On the limitations of magneto-frictional relaxation
arXiv:2201.07485 · doi:10.1080/03091929.2021.2021197
Abstract
The magneto-frictional method is used in solar physics to compute both static and quasi-static models of the Sun's coronal magnetic field. Here, we examine how accurately magneto-friction (without fluid pressure) is able to predict the relaxed state in a one-dimensional test case containing two magnetic null points. Firstly, we show that relaxation under the full ideal magnetohydrodynamic equations in the presence of nulls leads necessarily to a non-force-free state, which could not be reached exactly by magneto-friction. Secondly, the magneto-frictional solutions are shown to lead to breakdown of magnetic flux conservation, whether or not the friction coefficient is scaled with magnetic field strength. When this coefficient is constant, flux is initially conserved, but only until discontinuous current sheets form at the null points. In the ensuing weak solution, we show that magnetic flux is dissipated at these current sheets. The breakdown of flux conservation does not occur for an alternative viscous relaxation scheme.
arXiv comment15 pages, 7 figures. This article has been accepted for (open access) publication in Geophysical & Astrophysical Fluid Dynamics, published by Taylor & Francis
References in corpus (16)
- Athena: A New Code for Astrophysical MHD
- The Sun's Global Photospheric and Coronal Magnetic Fields: Observations and Models
- A Method for Data-Driven Simulations of Evolving Solar Active Regions
- Solar Force-free Magnetic Fields
- Coronal Magnetic Field Evolution from 1996 to 2012: Continuous Non-Potential Simulations
- Modeling the Dispersal of an Active Region: Quantifying Energy Input into the Corona
- Testing magnetofrictional extrapolation with the Titov-Démoulin model of solar active regions
- The Coronal Global Evolutionary Model: Using HMI Vector Magnetogram and Doppler Data to Determine Coronal Magnetic Field Evolution
- Comparative Study of Data-driven Solar Coronal Field Models Using a Flux Emergence Simulation as a Ground-truth Data Set
- Asymptotic, non-linear solutions for ambipolar diffusion in one dimension
- Magnetic Flux Rope Identification and Characterization from Observationally-Driven Solar Coronal Models
- Simulating the Coronal Evolution of Bipolar Active Regions to Investigate the Formation of Flux Ropes
- On the formation of current sheets in response to the compression or expansion of a potential magnetic field
- Two Classes of Eruptive Events During Solar Minimum
- Magnetic field relaxation and current sheets in an ideal plasma
- Comparison of Methods for modelling Coronal Magnetic Fields