Modeling of two-ribbon flares by the fast reconnection mechanism

The three-dimensional (3D) spontaneous fast reconnection model is applied to explosive heating in the shape of a pair of ribbons observed in the solar chromosphere, where plasma density is much larger than in the solar corona. In accordance with the onset of fast reconnection in the corona, 3D magnetic field dipolarization is caused by the fast reconnection jet, so that an extreme increase in the chromospheric current density suddenly occurs in a pair of local regions near the separatrix layers because of large-scale redistribution of the current system. Accordingly, chromospheric joule heating impulsively occurs in the thin layers, and the joule heating is interpreted to be sustained by a generator in the coronal fast reconnection region, in the form of u·(JxB)<0, provided by the fast reconnection jet ahead of the magnetic loop. Hence, the chromospheric temperature is drastically enhanced in a pair of local regions, which move away with time, eventually leading to definite chromospheric evaporation; simultaneously, the coronal flare loop is expanding outward. These results are consistent with the well-known morphological features of two-ribbon flares