Double-loop configuration of solar flares

We analyzed several flares, which are presumed to be caused by interactions between an emerging loop and an overlying loop. We call such a basic combination of loops a 'double-loop configuration', and we reveal its topology on the basis of the microwave and soft X-ray observations of the flares and the magnetograms. In many cases, the magnetic field of the flare loops shows a 'bipolar + remote unipolar' structure, rather than a quadrapole structure. The footpoints of two loops are distributed in three magnetic patches, and two of the footpoints of the loops, one from the emerging loop and the other from the overlying loop, are included in a single magnetic polarity patch. Therefore, the two loops form a 'three-legged' structure, and the two loops are not anti-parallel as assumed in the traditional reconnection models. Typically, the emergence of a parasitic polarity near the major preceding-polarity region or the following one in an active region creates this configuration, but, in one of the analyzed flares, two active regions are involved in the configuration. Not only the flares, but various other active phenomena - microflares, thermal plasma flows like jets, and surges - occur in the same magnetic configuration. Hence, the interaction between two loops, which forms the three-legged structure, is an important source of the various types of activity.