Dynamics of the 0.3–100 MeV Proton Energy Spectra in the Inner Heliosphere in Quiet Periods of 1974

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Dynamics of the 0.3–100 MeV Proton Energy Spectra in the Inner Heliosphere in Quiet Periods of 1974–1991

Zeldovich, M. A. / Kecskemety, K. / Logachev, Yu. I. / Surova, G. M.

Abstract Variations of the proton spectra in the 0.3–100 MeV energy range based on the data of various instruments installed onboard the IMP-8 satellite are studied for “very quiet,” “quiet,” and “quasi-stable” solar activity periods during the years 1974–1991. As many as 118 spectra were approximated by two power laws: the left-hand and galactic branches of the spectrum were fitted by the AE–γ function and a dependence of the CE type, respectively, the sum J(E) = AE–γ + CE providing the total spectrum. It is shown that the spectra vary within a solar cycle with a shift of the minimum energy (Emin) to higher energies with increasing solar activity. It follows from the relations between the spectrum parameters thus obtained that, in particular periods of time, an increase (decrease) of the particle flux in the low-energy branch of the spectrum and an intensification (depression) of the GCR particle flux modulation take place simultaneously. This is manifested in a shift of the spectrum parallel to the energy axis. The study of the spectra in the most quiet time during three successive solar minima have shown that low-energy (0.3–10 MeV) protons, as well as GCR, are subject to the 22-year variation in the solar magnetic cycle.