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In this study the dynamics of the coupled troposphere/stratosphere system was investigated using the atmospheric circulation model MAECHAM5/ocean mixed layer coupled model. The focus was on the impact of the stratosphere on the troposphere. The January climatology of the model agrees well with the observations, especially in the extratropical region and below the uppermost model levels (where the sponging effect is strong). The dynamics that maintains the middle atmospheric circulation in MAECHAM5 is consistent with the middle atmospheric dynamics known from previous studies. The three-dimensional structure of the Northern Annular Mode (NAM) in MAECHMA5 agrees well with that observed. The NAM dominates not only the variability in but also the covariability between troposphere and stratosphere north of 20°N. A lag composite analysis based on the 50hPa NAM-Index (NAMI), a measure of the strength of the 'stratospheric mode', shows that strongly positive stratospheric NAM-phases are associated with strong anomalous westerlies in high latitudes and a temperature quadrupole between troposphere and lower mesosphere. The lower part of this quadrupole shows a dipole structure with an anomalous cold (warm) polar (mid-latitude) troposphere and stratosphere and is associated with a positive shear of the anomalous westerlies there. This dipole strengthens (weakens), together with the anomalous westerlies, in the NAM-increase (decrease) phase. The upper part of the temperature quadrupole shows a coherent dipole with an anomalous warm (cold) polar (mid-latitude) upper stratosphere and lowermost mesosphere and is associated with a negative shear of the anomalous zonal flow there. The warm pole in mesosphere and upper stratosphere strengthens and propagates downward together with anomalous easterlies, especially in the NAM-decrease phase. The dynamics during strong vortex is analyzed by computing the wave, residual Coriolis, and non-resolved (residual) forcing in the Transformed Eulerian Mean formulation (TEM). NAM temperature, ...