    hPa

    Updated Through
    2024-03-31

    Next Update
    2025-05-01

    Start Date
    1899-01-01

    File Notes
    NDJFM North Pacific Indices: The station index value for year N refers to an average of November and December year N-1 and January, February, and March year N. (Example: The 1999 value contains the average of November and December 1998 and January, February, and March 1999.)

    CAS Citation
    NP Index Data provided by the Climate Analysis Section, NCAR, Boulder, USA, Trenberth and Hurrell (1994). Updated Regularly. Accessed DD Month YYYY [list date you accessed the data].

  3. North Pacific Index Anomalies (NDJFM)

    Missing Value
    -999

    Units
    hPa

    Updated Through
    2024-03-31

    Next Update
    2025-05-01

    Start Date
    1899-01-01

    File Notes
    NDJFM North Pacific Index anomalies based on 1925-1989 mean of 1008.9 hPa NDJFM North Pacific Indices: The station index value for year N refers to an average of November and December year N-1 and January, February, and March year N. (Example: The 1999 value contains the average of November and December 1998 and January, February, and March 1999.)

    CAS Citation
    NP Index Data provided by the Climate Analysis Section, NCAR, Boulder, USA, Trenberth and Hurrell (1994). Updated Regularly. Accessed DD Month YYYY [list date you accessed the data].

Data Access
None
Usage Restrictions
None

Cite this page

Acknowledgement of any material taken from or knowledge gained from this page is appreciated:

Hurrell, James &, Phillips, Adam & National Center for Atmospheric Research Staff (Eds). Last modified "The Climate Data Guide: North Pacific (NP) Index by Trenberth and Hurrell; monthly and winter.” Retrieved from https://climatedataguide.ucar.edu/climate-data/north-pacific-np-index-trenberth-and-hurrell-monthly-and-winter on 2024-06-18.


Citation of datasets is separate and should be done according to the data providers' instructions. If known to us, data citation instructions are given in the Data Access section, above.


Acknowledgement of the Climate Data Guide project is also appreciated:

Schneider, D. P., C. Deser, J. Fasullo, and K. E. Trenberth, 2013: Climate Data Guide Spurs Discovery and Understanding. Eos Trans. AGU, 94, 121–122, https://doi.org/10.1002/2013eo130001

Key Figures

Other Information

Earth system components and main variables

Years of record
to
Data time period extended
Yes, data set is extended
Timestep
Monthly, Seasonal
Formats:
Input Data

SLP from NCAR (Trenberth/Palino) SLP

Vertical Levels:
None
Missing Data Flag
None
Ocean or Land
None
Spatial Resolution
None
Model Resolution (reanalysis)
None
Data Assimilation Method
None
Model Vintage (reanalysis)
None