Multiscale structure of solar magnetic fields usign a force-free field model at flare sites

Solar photospheric magnetograms are used to compute the upper atmosphere magnetic fields in active regions, around the time of solar flares occurrence. The computations are based on a force-free filed (FFF) model which is justified before the flare onset. Analytical computations can be done for linear FFF which allow to locate neutral points that are likely places where magnetic reconnection can occur and hence originate the solar flare. Nonlinear FFF are computed using vector magnetograms for two events at pre- and post-flare times and they are used to compute the current density distribution. This is analyzed with proper orthogonal decomposition (POD) methods to obtain mutiscale structure in 3D. Scree diagrams show fields coherence. Analyzing the small-scale PDF it is shown that there is space intermittency in the fileds, revealed by long-tailed PDFs. This property is also observed in temperature maps of the solar corona during flares which suggests that there is a current-temperature correlation. This is expected for magnetic reconnection events. There is little difference between pre- and post-flare results since a FFF model is not so good after flare onset, but the energy content seems to be smaller in post-flare times.