Fragment driven magnetic reconnection

The heating of the million degree, diffuse coronal plasma may be caused by a large number of events that are too small to be identified by present days observations. One explanation for these events could be the local interaction between magnetic flux systems that divide space into numerous flux regions. When such regions are independently advected by photospheric motions the expected outcome is the formation of enhanced current concentration at specific locations in space. Due to magnetic resistivity, these currents dissipate and heat the plasma. In this paper, we investigate a simple model where two, initially unconnected, flux systems are forced to interact in response to the imposed boundary driving by solving the non-ideal 3D MHD equations numerically. The reconnection rate of the dynamical process is determined and compared with the corresponding rate for the potential evolution of the magnetic field. This shows that the dynamic reconnection rate is about a factor of two smaller than the potential (perfect, instantaneous) rate for realistic solar driving velocities demonstrating that this three-dimensional magnetic reconnection process is fast. The energy input for a fixed advection distance is found to be independent of the driving velocity. The Joule dissipation associated with the reconnection process is also found to be basically dependent on the advection distance rather than driving velocity. This implies that the timescale for the event determines the effect the heating has on the temperature increase. Finally, the numerical experiments indicate that the observational structure of the reconnection site changes dramatically depending on the phase of the evolution of the passage of the two flux sources. In the initial phase, where the sources become connected, the heating is confined to a compact region. For the disconnecting phase the energy gets distributed over a larger area due to the reconnected field line connectivity.