Changes in ocean conditions in the eastern North Pacific are commonly attributed to unusual equatorial warming or cooling, but particularly in the case of warm events, the relationship is not always strong. Cold events seem to be more strongly coupled to higher latitudes. In most such cases, cooling at higher latitudes appeared to be simultaneous with that at the equator. Warm and cold equatorial events are not distributed evenly through the record. One might wonder if this long cool period set the stage for the subsequent regime shift.
Intensity is defined as the average of the extreme anomalies during three consecutive months.
Sea Grant Program, Univ. of Washington.