SPONTANEOUS RECONNECTION OF LINE-TIED FLUX TUBES

A model is presented, for spontaneous reconnection of coronal magnetic fields subject to axial line-tying. An initial equilibrium representing multiple flux tubes of alternating helicity is shown to be linearly unstable to a line-tied generalization of island coalescence. Numerical time-dependent simulations of the nonlinear evolution of this system reveal the rapid ideal development of intense current layers between current tubes with the same sign of helicity. The flow which arises from this stage leads to equally rapid dissipation of the current layer. This is accompanied by reconnection as it can be defined for three-dimensional line-tied fields. The current layers form at the ''top'' of the flux tubes, away from the line-tied ends. In this region the reconnection very much resembles the resistive phase of two-dimensional coalescence. The structure of the current layer near the line-tied ends hints at a generalization of current-sheet theories to three dimensions. Reconnection can liberate more than 20% of the free magnetic energy in the initial equilibrium.