December-February average eastern and central Pacific sea surface temperature deviations from average: Part a: Niño 1+2 (east Pacific; on x-axis) and Niño 3.4 (central Pacific; on y-axis) departures from average; and Part b: E (east Pacific; x-axis) and C (central Pacific; y-axis) departures from average. The year corresponding to December is indicated. Extraordinary El Niño events are indicated in red, while other eastern Pacific and central Pacific El Niño events are in green and blue, respectively. Gray indicates non- El Niño years. In both parts (a) and (b), the dotted lines are an attempt to summarize the relationships shown by the dots, and the abrupt change of the slope of the dotted line highlights the uniquely different behavior shown by the 1982 and 1997 cases, and to a much smaller extent the 1972 case.