Inferring the magnetic field vector in the quiet Sun. III. Disk variation of the Stokes profiles and isotropism of the magnetic field

TL;DR

This study investigates the angular distribution of magnetic fields in the quiet Sun using high-quality Hinode data, revealing non-isotropic distributions and latitude-dependent variations in the magnetic field vector.

Contribution

It introduces a novel method comparing theoretical and observed Stokes profile histograms to infer the magnetic field distribution without traditional inversions.

Findings

Stokes profiles with signals above 2×10^{-3} cannot be explained by isotropic magnetic fields.

Observed histogram differences across latitudes are due to intrinsic magnetic field distribution variations.

Magnetic field distributions vary with latitude, not just line-of-sight effects.

Abstract

We have studied the angular distribution of the magnetic field vector in the solar internetwork employing high-quality data (noise level $\sigma \approx 3\times 10^{-4}$ in units of the quiet-Sun intensity) at different latitudes recorded with the Hinode/SP instrument. Instead of applying traditional inversion codes of the radiative transfer equation to retrieve the magnetic field vector at each spatial point on the solar surface and studying the resulting distribution of the magnetic field vector, we surmised a theoretical distribution function of the magnetic field vector and used it to obtain the theoretical histograms of the Stokes profiles. These histograms were then compared to the observed ones. Any mismatch between them was ascribed to the theoretical distribution of the magnetic field vector, which was subsequently modified to produce a better fit to the observed histograms. With this method we find that Stokes profiles with signals above $2\times 10^{-3}$ (in units of the continuum intensity) cannot be explained by an isotropic distribution of the magnetic field vector. We also find that the differences between the histograms of the Stokes profiles observed at different latitudes cannot be explained in terms of line-of-sight effects. However, they can be explained by a distribution of the magnetic field vector that inherently varies with latitude. We note that these results are based on a series of assumptions that, although briefly discussed in this paper, need to be considered in more detail in the future.