Interannual Variability of the Indonesian Throughflow Transport: A Revisit Based on 30-Year Expendable Bathythermograph Data

Based on 30-year repeated expendable bathythermograph (XBT) deployments between Fremantle, Western Australia and the Sunda Strait, Indonesia from 1984 to 2013, interannual variability of geostrophic transport of the Indonesian Throughflow (ITF) and its relationships with El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) are investigated. The annual average ITF geostrophic transport across the XBT section referenced to 400 m is estimated to be about 5 Sv, and the ITF transport has strong annual and semiannual variations, with peak values of about 10 Sv in August-September. The IOD induced coastal Kelvin waves along the Sumatra-Java coast of Indonesia and ENSO induced coastal Kelvin waves along the northwest coast of Australia, together with the radiated Rossby waves, influence the interannual variations of the ITF transport. The ITF transport is stronger at La Niña phase and weaker at El Niño phase, with the Niño3.4 index leading the ITF variability by about 7 months. The Indian Ocean wind variability associated with the IOD to a certain extent offset the Pacific ENSO influences on the ITF transport during the developing and mature phases of El Niño and La Niña, due to the co-varying IOD variability with ENSO.