An Intersection of Oceanic Waveguides: Variability in the Indonesian Throughflow Region

Temperature and sea level variability within the Indonesian seas and southeast Indian Ocean are described on expendable bathythermograph deployments along volunteer merchant shipping lines under way since 1983. These data resolve variability at time scales ranging from the intraseasonal to the interannual. A lagged regression technique reveals that anomalies from a mean seasonal cycle of temperature and sea level for to interannual time scales can be largely understood in terms of free Kelvin and Rossby waves generated remote zonal winds along the equator of the Indian and Pacific Oceans, with local wind forcing appearing play a minor role. About 60%–90% of sea level variability and 70% of thermocline temperature variability be accounted for in this way. Variations in zonal Pacific equatorial winds force a response along the Arafura/ shelf break through Pacific equatorial Rossby waves exciting coastally trapped waves off the western of New Guinea, which propagate poleward along the Australian west coast. The signature of this Pacific radiating westward across the Banda Sea and into the subtropical south Indian Ocean within 1500 km the coast is also prevalent. Equatorial Indian Ocean wind energy propagates along the Sumatra–Java–Nusa waveguide to penetrate the Savu Sea, the western Banda Sea and Makassar Strait, thus having an on the western internal seas. Hence the region comprises the intersection of two ocean waveguides, as predicted by Clarke and Liu.