Enhancement of ionizing radiation during a solar flare

Measurements of electron concentrations in the ionosphere, between 100 and 250 km altitude, were used to compute the increase in solar ionizing radiation during two flares on 21 and 23 May 1967. Since the altitude of maximum absorption of the solar energy (approximately unit optical depth) depends on the wavelength of the radiation, it is possible to estimate separately the energy enhancement in different portions of the spectrum. An ionizing energy flux increase of nearly 5 erg cm^–2 sec^–1 was observed on 21 May, while on the 23rd, the increase was over 7 erg cm^–2 sec^–1. In both flares, most of the absolute increase occurred in the 20–205 Å region of the spectrum, although the relative increase was much larger at the shorter wavelengths.