1. E. M. Zhulina, in: Studies of Shortwave Propagation [in Russian], Nauka, Moscow (1974), p. 215.
2. H. F. Bates, J. Geophys. Res.,75, No. 1, 143 (1970).
3. E. L. Boyarintsev et al., in: Research on Geomagnetism and Aeronomy, of the Auroral Zone [in Russian], Nauka, Moscow (1973), p. 147.
4. E. M. Zhulina and L. P. Kuperov, in: Problems of Shortwave Propagation [in Russian], Part 1, IZMIR AN, Moscow (1973), p. 68.
5. I. Ya. Ostrovskii and Sh. G. Shlionskii, in: Problems of Shortwave Propagation [in Russian], Part 2, IZMIR AN, Moscow (1974), p. 52.