Prospects and Limitations of Seasonal Atmospheric GCM Predictions
Abstract Climate simulations and hindcast experiments of increasingly large ensemble size are being performed to determine the predictive capability of atmospheric general circulation models (AGCMs) on seasonal or longer time scales. These have exhibited large sensitivity to anomalous boundary forcing associated with global sea surface temperatures (SSTs). Large-scale patterns of climate anomalies are at times generated in the extratropics when the AGCM is forced by the SSTs associated with El Nino events. It remains to be determined whether on average such results imply useful predictive skill for seasonal means in the extratropics. Indeed, given the prospects for small, if not negligible, skill in the extratropics as revealed in variance tests of boundary-forced potential predictability, one is forced to question and examine the limits of AGCM methods. These issues are addressed within the context of a large ensemble of climate simulations using an AGCM forced with observed SSTs for the 1982–93 period. ...