Penetration characteristics of VLF wave from atmosphere into the lower ionosphere

Many papers have indicated that earthquake happens associated with a width frequency band of VLF (Very Low Frequency), ULF (Ultra Low Frequency), ELF (Extremely Low Frequency) electromagnetic radiation, which have been recorded by satellites in the ionosphere and low magnetosphere. In this paper, the reflection and transmission coefficient of the homogeneous half-space ionosphere has been calculated using propagation matrix method. Simultaneously the Booker quartic equation is solved to get the refractive index in the ionosphere. The analysis of the factors which influence the reflection and transmission coefficient of the ionosphere and the propagation characteristics in the ionosphere of VLF wave have been performed, such as wave frequency, incident angle, geomagnetic inclination, electron density and collision frequency in the ionosphere to provide fundamental basis for further studies on numerical calculation of propagation of ULF/VLF waves in the stratified ionosphere and support the study of seismo-ionosphere coupling mechanism. The results show that it is easier for the TE (Traverse Electric) wave radiated by vertical electric dipole to penetrate into the ionosphere, but the TM (Traverse Magnetic) wave radiated by horizontal electric dipole is reflected again and again in the ground-ionosphere waveguide. It is easier to observe the VLF wave anomaly when the electron density is lower or at the high-latitude region. The O wave experiences severer attenuation than X wave, so X wave is a penetration mode whereas O wave is a non penetration mode in the ionosphere. The attenuation of the two characteristic wave decrease as the decrease of the angle between the geomagnetic field and wave vector, that is to say the attenuation is the smallest when longitudinal propagation. When the geomagnetic field is considered, the ULF/VLF wave related with earthquake can penetrate into the ionosphere which is confirmed by the satellite observation. But the further physical mechanism will be delved in the future.