1. Krymskii, G.F., Altukhov, A.M., Kuz’min, A.I., et al., Geomagn. Aeron., 1966, vol. 6, no. 6, p. 991.
2. Nagashima, K., Rep. Ionos. Space Res. Jpn., 1971, vol. 25, no. 3, p. 189.
3. Belov, A.V., Dorman, L.I., and Yanke, V.G., Proc. 18th Int. Cosmic Ray Conf., Bangalore, 1983, vol. 10, p. 144.
4. Alanko, K., Usoskin, I.G., Mursula, K., and Kovaltsov, G.A., Adv. Space Res., 2003, vol. 32, no. 4, p. 615.
5. Usoskin, I.G., Alanko-Huotari, K., Kovaltsov, G.A., and Mursula, K., J. Geophys. Res.: Space Phys., 2005, vol. 110, A12108.