Introduction

Internal gravity waves are the cause for most of the spatial and temporal fluctuations in stratospheric temperature and wind. For example, the adiabatic cooling near the crest of hydrostatic mountain waves favors the nucleation of supercooled droplets and thus the formation of polar stratospheric clouds (e.g. Wirth et al., 1999). Upward propagating gravity waves transport momentum to the middle atmosphere and are now well appreciated to play a dominant role in driving the circulation of the atmosphere (e.g. Alexander and Rosenlof., 1996). Since the present GCMs and climate models are not able to resolve the whole gravity wave spectrum, a better characterization of stratospheric gravity wave activity in terms of wave energies, periods, phase speeds, propagation directions, and spectral parameters is needed. This can be achieved by means of observational, theoretical and modeling studies.

The present work constitutes the South-German contribution to the global gravity wave climatology within SPARC, see Vincent, this issue. This climatology is based on high vertical resolution radiosonde data of about 16 groups in 13 countries, and follows the previous work of Allen and Vincent, 1995 and Vincent et al., 1997. A significant improvement for our region is reached by analyzing the data with the new adaptive altitude range. Our results help to better understand the different sources of gravity wave activity in the lower stratosphere (Nastrom and Fritts, 1992 and Fritts and Nastrom, 1992).