Pathways of Intraseasonal Variability in the Indonesian Throughflow Region

The recent INSTANT measurements in the Indonesian archipelago revealed a broad spectrum of time scales that influence Throughflow variability, from intraseasonal (20-90 days) to interannual. The different time scales are visible in all transport and property fluxes and are the result of remote forcing by both the Pacific and Indian Ocean winds, and local forcing generated within the regional Indonesian seas. This study focuses on the time-dependent three-dimensional intraseasonal variability (ISV) in the Indonesian Throughflow (ITF) region, in particular at the locations of the INSTANT moorings at the Straits of Lombok, Ombai and Timor. The Bluelink ocean reanalysis in combination with the observations from the INSTANT observing program reveals that deep-reaching sub-surface ISV in the eastern Indian Ocean and ITF is closely linked with equatorial wind-stress anomalies in the central Indian Ocean. Having travelled more than 5000km in about 14 days, the associated Kelvin waves can be detected as far east as the Banda Sea. ISV near the Straits of Ombai and Timor is also significantly influenced by local wind forcing from within the ITF region. At the INSTANT mooring sites the ocean reanalysis agrees reasonably well with the observations. Intraseasonal amplitudes are about ±1.0 o C and ±0.5m/s for potential temperature and velocity anomalies. Associated phases of ISV are very similar in observations and the reanalysis. Where differences exist they can be traced backed to likely deficits in the reanalysis, namely the lack of tidal dissipation, insufficient spatial resolution or errors in surface