Characteristics of the Earth-ionosphere Waveguide for VLF Radio Waves


Book Description

The principal results of this technical note are graphical presentations of the attenuation rates, phase velocities, and excitation factors for the dominant modes in the earth-ionosphere waveguide.The frequency range considered is 8 kc/s to 30 kc/s. *The model adopted for the ionosphere has an exponential variation for both the electron density and the collision frequency, and the effect of the earth's magnetic field is considered.Comparison with published experimental data confirms that the minimum attenuation of VLF radio waves in daytime is approximtely at 18 kc/s, while at night it is somewhat lower.The directional dependences of propagation predicted by the theory are also confirmed by experimental data.(Author).



















Propagation Characteristics of VLF Waves Below a Stratified and Generally Anisotropic Ionosphere


Book Description

The research constitutes one method of formulation for the calculation of very low frequency radio wave propagation characteristics of the earth-ionosphere waveguide. It involves a brief consideration of some general properties of the ionosphere which influence the propagation of VLF (very low frequencies) waves. In the analysis, the waveguide is the area formed by the earth and the lower conducting region of the ionosphere. The propagation characteristics are obtained from the solution of a modal equation which is formulated directly in terms of the reflection coefficients of both the ionosphere and earth. The coupled vacuum mode theory of Poeverlein is extended to include the earth's curvature effects by assuming the ionosphere as a cylindrical stratified medium. The modal equation is solved by an iterative procedure and propagation characteristics are obtained for a variety of ionospheric conditions for different directions of propagation. A comparison of the numerical results is made with different formulations in the literature. (Author).










Resonances in the Earth-Ionosphere Cavity


Book Description

This book on electromagnetic resonance phenomena describes a general approach to physical problems, ways to solve them, and properties of the solutions obtained. Attention is given to the discussion and interpretation of formal and experimental data and their links to global atmospheric conditions such as the dynamics of global thunderstorm activity, variations of the effective height of the lower ionosphere, etc. Schumann resonance is related to worldwide thunderstorm activity, and simultaneously, to global properties of the lower ionosphere. Transverse resonance is predominantly a local phenomenon containing information on the local height and conductivity of the lower ionosphere and on nearby thunderstorm activity. Transient events in ELF-VLF radio propagation are also treated. These are natural pulsed radio signals and/or abrupt changes of manmade VLF radio signals. The transients associated with cloud-to-ionosphere discharges (red sprites, blue jets, trolls) are discussed, and clarification of the underlying physical ideas and their practical applications to pioneer results achieved in the field recently are emphasised.