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  Current systems of coronal loops in 3D MHD simulations

Warnecke, J., Chen, F., Bingert, S., & Peter, H. (2017). Current systems of coronal loops in 3D MHD simulations. Astronomy and Astrophysics, 607: A 53. doi:10.1051/0004-6361/201630095.

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Item Permalink: http://hdl.handle.net/11858/00-001M-0000-002E-8748-8 Version Permalink: http://hdl.handle.net/21.11116/0000-0001-5B17-0
Genre: Journal Article

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 Creators:
Warnecke, Jörn1, 2, Author              
Chen, Feng1, 2, Author              
Bingert, S., Author              
Peter, Hardi1, 2, Author              
Affiliations:
1Department Sun and Heliosphere, Max Planck Institute for Solar System Research, Max Planck Society, ou_1832289              
2Max Planck Research Group in Solar and Stellar Magnetic Activity, Max Planck Institute for Solar System Research, Max Planck Society, Justus-von-Liebig-Weg 3, 37077 Göttingen, DE, ou_2265638              

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Free keywords: magnetohydrodynamics (MHD) / Sun: corona / Sun: magnetic fields
 MPIS_GROUPS: Research Group Solar Stellar Mag Activity
 Abstract: Aims. We study the magnetic field and current structure associated with a coronal loop. Through this we investigate to what extent the assumptions of a force-free magnetic field break down and where they might be justified. Methods. We analyze a three-dimensional (3D) magnetohydrodynamic (MHD) model of the solar corona in an emerging active region with the focus on the structure of the forming coronal loops. The lower boundary of this simulation is taken from a model of an emerging active region. As a consequence of the emerging magnetic flux and the horizontal motions at the surface a coronal loop forms self-consistently. We investigate the current density along magnetic field lines inside (and outside) this loop and study the magnetic and plasma properties in and around this loop. The loop is defined as the bundle of field lines that coincides with enhanced emission in extreme UV. Results. We find that the total current along the emerging loop changes its sign from being antiparallel to parallel to the magnetic field. This is caused by the inclination of the loop together with the footpoint motion. Around the loop, the currents form a complex non-force-free helical structure. This is directly related to a bipolar current structure at the loop footpoints at the base of the corona and a local reduction of the background magnetic field (i.e., outside the loop) caused by the plasma flow into and along the loop. Furthermore, the locally reduced magnetic pressure in the loop allows the loop to sustain a higher density, which is crucial for the emission in extreme UV. The action of the flow on the magnetic field hosting the loop turns out to also be responsible for the observed squashing of the loop. Conclusions. The complex magnetic field and current system surrounding it can only be modeled in 3D MHD models where the magnetic field has to balance the plasma pressure. A one-dimensional coronal loop model or a force-free extrapolation cannot capture the current system and the complex interaction of the plasma and the magnetic field in the coronal loop, despite the fact that the loop is under low-β conditions.

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Language(s): eng - English
 Dates: 2017-12-062017
 Publication Status: Published online
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1051/0004-6361/201630095
 Degree: -

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Title: Astronomy and Astrophysics
  Other : Astron. Astrophys.
Source Genre: Journal
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Publ. Info: Berlin : Springer-Verlag
Pages: - Volume / Issue: 607 Sequence Number: A 53 Start / End Page: - Identifier: ISSN: 0004-6361
CoNE: https://pure.mpg.de/cone/journals/resource/954922828219_1