Spectral Inversion of Multi-Line Full-Disk Observations of Quiet Sun Magnetic Fields

TL;DR

This paper applies spectral inversion techniques to full-disk solar observations to analyze quiet Sun magnetic fields, revealing a limb-dependent magnetic field strength distribution and identifying two distinct magnetic element populations.

Contribution

It demonstrates the simultaneous inversion of 15 spectral lines using the SIR code on quiet Sun data, providing new insights into magnetic field distributions and their altitude dependence.

Findings

Weaker magnetic fields are observed closer to the solar limb.

Two magnetic element populations are identified: strong fields with high temperatures and weak fields with low temperatures.

The study enhances understanding of magnetic field variations in the quiet Sun.

Abstract

Spectral inversion codes are powerful tools to analyze spectropolarimetric observations, and they provide important diagnostics of solar magnetic fields. Inversion codes differ by numerical procedures, approximations of the atmospheric model, and description of radiative transfer. Stokes Inversion based on Response functions (SIR) is an implementation widely used by the solar physics community. It allows to work with different atmospheric components, where gradients of different physical parameters are possible, e.g., magnetic field strength and velocities. The spectropolarimetric full-disk observations were carried out with the Stokesmeter of the Solar Telescope for Operative Predictions (STOP) at the Sayan Observatory on 3 February 2009, when neither an active region nor any other extended flux concentration was present on the Sun. In this study of quiet Sun magnetic fields, we apply the SIR code simultaneously to 15 spectral lines. A tendency is found that weaker magnetic field strengths occur closer to the limb. We explain this finding by the fact that close to the limb, we are more sensitive to higher altitudes in an expanding flux tube, where the field strength should be smaller since the magnetic flux is conserved with height. Typically, the inversions deliver two populations of magnetic elements: (1) high magnetic field strengths (1500-2000 G) and high temperatures (5500-6500 K) and (2) weak magnetic fields (50-150 G) and low temperatures (5000-5300 K).