Coupling is key for the tropical Indian and Atlantic oceans to boost super El Niño

The influences of the tropical Indian and Atlantic oceans on the development of El Ni & ntilde;o Southern Oscillation (ENSO), especially regarding super El Ni & ntilde;o events, have been a subject of debate. In particular, several studies argue that these cross-basin influences may be mere statistical artifacts resulting from the high auto-correlation of ENSO. To clarify this issue, we conduct a series of perfect model hindcast experiments to untangle the individual and synergistic effects of the tropical Indian and Atlantic oceans. Our results clearly demonstrate that without these cross-basin effects, the Pacific warming would rarely reach super El Ni & ntilde;o level. Specifically, the individual effect of the Indian Ocean efficiently enhances the development of super El Ni & ntilde;o events. In contrast, the Atlantic's effect is initially limited because it fails to establish the Bjerknes feedback in the Pacific. However, when coupled with the Indian Ocean, the Atlantic's effect becomes more pronounced as it is amplified by the Bjerknes feedback established by the Indian Ocean.