Modeling the Solar Corona: Testing Nonlinear Force-Free Methods with a Magneto-Hydrostatic Test Case

Abstract:

The solar corona is the outer atmosphere of the Sun and it is where highly energetic solar events take place, e.g. solar flares. The coronal magnetic field is thought to be in a force-free state, meaning that the magnetic Lorentz force is self-balanced. Furthermore, we cannot reliably measure the vector magnetic field in the corona. This motivates Nonlinear Force-Free Field (NLFFF) extrapolations of the coronal magnetic field using photospheric magnetic data as boundary conditions. Photospheric data is not in a force-free state, which leads to an inconsistency between the boundary conditions and the assumptions of the model. However, by using a Linear Magneto-HydroStatic model (LMHS), which deliberately takes into account gravity and gas pressure forces, as boundary conditions to a force-free model we can examine the effect of this inconsistency in the modeling. In the LMHS model, the non-magnetic contribution to the forces is controlled by a single parameter. We consider several test cases with different values of this parameter. It is hypothesized that NLFFF model will not experience much change when this parameter is set to zero, providing a consistent control test case. Nevertheless, by increasing non-magnetic contributions, we seek to test the limits of the NLFFF model and determine the deviation from the original LMHS model using various methods of comparison (point-wise comparison, field line tracings, magnetic energy calculations, Lorentz force calculations).

This material is based upon work supported by the National Science Foundation under Grant No. 1841962. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.