Magnetic Field and Plasma Diagnostics for Solar Coronal Mass Ejections: A Case Study Using the Forward Modeling Approach

The proposed COronal Solar Magnetism Observatory (COSMO) Large Coronagraph (LC) will provide unique observations to study coronal mass ejections (CMEs) with its ability to diagnose the magnetic field and plasma properties in the solar corona. Here we take a realistic magnetohydrodynamic CME model, and synthesize the signals of several coronal emission lines (CELs) to perform forward modeling of COSMO LC observation of a CME. We use the Stokes parameters of the Fe xiii 10747 ̊A line to diagnose the magnetic field and plasma properties of the CME flux rope. The results show that COSMO LC can provide magnetic field measurements of CME progenitors with a high spatial resolution (pixel size = 2′′). During the CME eruption, the COSMO LC observation may be used to qualitatively study the evolution of magnetic field by using a lower spatial resolution (pixel size = 6′′). We then use the synthetic signals of several other CELs to diagnose the physical conditions in the CME leading front, including the shock. The COSMO LC observations of the Fe xiii 10798/10747 ̊A and Ar xiii 8300/10143 ̊A line pair could provide density diagnostics of the front. By observing several CELs with different formation temperatures, the COSMO LC could be used to diagnose the temperature and ionization states in the front. We suggest that the Fe xiii 10747 ̊A line should be given the highest priority when observing CMEs, while observations of the Fe xiii 10798 ̊A, Fe xiv 5303 ̊A, Fe xv 7062 ̊A, and Ar xiii 10143 ̊A lines can also provide valuable information on CMEs.