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:
- 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).
Technical Notes
The North Pacific Indices produced by NCAR's Climate Analysis Section are based on Trenberth and Hurrell (1994). They are currently offerred as ascii text files in a 2-column YYYYMM and VALUE format, for monthly index, November thru March (NDJFM) anomaly, and NDJFM index values.
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. Use this page to find the latest file rather than bookmarking the file that you downloaded last time.
Questions about this dataset? Contact Adam Phillips (asphilli (AT) ucar.edu).
Years of Record
Formats
Timestep
Data Time Period Extended?
Domain
Input Data
Download Data
Monthly North Pacific Index [23.3 KB file] Details:
23.3 KB updated through: 2022/03 missing value: -999.0 Units: hPa Next update 2023/04 or as requested.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].
Download Data
NDJFM North Pacific Index [1.99 KB file] Details:
1.99 KB updated through: 2022/03 missing value: -999.0 Units: hPa Next update 2023/04 or as requested.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].
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.)
Download Data
NDJFM North Pacific Index anomalies [1.88 KB file] Details:
1.88 KB updated through: 2022/03 missing value: -999.0 Units: hPa Next update 2023/04 or as requested.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].
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.)
