The eruption of a prominence-carrying coronal flux rope: Forward synthesis of the magnetic field strength measurement by the COronal Solar Magnetism Observatory Large Coronagraph

From a magnetohydrodynamic (MHD) simulation of the eruption of a prominence hosting coronal flux rope, we carry out forward synthesis of the circular polarization signal (Stokes V signal) of the Fe xiii emission line at 1074.7 nm produced by the MHD model as measured by the proposed COronal Solar Magnetism Observatory (COSMO) Large Coronagraph (LC) and infer the line-of-sight magnetic field, B LOS, above the limb. With an aperture of 150 cm, an integration time of 12 minutes, and a resolution of 12 arcsec, the LC can measure a significant B LOS with a sufficient signal-to-noise level, from the simulated flux rope viewed nearly along its axis with a peak axial field strength of about 10 G. The measured B LOS is found to relate well with the axial field strength of the flux rope for the height range of the prominence and can discern the increase with height of the magnetic field strength in that height range that is a definitive signature of the concave upturning dipped field supporting the prominence. The measurement can also detect an outward-moving B LOS due to the slow rise of the flux rope as it develops the kink instability, during the phase when its rise speed is still below about 41 km s−1 and up to a height of about 1.3 solar radii. These results suggest that the COSMO LC has great potential to provide quantitative information about the magnetic field structure of coronal mass ejection precursors (e.g., the prominence cavities) and their early evolution for the onset of eruption.