Influence of the Madden-Julian Oscillation on the Indonesian Throughflow and Upper Ocean Variability in the Indonesian Seas

Abstract:

Previous studies indicate that equatorial zonal winds in the Indian Ocean largely influence the Indonesian Throughflow (ITF) transport, and thus they could impact the upper ocean variability in the Indonesian Seas. Since strong equatorial zonal winds in the Indian Ocean are often observed during MJO events, they could generate significant upper ocean variability through oceanic processes. This study investigates upper ocean variability in the Indonesian Seas caused by the MJO-induced equatorial zonal winds using the global eddy-resolving ocean general circulation model (HYCOM).

During the intensive observation period of DYNAMO field campaign (fall/winter 2011), three active episodes of large-scale convection associated with the MJO passed eastward across the tropical Indian Ocean. Surface westerly winds near the equator were particularly strong during the events in late November and late December, exceeding 10 m/s. These westerlies generate strong eastward jets on the equator, and downwelling near the eastern boundary.These equatorial jets are realistically simulated by HYCOM. The analysis of the model output demonstrates that anomalous positive SSH at the eastern boundary propagates along the coast of Sumatra and Java as coastal Kelvin waves, which largely reduces the ITF transport at Makassar Strait during January-February. The impact of ITF variability on upper ocean temperature and salinity in the Indonesian Seas is further discussed based on the analysis of HYCOM output.