Connections between the Pacific Ocean tropics and midlatitudes on decadal timescales

Connections between the tropical and midlatitude Pacific on decadal timesca les are examined using a 137-yr run of a fully coupled ocean-atmosphere gen eral circulation model. It is shown that the model does a credible job of s imulating both ENSO-scale and decadal-scale variability, and that there are statistically significant correlations between thr midlatitudes and Tropic on decadal timescales. Three physical mechanisms linking the regions are e xamined: 1) Oceanic advection along isopycnal surfaces from the midlatitude subduction regions to the Tropics, 2) coastally trapped or Kelvin wave pro pagation between the Tropics and midlatitudes, and 3) near-simultaneous com munication between the regions affected by changes in the atmosphere. It is found that communication via the atmosphere explains the strongest correla tions found in the model. Further evidence is presented that is consistent with the idea that midlatitude sea surface temperature anomalies drive chan ges in the trade wind system that alter the east-west slope of the tropical thermocline, thereby effecting decadal-timescale changes in ENSO activity.