Mesospheric transport processes and energy budget are tied closely to gravity wave activity. Any means of monitoring dynamics reliably can only contribute to our understanding of the physics of the mesosphere. In this study we employ temperature data derived from hydroxyl (OH) emission from around 85 km and combine it with the theory of Hines <1960> to investigate the practicality of deducing fluctuations in horizontal wind speed. Myrab¿ and Harang <1988> have used a simplified theory <Hines, 1965> but, apparently, to deduce tidal fluctuations in the horizontal wind; this prompts us to investigate the range of timescales for which the Hines <1965> result and the assumptions implicit therein may be used in practice. Our conclusion is that this theory may not be extended to scales of dynamics outside those intended by Hines. Thus while the Myrab¿ and Harang <1988> results seem plausible, they are probably incorrect. ¿ 1999 American Geophysical Union