Re-emergence of Indian Ocean Equatorial undercurrent under early positive Indian Ocean Dipole

The re-emergence of swift and transient Equatorial Undercurrent in the Indian Ocean significantly redistributes mass and heat across the basin, exacerbating large uncertainties in regional climate projections. Although canonical positive Indian Ocean Dipole events typically phase-lock with autumnal re-emergence of Equatorial Undercurrent, here we report an unusual summer re-emergence in 2008 under the early Dipole event that developed and matured in summer. This anomalous re-emergence challenges conventional understanding of Dipole-undercurrent teleconnections, unveiling two critical mechanisms: First, enhanced summer wind-thermocline couplings during early Dipole events intensify equatorial wave activity, driving the undercurrent’s summer re-emergence, with preceding La Niña conditions further amplifying this effect through slow-propagating boundary-reflected waves. Second, future projections using coupled climate models indicate that such summer re-emergence events may become more frequent under global warming due to shifts in anomalous Walker Cells. These findings enrich our understanding of global undercurrent diversity and facilitate subsequent research on tropical circulation-ecological effects. The seasonally vanishing Indian Ocean Equatorial Undercurrent can re-emerge in boreal summer under enhanced wind-thermocline coupling due to a rare summer-peaking Indian Ocean Dipole, according to analysis of mooring data and wave dynamics