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Studies on the Phase Spectra of VLF Sferics.
TEXAS UNIV AT AUSTIN APPLIED RESEARCH LABS
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The phase characteristics of long range sferic signals are studied in detail over the frequency range of 9 to 20 kHz. When the experimentally measured phase of a sferic is fitted with a straight line by the method of least squares, the deviation of the phase from this straight line shows a pattern that is characteristic of the nature of the propagation path. The phase deviation for daytime paths of length greater than 4000 km behaves as predicted by the theoretical behavior of the first propagation mode daytime paths of ranges between 1500 and 3500 km can be explained by two modes. The agreement between experimental and theoretical values suggests that the phase of the sources of these atmospherics is a linear function of frequency. Although absolute values of group velocity cannot be determined, the variation of group velocity with frequency agrees with the theoretical predictions based on one and two modes of the earth-ionosphere cavity.
APPROVED FOR PUBLIC RELEASE