Polarization Diagnostics Applied to Coronal Mass Ejections and the Background Solar Wind

TL;DR

This paper explores how polarization measurements from the PUNCH mission can accurately locate and analyze coronal mass ejections and solar wind structures, highlighting diagnostic challenges and opportunities.

Contribution

It introduces a method to assess the 3D positioning accuracy of CMEs and solar wind features using polarization data, advancing solar corona diagnostics.

Findings

Polarization ratios can locate CMEs in 3D with certain accuracy.

Background solar wind density falloff can be inferred from polarization.

Line-of-sight extent affects the diagnostic precision.

Abstract

The ratio of radially to tangentially polarized Thomson-scattered white light provides a powerful tool for locating the 3D position of compact structures in the solar corona and inner heliosphere, and the Polarimeter to Unify the Corona and Heliosphere (PUNCH) has been designed to take full advantage of this diagnostic capability. Interestingly, this same observable that establishes the position of transient blob-like structures becomes a local measure of the slope of the global falloff of density in the background solar wind. It is thus important to characterize the extent along the line of sight of structures being studied, in order to determine whether they are sufficiently compact for 3D positioning. In this paper, we build from analyses of individual lines of sight to three-dimensional models of coronal mass ejections (CMEs), allowing us to consider how accurately polarization properties of the transient and quiescent solar wind are diagnosed. In this way, we demonstrate the challenges and opportunities presented by PUNCH polarization data for various quantitative diagnostics.