Coronal heating driven by random foot point motions: the effects of magnetic field topology

ABSTRACT We investigate the effects of magnetic field geometry on energy injection and dissipation, current sheet formation, magnetic reconnection rates and plasma dynamics in the solar corona when energized by random foot point motions. Using a series of 3D magnetohydrodynamics simulations, we compared the effects of high- and low-amplitude random velocity drivers acting on two different initial magnetic fields; (a) a uniform field case and (b) a tectonics case, in which the field is anchored in localized flux patches. In all simulations, the imposed drivers stress the field, generating small scales and leading to energy dissipation through Ohmic and viscous heating. The rates of energy injection, current formation, magnetic reconnection, and the associated energy dissipation are higher when the field is concentrated in flux patches at the simulation boundary. As such, expected heating rates are larger with a tectonics field. However, when high-amplitude driving is imposed on an initially uniform field, flux patches spontaneously form as the field evolves to become a tectonics field. As a result, energy injection and dissipation rates converge to become independent of the initial field state in the high-amplitude cases. As coronal field foot points are typically embedded in concentrated flux patches, we confirm that tectonics is a viable model for coronal heating. Unsurprisingly, we find that the nature of an initial field only influences heating rates as long as this field persists. However, whether solar atmospheric heating is dominated by transverse foot-point motions, as considered here, or by flux emergence events remains an unanswered question.