Abstract
Abstract The primary effect of El Nino–Southern Oscillation (ENSO) sea surface temperature (SST) anomalies is to force distinct midlatitude patterns, and not only to modify the probability of the internal variability patterns [such as the Pacific–North American (PNA) pattern of Wallace and Gutzler]. Both the spatial structure and probability distribution of the external ENSO pattern are distinct from the PNA pattern. Ensemble general circulation model (GCM) integrations for 30 winters have been analyzed in the Pacific–North America region. These winters span the recent period of 1981/82 through 1998/99, plus 12 earlier winters; the entire dataset includes six El Nino (warm) and seven La Nina (cold) events. The ensemble size is nine simulations. Empirical orthogonal function (EOF) analysis is carried out for all GCMs and observed seasonal means, for the GCM ensemble means, and for the GCM deviations about the ensemble means. EOF-1 of the GCM 200-hPa height (Z) ensemble mean agrees well with EOF-1 of all GC...
Published Version
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