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

TL;DR

This study analyzes Type III radio bursts observed by the Parker Solar Probe, focusing on their occurrence, spectral properties, and polarization, providing initial insights into their behavior in the inner heliosphere.

Contribution

It presents the first detailed characterization of Type III radio bursts in the inner heliosphere, including polarization measurements and spectral analysis, during PSP's second solar encounter.

Findings

Type III bursts show increased occurrence during the second encounter.

Observed polarization degrees range from 0.15 to 0.38.

Spectral and polarization properties suggest possible emission mechanisms.

Abstract

We present initial results from the Radio Frequency Spectrometer (RFS), 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 which display circular polarization in the right hand polarized sense, with a degree of polarization of 0.15-0.38 in the range from 8-12 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 $o$ and $x$-mode simultaneously. Direct in situ observations in future PSP encounters could provide data which can distinguish these mechanisms.