On the contribution of solar-flare alpha particles to polar cap absorption events

A series of calculations have been carried out to determine the relative importance of ionization from solar-flare α particles to polar cap absorption events. The exponential rigidity spectrums for solar-flare radiation discussed by Freier and Webber were used. To illustrate the actual magnitudes involved, typical fluxes, rigidity spectrums, and proton-α particle ratios from major polar cap events have been used. The electron production rates, electron densities, and specific absorption as a function of altitude for a proton-α particle ratio of unity are presented for a location with cutoff rigidity Pc = 470 Mv. These results indicate that α particles contribute significantly, producing as much as 75 per cent of the ionospheric absorption when the proton-α particle ratio is unity.