Magnetic topology of a complex active region

Abstract

We present a detailed analysis of the magnetic topology of AR 6233 on two consecutive days (August 28 and 29, 1990). We compare the location of the magnetic separatrices and separators with off-band Hα observations and other flare manifestations, such as intense non-thermal electron precipitation and high coronal pressure sites, for two flares that occurred on these days. Because transverse magnetograms indicate that strong magnetic shear is present along the longitudinal inversion line, where flare brightening are located, the observed photospheric magnetic field is modeled in an approach in which a combination of sources with current-free and non current-free magnetic held is used. This model allows us to obtain a better ht between the observed and modeled transverse held. Then, we find a closer relationship between separatrices and hare features. The results of a current-free and of a linear force-free approach are also discussed. As in other haring regions studied previously, chromospheric flare brightening are found on separatrices. The topological structure obtained for these flares is rather complex and cannot be explained by classical flare models. We find that the connectivity of field lines may change drastically from one edge of an Ha; ribbon to the other. Electron precipitation and high coronal pressure sites, and some photospheric intense currents are also found in the immediate vicinity of separatrices. The early kernels of August 28 flare are found closer to the separatrices of the non-potential held, while the later are closer to those of the potential held. All these results agree with the hypothesis that magnetic energy is stored in field-aligned currents and released due to magnetic held reconnection, with a noticeable relaxation of the held, either at the separator region or on separatrices.