| Summary: | The Pacific Walker circulation variability is associated with El Niño-Southern Oscillation and Interdecadal Pacific Oscillation and affects the global climate. The Walker circulation has strengthened since the comprehensive satellite observations began. This trend apparently contradicts with climate model simulations driven by historical radiative forcing, which show its weakening. Regarding this model-observation inconsistency, recent studies argue the influence of biases in the South Pacific and Southern Ocean. In the present study, we examine the remote influence of extratropical SST variability on the Pacific Walker circulation by extratropical ocean pacemaker experiments with a climate model. Restoring SST variability toward observations poleward of 15º latitudes in the Pacific (with a linearly tapering buffer zone between 10º and 15º) greatly constrains the Walker circulation variability in the interannual to multidecadal time scales. This extratropical pacemaker effect remains, albeit weaker, if the restoring region is limited to poleward of 25º latitudes. These results suggest the importance of subtropical and midlatitude SST variability in attributing, predicting, and projecting the Walker circulation changes.
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