Predicting and observing el nino.

In October 1974 the occurrence of a weak El Niño event was predicted for early 1975 on the basis of the southern oscillation index. An expedition was organized to observe the event in the waters off Peru and Ecuador during two cruises in order to study its occurrence and its development with time. During the first cruise a massive transgression of warm low salinity water across the equator to 4 degrees S was observed, as well as a depression of the thermocline along the equator and off the coast of South America, indicating the start of El Niño development. During the second cruise the oceanographic situation had changed and conditions were returning to normal.