Two-dimensional MHD models of solar magnetogranulation. Dynamics of magnetic elements

TL;DR

This study uses 2D MHD simulations to analyze the dynamics of solar magnetic elements, revealing velocity patterns, asymmetry behaviors, and the impact of spatial resolution on spectral line profiles.

Contribution

It provides new insights into the velocity fields and spectral asymmetries of magnetic elements in the solar photosphere using realistic 2D MHD models.

Findings

Downflows dominate in network magnetic elements with velocities up to 9 km/s.

V-profile asymmetry depends strongly on spatial resolution, affecting observed profiles.

Vertical velocities exhibit nonlinear oscillations with 5-minute and 3-minute periods.

Abstract

We present the results of a statistical analysis of the Doppler shifts and the asymmetry parameters of V profiles of the Fe I 630.25 nm line produced by 2D MHD simulations of solar granulation. The realism of the simulations tested using the magnetic ratio of Fe I 524.71 and 525.02 nm lines. The Stokes spectra were synthesized in snapshots with a mixed polarity field having a mean magnetic flux density of 0.2 mT and mean unsigned field strength of 35 mT. We found that downflows with a velocity of 0.5 km/s predominate, on the average, in areas with some network magnetic elements at the disk center. In separate strong fluxtubes the average velocity is equal to 3 km/s and the maximum velocity is 9 km/s. In weak diffuse magnetic fields upflows dominate. Their average velocity is 0.5 km/s and maximal one is 3 km/s. The V-profile asymmetry depends on the spatial resolution. The V profiles synthesized with high spatial resolution (35 km) have average amplitude and area asymmetries -1%, 1%, respectively. The asymmetry scatter is \pm70% for weak profiles and \pm10% for strong ones. The profiles with low spatial resolution (700 km) have average amplitude and area asymmetries 3%, -2\%, respectively. Low spatial resolution is a reason why the amplitude asymmetry is always positive and greater than the area asymmetry in V profiles observed. We found weak correlation between the asymmetry of V profiles and velocity. Upflows cause negative asymmetry, on the average, and downflows cause positive asymmetry. We examined center-to-limb variations of vertical velocity in magnetic elements. Beginning from cos theta = 0.9, the average velocity abruptly increases from 0.5 to 2 km/s and then slightly varies closer to the limb. We found nonlinear oscillations of vertical velocity with power peaks in the 5-minute and 3-minute bands.