Abstract
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.
Highlights
The southeastern tropical Indian Ocean (SETIO) plays an important role in ocean and atmosphere dynamics of Indian Ocean
As we are interested in investigating characteristics of the main ocean currents that exist in the SETIO adjacent to the Sumatran and Javan southern coasts, such as the South Java Current (SJC), Indonesian Throughflow (ITF), and South Equatorial Current (SEC), in this study we only considered major components of those currents, namely the zonal current component, which was analyzed from the surface to 800 m depth
Results of this study show that a maximum value of the eastward current at ASM, AWJ, and AEJ is found at a certain depth, and this strengthening of eastward flows is supposed to be attributed to a baroclinic Kelvin wave
Summary
The southeastern tropical Indian Ocean (SETIO) plays an important role in ocean and atmosphere dynamics of Indian Ocean. Several features make the SETIO region unique This is partly due to the presence of the Indonesian Throughflow (ITF) (Gordon, 1986; Wyrtki, 1987; Murray and Arief 1988; and publications made thereafter), which transfers warm and fresh Pacific waters to the Indian Ocean and contributes to variability of sea surface temperature (SST) in the SETIO, in the area off Java and Sumatra, which in turn affects the climate system both at regional and global scales (Clark et al, 2003; Saji and Yamagata, 2003). It has been recognized that the SJC and SJUC play an important role in distributing warm and fresh water into and out of the southeastern Indian Ocean and in turn influence the global climate system (e.g., Fieux et al, 1994, 1996; Sprintall et al, 1999, 2010; Wijffels et al, 2002; Wijffels and Meyers, 2004)
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