Relative Contributions of the Winter South Atlantic Subtropical Dipole and Atlantic Niño to ENSO in the Following Winter

Abstract Studies have indicated that both the Atlantic Niño/Niña and South Atlantic subtropical dipole (SASD) mode in boreal winter can trigger El Niño–Southern Oscillation (ENSO) in the following winter, with a 1-yr lead time. However, their relative contributions to ENSO evolution are unknown. Using observational data and Coupled Model Intercomparison Project phase 6 (CMIP6) model simulations, this study demonstrates that the majority of SASD (Atlantic Niño) events occur independently of winter Atlantic Niño (SASD) events (including strong and weak events). Winter Atlantic Niño (Niña) events, which are not accompanied by warming (cooling) events of the SASD, are conducive to initiating La Niña (El Niño) events in the subsequent winter. However, winter SASD events, which are independent of Atlantic Niño/Niña events, cannot give rise to the Atlantic Niño/Niña through anomalous precipitation and surface winds along the equatorial Atlantic. Consequently, they are incapable of triggering significant effects in the tropical Pacific Ocean via the Walker circulation. Therefore, winter Atlantic Niño/Niña events play more important pivotal roles in interbasin interactions with ENSO evolution in the subsequent winter, whereas winter SASD events do not independently contribute to the initiation of ENSO events. The SASD appears to act synergistically with winter Atlantic Niño/Niña to affect ENSO variability. Significance Statement The leading influence of interbasin interactions on El Niño–Southern Oscillation (ENSO) development has gained increasing attention, and the considerable role of the Atlantic Ocean has been highlighted. Previous studies demonstrated that both the South Atlantic subtropical dipole (SASD) and Atlantic Niño/Niña during boreal winter contributed to the occurrence of ENSO 1 year later. However, the relative roles of these two modes in the ENSO evolution a year later are not yet clear. Our results suggest a more important role of winter Atlantic Niño/Niña in ENSO evolution in the subsequent winter, which could overcome the spring predictability barrier of ENSO. However, winter SASD events do not independently contribute to the initiation of ENSO events. These results highlight the distinct roles of the South Atlantic and equatorial Atlantic in interbasin interactions with the tropical Pacific and 1-yr leading ENSO predictions.