1. J. A. Fejer, J. Atm. Terr. Phys.,7, 322 (1955).
2. A. J. Ferraro, H. S. Less, and S. Weisbroad, J. Geophys. Res.,62, 1169 (1963).
3. R. A. Smith, in: Proceedings of the Conference on the Physics of the Lower Ionosphere, Ottawa (1966).
4. I. M. Vilenskii and N. I. Izraileva, Geomagn. Aeronom.,10, 46, 740 (1970).
5. I. M. Vilenskii and N. I. Izraileva, Paper Read at the All-Union Conference on Ionospheric Physics [in Russian], Erevan (1973).