1: A century of El Niño
The Southern Oscillation Index (red line) is the sea-level pressure measured at Tahiti minus that measured at Darwin. The CT Index (blue) is the anomaly in the sea-surface temperature averaged over the region between 5° south and 5° north, and between the Date Line and 90° west. The inverse relation between the two indices is clear, as is the variation in the onset, duration and strength of the events. The El Niño events of 1990/4 and 97/8 can be clearly seen.