Force-free fields in the solar corona and the identification of solar flare sites

The magnetic fields in the solar atmosphere are computed from the magnetometer data measured in the photosphere using the approximation of linear force-free fields. The magnetic fields correspond to an active region where a solar flare erupted at some time and the computations were made before and after the flare. From the field configuration a search was made of the possible regions for magnetic reconnection by making planar cuts at places of large field variations. The potential reconnection site is characterized by the presence of a neutral point in the projected field. It is found that these points are not far from the actual site where the solar flare appeared, even though the linear model is relatively simple. This analysis is performed for two active regions with similar results. The force-free parameter α is computed from vector magnetograms in order to assess how far it is from the constant value required by the linear approximation.