I. N. Atroshchenko | Searcharxiv

arXiv2010

Numerical simulation of the interaction between solar granules and small-scale magnetic fields

We have carried out numerical simulation based on the equations of radiation magnetohydrodynamics to study the interaction of solar granules and small-scale magnetic fields in photospheric regions with various magnetic fluxes. Four sequences of 2D time-dependent models were calculated for photospheric regions with average vertical magnetic fluxes of 0, 10, 20, and 30 mT. The models exhibit no substantial variations in their temperature structure with varying average field strength, while the density and gas pressure profiles display gross changes. The solar granulation brightness field also varies substantially with magnetic flux. The contribution of the small-scale component to the intensity power spectrum increases with average field strength, whereas the large-scale component (of about a granule size) contributes less, the total rms intensity fluctuations being approximately the same. Thus the observed decrease in rms intensity fluctuations with growing average magnetic flux can be interpreted as smoothing of the small-scale component in the power spectrum by the modulation transfer function of the telescope.

astro-ph.SR↗

arXiv2009

Origin of Extremely Asymmetric Stokes V Profiles in an Inhomogeneous Atmosphere

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.

astro-ph.SR↗