• Graphics of daily time series of WP index (click here)

• Text file of the daily time series of WP index (NCEP1) (JRA55)
• Text file of the monthly time series of WP index (NCEP1) (JRA55) (JRA3Q) (ERA5)

The definition of WP index

1) EOF was applied to a temporal covariance matrix of geopotential height fields for individual calendar months using a monthly geopotential height field at 500 hPa for the western Pacific region (120-180E, 20-80N).
2) The daily time series of the WP index is obtained by projecting daily geopotential height anomalies onto the EOF of each month.

Details are shown in Oshika et al. (2015) and Nakamura et al. (2015).

References

Oshika, M., Y. Tachibana and T. Nakamura (2015) Impact of the winter North Atlantic Oscillation (NAO) on the Western Pacific (WP) pattern in the following winter through Arctic sea ice and ENSO: part I-observational evidence.Climate Dynamics, 45, 1355-1366. doi: 10.1007/s00382-014-2384-1. (Link)

Nakamura, T., M. Hara, M. Oshika and Y. Tachibana (2015) Impact of the winter North Atlantic Oscillation (NAO) on the Western Pacific (WP) pattern in the following winter through Arctic sea ice and ENSO. Part II: multi-model evaluation of the NAO-ENSO linkage, Climate Dynamics, 45, 3547-3562. doi: 10.1007/s00382-015-2556-7. (Link)

Ando, Y., M. Ogi and Y. Tachibana (2015) Abnormal Winter Weather in Japan during 2012 Controlled by Large-Scale Atmospheric and Small-Scale Oceanic Phenomena. Monthly Weather Review, 143, 54-63, doi: 10.1175/MWR-D-14-00032.1. (Link)

Wallace, J. M. and D. Gutzler (1981) Teleconnections in the geopotential height field during the Northern Hemisphere winter. Monthly Weather Review, 109, 784-812. doi: 10.1175/1520-0493(1981)109<0784:TITGHF>2.0.CO;2. (Link)