Extended Data Fig. 3

3d representations of the mean sea surface topography. a, b, Averaged over 6 months after (a) warm (positive) and (b) cold (negative) ENSO-IOD phases, respectively induced by regional anti-cyclonic (AC) positive and cyclonic (C) negative wind stress curls along the equatorial Indian Ocean west of 100^°E, which is coupled to the atmospheric Pacific Walker Cell circulation^10,24. In contrast, sea surface height (SSH) variability in the eastern Indian Ocean is derived from the western Pacific Ocean via the Indonesian Throughflow (ITF; Extended Data Figs. 1a, 2c-f). Black arrows indicate schematic representation of the zonal Walker circulation. During positive ENSO phases, the center of atmospheric deep convection shifts eastward, resulting in anomalous descending air masses over the western Pacific Ocean and Maritime Continent⁶³. The corresponding anomalous easterlies induce down-welling Rossby waves in the central Indian Ocean that propagate westward as positive SSH anomalies, increasing the thermocline depth at the SCTR while decreasing the meridional SSH gradient and corresponding SEC in the western Indian Ocean^10,24 (Extended Data Fig. 2b). Conversely, the SSH gradient and in turn the SEC flow increases during negative ENSO phases. The associated westerlies/easterlies induce upwelling and thermocline shoaling (dark blue) in the western/eastern Indian Ocean, and in turn promote deep atmospheric convection and excess rainfall over the Maritime Continent/eastern Africa via sea atmospheric interactions^10,17. The Mozambique Channel Throughflow (MCT) that is related to the westward flow of the SEC north of Madagascar therefore increases following a negative-cold ENSO-IOD phase (b) and vice versa (a).