Three evolution patterns of Central‐Pacific El Niño

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.