The wind in the lower thermosphere is generally considered to be composed of prevailing, tidal, and gravity wave components, but observational data are too scanty and heterogeneous to enable specification of the contribution of each component. This paper computes the tidal winds from theory, adding to the existing theory of atmospheric solar tides the effects of heat conductivity and the absorption of solar radiation in the thermosphere. Comparison of the theoretical results with observations indicates that major features of the vapor trail drifts --such as the wind speed maximum near 105 km altitude, the velocity oscillations below it, and the quiescent region above --can be explained in terms of interference between tidal modes propagating in an atmosphere with dissipation. Results also indicate that variations in water vapor excitation may be a source of the day-to-day changes observed in the Sq current system. (See also R-585.) 16 pp. Ref.
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