Intraseasonal Ocean Surface Variability Response to the Madden-Julian Oscillation: A Comparative Study of the Malacca Strait and the Indian Ocean
DOI:
https://doi.org/10.70561/geocelebes.v10i2.53104Keywords:
Intraseasonal variability, Maritime Continent, ocean surface anomalies, Outgoing longwave radiation, Phase composite analysisAbstract
The Madden–Julian Oscillation (MJO) is the dominant mode of tropical intraseasonal variability, strongly modulating atmospheric convection and upper-ocean conditions across the Maritime Continent. However, its influence on narrow semi-enclosed straits relative to adjacent open-ocean regions remains insufficiently understood. This study investigated phase-dependent atmospheric and ocean-surface responses to active MJO events in the Malacca Strait (MS) and eastern Indian Ocean (IO) using daily ERA5 reanalysis and Copernicus Marine Service data for 2000-2025. Variables were interpolated onto a common 0.25° × 0.25° grid, converted to daily anomalies, and classified into eight MJO phases using the OLR-based MJO Index (OMI). Power spectral density and phase composite analyses were applied to outgoing longwave radiation (OLR), surface wind, precipitation, sea surface temperature (SST), sea surface salinity (SSS), and significant wave height (SWH). Both regions exhibited dominant OLR variability at 43-45 days, with stronger spectral power and more coherent convective signals found in the eastern IO. During phases 4-6, enhanced convection was associated with negative OLR anomalies, stronger westerly winds, and increased precipitation, whereas these responses were weaker within the MS. SST shifted from positive anomalies during phases 1-3 to negative anomalies during phases 5-7, while SSS freshening occurred earlier and more extensively in the eastern IO. SWH also increased more strongly in the eastern IO. These findings demonstrate that the semi-enclosed MS spatially modulates and attenuates MJO-related atmosphere-ocean responses, with implications for subseasonal marine monitoring and forecasting across the Maritime Continent.
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