Ionospheric observations during the annular solar eclipse of 20 May 1966—IV D-region electron densities derived from measurements of partial reflections

Absorption of radio waves during a solar eclipse

“…Secondly, the decrease in electron density N(h) is not necessarily in direct proportion to the decrease in electron-ion production rate q or the ionizing radiation flux F at different altitudes, e.g. N varies as q in the lower D-region whereas N may vary as (q)t/2 or in some other way in the upper D and lower E regions (Jespersen and Pedersen 1970;Haug et al 1970;Kane 1970). Such a dependence of N on q would cause comparatively greater decrease in L,a in the D-region than increase in L~ in the E-region where height of reflection increases at a given frequency during the eclipse.…”

“…Such a dependence of N on q would cause comparatively greater decrease in L,a in the D-region than increase in L~ in the E-region where height of reflection increases at a given frequency during the eclipse. Elwert (1958) and Taubenheim and Serafimov (1969) showed that 10 to 15 % of coronal x-rays remained unobscured even during totality of the solar eclipse, but according to Willmore (1970) and Haug et al (1970), the quiet-sun x-rays are not important for ionization at around 75 km altitude. All these factors concerning radiation and ionization suggest a greater decrease in L~ than an increase in L d. Hence, neither L t nor At(f) is likely to have any definite correlation with the unobscured part of the solar disc.…”