Decadal Modulation of the Relationship Between Tropical Southern Atlantic SST and Subsequent ENSO by Pacific Decadal Oscillation.

This study identifies the relationship between tropical southern Atlantic (TSA) sea surface temperature anomaly (SSTA) and the El Niño‐Southern Oscillation (ENSO) and focuses on how the Pacific Decadal Oscillation (PDO) modulates this relationship. Results suggest a significant but non‐stationary interannual TSA‐ENSO relationship which undergoes a significant decadal shift. A strong TSA‐ENSO relationship is observed during the positive PDO phase, while this relationship is weak during the negative PDO phase. Two processes, involving the anomalous Pacific Walker circulation (PWC) and the intensity of air‐sea interactions over the Pacific, are proposed for this decadal shift. During the positive PDO phase, the weak and variable PWC and strong air‐sea interaction facilitate the development of SSTA in the tropical Pacific triggered by TSA SSTA, resulting in a strong TSA‐ENSO relationship and vice versa. These findings emphasize the important role of the modulation of PDO on the TSA‐ENSO relationship. Plain Language Summary: The present study finds a significant TSA‐ENSO relationship that anomalous warm (cold) TSA sea surface temperature (SST) in the preceding winter is closely linked to the cold (warm) ENSO in the subsequent summer and winter. However, the TSA‐ENSO interannual relationship is non‐stationary, which is strong during the positive PDO phase and weak during the negative PDO phase. Two processes responsible for this non‐stationary relationship are proposed. During the positive PDO phase, the weak and variable PWC is more susceptible to the TSA forcing, resulting in a strong TSA‐ENSO relationship. Meanwhile, the strong air‐sea interaction in the tropical Pacific also facilitates the development of SSTA triggered by TSA SSTA, leading to a strong and robust TSA‐ENSO relationship. During the negative PDO phase, the situations of PWC and air‐sea interaction are opposite and thus lead to a weak TSA‐ENSO relationship. These findings could help to improve our understanding of the decadal variability of the ENSO evolution. Key Points: The relationship between tropical southern Atlantic (TSA) SST and subsequent El Niño‐Southern Oscillation (ENSO) is stronger in positive Pacific Decadal Oscillation (PDO) than in negative PDOIn positive PDO, the TSA SST anomaly easily exerts an impact on ENSO because of a weaker and more variable Walker circulationIn positive PDO, the stronger air‐sea interaction over the tropical Pacific facilitates the maintenance of local SST and wind anomalies [ABSTRACT FROM AUTHOR]