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Summary and Conclusions

This study constitutes the South-German contribution to the global gravity wave climatology within SPARC (see Vincent, this issue). The results derived with the newly developed adaptive analysis height range were critically compared with those of the fixed altitude range used for the global climatology. Both methods give high stratospheric energy densities occuring mostly in winter, associated with large tropospheric wind shear, small tropospheric directional shear and large surface wind speed. Lower stratospheric energies are found in summer. For the investigated region the use of the AAR analysis shows a stronger half-yearly trend in stratospheric energy density than the FAR analysis, and makes thus seasons better comparable. It avoids the overestimation of stratospheric energy density of the FAR analysis in summer. Furthermore, higher energy densities are found for MO compared to STU. This could be due to the fact that Munich lies closer to the Alps than Stuttgart and some of the MO-profiles are thereby certainly influenced by the effect of these mountains. The dependence of stratospheric energy density on tropospheric wind conditions support the hypothesis that the main source of stratospheric gravity wave activity in the investigated region is the jet stream excitation. Up to now the relative contribution of convective or orographic excitation is not clear for the investigated region. Since the Alps are very complex, 90° propagating mountain waves are possibly a part of the sources for the observed stratospheric energy densities.

For further investigations idealized studies and realistic model studies are needed. Together with this observational study they should lead to a reliable identification of the different gravity wave generation mechanisms.

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