Effects of initial conditions on magnetic reconnection in a solar transient

Abstract

Coronal magnetic field extrapolations are necessary to understand the magnetic field mor-phology of the source region in solar coronal transients. The extrapolation models arebroadly classified into nonforce-free and force-free, depending on whether the model al-lows 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 toexplore magnetic reconnection (MR)-the underlying cause of the transients. It is then im-perative to study the influence of different extrapolation models on simulated evolution. Forthis purpose, the numerical model EULAG-MHD is employed to carry out simulations withdifferent initial magnetic and velocity fields obtained through nonforce-free and force-freeextrapolations. The selected active region is NOAA 11977, hosting a C6.6 class eruptiveflare. Both extrapolations are found to be in good agreement with the observed line-of-sightand transverse magnetic fields. Further, a morphological comparison on the global scaleand particularly for selected topologies, such as a magnetic null point and a hyperbolic fluxtube (HFT), suggests that similar magnetic field line structures are reproducible in bothmodels, although the extent of agreement between the two varies. Astoundingly, generationof a three-dimensional null near the HFT is observed in all the simulations, inferring theevolution to be independent of the particular initial field configuration. Moreover, the mag-netic field lines (MFLs) undergoing MRs at the null point and HFT evolve similarly, furtherconfirming the near independence of reconnection details on the chosen initial conditions.Consequently, both the extrapolation techniques can be suitable for initiating data-drivenand data-constrained simulations.