Variations in radio signal phase at propagation in the parabolic layer of disturbed ionospheric plasma

The problem of electromagnetic-wave propagation in anisotropic plasma cannot usually be described by exact analytical solutions even in simplest model cases. One of main approximate methods is a geometric optics which provides an illustrative description of radio wave propagation in terms of ray paths [1]. Applicability boundaries of the method (wavelength is smaller than the typical scales of the medium) generally work quite well in the problem of ionospheric propagation of radio waves. Isotropic approximation, i.e. neglect the effect of the Earth's magnetic field, is widely used to simplify the ray-optical description of ionospheric propagation of radio waves. In particular, the advantage of this approach is that for a set of ionospheric models it allows to obtain analytical solutions for the parameters of the ray path. It has been extensively discussed in the literature that the isotropic approximation works quite well for ionospheric sounding being representative of the ordinary mode.