Flaring Loop Motion and a Unified Model for Solar Flares

Abstract

We performed 2.5-dimensional numerical simulations of magnetic reconnection for several models, some with the reconnection point at a high altitude (the X-type point in magnetic reconnection), and one with the reconnection point at a low altitude. In the high-altitude cases, the bright loop appears to rise for a long time, with its two footpoints separating and the field lines below the bright loop shrinking, which are all typical features of two-ribbon flares. The rise speed of the loop and the separation speed of its footpoints depend strongly on the magnetic field B_0, to a medium extent on the density rho_0, and weakly on the temperature T_0, the resistivity eta, and the length scale L_0, by which the size of current sheet and the height of the X-point are both scaled. The strong B_0 dependence means that the Lorentz force is the dominant factor; the inertia of the plasma may account for the moderate rho_0 dependence; and the weak eta dependence may imply that ``fast reconnection'' occurs; the weak L_0 dependence implies that the flaring loop motion has geometrical self-similarity. In the low-altitude case, the bright loops cease rising only a short time after the impulsive phase of the reconnection and then become rather stable, which shows a distinct similarity to the compact flares. The results imply that the two types of solar flares, i.e., the two-ribbon flares and the compact ones, might be unified into the same magnetic reconnection model, where the height of the reconnection point leads to the bifurcation.