Specified time-varying sea-surface temperatures (SST) of the extreme phases of El Niño-Southern Oscillation (ENSO), sea ice extent and different initial atmospheric flow configurations over the midlatitudes are used in a series of general circulation model (GCM) experiments to analyze variability over the Pacific North American (PNA) sector. These experiments are performed with the second-generation Canadian Climate Centre atmospheric general circulation model, CCC-GCM2 (hereafter referred to as AGCM2). Two-way analysis of variance (ANOVA) and Empirical Orthogonal Function (EOF) techniques are applied to the model results to assess and quantify the effects of the prescribed sea-surface temperatures and different initial flow regimes (zonal and meridional) on the modes of midlatitude variability over the PNA sector. Results show that the prescribed ENSO sea surface temperatures significantly influence the midlatitude simulated variability at 500 hPa in a form of the PNA teleconnection pattern. In addition, the initial flow configuration is seen to have a small but significant effect on midlatitude variability. The interaction between the ENSO effect and the initial flow configuration does not significantly influence the midlatitude atmospheric variability. This indicates the effects of the perturbation of the ENSO SST and the internal atmospheric dynamics on the total variability are additive. The contribution to the total variability over the PNA sector by the specification of the initial atmospheric flow regime also manifests itself in a PNA-like pattern.
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