Coronal magnetic field and emission properties of small-scale bright and faint loops in the quiet Sun

¹ Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
² Space Research and Technology Institute, Bulgarian Academy of Sciences, Acad. Georgy Bonchev Str., Bl. 1, 1113 Sofia, Bulgaria
³ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité, 5 place Jules Janssen, 92195, Meudon, France; Laboratoire Cogitamus, F-75005 Paris, France
⁴ School of Mathematics and Statistics, University of St Andrews, North Haugh, St Andrews, KY16 9SS Scotland, UK

Received: 12 April 2024
Accepted: 10 July 2024

Abstract

Context. The present study provides statistical information on the coronal magnetic field and intensity properties of small-scale bright and faint loops in the quiet Sun.

Aims. We aim to quantitatively investigate the morphological and topological properties of the coronal magnetic field in bright and faint small-scale loops, with the former known as coronal bright points (CBPs).

Methods. We analyse 126 small-scale loops of all sizes using quasi-temporal imaging and line-of-sight magnetic field observations. These observations are taken by the Atmospheric Imaging Assembly (AIA) in the Fe XII 193 Å channel and the Helioseismic Magnetic Imager (HMI) on board the Solar Dynamics Observatory. We employ a recently developed automatic tool that uses a linear magneto-hydro-static (LMHS) model to compute the magnetic field in the solar atmosphere and automatically match individual magnetic field lines with small-scale loops.

Results. For most of the loops, we automatically obtain an excellent agreement of the magnetic field lines from the LMHS model and the loops seen in the AIA 193 Å channel. One stand-out result is that the magnetic field is non-potential. We obtain the typical ranges of loop heights, lengths, intensities, mean magnetic field strength along the loops and at loop tops, and magnetic field strength at loop footpoints. We investigate the relationship between all those parameters. We find that loops below the classic chromospheric height of 1.5 Mm are flatter, suggesting that non-magnetic forces (one of which is the plasma pressure) play an important role below this height. We find a strong correlation (Pearson coefficient of 0.9) between loop heights and lengths. An anti-correlation is found between the magnetic field strength at loop tops and loop heights and lengths. The average intensity along the loops correlates stronger with the average magnetic field along the loops than with the field strength at loop tops.

Conclusions. The latter correlation indicates that the energy release in the loops is more likely linked to the average magnetic field along the loops than the field strength on the loop tops. In other words, the energy is probably released all along the loops, but not just at the loop top. This result is consistent with a recent benchmarking radiative 3D MHD model.