From 30 Years of Data, Scientists Uncover the Behaviour of the South Java Coastal Current

The Climate and Atmospheric Research Centre, together with the Artificial Intelligence and Cyber Security Research Centre of the National Research and Innovation Agency (BRIN), in collaboration with the Department of Marine Science at Padjadjaran University (UNPAD), have carried out a comprehensive reconstruction of the dynamics of the South Java Coastal Current (SJCC).

The long-term study, which observed data from 1993 to 2023, maps how global climate phenomena influence the circulation of the sea current, which acts as a driver of weather and maritime wealth in Indonesia’s southern region.

For information, the SJCC is a surface current that predominantly flows eastward along the coast from western Sumatra to the southern coast of Java and Sumba Island.

This current carries warm water masses from the tropical Indian Ocean, playing a crucial role in regulating rainfall patterns, sea surface temperature, and the productivity of fisheries in the area.

“Generally, the surface current flowing eastward forms year-round. On intraseasonal scales, the SJCC shows a dominant periodicity cycle of about 76 days. However, its strength and extent change drastically when interacting with global climate phenomena such as the Indian Ocean Dipole (IOD) and El Niño-Southern Oscillation (ENSO),” said Yosef on Monday, 18 May 2026, quoted from BRIN’s site.

The study reveals that under normal conditions from June to September (the southeast monsoon), the eastward-flowing surface current forms mainly along the southern coast of Java.

This occurs due to pressure from the South Equatorial Current whose intensity is increasing. The mass of water from the SJCC during the southeast monsoon is indicated to originate from the Java Sea entering through the Sunda Strait.

However, the story is different when the Negative IOD (as in 2016) or La Niña (as in 2010) occurs. In those conditions, the SJCC strengthens massively along the southern Java coast, triggered by the weakening of the southeast monsoon and the increasing intensity of equatorial Kelvin waves.

Conversely, during October to January, when Positive IOD (as in 2019) and El Niño (as in 2015) occur, the SJCC current weakens significantly or is even suppressed.

Specifically, the study highlights 2023 as an extreme period where Positive IOD and El Niño occurred simultaneously.

“Both phenomena occurring together lead to suppression or weakening of the SJCC current very strongly from September to December 2023. This condition was accompanied by a drastic drop in sea level height or Sea Level Anomaly reaching around -16 cm to -17 cm off the south coast of Java,” Yosef explained.

Through long-term data analysis of 30 years, the researchers concluded that the influence of the IOD phenomenon has a much stronger and more direct impact on SJCC variability than the ENSO phenomena (El Niño/La Niña).

“A deep understanding of the reconstruction of the SJCC current is not merely an academic exercise. It is a crucial instrument for Indonesia to improve the accuracy of regional circulation predictions, heat transfer, and local climate variability,” added Yosef.

For the real sector, this BRIN-UNPAD collaboration provides a scientifically valuable basis to strengthen global climate modelling, develop strategies for adapting to climate change in coastal areas, and support the national catch fisheries management sector.

This is because the SJCC current dynamics are closely related to the upwelling phenomenon (the stirring or rise of seawater from the depths to the surface). This upwelling brings nutrients and other nutrients to the surface, making it a hub for high-value fisheries commodities relied upon by Indonesian fishers.