Power spectrum analysis of Indonesian Throughflow based on INSTANT data

The observational data from the International Nusantara Stratification and Transport(INSTANT) Program is used to investigate the variation of the Indonesian Throughflow(ITF).Specifically,the power spectrum of the flow in surface and thermocline layers in the three major outflow passages is analyzed.The results show that the flow in the surface layer of the Lombok and Ombai straits has an obvious annual cycle.During the monsoon transition period,the flow reverses at all depths at the Lombok and Ombai straits,whereas the current reveres only below 300 m in the Timor Passage.The variations of the currents in both surface and thermocline layers are high at intraseasonal time scale.The annual cycle is prevalent in surface layer,while the semiannual cycle dominates in thermocline layer.At tidal frequencies,each strait shows that the semi-diurnal tide M2 is dominant expect for the surface layer of the Lombok Strait where the diurnal tide K1 is dominant.