1. V. S. Troitskii, L. N. Bondar', A. M. Starodubtsev, M. R. Zelinskaya, K. M. Strezhneva, M. S. Kitai, and A. I. Sergeeva, Izv. Vyssh. Uchebn. Zaved., Radiofiz.,16, No. 3, 323 (1973).
2. Y. W. Swenson and W. W. Cochron, Science,181, 543 (1973).
3. M. P. Dolukhanov, Radio-Wave Propagation [in Russian], Svyaz', Moscow (1965).
4. A. I. Kalinin, V. N. Troitskii, and A. A. Shur, in: Radio-Wave Propagation [in Russian], Nauka, Moscow (1975).
5. J. A. Chalmers, Atmospheric Electricity, 2nd ed., Pergamon (1968).