Impacts of ENSO and IOD on Mesoscale Eddy Activity in the Southeastern Tropical Indian Ocean

Mesoscale eddies in the southeastern tropical Indian Ocean (SETIO) are crucial for regional circulation, heat transport, and ecosystem dynamics. Their interannual variability is closely associated with ENSO and IOD. Eddy activity is enhanced during pure La Niña and positive IOD years, but suppressed during pure El Niño and negative IOD years. When ENSO and IOD co-occur, their influences tend to counteract each other: the IOD dominates during the ENSO developing phase, whereas ENSO exerts a stronger influence during the decay phase. This variability is linked to changes in the Indonesian Throughflow and wind-driven upwelling associated with ENSO and IOD events. Numerical experiments further indicate that the interannual variability of SETIO eddies is primarily wind-driven, with winds over the equatorial Pacific, equatorial Indian Ocean, and SETIO all contributing significantly. Oceanic channel effects induced by equatorial Indo-Pacific winds are stronger than those arising from purely atmospheric processes.