The emergence of magnetic flux through a partially ionised solar atmosphereJ. E. Leake and T. D. Arber
Space and Astrophysics group, Dept. of Physics, University of Warwick, Gibbet Hill Road, CV4 7AL, Coventry, UK
(Received 24 August 2005 / Accepted 16 January 2006)
We present results from 2.5D numerical simulations of the emergence of magnetic flux from the upper convection zone through the photosphere and chromosphere into the corona. Certain regions of the solar atmosphere are at sufficiently low temperatures to be only partially ionised, in particular the lower chromosphere. This leads to Cowling resistivities orders of magnitude larger than the Coulomb values, and thus to anisotropic dissipation in Ohm's law. This also leads to localised low magnetic Reynolds numbers ( ). We find that the rates of emergence of magnetic field are greatly increased by the partially ionised regions of the model atmosphere, and the resultant magnetic field is more diffuse. More importantly, the only currents associated with the magnetic field to emerge into the corona are aligned with the field, and thus the newly formed coronal field is force-free.
Key words: magnetohydrodynamics (MHD) -- magnetic fields -- plasmas -- Sun: atmosphere -- Sun: sunspots -- Sun: magnetic fields
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