The Atlantic Niño is the dominant mode of interannual variability in the equatorial Atlantic Ocean, characterized by warm sea surface temperature anomalies in the central and eastern tropical Atlantic Ocean. A recent study has identified two types of the Atlantic Niño, with the warming centered in the central and eastern basin, respectively. Here we explore the formation mechanisms for the two types of the Atlantic Niño by analyzing observational data and performing numerical experiments. A heat budget analysis reveals the horizontal heat transport as the key driver shaping the distinct patterns between the central and eastern Atlantic Niño (CAN and EAN). This is linked to stronger eastward warm advection in the central basin in the CAN; in the eastern basin, the northward cold advection during the CAN and southward warm advection in the EAN have opposite effects. By contrast, thermocline deepening favors warming in both the central and eastern basin during the two Atlantic Niño types and thereby do not play an important role in differentiating them. Standalone atmospheric and oceanic model experiments reveals a crucial role of local air-sea coupling in driving the ocean current and thermocline anomalies during both the CAN and the EAN. These findings contrast with the equatorial Pacific, where the thermocline feedback predominantly contributes to the eastern basin warming during El Niño. The discrepancies across the two basins are linked to their different mean states.

Atlantic Niño,ENSO