Simulation of a flux emergence event and comparison with observations by Hinode

TL;DR

This study uses 3D MHD simulations and synthetic Hinode observations to analyze flux emergence, revealing how twisted flux tubes manifest in spectral lines and comparing simulation results with actual solar data.

Contribution

It introduces a detailed simulation approach that reproduces observed flux emergence signatures and compares synthetic spectra with Hinode data.

Findings

Spectral lines sample different parts of the flux tube during emergence.

Horizontal magnetic field values match observations.

Radiative cooling causes flux tube flattening in the photosphere.

Abstract

We study the observational signature of flux emergence in the photosphere using synthetic data from a 3D MHD simulation of the emergence of a twisted flux tube. Several stages in the emergence process are considered. At every stage we compute synthetic Stokes spectra of the two iron lines Fe I 6301.5 {\AA} and Fe I 6302.5 {\AA} and degrade the data to the spatial and spectral resolution of Hinode's SOT/SP. Then, following observational practice, we apply Milne-Eddington-type inversions to the synthetic spectra in order to retrieve various atmospheric parameters and compare the results with recent Hinode observations. During the emergence sequence, the spectral lines sample different parts of the rising flux tube, revealing its twisted structure. The horizontal component of the magnetic field retrieved from the simulations is close to the observed values. The flattening of the flux tube in the photosphere is caused by radiative cooling, which slows down the ascent of the tube to the upper solar atmosphere. Consistent with the observations, the rising magnetized plasma produces a blue shift of the spectral lines during a large part of the emergence sequence.