Statistics and Polarization of Type III Radio Bursts Observed in the Inner Heliosphere

Abstract

Abstract We present initial results from the Radio Frequency Spectrometer, the high-frequency component of the FIELDS experiment on the Parker Solar Probe (PSP). During the first PSP solar encounter (2018 November), only a few small radio bursts were observed. During the second encounter (2019 April), copious type III radio bursts occurred, including intervals of radio storms where bursts occurred continuously. In this paper, we present initial observations of the characteristics of type III radio bursts in the inner heliosphere, calculating occurrence rates, amplitude distributions, and spectral properties of the observed bursts. We also report observations of several bursts during the second encounter that display circular polarization in the right-hand-polarized sense, with a degree of polarization of 0.15–0.38 in the range from 8 to 12 MHz. The degree of polarization can be explained either by depolarization of initially 100% polarized o-mode emission or by direct generation of emission in the o-mode and x-mode simultaneously. Direct in situ observations in future PSP encounters could provide data that can distinguish these mechanisms.