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.
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) and/or Jim Hurrell (jhurrell (AT) ucar.edu).
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].
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].
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].
Hurrell, James & National Center for Atmospheric Research Staff (Eds). Last modified 27 Oct 2017. "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.
Funding: NSF | National Science Foundation
Based at: NCAR | National Center for Atmospheric Research
A Project of: Climate Analysis Section in Climate and Global Dynamics Laboratory
Created by: Climate Data Guide PIs and Staff