3D structure of arcade-type flares derived from the homologous flare series of 21, 24, and 27 February 1992

In February 1992, three flares, which we consider constitute a homologous f lare series (flares having basically the same configuration repeating in th e same situation), occurred in the active region NOAA 7070 and were observe d by Yohkoh SXT. In the present paper, we first discuss the homology of the se three flares, and derive the 3D structure by making use of the informati on obtained from the three different lines of sight at common phases. The r esult of this analysis made clear for the first time that the so-called 'cu sped arcade' at the maximum phase in the well-known 21 February 1992 flare is, contrary to the general belief, an 'elongated arch' created at the begi nning of the flare, seen with a shallow oblique angle. It is not the 'flare arcade' seen on axis as widely conceived. This elongated arch roughly coin cides with a diagonal of the main body of the soft X-ray arcade that came u p later. The magnetic structure responsible for the flare as a whole turned out to be a structure with quadruple magnetic sources - with the third and fourth sources also playing essential roles. The observationally derived i nformation in our paper provides strong restrictions to the theoretical mod els of the process occurring in arcade flares.