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Zusammenfassung:
A 20 year simulation of the high-top atmospheric General Circulation Model (GCM) HAMMONIA is used to investigate internally produced Sudden Stratospheric Warmings (SSWs). We detect 19 major SSWs and evaluate the model results by comparison to the ERA40 reanalysis dataset. Composites are built to analyze the climatological characteristics of SSWs, in particular to investigate the mesospheric precursors and differences between vortex splits and displacements. The vertical coupling processes from the stratosphere to the lower thermosphere are studied using transformed Eulerian-mean (TEM) analysis and diagnostics concerning the role of gravity waves. Consistent to recent studies, we find a mesospheric cooling and a weaker thermospheric warming accompanying the SSW. The large anomalies in the zonal mean winds and temperatures are explained by the interactions of EP-Flux divergence, mean flow advection and parameterized momentum deposition of gravity waves. We present an algorithm, based on geopotential height, to classify the events. Nine SSWs can be characterized as vortex splits, 10 as displacements. The differences between the two types are statistically significant suggesting splits are associated with larger anomalies in temperature and zonal wind. Investigation of the longitudinal dependence of zonal winds demonstrates the asymmetry of the climatological winter and of single events. Therefore, we do not find a criterion to sufficiently detect SSWs using mesospheric winds prior to the central date.
