Internetwork magnetic field as revealed by 2D inversions

TL;DR

This study uses advanced 2D inversion techniques on spectropolarimetric data to better understand the weak and complex magnetic fields in the Sun's internetwork regions, revealing a mostly monotonic distribution of magnetic field strength.

Contribution

The paper introduces and validates a 2D inversion method that effectively retrieves small-scale magnetic field properties from spectropolarimetric data, improving upon previous techniques.

Findings

The 2D inversion accurately recovers magnetic field strength distribution.

The mean field strength at optical depth unity is approximately 130 G.

Field strength decreases with height and becomes more horizontal in higher layers.

Abstract

Properties of magnetic field in the internetwork regions are still fairly unknown due to rather weak spectropolarimetric signals. We address the matter by using the 2D inversion code that is able to retrieve the information on smallest spatial scales, up to the diffraction limit, while being less susceptible to noise than most of the previous methods used. Performance of the code and the impact of the various effects on the retrieved field distribution is tested first on the realistic MHD simulations. The best inversion scenario is then applied to the real Hinode/SP data. Tests on simulations show: (1) the best choice of node position ensures a decent retrieval of all parameters, (2) code performs well for different configurations of magnetic field, (3) slightly different noise level or slightly different defocus included in the spatial PSF produces no significant effect on the results and (4) temporal integration shifts the field distribution to the stronger, more horizontally inclined field. Although the contribution of the weak field is slightly overestimated due to noise, the 2D inversions are able to recover well the overall distribution of the magnetic field strength. Application of the 2D inversion code on the Hinode/SP internetwork observations reveals a monotonic field strength distribution. The mean field strength at optical depth unity is $\sim 130$~G. At the higher layers, field strength drops as the field becomes more horizontal. Regarding the distribution of the field inclination, tests show that we cannot directly retrieve it with the observations/tools at hand, however the obtained distributions are consistent with those expected from simulations with a quasi-isotropic field inclination after accounting for observational effects.