The Indian Ocean Dipole Mode (IODM) impacts many surrounding and remote regions of the Indian Ocean, with devastating floods over East Africa but severe droughts in countries surrounding Indonesia during a positive IODM event. Understanding the dynamics is important for seasonal prediction and climate projections, but the role of meridional temperature and circulation anomalies remains unclear. Here, we show that in combination with the zonal structure of temperature and rainfall anomalies, northward contraction of the warm water pool over the eastern equatorial Indian Ocean region (EEIO) also generates an anomalous meridional cross-equatorial temperature gradient in the east. This meridional temperature gradient controls northward retreat of the atmospheric convection in association with northward cross-equatorial winds, and hence declining rainfall over the EEIO. Our results have important implications for the mean state change under greenhouse warming.
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