Scintillation of radio astronomical sources due to anisotropic inhomogeneities in the ionospheric plasma

Abstract

We have investigated the properties of scintillation of sources of cosmic radio emission due to inhomogeneities in the ionospheric F-region. The inhomogeneities are elongated along the geomagnetic field lines. We show that when the line of sight coincides with the magnetic field direction, we should observe an increase in the magnitude of the scintillation index. The amount of the increase, as well as the angular range in which it occurs, depend on the explicit shape of the spectrum of spatial scales of the inhomogeneities. We have given consideration to models which have been adopted in the literature for three-dimensional and two-dimensional anisotropy in the ionospheric turbulence. Based on this analysis, we propose a diagnostic method for the inhomogeneous ionospheric plasma. It is based on multifrequency measurements of the scintillation index of radio astronomical sources which culminate near the direction of the geomagnetic field lines at the latitude of the observing point. We establish the limits which are imposed on our proposed method because of the finite dimensions of the sources.