Interannual Variability of Marine Heat Waves in the South Indian Ocean

Abstract Marine heat waves (MHWs) are significant extreme climate events within the oceanic system that profoundly impact ecosystems and socioeconomic conditions. The south Indian Ocean (SIO) plays a critical role in both global and regional climate regulation, influencing climate variability in regions such as Africa and East Asia. This study systematically investigates the interannual variability and dynamic mechanisms of MHWs in the SIO based on satellite sea surface temperature data and reanalysis datasets from 1982 to 2021. The MHWs in the SIO exhibit significant interannual variability associated with El Niño–Southern Oscillation (ENSO). The mean intensity anomaly of MHWs in the SIO region of 60°–90°E, 15°–25°S is significantly correlated with the Niño-3.4 index with a correlation coefficient of 0.57, lagging the Niño-3.4 index by 3 months. The mixed-layer heat budget analysis indicates that the energy source for MHWs in the SIO is mainly from the atmospheric net surface heat flux, particularly influenced by latent heat and longwave radiation. During the decaying phases of El Niño events, abnormal northwesterly winds suppress the background southeasterly winds, reducing evaporation and suppressing latent heat release from the ocean. The increase in total clouds in the SIO weakens the shortwave radiation reaching the ocean surface, but the increase in high clouds strengthens the longwave radiation as a greenhouse effect. Meanwhile, the relatively shallow mixed-layer depth could promote the formation of MHWs. This study contributes to a deeper understanding of MHWs in the SIO and their relation to large-scale ocean–atmosphere processes.