THE FORM OF IDEAL CURRENT LAYERS IN LINE-TIED MAGNETIC-FIELDS

It has been argued that a magnetic field which is initially continuous and is line-tied to rigid boundaries in a continuous manner cannot de velop tangential discontinuities or current sheets. This would appear to have many consequences in those theories of reconnection and corona l heating which are based on the existence of such current sheets. It is shown here that while the nonexistence of current sheet may hold in a strict sense, it is possible for simple magnetic geometries to spon taneously develop current layers of nonzero thickness which are indist inguishable, in a practical sense, from genuine current sheets. The th ickness of these layers can easily be more than six orders of magnitud e smaller than the apparent length scale of the initial equilibrium. W e suggest that numerical magnetohydrodynamics simulations have encount ered such features, but lacked sufficient resolution to distinguish th em from current sheets. Turbulent motion of photospheric footpoints wi ll generate this type of current layer in about one eddy turnover.