Magnetic flux emergence in granular convection: radiative MHD simulations and observational signatures^*

¹ Max Planck Institute for Solar System Research, 37191 Katlenburg-Lindau, Germany e-mail: [cheung,msch]@mps.mpg.de; cheung@lmsal.com
² Instituto de Astrofísica de Canarias, 38200 La Laguna (Tenerife), Spain e-mail: fmi@ll.iac.es
³ Dept of Astrophysics, Faculty of Physics, University of La Laguna, 38200 La Laguna (Tenerife), Spain

Received: 2 January 2007
Accepted: 19 February 2007

Abstract

Aims.We study the emergence of magnetic flux from the near-surface layers of the solar convection zone into the photosphere.

Methods.To model magnetic flux emergence, we carried out a set of numerical radiative magnetohydrodynamics simulations. Our simulations take into account the effects of compressibility, energy exchange via radiative transfer, and partial ionization in the equation of state. All these physical ingredients are essential for a proper treatment of the problem. Furthermore, the inclusion of radiative transfer allows us to directly compare the simulation results with actual observations of emerging flux.

Results.We find that the interaction between the magnetic flux tube and the external flow field has an important influence on the emergent morphology of the magnetic field. Depending on the initial properties of the flux tube (e.g. field strength, twist, entropy etc.), the emergence process can also modify the local granulation pattern. The emergence of magnetic flux tubes with a flux of 10¹⁹ Mx disturbs the granulation and leads to the transient appearance of a dark lane, which is coincident with upflowing material. These results are consistent with observed properties of emerging magnetic flux.