Multidecadal Variations in the Tropical Western Pacific Driven by Externally-Forced AMV-Like Changes

Multidecadal sea surface temperature (SST) variations in the tropical western Pacific (TWP) have been attributed to nonlinear external forcing and remote influences from the Atlantic Multidecadal Variability (AMV). However, the AMV resulted from both internal variability (IV) and external forcing. Thus, the origins of the TWP SST variations are not well understood. By analyzing observations and model simulations, we show that more than half of the decadal to multidecadal SST variations in TWP during 1920-2020 resulted from external forcing with the forced component correlated with AMV, while the internal component is unrelated to AMV. Furthermore, about 43%-49% of the forced AMV-like SST variations in TWP result from remote influences of the forced AMV in the Atlantic via atmospheric teleconnection over the North Pacific, with the rest from other remote or local processes. Sea surface temperature (SST) variations in the North Atlantic Ocean and Pacific Ocean are linked on multidecadal time scales. Previous studies have indicated that the Atlantic multidecadal SST variations (referred to as Atlantic multidecadal variability, AMV) not only influence the decadal SST variations in the tropical central-eastern Pacific (referred to as Interdecadal Pacific Oscillation), but also modulate the multidecadal SST variations in the tropical western Pacific (TWP). Since the TWP SST variations can result from both local external forcing and remote influences from AMV, the exact origins of TWP's multidecadal variability remains unclear. Here we analyze observations and model experiments to show that similar to 56% of the decadal to multidecadal SST variations in TWP during 1920-2020 resulted from nonlinear external forcing, with the rest from internal variability (IV), and the forced SST variations in TWP are correlated with AMV while the IV-induced variations are unrelated to AMV. Both the local external forcing and remote influences from the forced AMV in the Atlantic contribute to the forced multidecadal SST variations in TWP. Atlantic Multidecadal Variability (AMV) is mainly correlated with the forced decadal sea surface temperature (SST) variations in tropical western Pacific (TWP) during 1920-2020 About 43%-49% of forced TWP SST variations, which account for more than half of the total decadal variations, come from the Atlantic Ocean The connections between the externally-forced AMV and TWP SST are through the extratropical pathway in the North Pacific