Impact of Atlantic multidecadal oscillation on interannual relationship between ENSO and East Asian early summer monsoon

Impact of the Atlantic multidecadal oscillation (AMO) on the interannual relationship between the El Nino-Southern Oscillation (ENSO) and East Asian early summer monsoon (EAESM) is investigated using observations and community atmosphere model (CAM) outputs. We find that the interannual ENSO-EAESM relationship displays a prominent decadal variation during 1951-2018, which is consistent with the AMO phase change, that is, a high ENSO-EAESM correlation appears during the negative AMO phase, while no significant correlation is found during the positive AMO phase. Further analyses reveal that the AMO-related sea surface temperature anomalies (SSTAs) in the western North Pacific, rather than in the North Atlantic, modulate the interannual relationship between the El Nino and EAESM. These SSTAs can prolong the existence of the anomalous western North Pacific anticyclone (WNPAC) from the ENSO mature winter to the subsequent early summer, thus affecting the ENSO-EAESM relationship for the El Nino events. In contrast, the AMO modulates the interannual relationship between the La Nina and EAESM through the North Atlantic and North Pacific. The North Atlantic warming-induced anomalous anticyclone weakens the background cyclone over the western North Pacific during the positive AMO phase, and the mid-latitude air-sea interaction in the North Pacific also influence the anomalous cyclone. The observed AMO's impact on the interannual relationship between the ENSO and EAESM is confirmed by atmosphere general circulation model simulations using the CAM.