Solar Physics: 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.
Twisted croissant CME model for right-handed (top) and left-handed (bottom) flux ropes, for three orientations of the ropes (rotating about the Y −axis. Axes are plotted in units of R◦, and color bar shows distance along the line of sight as determined from white light polarization, in the same units. The green curved arrows show circulation about an axis that establishes flux rope chirality, while the pink arrow tracks a misleading apparent circulation of the opposite sign.