Ionospheric effects of solar flares. III. The quantitative relationship of flare X-rays to SID's

Abstract

This paper describes the effects of changes in the spectral distribution of solar X-rays below 10 Å, on the nature and magnitude of Sudden Cosmic Noise Absorption (SCNA) and compares 50 SCNA's with X-ray flares for which spectral distributions could be deduced. It is observed that the SCNA increases by an order of magnitude when the equivalent spectral temperature increases from 2×10⁶ °K to 8×10⁷ °K even though the total X-ray flux below 10 Å is kept constant. It is further observed, from an examination of the threshold case, and from quantitative study of 50 flare events, that the required recombination coefficients in the region 70–90 km are considerably lower than those recently given by Reid (1970), and that these generally fall into one of three categories: one very low, similar to that of Mitra (1968); another relatively high (but lower than that of Reid) with values around 2×10^-5 cm³ sec^-1 at 70km and 4×10^-6 cm³ sec^-1 at 80 km, and the third, intermediately between the two and approximating to the models of Adams and Masley (1965) and Mitra and Banerjee (1970). It is suggested that Reid's recombination coefficient model, which is not consistent with any of the flare models, represents the quiet time situation and that during the flare there is a decrease in the coefficient.