Relationship between the topological skeleton, current concentrations, and 3D magnetic reconnection sites in the solar atmosphereR. C. Maclean1, J. Büchner2, and E. R. Priest1
1 Institute of Mathematics, University of St Andrews, The North Haugh, St Andrews, Fife, Scotland, KY16 9SS, UK
2 Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany
Received 12 September 2007 / Accepted 26 September 2008
Aims. The aim of this work is to determine the relationship between the 3D structure of the coronal magnetic field, diagnosed by the topological skeleton, and current concentrations as potential sites of 3D reconnection.
Methods. We utilised the results of 3D numerical MHD simulations of an observed EUV bright point (BP) in the solar atmosphere. The simulations are based on MDI line-of-sight magnetogram data from 13 June 1998. We analysed the results of the simulations using the method of magnetic charge topology. Three different methods of reducing the magnetogram to a set of point magnetic sources are tested.
Results. Observations of the BP show a rotation of one of its main magnetic source regions. Numerical simulations of this rotational motion result in a localised build-up of parallel electric current, which is dissipated by anomalous resistivity, causing 3D magnetic reconnection and BP heating. The magnetic topological structure of the simulated BP was also calculated, and a portion of the topological separatrix surface bounding the magnetic flux of the rotating source region is found to correspond to the locations of current build-up and heating. All three magnetogram reduction methods produce similar results for the large-scale magnetic field structure.
Conclusions. Magnetic topology is a useful method for predicting the locations of coronal current concentrations, insofar as the results of our simulations show that strong integrated parallel electric fields are found only along topological separatrix surfaces. However, further investigation is necessary to determine exactly which parts of the reconstructed separatrices will host the electric currents. Topological magnetic field reconstructions also cast light on the location of coronal BP heating, which occurs as a result of the dissipation of the currents by 3D reconnection. The choice of the magnetogram reduction algorithm does not greatly affect the large-scale topological features of the resulting reconstructed magnetic field. Further work is required to compare these results with data for other observed BPs.
Key words: Sun: atmosphere -- Sun: corona -- Sun: magnetic fields -- magnetohydrodynamics (MHD) -- methods: numerical
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