Frequency changes and refraction of radio waves propagating through the plasma around the sun

Abstract

Using the spacecraft Venera-15 and -16 in radio occultation experiments with the plasma around the Sun, we have measured the frequency of decimeter radio waves. Analysis of the results shows that when the line of sight moves in the direction of increasing electron density (i.e., as the instrument is approaching the Sun), there is an increase in the frequency of the radio waves. When the line of sight is receding from the Sun, the frequency shift has a negative sign. For decimeter waves, typical values of the frequency shift are 2.53 Hz when the line of sight passes the Sun with an impact parameter of 3 solar radii. We show that smooth structure in the solar corona affects the frequency change and the refraction of decimeter waves for lines of sight with impact parameters up to 6 solar radii. We determine the angle of radio wave refraction in the plasma around the Sun as a function of the impact parameter of the line of sight. Significant frequency shifts which have been detected at large impact parameters are identified with large-scale plasma formations moving at high speed.