Sunrise effects in the lowerD-Region by solar eclipse

Abstract

In contrast to the well known fact that the ionospheric absorption minimum falls behind the maximum phase of the solar eclipse, in the present work the reverse effect is discovered and analysed, namely that the ionospheric absorption minimum falls before the maximum phase of the eclipse, while the maximum absorption comes behind it. Such anomalies can be observed only on paths of long waves at oblique incidence of the layer (length of the path over 1300 km). The theoretical analysis shows that the established effects are due to the considerable increase of the factor of negative ions, respectively of the effective recombination coefficient α′ in the first phase of the eclipse for heights between 65 and 70 km, i. e. in the lower boundary of theD-Region (CR-Layer). In the second phase of the eclipse α′ falls rapidly because of which at a constant electron production inCR-layer a strong increase of the absorption is observed similar to the known sunrise effects in theD-Region. The electron drift is intensified about the maximum phase of the eclipse.