Intraseasonal variability in the indo-pacific throughflow and the regions surrounding the Indonesian seas

Intraseasonal oscillations in sea level, sea surface temperature, and upper ocean how field have recently been observed in various locations surroundi ng the Indonesian seas. While the observed oscillations at these locations have similar wave periods ranging from 30 to 85 days, their forcing mechani sms can involve different dynamic processes. In order to clarify the dynami c processes essential for the observed intraseasonal signals, the authors a dopted in this study a fine-resolution 1 1/2-layer reduced-gravity model an d carried out a series of model experiments by varying coastline geometry a nd surface wind forcing. From these carefully designed experiments, they sh ow that the intense 50-day oscillations observed at the entrance of Celebes Sea are a result of Rossby wave resonance in which the frequency of cyclon ic eddy shedding by the retroflecting Mindanao Current matches that of the gravest Rossby mode of the semi-enclosed Celebes Sea basin. These 50-day os cillations of the Celebes Sea have a large impact on the throughflow in the Makassar Strait and Banda Sea, but do not contribute significantly to the throughflow changes in the Lombok, Ombai, and Timer Straits. The observed intraseasonal signals along the Sumatra/Java coasts in the eas tern Indian Ocean are dominated by oscillations with wave periods of 50 and 85 days. The origin of these wave signals can be traced back to the centra l equatorial Indian Ocean where the surface zonal wind fluctuates intraseas onally with the same wave periods. The remotely induced coastal Kelvin wave s along the Sumatra/Java coasts strongly influence the Lombok Strait, but e xert no direct influence upon the Ombai and Timer Straits farther to the ea st; the gap of the Lombok Strait is found to conduit the Kelvin wave signal s effectively into the Makassar Strait and the Banda Sea. The intraseasonal signals observed in the Timer Passage have a dominant wave period of 30-35 days. The model simulation further suggests the presence of a second spect ral peak around 85 days. Both of these intraseasonal signals are attributab le to the local, along-archipelago wind near the Timer Passage.