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