Coronal magnetic field evolution under reconnective relaxation

The nonlinear evolution of a partially open coronal magnetic configuration is considered, assuming that corona responds to photospheric footpoint motions by small-scale reconnection events that produce a relaxed lower-energy state while conserving the global magnetic helicity of the system. The results of numerical calculations for such a relaxed equilibrium show an essential role of the amount of helicity injected to the closed-field region. If photospheric perturbations are incoherent (small-scale shearing with inefficient helicity injection), the relaxed state becomes close to an initial potential field. In this case reconnective relaxation does not result in a substantial global evolution, just providing heating of the corona (Vekstein et al, 1993). On the contrary, sufficient injection of the magnetic helicity can lead to a considerable restructuring of the coronal magnetic configuration, with possible change of its topology (formation of magnetic islands), and even catastrophic loss of equilibrium (Wolfson et al, 1994)