Monsoonal Wind‐Driven Ocean Dynamics Drive Seasonal Sea Surface Temperature Variability in the Indonesian Seas

Abstract

The governing mechanisms of sea surface temperature (SST) variability in the Indonesian seas, which exerts a significant influence on atmospheric convection and Indo‐Pacific climate, are investigated using observations and high‐resolution regional ocean model simulations. Observations show that SST variability is dominated by the seasonal band, accounting for approximately 68% of the total variance, with 45% and 23% corresponding to the annual and semi‐annual components, respectively. Temperature variability extends to the thermocline depth and exhibits a distinct spatial pattern, characterized by the amplification of SST variability along the Indonesian Throughflow (ITF). Analysis of the model temperature variance budget indicates that this variability is largely driven by oceanic processes. Monsoon‐driven Ekman upwelling and downwelling act across and displace the shallow thermocline in this region, generating temperature anomalies at the thermocline depth. These anomalies are subsequently transmitted to the surface by the surface‐intensified mixing, which exchanges heat between the mixed layer and the ocean interior. At the surface, temperature anomalies are advected by the ITF, leading to the downstream amplification of the SST variability along its pathway, consistent with the observations. These results suggest that local and remote oceanic processes controlling the thermocline depth can modulate seasonal SST variability in the region, thus having potential implications for atmospheric convection and climate in the Indo‐Pacific and globally.