Our first computations have shown that the model is able to simulate the observational vertical structure of NAM patterns in the troposphere as well as in the stratosphere.
As a next step, an SSA- and a Wavelet-analysis of the Northern Annular Mode Index (NAMI) were conducted over all levels between the surface and 2 hPa. They provide a compact statistical description of the spacial and temporal variability of the circulation in troposphere and stratosphere. The synoptical and the quasi-stationary time scales explain for example about 34% of the NAMI variance at 1000hPa (using a window length of 40 days) and the stationary time scales explain over 90 % of the variance at 50 hPa (using window lengths of 100 days and 200 days).
Also, a lag-canonical correlation analysis of the geopotential height at 50hPa and 1000hPa with the maximal lag of 15 days was conducted after reducing the data dimension by conventional EOF-analysis. The correlation between the two canonical correlation coefficients shows more than one peak at positive as well as at negative time lags. The shifting of the corresponding canonical correlation patterns is consistent with the up- and downward propagation of the geopotential anomalies.
Furthermore, a lag-composite and a cross-Wavelet analysis were carried out. They show evidence of the downward propagation of the geopotential anomalies and the persistence of these anomalies between 100 and 200hPa consistent with observational results.
The poster presents these results as well as those of ongoing work, which adresses the impact of the stratosphere on the tropospheric stationary, quasi-stationary and synoptical time scales based on Transformed Eulerian-Mean diagnostics of model data and observations
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