The eruption of a prominence carrying coronal flux rope forward synthesis of the magnetic field strength measurement by COSMOS

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Tuesday, November 13, 2018

From a magnetohydrodynamic (MHD) simulation of the eruption of a prominence hosting coronal flux rope, Yuhong Fan and others carry out forward synthesis of the circular polarization signal (Stokes V signal) of the FeXIII emission line at 1074.7 nm produced by the MHD model. This was measured by the proposed COronal Solar Magnetism Observatory (COSMO) Large Coronagraph (LC) and infer the line-of-sight magnetic field BLOS above the limb.

(a) The inferred line-of-sight (LOS) magnetic field B_LOS obtained from the forward synthesis of the circular polarization signal from the MHD model data at a time during the quasi-static phase of the flux rope; (b) The same as (a) but only show the pixels of the measured B_LOS with sufficient signal to noise ratio; (c) The axial field strength in the mid cross-section of the flux rope; (d) The 3D field lines of the coronal magnetic field as viewed from the observer’s perspective, with the LOS parallel to the axis of the emerging flux rope.
Figure caption: (a) The inferred line-of-sight (LOS) magnetic field B_LOS (where the x-direction is the LOS direction) obtained from the forward synthesis of the circular polarization signal from the MHD model data at a time during the quasi-static phase of the flux rope; (b) The same as (a) but only show the pixels of the measured B_LOS with sufficient signal to noise ratio; (c) The axial field strength in the mid cross-section of the flux rope; (d) The 3D field lines of the coronal magnetic field as viewed from the observer’s perspective, with the LOS parallel to the axis of the emerging flux rope.

With an aperture of 150 cm, integration time of 12 min, and a resolution of 12 arcsec, the LC can measure a significant BLOS with 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 BLOS 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 BLOS 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 and up to a height of about 1.3 solar radii. These results suggest that the COSMO LC has great potential in providing quantitative information about the magnetic field structure of CME precursors (e.g. the prominence cavities) and their early evolution for the onset of eruption.

Publication Name: The Astrophysical Journal

First HAO Author's Name: Yuhong Fan

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