West Pacific Oscillation

Z500 anomaly 25–40°N minus 50–70°N, both 140°E–150°W, standardized (NOAA/PSL daily WPO boxes). Negative = high heights over the Bering Sea / Kamchatka (cold-air delivery to North America). — NOAA PSL, https://psl.noaa.gov/data/timeseries/daily/WPO/; Linkin & Nigam 2008, J. Climate 21, 1979–1997, doi:10.1175/2007JCLI2048.1