Interdecadal modulation of El Ni\xf1o\u2013tropical North Atlantic teleconnection by the Atlantic multi-decadal oscillation

Abstract

It has been well documented that El Niño (La Niña) 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 Niño–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 Niño 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 Niño 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 Niño 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 Niño on TNA-SST is expected to ensue.