Origin of Extremely Asymmetric Stokes V Profiles in an Inhomogeneous Atmosphere

TL;DR

This study investigates the origin of extremely asymmetric Stokes V profiles in the solar photosphere, linking their formation to complex magnetic field gradients and turbulent plasma motions revealed by 2-D MHD simulations.

Contribution

It demonstrates that extreme asymmetries in Stokes V profiles are caused by polarity reversals and complex gradients in magnetic fields, supported by detailed MHD simulation analysis.

Findings

Asymmetric profiles are linked to polarity reversals along the line of sight.

Profiles with more lobes indicate greater magnetic field complexity.

Turbulence and vortices contribute to magnetic field mixing at granule edges.

Abstract

The formation of unusually shaped Stokes V profiles of the Fe I 630.2 nm line in the solar photosphere are investigated. The results of numerical 2-D MHD simulation of solar magnetogranulation are used for this. In their properties, the synthetic unusual profiles with extremely asymmetry are similar to the unusual profiles observed with a spatial resolution better than 1" in the network and internetwork regions. According to our results the unusual profiles mostly appear in clusters along the polarity inversion lines in the regions of weak magnetic fields with mixed polarity. As a rule, they are located at the edges of granules and lanes, and sometimes they are met close to strong magnetic field concentrations with high velocity and magnetic field strength gradients. They turned out to appear as clusters in the regions where large granules disintegrate and new magnetic flux tubes begin to form. The unusual $V$ profiles may have from one to six lobes. The one-lobe and multilobe profiles are of the same origin. The processing causing the extreme asymmetry of the profiles are characterized by one or several polarity reversal along the line of sight as well as by complicated velocity and field strength gradients. The greater the number of profile lobes, the greater is the probability of the field gradient sign change. Hence it follows that the magnetic field should be very complicated in the regions of formation of extremely asymmetric $V$ profiles. This is confirmed by immediate results of MHD granulation simulations, which demonstrate the formation of vortices and turbulence by the velocity shear at down draft edges. These processes add complexity to the magnetic field structure by mixing field polarities, particularly at the edges of granules.