Two distinct types of the Indian Ocean Dipole.

The Indian Ocean Dipole (IOD), traditionally defined by the sea surface temperature (SST) anomaly gradient between the tropical western and eastern Indian Ocean, is revealed here to comprise two distinct types. Using multiple systematic approaches, including standard deviation analysis and SST mode combinations, we identify a western-eastern type and a central-eastern type, distinguished by their SST anomaly patterns, seasonal evolution, and feedback mechanisms. The western-eastern type reaches its peak later in boreal autumn due to a strong but delayed wind-thermocline-SST feedback, whereas the central-eastern type peaks earlier, governed by a weaker and earlier feedback. Crucially, the positive western-eastern type-more strongly linked to enhanced East African rainfall than the traditional IOD-has intensified in recent decades, heightening the risk of rainfall-related disasters across East Africa. These findings refine the conceptual framework of the IOD and underscore the growing climate hazard posed by its changing characteristics.