Impact of quasi-decadal variability in the tropical Pacific on ENSO modulations

The impact of quasi-decadal (QD: 8 to 18 years) variability in the tropical Pacific on ENSO events is investigated. It is found that there is a significant difference in the behavior of ENSO events between the phases of positive and negative anomalies of the QD Nino-3.4 index. During the period of negative QD-scale Nino-3.4 index, ENSO events, especially La Nina events, occur more frequently, and larger amplitudes of thermal anomalies related to El Nino events appear over the central to eastern equatorial Pacific. Furthermore, propagations of upper ocean heat content anomaly and a phase relationship between upper ocean heat content and Nino-3 index in the equatorial Pacific, which have been pointed out by previous studies, are clearly detected during the period of negative QD Nino-3.4 index.