Some problems of VLF wave propagation in the magnetosphere

The geometric optical picture of very low frequency (VLF) wave propagation in the Earth plasmasphere under the assumption of the geomagnetic field dipolarity is studied. It is shown by means of numerical calculations that in the preequatorial region a wave becomes electrostatic one. If the wave frequency is not too small as compared with the equatorial value of the cyclotron frequency at the initial α-shell, all trajectories begin focusing at the approach to the equator and finish in the opposite hemispheres on near α-shells. For these conditions analytical solutions of the geometric optics equations are obtained