Letter to the Editor

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

¹ Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Strasse 2, 37191 Katlenburg-Lindau, Germany e-mail: yelles@mps.mpg.de
² Instituto de Astrofísica de Canarias, C/ vía Láctea, s/n, 38205 La Laguna (Tenerife), Spain
³ Lockheed Martin Solar and Astrophysics Laboratory, Palo Alto, CA 94304, USA
⁴ School of Space Research, Kyung Hee University, Yongin, Gyeonggi 446-701, Korea

Received: 26 August 2009
Accepted: 28 October 2009

Abstract

Aims. 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.

Methods. 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 Å and Fe I 6302.5 Å 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.

Results. 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.