Electromagnetic wave radiation in low frequency range from modulated electron beam antenna in ionosphere

Abstract

Summary form only given. Ohnuki and Adachi (1990) discussed EM radiation in the lower hybrid frequency range from a density-modulated electron beam antenna of finite length injected along the Earth magnetic field into the ionosphere. It has been predicted for the ground observation that the penetration of VLF whistlers radiated by the beam antenna into the the free space above the ground is possible only in the magnetic equatorial region. This paper discusses theoretically the Poynting power density and wave normal direction for LF whistler waves radiated by the beam antenna of finite length injected along the magnetic field into the ionosphere. The power density in the direction of strong peak of radiation inside the group velocity resonance cone angle is calculated in VLF and LF. It is found that the radiation power density in the frequency region a little higher than the lower hybrid resonance frequency region is extremely intense, and that the one in the LF range for the nighttime of the ionosphere is fairly intense up to f/sub He///sup 2/, where f/sub He/ is electron cyclotron frequency, while the radiation power density in the frequency region above f/sub He///sup 2/ is found to become small and to decrease rapidly as wave frequency increases. The wave normal direction of the maximum radiation measured from the direction of the beam antenna is calculated in both the VLF and LF regions. The results show that the wave normal direction is generally very large, and that the relatively small angle of the wave normal direction exists only in the frequency region near and above f/sub He///sup 2/. It is concluded theoretically that the possibility of ground observation of the EM wave radiated from the density-modulated electron beam in both the VLF and LF ranges exists only in the magnetic equatorial region.