How Should One Optimize Nonlinear Force-Free Coronal Magnetic Field Extrapolations from SDO/HMI Vector Magnetograms?

By T. Wiegelmann, J. Thalmann, B. Inhester, T. Tadesse, Xudong Sun, J. Todd Hoeksema. 2012

148 citations recorded by the source corpus.

The Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) provides photospheric vector magnetograms with a high spatial and temporal resolution. Our intention is to model the coronal magnetic field above active regions with the help of a nonlinear force-free extrapolation code. Our code is based on an optimization principle and has been tested extensively with semianalytic and numeric equilibria and applied to vector magnetograms from Hinode and ground-based observations. Recently we implemented a new version which takes into account measurement errors in photospheric vector magnetograms. Photospheric field measurements are often affected by measurement errors and finite nonmagnetic forces inconsistent for use as a boundary for a force-free field in the corona. To deal with these uncertainties, we developed two improvements: i) preprocessing of the surface measurements to make them compatible with a force-free field, and ii) new code which keeps a balance between the force-free constraint and deviation from the photospheric field measurements. Both methods contain free parameters, which must be optimized for use with data from SDO/HMI. In this work we describe the corresponding analysis method and evaluate the force-free equilibria by how well force-freeness and solenoidal conditions are fulfilled, by the angle between magnetic field and electric current, and by comparing projections of magnetic field lines with coronal images from the Atmospheric Imaging Assembly (SDO/AIA). We also compute the available free magnetic energy and discuss the potential influence of control parameters.

Subfields: Astronomy and Astrophysics, Molecular Biology

View Paper: https://www.semanticscholar.org/paper/36fd7b285ee3c3d36acbd020e39a910677381269

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In Astronomy and Astrophysics

1. M. Temmer
2. J. Thalmann
3. T. Wiegelmann
4. S. Solanki
5. C. Farrugia
6. Yuming Wang
7. N. Lugaz
8. I. Usoskin

In Molecular Biology

1. J. Thalmann
2. T. Wiegelmann
3. S. Solanki
4. C. Farrugia
5. N. Lugaz
6. Yuming Wang
7. M. Temmer
8. I. Usoskin

Citations in the corpus

• Solar Force-free Magnetic Fields (2012, unknown): “Some datasets from SDO/HMI do not necessarily require preprocessing, see, e.g., Wiegelmann et al. (2012).”
• The Interaction of Successive Coronal Mass Ejections: A Review (2016, methodology): “With the aid of a non-linear force-free field (NLFFF) extrapolation method (Wiegelmann et al., 2012), Sun et al. (2012) investigated the evolution of the magnetic field and its energy in the AR from 12 –17 February 2011.”
• The magnetic field in the solar atmosphere (2014, background): “Only exceptionally, however, active-region vector magnetograms fulfill the forcefree criteria (for such an example see Wiegelmann et al., 2012).”