Coherent intraseasonal oceanic variations in the eastern equatorial Indian Ocean and in the Lombok and Ombai Straits from observations and a high‐resolution OGCM

Abstract

Ongoing acoustic Doppler current profilers (ADCP) observation in the eastern equatorial IndianOcean and a recent International Nusantara Stratification and Transport (INSTANT) experiment in the Indonesian Throughflow (ITF) straits have shown coherent intraseasonal oceanic variations in this region. The intraseasonal variations are dominated by 30-70 day variations, with a tendency for the observed currents in the eastern equatorial Indian Ocean to lead those at the Lombok and Ombai Straits. Phase speed of these eastward propagating signals estimated using lag correlation analysis does not correspond to one particular baroclinic mode, though it is in the range expected for the first two baroclinic modes. In this study, the dynamics underlying this intraseasonal coherency is evaluated using output from a high-resolution ocean general circulation model developed for the Earth Simulator (OFES). The results from model simulation of January 2001 through December 2007 show that the first two baroclinic modes dominate the intraseasonal variations in this region. While the first and second baroclinic modes have comparable contribution to the intraseasonal oceanic variations in the eastern equatorial Indian Ocean and in the Ombai Strait, the intraseasonal oceanic variations in the Lombok Strait are dominated by the first baroclinic mode. Moreover, the analysis reveals that the intraseasonal variability at all mooring sites is mostly confined in the upper layer above 100 m depth. Both equatorial wind from the Indian Ocean and alongshore winds off Sumatra and Java play important roles in generating intraseasonal variations in the Lombok and Ombai Straits.

Atmosphere‐ocean coupled processes in the Madden‐Julian oscillation

“…The Indonesian Throughflow cools and freshens the eastern Indian Ocean [Gordon, 2005]. Indian Ocean Kelvin waves forced by westerly wind bursts (section 3.3.4) are partially transformed to coastal Kelvin waves, where they can modulate the Throughflow [Gordon, 2005;Sprintall et al, 2009;Gordon et al, 2010;Drushka et al, 2010;Sprintall et al, 2010;Iskandar et al, 2014] and tidal mixing [e.g., Schiller et al, 2010]. From the perspective of MJO convection, the Maritime Continent presents reduced ocean area, steep island terrain, and strongly forced diurnal convection, all of which may interfere with the intraseasonal convection and associated air-sea interactions.…”

Cross-calibrating ALES Envisat and CryoSat-2 Delay–Doppler: A coastal altimetry study in the Indonesian Seas

“…High-resolution modelling studies have suggested that the intra-seasonal variability has a time scale of 30-60 days (e.g. Iskandar et al (2006Iskandar et al ( , 2014) and the only known mooring data in this region shows deep fluctuations in this current to last at least a couple of weeks (see Figs. 2b-d of Sprintall et al (1999)).…”

Intraseasonal coastal upwelling signal along the southern coast of Java observed using Indonesian tidal station data

“…The significant correlations and respective time lags (Table ) suggested that the signals were propagated along the coasts by coastal Kelvin waves, as discussed by Iskandar et al . [].…”

“…Each correlation was statistically significant at the 99% level and the correlation coefficient of two adjacent stations was high (>0.7), which suggested that the observational data were reliable. The significant correlations and respective time lags (Table 1) suggested that the signals were propagated along the coasts by coastal Kelvin waves, as discussed by Iskandar et al [2014].…”