DC coronal heating and the nonlinear evolution of current sheets

Abstract

Recent theoretical developments have re-awakened interest in the role of electric current sheets in DC coronal heating [Parker. Astrophys. J. 330, 474, 1988; Priest et al. Astrophys. J. 576, 522, 2002]. Dahlburg et al. [Dahlburg et al. Adv. Space Res. 32, 1029, 2003; Dahlburg et al. Astrophys. J. 622, 1191, 2005] reported the existence of a “secondary instability” that could explain the required “switch-on” effect required for adequate energy storage. This ideal, three-dimensional instability also provided a straightforward explanation for the subsequent fast release of energy, as the rapid growth of the mode eventually results in a state of turbulent magnetic reconnection. Earlier studies of the secondary instability were limited to systems with relatively simple perturbations, viz., resistive stability eigenmodes. A current sheet in the Sun is likely to be subject to much more complex perturbations involving a waves of various wavelengths and amplitudes. We describe the evolution of three-dimensional electric current sheets disturbed by random 3D perturbations. We find that the significant characteristics of secondary instability are also observed in this case. The numerical results are compared to solar observations.