Study of magnetic relaxation in MHD simulations of energetically different flares

Abstract

The scenario of magnetic energy dissipation in solar flares due to reconnection merits investigation from the perspective of magnetohydrodynamic (MHD) relaxation. For this purpose, we carry out data-constrained MHD simulations with the EULAG-MHD numerical model for three energetically different flares, identified as B6.4, C4.0, and M1.1 in the GOES scheme. A magnetic field reconstruction in the solar atmosphere using a non-force-free field extrapolation model identifies magnetic null points for the B6.4 and C4.0 flares and a hyperbolic flux tube for the M1.1 flare as primary reconnection sites. The simulated evolution of the magnetofluid exhibits reconnection at these sites—exemplified by the slipping reconnection in the null point topology of the B6.4 flare. An estimation of the dissipated magnetic energy using three different volumes of integration within the computational domain amounts to ≈7%, 16.8%, and 33% of the available free magnetic energy in the simulation of B6.4, C4.0, and M1.1 flares. The angle (θ) between the current density and the magnetic field at the reconnection site decreases by 75.92°, 41.37°, and 40.13°, respectively, implying more alignment. The amount of dissipated magnetic energy in the simulated dynamics of each flare is in concurrence with the general energy relation between the classes of chosen flares. Furthermore, the increase in alignment at the reconnection sites suggests the occurrence of magnetic relaxation locally.