Equatorial SOI (Walker)

Standardized SLP anomaly, eastern equatorial Pacific (5°S–5°N, 130–80°W) minus Indonesia (5°S–5°N, 90–140°E), 30-day means, re-standardized. Positive = strong Walker circulation (La Niña). — NOAA CPC equatorial SOI, https://www.cpc.ncep.noaa.gov/data/indices/