| dc.description.abstract | Solar radio emission provides a remote sensing probe for the solar corona, interplanetary space, and the solar transient activity. In this study, we analyze the interplanetary type III solar radio burst with circular polarization in the inner heliosphere observed by Parker Solar Probe (PSP) from 10.5 kHz to 19.2 MHz during its first thirteen orbits (2018-2022). We also examine two polarized type III events on 27 January 2020 and 13 September 2020 to find their potential radio source from radio observations observed by Solar Terrestrial Relations Observatory (STEREO), Wind, and EUV images observed by Solar Dynamic Observatory/Atmospheric Imaging Assembly (SDO/AIA). Besides, we investigate case studies of complex type III burst on 05 September 2022 and seven Type III storm events between 2021 and 2022.
There are four properties of interplanetary type III solar radio burst we analyzed: high/low cut-off frequencies, frequency drift rate, circular polarization, and decay time. The results indicate that the high cut-off frequency of the polarized signal is close to the high cut-off frequency of the total intensity, but the lower cut-off frequency of the polarized signal is generally higher than the lower cut-off frequency of the total intensity. The spectral index of the frequency drift rate is slightly larger than that of the past observations. The number of right-hand circular polarization (RHC) events is higher than that of left-hand circular polarization (LHC) events; the maximum polarization is between 0.4 and 1. We apply the SEA analysis (Superposed Epoch Analysis) for the polarized Type III events from Orbit 1 to Orbit 8. There are two types of polarized patterns examined: one is non-circular polarized signal after the maximum total intensity, the other is the longer lasting polarized signal with decreasing frequency. For decay time, it has a slightly different tendency of frequency in different frequency ranges and different patterns of polarized signal.
In the case studies, the potential radio sources of two polarized type III events studied in this paper are all caused by small eruptions on the solar surface. For the complex type III radio burst events, the polarized signal appears only near the lower cut-off frequency, which is very different from most type III radio bursts. After comparing the coronagraph images, it is confirmed that the complex type III radio burst was caused by Far-side coronal mass ejection (CME) event. For the results of type III storms, the number of analyzed LHC and RHC storms are close to each other. Furthermore, our findings suggest that the signals within storms have obvious polarization and most of them have frequency drift. | en_US |