Interdecadal modulation of El Nino-tropical North Atlantic teleconnection by the Atlantic multi-decadal oscillation

It has been well documented that El Nino (La Nina) is able to induce sea surface temperature (SST) warming (cooling) in the tropical North Atlantic (TNA) in the following spring. Based on the observational analysis, in this study we found that such a lagged El Nino-TNA SST relationship is non-stationary and depends on the phase of Atlantic multi-decadal oscillation (AMO). During the AMO negative phase, the influence of El Nino on TNA-SST becomes intensified and lasts longer till the following summer to fall, and vice versa. We demonstrated that such a modulation is through atmospheric teleconnection change because El Nino during the AMO negative phase tends to have a stronger and eastward-shifting SST warming over the eastern Pacific and the SST warming persists longer throughout late spring. It is further shown that both extratropical and tropical teleconnections are important in causing the non-stationary El Nino effect according to the AMO phase. The extratropical teleconnection is through the Pacific-North America pattern, while the tropical teleconnection is via anomalous Walker circulation. The extratropical teleconnection acts primarily during winter to early spring, while the tropical teleconnection appears more important in spring. If AMO remains in its positive phase in the near future, a weak influence of El Nino on TNA-SST is expectedto ensue.