Two Tropical Routes for the Remote Influence of the Northern Tropical Atlantic on the Indo-Western Pacific Summer Climate

This study investigates the influence of sea surface temperature (SST) in the northern tropical Atlantic (NTA) on the Indo-western Pacific summer climate by analyzing record-high NTA SSTs in summer 2010. In that time, a decaying El Nino and developing La Nina were accompanied by widespread anomalous climate conditions in the Indo-western Pacific. These conditions are typical of summers that follow El Nino events and are often explained as being due to the influence of Indian Ocean warming induced by El Ninos. Meanwhile, the record-high NTA SSTs that resulted from the influence of El Nino, the negative phase of the North Atlantic Oscillation and the interdecadal-and-longer NTA SST variability are one of the possible causes of anomalous conditions in the Indo-westem Pacific. The results of sensitivity experiments using a coupled atmosphere-ocean model clearly indicate that the high NTA SSTs had a considerable influence on the summer weather in the Indo-western Pacific via two tropical routes: an eastbound route that involved a reinforcement of the atmospheric equatorial Kelvin wave and a westbound route that involved altering the Walker circulation over the Atlantic-Pacific region. The altered Walker circulation facilitated the transition to La Nina, amplifying the impact on the western North Pacific monsoon. Further evaluation reveals that both the interannual and interdecadal-and-longer variability of the NTA SST contributed to the anomalous Indo-western Pacific summer. The results highlight the interannual to multidecadal predictability of the Indo-westem Pacific summer climate that originates in the NTA.