Energy Spectrum of Galactic 10–100 MeV Protons in Quiet Sun Periods

Abstract

The dynamics of the proton energy spectrum during the solar cycle is studied. The spectra were determined by 1–100 MeV particle fluxes measured by different instruments mounted aboard the Earth's IMP-8 satellite for more than one hundred quiet-time intervals in the period between 1974 and 1991. The galactic branch of the spectra (Ep > 10 MeV) constructed for every quiet interval was fitted by a power law function, J =CEν. The theory predicts that in the 1–100 MeV energy range, where the adiabatic cooling of particles is dominant, ν = 1, while we have derived a ν double-peak distribution. The main maximum has the mean value 〈ν〉 = 1.35. The mean value of the second, much weaker maximum, is 〈ν〉 = 0.95. Within the main maximum, ν values are distributed in accordance with the Gaussian law with a standard deviation 〈D/ν〉 = 0.12. The substantial difference of ν from unity requires the elaboration of a new model of modulation processes in the inner heliosphere. The ν values corresponding to the second maximum show that modulation processes correspond sometimes to theoretical conceptions. It is shown that ν correlates weakly with parameters A and γ describing the solar branch of the spectrum (J(E) = AE–γ). At the same time, a more significant correlation is observed between ν and the solar activity index, Rz , the counting rate of the Deep River neutron monitor, and the energy value in the minimum of the energy spectrum flux, Emin .