Energetics and Emission in a Simulated Solar Flare Initialized by a Non-force-free Magnetic Field

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Abstract
Solar flare simulations are commonly initialised using nonlinear force-free field (NLFF) extrapolations derived from photospheric vector magnetograms. However, the force-free assumption neglects plasma forces and may limit the available free magnetic energy. In this work, we perform a controlled comparison of two three-dimensional resistive magnetohydrodynamic simulations of the X2.1-class flare that occurred on 2011 September 6 in NOAA Active Region 11283. The simulations differ only in their initial magnetic configuration: one is based on a conventional NLFF extrapolation, while the other employs a non-force-free extrapolation. Both models are evolved in an identical stratified atmosphere using the same numerical framework, enabling direct assessment of how the initial magnetic assumptions influence flare dynamics and energetics. We find that the non-force-free model undergoes more extensive magnetic restructuring and releases approximately twice as much magnetic energy (≈4.4 × 10 31 erg) as the NLFF case (≈2.3 × 10 31 erg), bringing the energy budget into closer agreement with expectations for X-class flares. Synthetic extreme-ultraviolet emission in the 94 Å channel is computed for both simulations and compared with observations from the Solar Dynamics Observatory. The non-force-free model produces a brighter and more spatially extended emission structure that more closely resembles the observed flare morphology and light curve. These results demonstrate that assumptions made in constructing the preflare coronal magnetic field can significantly affect flare energetics and observable signatures and suggest that non-force-free extrapolations provide a promising pathway toward more realistic data-constrained flare modelling.
Funding Information
  • UKRI ∣ Science and Technology Facilities Council (ST/Y001141/1)
  • EC ∣ European Research Council (ERC-2018-SyG)
  • Agence Nationale de la Recherche (ANR-22-CE31-0013-01)

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