Effects of Initial Conditions on Magnetic Reconnection in a Solar Transient

Coronal magnetic field extrapolations are necessary to understand the magnetic field morphology of the source region in solar coronal transients. The extrapolation models are broadly classified into nonforce-free and force-free, depending on whether the model allows for a Lorentz force or not. Presently, these models are employed to carry out state-of-the-art data-driven and data-constrained magnetohydrodynamics (MHD) simulations to explore magnetic reconnection (MR)—the underlying cause of the transients. It is then imperative to study the influence of different extrapolation models on simulated evolution. For this purpose, the numerical model EULAG-MHD is employed to carry out simulations with different initial magnetic and velocity fields obtained through nonforce-free and force-free extrapolations. The selected active region is NOAA 11977, hosting a C6.6 class eruptive flare. Both extrapolations are found to be in good agreement with the observed line-of-sight and transverse magnetic fields. Further, a morphological comparison on the global scale and particularly for selected topologies, such as a magnetic null point and a hyperbolic flux tube (HFT), suggests that similar magnetic field line structures are reproducible in both models, although the extent of agreement between the two varies. Astoundingly, generation of a three-dimensional null near the HFT is observed in all the simulations, inferring the evolution to be independent of the particular initial field configuration. Moreover, the magnetic field lines (MFLs) undergoing MRs at the null point and HFT evolve similarly, further confirming the near independence of reconnection details on the chosen initial conditions. Consequently, both the extrapolation techniques can be suitable for initiating data-driven and data-constrained simulations.