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Irregularities in the Quiet Ionosphere and Their Effect on Propagation

Abstract : The primary purpose of this investigation was to determine the nature and characteristics of a class of large, weak ionospheric irregularities which in certain circumstances significantly affect long-distance HF radio-wave propagation. A further purpose was to determine the relative practical importance of the diffraction produced by these inhomogeneities, in relation to the influence of other mechanisms such as Faraday rotation and scattering by small irregularities. Measurements of quasi-periodic variations in phase-path length have been made on a 2600 km one-hop lower-ray F-region path. Variations of 8 to 75 wavelengths are regularly observed during winter daylight hours. A model of the irregularities has been devised and has been used to predict the signal-strength fluctuations which would result from propagation through a medium described by the model.