Characteristics of Circular Polarized Type III Radio Bursts in the Inner Heliosphere

Solar Type III radio bursts, characterized as the fast frequency drift with time, are among the most common radio emissions and are the powerful tool to diagnose the accelerated electron beams and ambient plasma medium. In this study, 42 circular polarized type III radio bursts are analyzed quantitatively using Parker Solar Probe (PSP) observations from October 2018 to May 2021. Our results reveal that the low-cutoff frequency of circular polarization signature is above 1 MHz regardless of the low-cutoff frequency of type III intensity. The maximum degree of circular polarization in most of our cases appear simultaneously or earlier than the peak total intensity. We suppose that the type III bursts with the large time lag of maximum degree of circular polarization relative to the peak total intensity might come from the harmonic emissions. This study provides a new insight into the understanding for circular polarized type III bursts.