A Decadal Weakening in the Connection between ENSO and the Following Spring SST over the Northeast Tropical Atlantic after the Mid-1980s

Abstract

Abstract The north tropical Atlantic (NTA) displays significant sea surface temperature anomalies (SSTA) during the ENSO decaying spring. This study identifies a largely weakened impact of ENSO on the SSTA concentrated over the northeast tropical Atlantic (NETA) after the mid-1980s, while the impacts on the SSTA over the northwest tropical Atlantic (NWTA) are stable during the whole period. Different SST datasets can recognize this weakened connection between ENSO and the NETA SSTA, suggesting the robustness in this decadal variation. The El Niño–related teleconnections shift westward after the mid-1980s, and thus the anomalous southwesterly, leading to the positive NTA SSTA via the wind–evaporation–SST feedbacks, is restricted over the NWTA without extending eastward. As a result, the positive SSTA rises only over the NWTA but is diminished over the NETA. The regime shift in these circulation anomalies is due to the westward shift in the El Niño–induced convection and circulation anomalies from the eastern equatorial Pacific (EEP) to the central equatorial Pacific (CEP). Further analysis indicates that the intensified zonal SST gradient over the equatorial Pacific leads to a westward shift of Pacific Walker circulation after the mid-1980s. The westward shift of Walker circulation contributes to the convergent circulation anomalies over the CEP and thus results in the El Niño–induced precipitation anomalies concentrated there. Significance Statement Previous studies have indicated a positive connection between ENSO and the succeeding spring SSTA over the north tropical Atlantic (NTA), and this connection tends to be unstable. This study identifies a decadal weakening in the connection between ENSO and the SSTA actually concentrated over the northeast part of tropical Atlantic (NETA) after the mid-1980s. Further analysis indicates that the decadal changes in the ENSO–NETA connection are due to the westward shift in the ENSO-related convection and teleconnections, resulting from the westward shift of Pacific Walker circulation, induced by the intensified zonal SST gradient over the equatorial Pacific after the mid-1980s. The result implies a decadal change in NTA SSTA structure, which may bring different climate anomalies in the surrounding area.