Federal State Budgetary Scientific Institution
Yu.G. Shafer Institute of Cosmophysical Research and Aeronomy
of Siberian Branch of the Russian Academy of Sciences

Most Important Scientific Results of Institute of Cosmophysical Research, Siberia Branch, Russian Academy of Science in 2020

Mass Composition of Cosmic Rays in the EeV Energy Range

Authors: S.P. Knurenko, I.S. Petrov

Published: S.P. Knurenko, I.S. Petrov. Mass composition of cosmic rays determined by the muon fraction with εthr>1 GeV in air showers with energy greater than 5 EeV. // Physical Review D. 2020. Vol.102. P.023036. DOI:10.1103/PhysRevD.102.023036.

Based on relative abundance of muons in extensive air showers recorded at the Yakutsk installation, the atomic weight of primary particles of cosmic radiation in the energy range above 5 × 1018 EeV has been estimated. Comparison of experimental data with calculations performed within the QGSjet-II-04 hadron interaction model,  has revealed  the following ratio of particles in the cosmic ray flux near the Earth: 50 ± 10% are protons and helium nuclei, 32 ± 6% are carbon, nitrogen and oxygen nuclei, 16 ± 8% are iron nuclei, and about 2% are ultrahigh energy gamma quanta. The obtained result is important for understanding the nature of ultra-high-energy cosmic rays.

Fig. 1. The fraction of extensive air showers (EASs) initiated by various primary particles from the total number of showers (w0) as a function of the relative number of muons at a distance of 600 m per unit of average particle energy (ρμ, 0). The colored lines show the theoretical predictions of the fraction of muons in EASs caused by various particles of cosmic rays with energies (5-50) · 1018 EeV, the histogram is the data of the Yakutsk installation.

Theory of the Formation of Forbush Decrease

Authors: A. S. Petukhova, I. S. Petukhov, S. I. Petukhov

Published: Petukhova A.S., Petukhov I.S., Petukhov S.I. Forbush Decrease Characteristics in a Magnetic Cloud // Space Weather, 2020, e2020SW002616 doi: 10.1029/2020SW002616 https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020SW002616

A theory of  formation of Forbush decrease in an electromagnetic field of a magnetic cloud has been presented. A model of a magnetic cloud in the form of a loop rooted in the Sun surface has been  proposed.The Forbush decrease has been found to be formed due to energy losses and quasi-trapping of cosmic rays in the helical magnetic field. Comparison of calculated characteristics of the Forbush decrease with observations has found that the amplitudes of the Forbush decrease quantitatively, and the anisotropy qualitatively are in agreement with the measurements. Understanding of the processes occurring in a coronal mass ejection will help to use cosmic ray research and forecast of  space weather.

Fig. 2 (a, b) Components of magnetic field strength versus world time(vg). Thin lines are measurements, thick lines are calculation. (v,g ) Speed of plasma motion  (d, e). Amplitude of Forbush decrease. In the Fig. (c-f) black lines are measurements, red lines are calculation. The vertical dashed lines are the boundaries of the magnetic cloud.