| Summary: | A comparative diagnostic study of upper-air persistent atmospheric events, as simulated by a general circulation model (GCM) and as observed, is presented. We start with an overview of the several theories that attempt to explain such phenomena. Particular emphasis is put on the model approach of Shutts (1983). We next show that the spatial distributions of persistent events is qualitatively similar in the GCM and observational data. The North-Atlantic events are extracted and a rotated empirical orthogonal function (REOF) analysis is done on the resulting data sets. The two REOF sets that are thus obtained are shown to greatly resemble one another. Both explain roughly 50% of their original data's variance. The relationships between the modes within a set are presented, so as to understand their probable combined evolution. The fourth chapter contains an evaluation of Shutt's theory. There, the third chapter's results are used to isolate a particular class of events, namely the strong +ATL2 dipoles. The time-tendencies associated to short time-scale synoptic waves are evaluated, using an E-vectors approach, taking care to distinguish between the onset, mature and demise phases of the events. It seems that these synoptic waves have a significant impact of the average life-cycle of this +ATL2 type of events, whether they be simulated by a GCM or obtained from a NMC set of analyses.
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