Pacific–Japan pattern (vorticity)

850-hPa relative-vorticity anomaly 20–30°N, 120–150°E minus 30–40°N, 140–180°E. Positive = cyclonic to the south, anticyclonic near Japan (Nitta's positive PJ: active Philippine-Sea convection, hot Japan). Box definition as specified for Forecast Context; published PJ indices differ (e.g. Kubota et al. 2016 use a two-point height/SLP difference). — Nitta 1987, J. Meteor. Soc. Japan 65, 373–390; Kubota, Kosaka & Xie 2016, Int. J. Climatol. 36, 1575–1589, doi:10.1002/joc.4441