Long-term El Nino-Southern Oscillation (ENSO)-like variation with special emphasis on the South Pacific

Mechanisms for El Nino-Southern Oscillation (ENSO)-like decadal (7-35 years) variability are analyzed using observational data. When a decadal positive temperature anomaly occurs in the eastern tropical Pacific, the atmospheric response excites negative wind stress curl in the western tropical South Pacific, which causes the thermocline to shoal and induce a negative temperature anomaly there. The cold anomaly moves northwestward to the western and central equatorial region and then turns eastward along the equator to reverse the original temperature anomaly in the east. The eastward propagation of the oceanic signal along the equatorial thermocline correlates with a zonal wind anomaly. The cold anomaly in the east grows through tropical air-sea interaction and induces a positive wind stress curl, in the western tropical South Pacific associated with the atmospheric teleconnection in the Southern Hemisphere. Subsequent evolution of the negative phase is similar to that of the positive phase. The complete scenario for this ENSO-like decadal variability due to the air-sea interaction processes within the tropics has a period of similar to 14 years. We also discuss ENSO-like variation on the interdecadal (> 35 years) timescale, with possible relationship to the 1976-1977 climate regime shift.