STUDIES OF IONOSPHERIC ABSORPTION OF RADIO WAVES BY THE COSMIC NOISE METHOD

Abstract : The theory of measurements of nondeviative absorption of radio waves is reviewed. It is pointed out that the discrepancy between classical magnetoionic theory and generalized theory, in which the energy dependence of the electron collision frequency is taken into account, isAPPRECIABLE IN MOST OF THE LOWER IONOSPHERE. It is also shown that the use of the generalized theory does not involve more work at the ordinary riometer frequencies than does the magnetoionic theory. The results of riometer measurements of quiet day absorption, sudden cosmic noise absorption, absorption associated with aurora and geomagnetic disturbances, and of polar cap absorption are reviewed. Special emphasis is placed in the last part of the paper on the problem of the variation of cosmic noise absorption in the twilight periods and the interpretation of the observations relevant to it. (Author)