Indian Ocean Dipole (IOD)

The Indian Ocean Dipole (IOD) is a coupled ocean-atmosphere mode defined by the SST difference between the western tropical Indian Ocean and the southeastern tropical Indian Ocean off Sumatra, measured as the Dipole Mode Index. A positive IOD has anomalously warm western and cool eastern SST, shifting convection west, bringing drought to Indonesia and Australia and heavier rain to East Africa. The negative phase reverses this. The IOD peaks in boreal autumn, often co-occurs with ENSO, and modulates the monsoon and tropical cyclone activity across the basin.