We calculate the mean-flow accelerations due to gravity wave packets observed in the lower stratosphere over Macquarie Island (55 ¿S, 159 ¿E) between February 1994 and April 1995. The parameters of the wave packets were extracted from twice-daily radiosonde soundings using a wavelet-based analysis method introduced by Zink and Vincent . The deduced wave parameters are used to directly compute momentum flux profiles in the lower stratosphere, and the shortcomings of this approach to assess mean-flow accelerations are discussed. We then use the observed wave packets as an input spectrum in a linear ray-tracing model. The vertical extent of the detected wave packets allows us to define an expression for wave intermittency, which enables us to compute zonal accelerations in the stratosphere and mesosphere. In the stratosphere the waves produce an acceleration of the mean flow, in accordance with predictions. In the mesosphere the inferred wave drag is 2--3 times larger than previous observational and theoretical estimates. ¿ 2001 American Geophysical Union