Indo-Pacific interactions through the Indonesian seas during the latest ENSO event (Invited Presentation)

The variations of the Indonesian Throughflow during the 2014 and 2015/2016 El Niño events are discussed using the mooring measurements in the Maluku Channel and the Halmahera Sea of the Indonesian seas. The moored current meter observations in the Maluku Channel of the Indonesian seas have shown reversals of flows within the upper thermocline in the springs of 2014, resulting in significant increase of the Indonesian Throughflow (ITF) transport toward the Indian Ocean. Upwelling Kelvin waves are generated by the ITF transport increases, which propagate eastward across the equatorial Pacific in summer to halt the onset of the 2014 El Niño. In early 2015, the current anomalies in the Maluku Channel are weak so that a major El Niño event was generated at the end of the year by the tropical Pacific ocean-atmosphere coupling. The interannual anomalies of the Maluku Channel currents are small during the mature phase of the 2015/2016 El Niño. In addition, mooring measurements in the Jailolo Strait of the Halmahera Sea have shown small interannual anomalies during the 2015/2016 El Niño. These observations challenge the existence of the interannual wave guide from the Pacific Ocean to the Indian Ocean in the eastern Indonesian seas.

During the summer of 2016, a strong negative Indian Ocean Dipole event forced record-breaking downwelling Kelvin waves propagating to the western equatorial Pacific Ocean through the Indonesian seas, which weakened the Indonesian Throughflow transport significantly. The anomalous transport is suggested to halt the onset of the 2016 La Niña and induce the 2017 warming at a one year time lag.