Atlantic Preconditions Contribute to Shaping the Autumn Indian Ocean Dipole–Winter Atlantic Niño Teleconnection

ABSTRACT The Atlantic Niño, a dominant climate phenomenon in the tropical Atlantic with substantial impacts on surrounding continents, is significantly modulated by the Indian Ocean dipole (IOD). However, the relationship between these two climate modes exhibits pronounced interdecadal variations over the past decades, and the underlying mechanisms remain elusive. With a focus on the possible causes of this non‐stationarity, we find that neither the IOD's own forcing strength nor the concurrent influence of Pacific ENSO alone can fully explain these interdecadal variations. Observational analyses and numerical experiments with CESM1.2.2 demonstrate that Atlantic preconditions play a crucial role in shaping the IOD–Atlantic Niño relationship. During the period when the IOD–Atlantic Niño relationship is weak, the positive phase of the boreal autumn IOD often coincided with cold sea surface temperature (SST) anomalies in the equatorial Atlantic in the preceding summer. These cold Atlantic conditions suppress the development of an Atlantic Niño in subsequent months. In contrast, during the period when the IOD–Atlantic Niño relationship is significant, the boreal autumn IOD generally occurred alongside normal Atlantic preconditions, favouring an in‐phase relationship between the boreal autumn IOD and the following winter Atlantic Niño. Furthermore, we find that the differences in the Atlantic preconditions are related to the type of ENSOs. Continuing ENSOs, developing from the previous winter and prevalent during the weak IOD–Atlantic Niño relationship period, induce pronounced tropical Atlantic preconditions in the following summer. In contrast, emerging ENSOs, developing later in the year and more common during the strong relationship period, are associated with normal Atlantic preconditions. These findings enhance our understanding of the IOD–Atlantic Niño teleconnection and have significant implications for the seasonal prediction of the latter.