Solar eclipse effects in low and medium frequency propagation

Abstract

The striking feature of solar eclipse effects in low and medium frequency propagation at oblique incidence is that the absorption remains nearly unaltered for a long time after the beginning and before the end of the eclipse but decreases by as much as 20–40 dB at higher degrees of occultation. This narrowness of the absorption anomaly duration becomes extremely pronounced with decreasing frequency and increasing transmitter distance. Otherwise, the reflection height varies continuously over the whole duration of the eclipse and, at very oblique incidence, roaches a deviation of about 5 km from normal. The mean time delay between the maximum of obscuration and the maximum of the observed ionospheric effects is 2–5 min. The experimental results may be explained by an appropriate electron density model demonstrating the predominant role of attachment and detachment processes in the lower ionosphere. Approximate values for the parameters of these processes and for the electron density gradient in the D-region have been obtained.