Stratification of canopy magnetic fields in a plage region. Constraints from a spatially-regularized weak-field approximation method
Abstract
Context. The role of magnetic fields in the chromospheric heating problem remains greatly unconstrained. Most theoretical predictions from numerical models rely on a magnetic configuration, field strength, and connectivity; the details of which have not been well established with observational studies for many chromospheric scenarios. High-resolution studies of chromospheric magnetic fields in plage are very scarce or non existent in general.
Aims: Our aim is to study the stratification of the magnetic field vector in plage regions. Previous studies predict the presence of a magnetic canopy in the chromosphere that has not yet been studied with full-Stokes observations. We use high-spatial resolution full-Stokes observations acquired with the CRisp Imaging Spectro-Polarimeter (CRISP) at the Swedish 1-m Solar Telescope in the Mg I 5173 Å, Na I 5896 Å and Ca II 8542 Å lines.
Methods: We have developed a spatially-regularized weak-field approximation (WFA) method, based on the idea of spatial regularization. This method allows for a fast computation of magnetic field maps for an extended field of view. The fidelity of this new technique has been assessed using a snapshot from a realistic 3D magnetohydrodynamics simulation.
Results: We have derived the depth-stratification of the line-of-sight component of the magnetic field from the photosphere to the chromosphere in a plage region. The magnetic fields are concentrated in the intergranular lanes in the photosphere and expand horizontally toward the chromosphere, filling all the space and forming a canopy. Our results suggest that the lower boundary of this canopy must be located around 400 - 600 km from the photosphere. The mean canopy total magnetic field strength in the lower chromosphere (z ≈ 760 km) is 658 G. At z = 1160 km, we estimate ⟨B∥⟩ ≈ 417 G.
Conclusions: In this study we propose a modification to the WFA that improves its applicability to data with a worse signal-to-noise ratio. We have used this technique to study the magnetic properties of the hot chromospheric canopy that is observed in plage regions. The methods described in this paper provide a quick and reliable way of studying multi layer magnetic field observations without the many difficulties inherent to other inversion methods.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- October 2020
- DOI:
- 10.1051/0004-6361/202038754
- arXiv:
- arXiv:2006.14487
- Bibcode:
- 2020A&A...642A.210M
- Keywords:
-
- polarization;
- Sun: chromosphere;
- Sun: magnetic fields;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- Accepted for publication on 2020-08-27