Distinct sources of dynamical predictability for two types of Atlantic Niño

Atlantic Nino, lasting approximately 3 months, manifests as pronounced sea surface temperature (SST) anomalies in the eastern equatorial Atlantic on the interannual time scale. There are two primary types of Atlantic Nino events: one peaking in boreal summer and the other in boreal winter. Sources of dynamical predictability for the two types of Atlantic Nino remain elusive. Through the analysis of seasonal forecasts and hindcasts from various climate models, the present study uncovers distinct sources of dynamical predictability for the boreal summer and winter Atlantic Nino. The prediction skill of the boreal summer Atlantic Nino is closely associated with SST anomalies in the Angola coast, especially those tied to the Benguela Nino. In contrast, the prediction skill of the boreal winter type is significantly influenced by the Indian Ocean Dipole (IOD) and El Nino-Southern Oscillation (ENSO). Due to the superior predictability of the IOD and ENSO in boreal autumn, there is an enhanced prediction skill for the boreal winter Atlantic Nino. Conversely, climate models often struggle to predict the Benguela Nino, leading to a diminished prediction accuracy for the boreal summer Atlantic Nino. Further analysis reveals that the strength of the simulated Atlantic-Benguela Nino connection is sensitive to the Benguela Nino-related surface wind anomalies over the equatorial western-central Atlantic and Angola coast. These results imply that the prediction skill of the Atlantic Nino, especially for the boreal summer type, might be further improved through better capturing the Atlantic-Benguela Nino connection in the models.