Highly Polarized Type III Storm Observed with Parker Solar Probe

TL;DR

The Parker Solar Probe observed a highly polarized Type III radio storm following a CME, revealing detailed polarization changes and properties of electron beams in the solar corona.

Contribution

This study provides the first detailed analysis of the polarization characteristics of a Type III storm observed close to the Sun, linking in situ measurements with remote radio observations.

Findings

Type III storm was highly circularly polarized.

Polarization transitioned from LHC to RHC across the current sheet.

Electron beam speed was approximately 0.1c.

Abstract

The Parker Solar Probe (PSP) spacecraft observed a large coronal mass ejection (CME) on 5 September 2022, shortly before closest approach during the 13th PSP solar encounter. For several days following the CME, PSP detected a storm of Type III radio bursts. Stokes parameter analysis of the radio emission indicates that the Type III storm was highly circularly polarized. Left hand circularly polarized (LHC) emission dominated at the start of the storm, transitioning to right hand circularly polarized (RHC) emission at the crossing of the heliospheric current sheet on 6 September. We analyze the properties of this Type III storm. The drift rate of the Type IIIs indicates a constant beam speed of $\sim$0.1$c$, typical for Type III-producing electron beams. The sense of polarization is consistent with fundamental emission generated primarily in the $O$-mode. The stable and well organized post-CME magnetic field neatly separates the LHC- and RHC-dominated intervals of the storm, with minimal overlap between the senses of polarization. The proximity of PSP to the source region, both in radial distance and in heliographic longitude, makes this event an ideal case study to connect in situ plasma measurements with remote observations of radio emission.