CONSTRAINTS ON FLARE MODELS SET BY THE ACTIVE-REGION MAGNETIC TOPOLOGY - MAGNETIC TOPOLOGY OF AR-6233

We present a detailed analysis of the magnetic topology of AR 6233 on two consecutive days (August 28 and 29, 1990) and compare the location of the magnetic separatrices and separators with off-band H alpha observations and other flare manifestations, such as intense nonthermal electron precipitation and high coronal pressure sites, for two flares that occured on these days. Since for one of the days of our analysis we have two magnetograms covering fields of view with different scale lengths, we analyzed the dependence of the topology of the region of interest on the presence of external magnetic field concentrations. We have found that considering these concentrations does not modify the location of separatrices in the region. Because transverse magnetograms indicate that strong magnetic shear is present along the longitudinal inversion line where flare brightenings 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 field is used. This model allows us to obtain a better fit 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 shown for comparison. As in other flaring regions studied previously, chromospheric flare brightenings are found on separatrices. The topological structure obtained for these flares is rather complex. We find that the connectivity of field lines may change drastically from one edge of a 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 hare are found closer to the separatrices of the nonpotential field, while the later are closer to those of the potential field. All these results agree with the hypothesis that magnetic energy is stored in field-aligned currents and released due to magnetic field reconnection, with a noticeable relaxation of the field, either at the separator region or on separatrices.