Magnetic field configuration in impulsive solar flares revealed with Yohkoh and Nobeyama Radioheliograph Original Research Article

The results of an analysis of 25 solar impulsive flares, observed simultaneously with microwave and X-ray imaging instruments, are presented. From the relative locations of microwave, hard X-ray, and soft X-ray sources, we have found that, for fourteen out of the 25 cases, at least two loops are involved. Typical sizes of the two loops are different from each other; one is typically ≤ 20″ and the other 30″–80″. In seven out of remaining thirteen cases, circular polarization images in microwaves show the bipolar structure at the location of a HXR source, indicating the existence of a small loop. These observations suggest that in the majority of impulsive flare events a system of two or more loops (or bipoles) interacts with each other, releasing magnetic energy and producing energetic electrons. Detailed analysis of two out of the 25 events supports this result.