Kiladis and van Loon (1988) used a standard
Southern Oscillation index (SOI) combined with an
Bulletin of the American Meteorological Society 2773
SST anomaly index for the eastern tropical Pacific
(within 4° of the equator from 160°W to the South
American coast) to define an “event” and required that
the SST anomaly had to be positive for at least three
seasons and be at least 0.5°C above the mean, while
the SOI had to remain negative and below -1.0 for the
same duration. They provide a listing of “Warm” and
“Cold” events from 1877 to 1982.