Abstract. Detailed ocean currents in the southeastern tropical
Indian Ocean adjacent to southern Sumatran and Javan coasts have not been fully
explained because of limited observations. In this study, zonal current
characteristics in the region have been studied using simulation results of
a 1/8∘ global hybrid coordinate ocean model from 1950 to 2013. The
simulated zonal currents across three meridional sections were then
investigated using an empirical orthogonal function (EOF), where the first
three modes account for 75 %–98 % of the total variance. The first temporal
mode of EOF is then investigated using ensemble empirical mode decomposition
(EEMD) to distinguish the signals. This study has revealed distinctive features of currents in the South Java
Current (SJC) region, the Indonesian Throughflow (ITF)–South Equatorial
Current (SEC) region, and the transition zone between these regions. The
vertical structures of zonal currents in southern Java and offshore Sumatra are
characterized by a one-layer flow. Conversely, a two-layer flow is observed
in the nearshore and transition regions of Sumatra. Current variation in the
SJC region has peak energies that are sequentially dominated by
semiannual, intraseasonal, and annual timescales. Meanwhile, the transition
zone is characterized by semiannual and intraseasonal periods with
pronounced interannual variations. In contrast, interannual variability
associated with El
Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) modulates the prominent intraseasonal
variability of current in the ITF–SEC region. ENSO has the strongest
influence at the outflow ITF, while the IOD's strongest influence is in southwestern
Sumatra, with the ENSO (IOD) leading the current by 4 months (1 month).
Moreover, the contributions (largest to smallest) of each EEMD mode at the
nearshore of Java and offshore Sumatra are intraseasonal, semiannual,
annual, interannual, and long-term fluctuations. The contribution of
long-term variation (19.2 %) in the far offshore eastern Indian Ocean is
larger than the interannual (16.3 %) and annual (14.7 %) variations.
Future studies should be conducted to investigate this long-term variation.