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Abstract
Two long-range integrations (6 and 10 years) have been carried out with the European Center for Medium Range Weather Forecasts (ECMWF) spectral model using a T21 truncation. The parameterization of the physical processes in the ground and in the sea-ice differ in the two experiments. No major difference has been found in the mean climate generated by the simulations. In both experiments, the chronology of the atmosphere simulated by the model is studied through principal component analysis of the 500 mb geopotential height field. The two sets of results are compared with each other and with reality.
The differences between the results of the two experiments are mainly in the annual cycle which is, however, correctly described. The non-seasonal signals are also described quite realistically: spatial patterns (blocking phenomena with splitting of the jet stream in winter. Greenland see-saw) as well as their persistence (autocorrelation) and their percentage of variance are found to be very satisfactorily captured.
