Relation between circular polarization of moving type IV bursts and polarity of photospheric magnetic fields

Abstract

Two-dimensional, high-resolution observations of about 30 moving type IV bursts allow us to compare the polarization structure of the radio sources high in the corona with the distribution of magnetic fields measured at the photospheric level. Left- and right-handed circularly polarized moving type IV bursts are associated with active regions dominated by magnetic fields of plus and minus polarity respectively. The result suggests that the polarity of magnetic fields within the type IV source which moves high in the corona (≳ 1R⊙ above the photosphere) is closely related to the polarity of local magnetic fields at the photosphere. The above relation between the sense of polarization and the polarity of magnetic field is contrary to what would be expected from the generally accepted synchroton hypothesis. One way of resolving this conflict is to postulate that the magnetic field within the radio source has the opposite polarity to that of the ambient magnetic fields.