Dissipation produced by viscous damping and thermal conduction is important in the study of atmospheric gravity waves, which are themselves important in a study of "irregular" motions in the upper atmosphere. The mathematics of this damping is considered in some detail here, and charts are given to assess the effects of viscous damping and thermal conduction at meteor heights in the upper atmosphere. The results of this paper are consistent with the conclusions of an earlier analysis, insofar as the two overlap, and extend the range of conditions considered.

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A simple form is derived for the differential equations governing the propagation of acoustic–gravity waves in an atmosphere whose temperature and horizontal wind velocity vary in an arbitrary manner with height. The condition for wave reflection is discussed in some detail, and the W.K.B. approximate solutions are derived and examined. Analytic solutions are obtained for exponential and for linear variations of temperature with height, and group velocities for ducted modes are studied with these models.

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We consider the interpretation of "spread F" ionograms, particularly those echoes that determine most of the radio bandwidth of the phenomenon. We compare expectations based on total internal reflection with theoretical descriptions based on underdense scattering. We conclude that "Rayleigh, .... Bragg," and "diffuse multiplerefractive" radio scattering theories are not consistent with observed properties of these echoes. The total-reflection interpretation is shown to be consistent with rocket and satellite data. Evidence for multiple refractive scatter is found, but it neither greatly nor subtly extends the observed radio bandwidth. Ionograms therefore indicate comprehensively the range of plasma densities within view of the ionosonde, even in conditions of spread F. Using digital ionosonde observations, much can be learned of the spatial structures of plasma density responsible for spread F at auroral and equatorial latitudes. As an example, we suggest how contemporary theory and simulations of the equatorial "bubble" phenomenon may be reconciled with the distinctive equatorial spread F pattern.