Tomography of the Solar Corona with the Metis Coronagraph I: Predictive Simulations with Visible-Light Images

The Solar Orbiter/Metis coronagraph records full-Sun visible-light polarized brightness (pB-) images of the solar corona. This work investigates the utility of a synoptic observational program of Metis for tomographic reconstruction of the three-dimensional (3D) distribution of the electron density of the global solar corona. During its lifetime, the mission's distance to the Sun will range over approximate to 0.3 - 1.0AU, while its solar latitude will span approximate to +/- 33 degrees. The limitations that this orbital complexity poses on tomographic reconstructions are explored in this work. Using the predicted orbital information of Solar Orbiter and 3DMHD simulations of the solar corona using the AlfvenWave Solar atmosphere Model (AWSoM), time series of synthetic Metis pB-images were computed and used as data to attempt tomographic reconstruction of the model. These numerical experiments were implemented for solar-minimum and solar-maximum conditions. In both cases, images were synthesized from three orbital segments, corresponding to extreme geometrical conditions of observation by Metis: aphelion, perihelion, and maximum solar latitude. The range of heights that can be reconstructed, the required data-gathering period, and the accuracy of the reconstruction, are discussed in detail for each case. As a general conclusion, a Metis synoptic observational program with a cadence of at least four images day(-1) provides enough data to attempt tomographic reconstructions during the whole lifetime of the mission, a requirement well within the two- to three-hour cadence of the current synoptic program. This program will allow implementation of tomography experimenting with different values for the cadence of the time series of images used to feed reconstructions. Its cadence will also provide continuous opportunities to select images avoiding highly dynamic events, which compromise the accuracy of tomographic reconstructions.