Role of the Indo-Pacific Oceanic channel in ENSO dynamics

Our understanding of the Indo-Pacific Ocean circulation has been advanced greatly in the past decades or so. The WPOC-ITF mooring arrays have provided direct synchronous time series measurements in the western tropical Pacific and in key straits of the Indonesian seas. Inter-ocean interactions are emerging as a hot research topic in the climate community nowadays. Existing theories of the ENSO have overlooked the role of the Indonesian Throughflow (ITF) and the western boundary currents due to lack of observations. In this talk, the effects of the ITF and the Mindanao Current (MC) on ENSO development and prediction are studied using satellite altimeter and reanalysis data combined with in situ hydrography and mooring data. The analyses suggest that the inter-basin interactions through the “oceanic channel” (a.k.a. the ITF) play an important role in ENSO predictability. The upwelling anomalies in the southeastern tropical Indian Ocean provide a better predictor beyond the one-year lead than the atmospheric bridge for La Niña prediction preceded by the Indian Ocean Dipole (IOD). Essentially all of the La Niña events following the positive IOD events are predicted successfully, above the 95% confidence, at the lead time of one year, underlining the importance of the “oceanic channel” dynamics in overcoming the spring barrier of ENSO prediction. The Mindanao Current (MC) is found to shift its path at the entrance of the Indonesian seas, intruding anomalously into the northern Maluku Sea in early El Niño years whereas shifting northward anomalously in La Niñas. The movement of the MC is found to force the ENSO onset over the intraseasonal wind rectification.