Extrapolation of the Solar Coronal Magnetic Field from SDO/HMI Magnetogram by a CESE--MHD--NLFFF Code

TL;DR

This paper presents a new MHD relaxation-based NLFFF model using CESE scheme to extrapolate the solar coronal magnetic field from SDO/HMI magnetograms, effectively reconstructing key active region structures.

Contribution

The paper introduces a novel CESE--MHD--NLFFF code for coronal magnetic field extrapolation, demonstrating its effectiveness on real active region data with detailed qualitative and quantitative assessments.

Findings

Successfully reconstructed coronal magnetic structures matching EUV observations

Achieved good force-free conditions in strong magnetic field regions

Reproduced complex features like flux ropes and sheared field lines

Abstract

Due to the absence of direct measurement, the magnetic field in the solar corona is usually extrapolated from the photosphere in numerical way. At the moment, the nonlinear force-free field (NLFFF) model dominates the physical models for field extrapolation in the low corona. Recently we have developed a new NLFFF model with MHD relaxation to reconstruct the coronal magnetic field. This method is based on CESE--MHD model with the conservation-element/solution-element (CESE) spacetime scheme. In this paper, we report the application of the CESE--MHD--NLFFF code to \SDO/HMI data with magnetograms sampled for two active regions (ARs), NOAA AR 11158 and 11283, both of which were very non-potential, producing X-class flares and eruptions. The raw magnetograms are preprocessed to remove the force and then inputted into the extrapolation code. Qualitative comparison of the results with the \SDO/AIA images shows that our code can reconstruct magnetic field lines resembling the EUV-observed coronal loops. Most important structures of the active regions are reproduced excellently, like the highly-sheared field lines that suspend filaments in AR 11158 and twisted flux rope which corresponds to a sigmoid in AR 11283. Quantitative assess of the results shows that the force-free constraint is fulfilled very well in the strong-field regions but apparently not that well in the weak-field regions because of data noise and numerical errors in the small currents.