Effects of Interannual Variability in the Eastern Indian Ocean on the Indonesian Throughflow

Abstract

The influences of the large-scale interannual variations in the eastern Indian Ocean on the variability of the Indonesian throughflow are investigated by using an ocean general circulation model, driven by the ERS satellite winds from July 1992 to June 1997. The empirical orthogonal function (EOF) analysis of the simulated surface dynamic height variability captures two dominant modes on an interannual time scale, which are quite consistent with the available observations. The first mode indicates large amplitude in the western tropical Pacific and has a strong relation to the El Niño events, while the second EOF exhibits the large amplitude in the eastern Indian Ocean. The simulated net Indonesian throughflow shows an interannual variation of amplitude of about 15 Sv, with large transport from the Pacific to the Indian Ocean during 1994/95 and small transport during 1992 and 1997. It turns out that the net throughflow variation shows a high correlation with the second EOF mode (r = 0.51) for the whole five-year simulation. On the other hand, the correlation with the first mode is rather low (r = −0.07). However, the relative importance of the EOF modes to the throughflow variability changes with time. The upper-layer transport above a depth of 230 m in the Indonesian archipelago is also affected by the second mode. The difference in the upper-layer transport across 1°S and 110°E generates warm water convergence/divergence with a magnitude of 4 Sv within the Indonesian Seas on the interannual time scale, which shows good correspondence with sea surface temperature variation averaged over the Indonesian archipelago.