Department of Earth System Science

[1] Three evolution patterns are identified for the Central-Pacific (CP) type of El Niño based on events that occurred during 1958–2007: (1) a symmetric-decaying pattern whose sea surface temperature anomalies grow and decay symmetrically with respect to a peak phase; (2) a prolonged-decaying pattern that decays slowly and is followed by a warm event in the eastern Pacific (EP); and (3) an abrupt-decaying pattern that terminates rapidly after the peak and is followed by a cold event in the EP. The depth of the equatorial thermocline is found to determine which evolution pattern occurs. If the CP El Niño occurs in a recharged thermocline state (i.e., deeper-than-normal depth), an EP warming may appear in the decaying phase of the CP event to slow down the decay, giving rise to the prolonged-decaying pattern. If the thermocline is in a discharged state (i.e., shallower-than-normal depth), an EP cooling may occur to abruptly terminate the CP El Niño. If the thermocline is in a neutral state (i.e., normal depth), the CP event may have a symmetric pattern of growth and decay. Although a few exceptions exist, these results indicate that the equatorial thermocline state at the peak phase of a CP El Niño event can be a potential predictor of the way the event may decay.