On the Indonesian Throughflow in the OCCAM 1/4 degree ocean model

Abstract

Abstract. The Indonesian Throughflow is analysed in two runs of the OCCAM 1/4 degree global ocean model, one using monthly climatological winds and one using ECMWF analysed six-hourly winds for the period 1993 to 1998. The long-term model throughflow agrees with observations and the value predicted by Godfrey's Island Rule. The Island Rule has some skill in predicting the annual signal each year but is poor at predicting year to year and shorter term variations in the total flow, especially in El Niño years.The spectra of transports in individual passages show significant differences between those connecting the region to the Pacific Ocean and those connecting with the Indian Ocean. On investigation we found that changes in the northern transports were strongly correlated with changes in the position of currents in the Celebes Sea and off Halmahera. Vertical profiles of transport are in reasonable agreement with observations but the model overestimates the near surface transport through the Lombok Strait and the dense overflow from the Pacific through the Lifamatola Strait into the deep Banda Sea. In both cases the crude representation of the passages by the model appears responsible.In the north the model shows, as expected, that the largest transport is via the Makassar Strait. However this is less than expected and instead there is significant flow via the Halmahera Sea.

Fifty Years of the Indonesian Throughflow*

“…Among the 50-yr time series, the strongest correlation is between the island rule IR SODA and V SODA (Table 4). Limiting the comparison to only low frequencies further improves the correlation, which is a stronger correlation than the one seen in previous work comparing the island rule and ITF transport from within a particular model (Humphries and Webb 2008). PDIFF is correlated with V SODA but not with IR SODA .…”

“…The ARLINDO period was dominated by a strong ENSO event, so it is not surprising that it is comparatively easy to predict its low-frequency variability given the known relationship between the strength of the ITF and ENSO (Gordon and Fine 1996;Humphries and Webb 2008;Meyers 1996 Under normal conditions, the Indian Ocean is characterized by warmer surface water in the east and cooler surface water in the west. A positive Indian Ocean dipole (IOD) event is defined when the eastern (western) surface waters are anomalously cool (warm) and is usually synchronized with ENSO (Murtugudde et al 2000;Saji and Yamagata 2006).…”

“…This study notes that, although flow through a wide channel between Australia and Asia would be independent of Indian Ocean conditions, the narrow, shallow channels of the Indonesian seas allow both ocean basins to exert control over the flow via frictional and nonlinear effects. Humphries and Webb (2008) analyzed the ITF in the Ocean Circulation and Climate Advanced Modelling Project (OCCAM) model run with 6-hourly European Centre for Medium-Range Weather Forecasts (ECMWF) winds from 1992 through 1998. This produced a reasonably realistic total throughflow with a strong annual cycle and a correlation with ENSO.…”

Temporal Changes in Reef Community Structure at Bintan Island (Indonesia) Suggest Need for Integrated Management

“…In recent geological time, an average transport of 0.13 Sv (¼ 10 6 m 3 sec À1 ) flows annually through this channel with the aid of the monsoondriven east-to-west current, forming about 10% of the Indonesian Throughflow Tkalich 2003, Humphries andWebb 2008). Such a connection is of immense biological interest because sea habitats along the Malacca Straits serve as the most equatorial interface for gene flow between marine populations in the Indian Ocean and South China Sea (Ge and Sun 2001, Leaw et al 2001, Casey et al 2004, Lourie and Vincent 2004, Reid et al 2006, Hoeksema 2007.…”