Flaring Loop Motion and a Unified Model for Solar Flares

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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 —eld lines below the bright loop shrinking, which are all typical features of two-ribbon —ares. The rise speed of the loop and the separation speed of its footpoints depend strongly on the magnetic —eld to a medium extent on the density and B 0 , o 0 , weakly on the temperature the resistivity g, and the length scale by which the size of current T 0 , L 0 , sheet and the height of the X-point are both scaled. The strong dependence means that the Lorentz B 0 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 ìì fast reconnection ˇˇ occurs; the weak dependence implies L 0 that the —aring 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 —ares. The results imply that the two types of solar —ares, i.e., the two-ribbon —ares and the compact ones, might be uni—ed into the same magnetic reconnection model, where the height of the reconnection point leads to the bifurcation. Subject headings: MHDmethods: numericalSun: —aresSun: magnetic —elds