Abundance of solar cosmic ray alpha particles

The abundance ratio of the fluxes of low-energy (1–10 Mev/nucleon) solar alpha particles to solar protons varies from flare to flare and with time within a single flare event. The fluxes of solar protons and alphas from seven of the large-flare events during the maximum of solar cycle 20 have been integrated over the duration of the events. The event-averaged 4He/¹H ratio is found to vary as 0.026 (Mev/nucleon)−0.2 in the range 1–10 Mev/nucleon. For particles compared as to equal energy per charge (a representation that may have less distortion from propagation effects) the ratio 4He/¹H ∼ 0.05 (Mev/Z)−0.2. In this representation, for 1 Mev/Z particles, the solar cosmic ray 4He/¹H ratio is compatible with (1) the average solar wind helium abundance and (2) a solar helium abundance determined from spectroscopic studies of prominences and the chromosphere but is less than (3) helium abundances predicted from some current models of the solar interior.