1. V. N. Ishkov, in Proceedings of the Interdisciplinary Colloquium on Cosmic Evolution Factors in Biosphere and Geosphere (VVN, St. Petersburg, 2014), p. 85.
2. S. A. Yazev and E. A. Spirina, Geomagn. Aeron. 49, 898 (2009).
3. M.-B. Kallenrode, J. Phys. G: Nucl. Part Phys. 29, 965 (2003).
4. B. Klecker, J. Phys.: Conf. Ser. 409, 1 (2013).
5. A. T. Altyntsev, V. G. Banin, G. V. Kuklin, and V. M. Tomozov, Solar Flares (Nauka,Moscow, 1982) [in Russian].