E index (eastern Pacific ENSO)

(PC1 − PC2)/√2 of tropical Pacific SST anomalies 10°S–10°N, 140°E–80°W (EOFs of monthly base-period anomalies, PCs unit variance; daily projection of 30-day means). — Takahashi et al. 2011, Geophys. Res. Lett. 38, L10704, doi:10.1029/2011GL047364