A general circulation model study of january climate anomaly patterns associated with interannual variation of equatorial Pacific sea surface temperatures

A general circulation model has been run in the perpetual January mode to produce several long-term simulations, each distinguished a different imposed equatorial Pacific sea surface temperature. From each of these simulations the authors have extracted an eight-member ensemble of 90-day averaged fields. Ensemble-mean difference maps are presented in this paper, together with an estimate of the statistical significance of features which appear in these maps. These results are compared with observational studies in the literature that present difference maps of Northern Hemisphere winter fields composited according to some index related to the two extremes of equatorial Pacific sea-surface temperature variation. The results show many anomaly patterns of high statistical significance that are also in good agreement with those observed. In the tropics, these include 990 mb wind, sea level pressure and rainfall anomalies constituting the southern Oscillation, as well as a 200 mb height anomaly at all longitudes.