38CVC Tropical Pacific Forcing on the Atlantic Multidecadal Variability

Recent studies highlighted that tropical Pacific sea surface temperature (SST) variability, associated with the Interdecadal Pacific Oscillation, leads to a near-contemporaneous response in northern tropical Atlantic SST, hence influencing the Atlantic Multidecadal Variability (AMV). Here, by using a tropical Pacific pacemaker experiment, we show that tropical Pacific-forced AMV is stronger than previously thought because of a neglected delayed response in the North Atlantic. We revealed that North Atlantic SST responds to tropical Pacific forcing by two stages. Here, using positive SST anomalies in the central-eastern tropical Pacific as an example, and vice versa. 1) An anomalously warm central-eastern tropical Pacific forces a near-contemporaneous tripole SST response in the North Atlantic by modulating both surface heat flux and ocean dynamics. The tripole response exhibits anomalous warming in the subpolar North Atlantic and northern tropical Atlantic, and anomalous cooling in the midlatitude. 2) The anomalous warming in the subpolar North Atlantic of the tripole response inhibits deep water formation and in turn weakens the Atlantic Meridional Overturning Circulation, finally leading to a monopole cooling SST response in the North Atlantic more than a decade later. The tripole and monopole responses both contribute to tropical Pacific-forced AMV, with the latter response a bit more important. We highlight that tropical Pacific forcing substantially influences the timing of AMV phase change and the intensity of the AMV. Better representing tropical Pacific forcing in climate models will improve the simulation and prediction of the AMV.