Boundary and initial flow induced variability over Pacific North America in CCC-AGCM simulations

Abstract

Specified time-varying sea-surface temperatures (SST) of the extreme phases of El Niño-SouthernOscillation (ENSO), sea ice extent and different initial atmospheric flow configurations over the midlatitudesare used in a series of general circulation model (GCM) experiments to analyze variabilityover the Pacific North American (PNA) sector. These experiments are performed with the secondgenerationCanadian Climate Centre atmospheric general circulation model, CCC-GCM2 (hereafterreferred 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 prescribedsea-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 temperaturessignificantly influence the midlatitude simulated variability at 500 hPa in a form of the PNAteleconnection pattern. In addition, the initial flow configuration is seen to have a small but significanteffect on midlatitude variability. The interaction between the ENSO effect and the initial flow configurationdoes not significantly influence the midlatitude atmospheric variability. This indicates the effectsof the perturbation of the ENSO SST and the internal atmospheric dynamics on the total variability areadditive. The contribution to the total variability over the PNA sector by the specification of the initialatmospheric flow regime also manifests itself in a PNA-like pattern.