A Theory of Meteors, and the Density and Temperature of the Outer Atmosphere to which it Leads

Some thirty years ago Teisserenc de Bort announced the discovery that the temperature gradient in the atmosphere, which amounts to some 6.5 . 10-5 degree/cm. for the first 10 km., becomes negligibly small at greater heights. Since this time it has become usual to treat the temperature as constant for all heights above this limit, and various detailed numerical estimates, extending to heights of hundreds of kilometres, have been published, which are based on this assumption. So far, however, no evidence for it has been adduced beyond the “ballon sonde” observations, which scarcely extend above 25 km. The purpose of this note is to examine how much information about conditions at greater heights may be gained from a study of meteors. For this purpose it is necessary to study in considerable detail the theory of what happens when a meteor appears. It will be seen that a consistent theory can be developed, which accounts for all the observed phenomena, and that this theory enables one to derive a considerable amount of information about conditions in the upper air. It will be shown that existing observations enable us to say with considerable certainty that the density at heights above 65 kilom. is very much higher than is commonly supposed, and that the temperature must increase from its value of something like 220° abs. at heights between 12 and 50 km., to something like 300° abs. at these heights. It is evident that accurate results can only be obtained when the required quantities, viz., heights of appearance and disappearance, length of path, velocity and luminosity have been determined for a number of meteors. It is hoped that experiments, now in progress to determine these quantities photographically, will enable more accurate calculations to be made. In the meantime, the broad results obtained from the data due to W. F. Denning and his co-workers may be outlined.