Influence of the vertical and horizontal magnetic field inhomogeneity on the Stokes parameters of the magnetically sensitive Fe I line 525.02 nm

TL;DR

This study investigates how vertical and horizontal magnetic field inhomogeneities affect the Stokes parameters of the Fe I 525.02 nm line, revealing asymmetries and sensitivities relevant for solar magnetic field diagnostics.

Contribution

It provides new insights into the effects of magnetic field gradients and inhomogeneities on Stokes profiles, enhancing understanding of solar magnetic structures.

Findings

Asymmetry in V profile peaks at -0.4 mT/km vertical gradient.

Line sensitivity to subtelescopic mixed polarity fields.

Strong-field areas become invisible at high heliocentric angles due to Wilson depression.

Abstract

Based on calculations of the Stokes parameters for the Holweger-Mliller model atmosphere, we study sensitivity of the Fe I 525.02 nm line to some kinds of vertical and horizontal magnetic field inhomogeneity. A noticeable asymmetry is shown to appear in the V profile peaks when the vertical gradient is -0.4 mT/km, which is typical of some theoretical flux tube models. The asymmetry is most pronounced in a pure longitudinal magnetic field and at a low macroturbulent velocity. A similar effect is observed for the Q profile in nonlongitudinal fields as well. The Fe I 525.02 nm line is sensitive also to subtelescopic fields of mixed polarity like those observed by Stenflo in IR lines. We argue that the Wilson depression in small-scale flux tubes renders strong-field areas invisible at heliocentric angles greater than 60--65 degrees, since they are screened by surroundings with weaker magnetic fields.