Moored Observations of the Timor Passage Currents in the Indonesian Seas

The structure and variability of the currents in the Timor Passage are studied based on the measurements from a subsurface mooring deployed in the center of the passage from September 2017 to December 2019. The annual mean currents are found to flow westward into the Indian Ocean in the upper 1,400 m, with a maximum velocity core at similar to 50 m. The mean volume transport through the Timor Passage into the Indian Ocean is estimated to be -9.9 +/- 1.0 Sv (1 Sv = 10(6) m(3) s(-1)) in the upper 1,400 m with much of this transport concentrated in the upper 480 m (-8.9 Sv). This value contrasts with the estimate of -7.5 Sv above 1,890 m based on INSTANT measurements. The transport during the 2019 positive Indian Ocean Dipole event was only slightly larger than that during the 2018 normal year in the upper 480 m. The variability in the along-strait velocity in the Timor Passage is dominated by an annual cycle in the upper 150 m and a semiannual cycle in the lower layer. The annual cycle in the upper layer is mainly driven by local monsoonal forcing. Downward energy propagation is observed below 200 m, which is shown to be mainly driven by remote Kelvin waves from the Indian Ocean. The transport variability through the Timor Passage is dominated by a semiannual cycle, associated with the semiannual circulation over the equatorial Indian Ocean, with the transport in the upper and lower layers largely canceling each other in the annual cycle.