Valori, G;
Guo, Y;
Pariat, E;
Anfinogentov, S;
Chen, F;
Georgoulis, M;
Liu, Y;
... Yang, S; + view all
(2017)
Magnetic Helicity Estimations in Models and Observations of the Solar Magnetic Field. III. Twist Number Method.
The Astrophysical Journal
, 840
(1)
, Article 40. 10.3847/1538-4357/aa6aa8.
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Abstract
We study the writhe, twist, and magnetic helicity of different magnetic flux ropes, based on models of the solar coronal magnetic field structure. These include an analytical force-free Titov–Démoulin equilibrium solution, non-force-free magnetohydrodynamic simulations, and nonlinear force-free magnetic field models. The geometrical boundary of the magnetic flux rope is determined by the quasi-separatrix layer and the bottom surface, and the axis curve of the flux rope is determined by its overall orientation. The twist is computed by the Berger–Prior formula, which is suitable for arbitrary geometry and both force-free and non-force-free models. The magnetic helicity is estimated by the twist multiplied by the square of the axial magnetic flux. We compare the obtained values with those derived by a finite volume helicity estimation method. We find that the magnetic helicity obtained with the twist method agrees with the helicity carried by the purely current-carrying part of the field within uncertainties for most test cases. It is also found that the current-carrying part of the model field is relatively significant at the very location of the magnetic flux rope. This qualitatively explains the agreement between the magnetic helicity computed by the twist method and the helicity contributed purely by the current-carrying magnetic field.
| Type: | Article |
|---|---|
| Title: | Magnetic Helicity Estimations in Models and Observations of the Solar Magnetic Field. III. Twist Number Method |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.3847/1538-4357/aa6aa8 |
| Publisher version: | https://doi.org/10.3847/1538-4357/aa6aa8 |
| Language: | English |
| Additional information: | This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions. |
| Keywords: | Sun: activity; Sun: corona; Sun: magnetic fields |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/1546159 |
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