Abstract
AbstractIn the PRediction Of climate Variations On Seasonal to interannual Time‐scales (PROVOST) ensemble of seasonal simulations, performed with the European Centre for Medium‐Range Weather Forecasts (ECMWF) atmospheric general‐circulation model forced by observed sea surface temperature (SST) for the 1979–1993 period, the consistency between individual members of the ensemble of simulated temperature at 850 hPa (T850) in Europe varies considerably from year to year. This interannual variability is assumed to be a consequence of slowly varying lower‐boundary forcings, most notably the SST forcing, plus a random part from the internal, chaotic atmospheric variability. In those years when the ensemble members show a particularly consistent pattern of T850 anomalies in Europe, the consistency is significantly higher than would be expected from the interannual variability, indicating that the SST forcing has a significant impact on the model simulated temperature. Composites of global SST indicate that the El Niño/Southern Oscillation (ENSO) might be linked to the high internal consistency of some of the winter season ensembles of T850 anomaly patterns in Europe. However, in some ENSO years the ensemble shows no consistent signal in Europe, so the occurrence of an ENSO event is not sufficient to ensure high internal ensemble consistency in Europe.In a separate approach, an attempt to linearly relate global SST anomaly patterns to the ensemble mean of T850, using canonical correlation analysis, also indicates a link between simulated T850 anomaly patterns in Europe and ENSO events. Mature El Niño (La Niña) conditions are associated with positive (negative) T850 anomalies in the model in southern Europe and negative (positive) anomalies in northern Scandinavia and over the Barents Sea in the January‐February season. A weaker relation is found between onsetting ENSO conditions and T850 anomalies in the model in the south‐eastern and westernmost parts of Europe in the July‐August season.Validations against re‐analysed observations of T850 show poor skill in Europe for the ensemble mean of simulated T850, and no obvious relation is found between internal ensemble consistency and skill. The link that is found in the model between ENSO and simulated T850 in Europe, is not evident between ENSO and re‐analysed T850.
Published Version
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