1. Yu.G.Mizun, The Polar Ionosphere [in Russian], Nauka, Leningrad (1980).
2. M. A. Geller, H. Volland, H. G. Mayr, et al., C. S. Deehr and J. A. Holtet, eds., Exploration of the Polar Upper Atmosphere, D. Reidel, Dordrecht (1980).
3. G. A. Hajj and L. I. Romans, Radio Sci ., 33, No. 1, 175 (1998).
4. A. I. Kucheryavenkov, O. I. Yakovlev, I. L. Kucheryavenkova, and L.N. Samoznayev, J. Commun. Tech. Electron., 43, No.. 8, 880 (1998).
5. W. Schreiner, S. Sokolovsky, C. Rocken, and D. Hunt, Radio Sci ., 34, No. 4, 949 (1999).