Forced field extrapolation of the magnetic structure of the Halpha fibrils in solar chromosphere

TL;DR

This study evaluates the effectiveness of forced magnetic field extrapolation in modeling the solar chromosphere's magnetic structure, showing it aligns well with observed Halpha fibrils up to certain heights, outperforming NLFFF methods.

Contribution

It demonstrates the accuracy of forced field extrapolation in representing chromospheric magnetic fields, especially where non-linear force-free assumptions fail.

Findings

Forced field extrapolation aligns with Halpha fibrils below 3600km.

Non-linear force-free field shows large misalignment in high-energy regions.

Force-free assumption fails at heights of 1400-1800km.

Abstract

We present a careful assess of the forced field extrapolation using Solar Dynamics Observatory/Helioseismic and Magnetic Imager (SDO/HMI) magnetogram. The convergence property is checked by several metrics. The extrapolated field lines below 3600km appear to be aligned with most Halpha fibrils observed by New Vacuum Solar Telescope (NVST). In the region where magnetic energy far larger than potential energy, field lines computed by forced field extrapolation still consistent with the patterns of Halpha fibrils while non-linear force free field (NLFFF) results show large misalignment. The horizontal average of lorentz force ratio shows the forced region where force-free assumption is failed can reach the height of $1400-1800km$. The non-force-free state of the chromosphere is also confirmed by recent radiation magnetohydrodynamics (MHD) simulation.