A Phenomenological Theory of Radar Echoes from Meteors

The Dominion Observatory and the National Research Council, Ottawa, Canada, have undertaken a program of combined visual, photographic, and radar observations of meteors. The observational data is summarized, and general conclusions have been drawn. The radar echoes obtained from meteors have been classified into basic types according to their appearance on the range-time record of the radar display. These types include echoes indicating approach, or recession, or both. Other observed features are: durations of echoes up to several minutes, complexity of structure for echoes from brighter meteors, and appreciable delays in the appearance of the echoes. A phenomenological theory is proposed, involving a number of postulates concerning the physical conditions in an M region in the upper atmosphere. A kinetic-energy mechanism, together with an ultraviolet radiation mechanism, are suggested to account for the ionization produced by the meteor. In the M region are visualized striae, or patches, which form a fine structure such that, within the striae, the physical properties of the atmosphere emphasize the creation and maintenance of meteoric ionization as compared to the ionization produced in the intervening spaces. A qualitative explanation for all the observed echo forms is advanced on the above hypothesis. The results of other investigators on different wavelengths are consistent with this analysis.