Impact of the tropical Indian Ocean basin mode on the Central-Pacific type of ENSO at the lag time of one year

The relationships between the tropical Indian Ocean basin (IOB) mode of sea surface temperature anomalies (SSTA) during winter and the central Pacific (CP) ENSO during the following fall-winter are investigated in observations for the period 1958–2018. Results show that the positive (negative) IOB in the tropical Indian Ocean is one possible contributor to the initiation of CP La Niña (El Niño) about one year later. This impact of IOB on the CP ENSO is most significant during 1980-2002. During this process, however, the forcing of positive IOB events on the CP La Niña events is more significant, compared to the weak impact of negative IOB on the CP El Niño. It is suggested that warming in the tropical Indian Ocean during winter produce an easterly wind anomalies over central-to-western Pacific, which result in warming in the central Pacific during the following fall-winter. This result implies that the positive IOB in the tropical Indian Ocean is one import factor in generation of the CP La Niña, which contributed to the asymmetry of the CP ENSO.