Observations of circularly polarized radio emission from the "Quiet" sun at frequencies <100 MHz

Abstract

The presence of the magnetic field makes the solar coronal medium birefringent. Research indicates that an appreciable degree of circular polarization (DCP) can be observed in the thermal radio emission at frequencies <100 MHz from the solar corona, due to the difference in the absorption coefficients of the ordinary ("o") and extraordinary ("e") modes of propagation in the magnetized coronal medium. Measurements of this DCP from observations are, however, rare. In this study, we report Stokes-I and Stokes-V observations of thermal radio emission from the "quiet" solar corona in the frequency range 50─80 MHz, using a one-dimensional radio interferometric polarimeter. The estimated DCP in the above frequency range is ≍2.5%─1.2%. The results indicate the potential in ground-based low-frequency radio observations to estimate the coronal magnetic field in the "quiet" corona in the heliocentric distance range (r < 2.0 R⊙), where solar radio emission in the above frequency range typically originates.