Equatorial Western-Central Pacific SST Responsible for the North Pacific Oscillation-ENSO Sequence

El Ni & ntilde;o-Southern Oscillation (ENSO), the dominant mode of interannual variability in the tropical Paci fi c, is well known to affect the extratropical climate via atmospheric teleconnections. Extratropical atmospheric variability may in turn in fl uence the occurrence of ENSO events. The winter North Paci fi c Oscillation (NPO), as the secondary dominant mode of atmospheric variability over the North Paci fi c, has been recognized as a potential precursor for ENSO development. This study demonstrates that the preexisting winter NPO signal is primarily excited by sea surface temperature (SST) anomalies in the equatorial western-central Paci fi c. During ENSO years with a preceding winter NPO signal, which accounts for approximately 60% of ENSO events observed in 1979-2021, signi fi cant SST anomalies emerge in the equatorial western-central Paci fi c in the preceding autumn and winter. The concurrent presence of local convection anomalies can act as a catalyst for NPO-like atmospheric circulation anomalies. In contrast, during other ENSO years, signi fi cant SST anomalies are not observed in the equatorial western-central Paci fi c during the preceding winter, and correspondingly, the NPO signal is absent. Ensemble simulations using an atmospheric general circulation model driven by observed SST anomalies in the tropical western-central Paci fi c can well reproduce the interannual variability of observed NPO. Therefore, an alternative explanation for the observed NPO- ENSO relationship is that the preceding winter NPO is a companion to ENSO development, driven by the precursory SST signal in the equatorial western-central Paci fi c. Our results suggest that the lagged relationship between ENSO and the NPO involves a tropical-extratropical two-way coupling rather than a purely stochastic forcing of the extratropical atmosphere on ENSO.