Mechanism of Sustained and Stable Warming in the Southwest Indian Ocean

In spite of a remarkable increase in greenhouse gas emissions, the global mean surface warming rate has slowed down since the 1990s. Most of the heat flux in the atmosphere absorbed by the ocean and the increase in heat content in the Indian Ocean is particularly prominent. Previous studies have shown that the enhanced Indonesian through flow (ITF) is the biggest contributor for the warming in the upper-700 m Indian Ocean. Analysis of observational data and model reanalysis data reveal that the warming trend from 1962～1982 in Southwest Indian Ocean (SWIO) is mixed with interannual oscillation, but during 1993～2018, the SWIO experienced a sustained and stable interdecadal warming trend, forming a basin warming region of 0.4～0.8 K decade^-1 near the east of Madagascar. Particle tracer analysis and the diagnostic equation of mixed-layer heat budget indicate that the heat transported through the Indonesian through flow has no direct influence on the warming of the region, but mainly due to the enhancement of long-wave radiant flux on the surface and the enhanced transport of the ocean currents from the equator to the region. These results broaden our cognition of the interannual heat balances in the Indian Ocean and interdecadal climate change and variability.