Correcting low-frequency solar radio source positions for ionospheric refraction

A technique for removing ionospheric refraction displacements in observations of solar radio source positions is presented. Radio data from a solar storm continuum burst show that the 160, 80, and 43 MHz source displacements vary as an inverse square function of the frequency, with a slow systematic drift of the source positions towards the south and east directions. A quasi-periodic variation on the order of 20 min is also present in the source position. The inverse square variation is modeled on the basis of refraction theory, and the slow drift by either the curvature or the smaller and larger density gradients of the ionosphere. Correction factors are formulated. The inverse square correction factor is sufficient for removing most ionospheric refraction effects.