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 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 n(0), 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 n 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.