A heliospheric density model and type III radio bursts

A heliospheric density model is derived by evaluating the spherical solutions of magnetohydrostatic equations including the thermal pressure and the gravitational force of the Sun. The model resulting as a special solution of Parker’s wind equation covers a range from the low corona up to 5 AU and, surprisingly, agrees very well with observations. Such a model is required for the interpretation of solar and interplanetary radio observations since the emission of the radio radiation is regarded to be generated near the local electron plasma frequency, which depends on the electron number density. Thus, the density model yields the radial distance of the radio source from the Sun and, consequently, the radial source velocity from the drift in dynamic radio spectra. The model is applied for estimating the velocity of electron beams generating solar and interplanetary type III radio bursts.