Connections between the Pacific Ocean Tropics and Midlatitudes on Decadal Timescales

Abstract

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