Effects of Fluctuations on Magnetic Reconnection and Heating in the Solar Corona

Abstract

The solar corona exhibits unusually high temperatures (10^6 K) compared to the temperature in the Sun's photosphere (5800 K). This coronal heating is one of the fundamental problems in solar physics that is yet to be resolved. Magnetic reconnection is thought to play a critical role in driving this enigmatic heating process. In this work, we present a newly-developed resistive magnetohydrodynamic (MHD) numerical model in which we investigate the effects of magnetic fluctuations, generated by the photospheric motion of footpoints at which the coronal field lines are anchored, on the reconnection rate and the heating process in the solar corona. The treatment of magnetic reconnection is done using OpenFOAM for numerically solving the resistive MHD equations, which are modified by implementing the fluctuations as source or sink terms. Our results show that the use of the uniform resistivity model in the framework of resistive MHD leads to slow reconnection process even if fluctuations are added. Moreover, compared to the case of no fluctuations using the Spitzer resistivity model and starting with a zero initial velocity, it is noticed when sinusoidal fluctuations are added that: (1) the reconnection process is enhanced since the reconnection rate $\eta J_z$ is almost $10$ times higher, and (2) the magnetic energy is diffused fast and extra amount of heat and high values of particle acceleration (jets) are generated. Furthermore, the results show also that sinusoidal fluctuations of shorter wavelength promote a faster formation of X-points through plasmoid restructuring of the magnetic field lines. The reconnection rate is thus enhanced leading to a rapid heating process by pumping extra thermal energy in the coronal regions surrounding the reconnection site. Therefore, the magnetic reconnection process influenced by magnetic fluctuations can be considered as an effective candidate which contributes in the solar coronal heating.