Impacts of Climate Modes on Interannual Mesoscale Eddy Variability in the Southeastern Tropical Indian Ocean

Mesoscale eddies in the southeastern tropical Indian Ocean (SETIO) are important for regional circulation, heat transport, and ecological process. The El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) are known to modulate these eddies, yet their effects to the interannual variability (IV) of eddy dynamics remain inadequately understood. Significant IV in SETIO eddies is primarily driven by baroclinic processes, with barotropic influences being secondary. Composite analyses show enhanced eddy activity during pure La Niña and positive IOD years, and reduced activity during pure El Niño and negative IOD years. In the case of concurrent ENSO-IOD events, these climate modes exert counteracting effects, with the IOD dominating eddy variability during ENSO developing years, and the ENSO exerting greater influence during its decay phase. Dynamically, ENSO impacts SETIO eddy dynamics mainly by changes in the Indonesian Throughflow (ITF), whereas the IOD's influence is related to wind-driven upwelling and partially attributable to ITF changes. Numerical experiments show that the IV of SETIO eddies is primarily wind-driven, with winds over the equatorial Pacific, equatorial Indian, and SETIO all significantly contributing to the variability, though the former have a stronger influence. Additionally, oceanic channel effects from equatorial Pacific and Indian winds are stronger than the influence of pure atmospheric processes. These findings offer new insights into the complex impacts of climate modes on oceanic dynamics, improving the predictability of SETIO eddy on interannual timescales and providing essential support for ecosystem and fisheries management decision-making.