Flaring Loop Motion and a Unified Model for Solar Flares

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 Ðeld lines below the bright loop shrinking, which are all typical features of two-ribbon Ñares. The rise speed of the loop and the separation speed of its footpoints depend strongly on the magnetic Ðeld to a medium extent on the density and B0, o0, weakly on the temperature the resistivity g, and the length scale by which the size of current T0, L 0 sheet and the height of the X-point are both scaled. The strong dependence means that the Lorentz B0 force is the dominant factor ; the inertia of the plasma may account for the moderate dependence ; o0 and the weak g dependence may imply that ““ fast reconnection ÏÏ occurs ; the weak dependence implies L 0 that the Ñaring 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 Ñares. The results imply that the two types of solar Ñares, i.e., the two-ribbon Ñares and the compact ones, might be uniÐed into the same magnetic reconnection model, where the height of the reconnection point leads to the bifurcation. Subject headings : MHD È methods : numerical È Sun: Ñares È Sun: magnetic Ðelds