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

Abstract

Temperature and sea level variability within the Indonesian seas and southeast Indian Ocean are described
\nbased on expendable bathythermograph deployments along volunteer merchant shipping lines under way since
\n1983. These data resolve variability at time scales ranging from the intraseasonal to the interannual. A lagged
\npartial regression technique reveals that anomalies from a mean seasonal cycle of temperature and sea level for
\nseasonal to interannual time scales can be largely understood in terms of free Kelvin and Rossby waves generated
\nby remote zonal winds along the equator of the Indian and Pacific Oceans, with local wind forcing appearing
\nto play a minor role. About 60%–90% of sea level variability and 70% of thermocline temperature variability
\ncan be accounted for in this way. Variations in zonal Pacific equatorial winds force a response along the Arafura/
\nAustralia shelf break through Pacific equatorial Rossby waves exciting coastally trapped waves off the western
\ntip of New Guinea, which propagate poleward along the Australian west coast. The signature of this Pacific
\nenergy radiating westward across the Banda Sea and into the subtropical south Indian Ocean within 1500 km
\nof the coast is also prevalent. Equatorial Indian Ocean wind energy propagates along the Sumatra–Java–Nusa
\nTenggara waveguide to penetrate the Savu Sea, the western Banda Sea and Makassar Strait, thus having an
\nimpact on the western internal seas. Hence the region comprises the intersection of two ocean waveguides, as
\nfirst predicted by Clarke and Liu.