Abstract
Measurements of cosmic noise absorption (A2 method) on 25 Mc/s in south-east Bulgaria during the solar eclipse of May 20, 1966, show a significant decrease of absorption by about 0.5 dB at the time of maximum eclipse. The contribution of the D- and E-regions of the ionosphere to this eclipse effect is only 0.22 decibels, determined by a comparison with simultaneous Al absorption measurements (pulse reflection) on 3.86 Mc/s. There remains a significant eclipse effect which must be ascribed to a decrease of electron density in the lower F-region. The eclipse variation of the maximum F2-layer electron density appears not to be representative for this F-region effect.
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