| Ensemble of seasonal forecasts done with four atmospheric models over 26 winters and springs (1969-1994) are used to investigate the Northern Hemispheric model responses to SST anomalies and to compare them with observations. The response, for winter (DJF) and spring (MAM), is obtained as the regression of the 500hPa geopotential heights against the main modes of sea surface temperature (SST) variability over two different regions of the world oceans. The regression against the main mode of the equatorial Pacific Ocean SST, takes the expected form of the Pacific-North-America (PNA) pattern both in models and observations. The response to the North Atlantic SST is an AO/NAO-like signal for the observations and also, to varying degrees, for the models. The similarity of the regression to the third mode of equatorial Pacific SST and to the first mode of North Atlantic SST during the spring season is discussed, along with the nonlinear features of the ENSO influence. |
