Tomography of the Solar Corona with the Metis Coronagraph II: Three-Dimensional Reconstructions of the Electron Density and Comparison with Reconstructions Based on LASCO-C2

Abstract

We carried out tomographic reconstructions of the three-dimensional distribution of the electron density of the solar corona based on white light polarized brightness (pB) images taken by the Metis coronagraph on board the Solar Orbiter (SolO) mission. We selected three different time intervals during 2022, and further implemented independent synchronous reconstructions based on LASCO-C2 pB images for comparison purposes. The range of elongations covered by the field-of-view (FoV) of Metis considerably varies as SolO describes its highly eccentric orbit whereas that of LASCO-C2 remains almost constant. During the selected time intervals, their FoVs partially overlap, allowing a comparison of the reconstructions within the regions in common. The shape and size of the reconstructed coronal structures, streamers and coronal holes, are consistent, demonstrating the suitability of the images of the synoptic program of Metis for tomographic reconstruction of the coronal electron density over its varying FoV. A comparison between the two tomographic reconstructions for each analyzed time interval, shows that the Metis-to-C2 ratio of reconstructed electron density has a median value of \approx 1.7. This is consistent with the observed ratio of the pB measurements of the two instruments. Our analysis thus also illustrates the value of tomography as a tool for intercalibrating solar coronagraphs irrespective of their spatial location as long as their FoV partially overlap.