Evolution of force-free electric currents in the solar atmosphere

The new 3-D numerical model studying evolution of force-free electric currents in the solar atmosphere is presented. The initial dipole magnetic field is considered in a simplified active region. Starting from a low electric current, which penetrates the photosphere, and increasing the current intensity, the path of force-free electric current and the corresponding magnetic field are computed. The virtual mirror current representing the effect of the inertial photosphere is considered. The single and the multiple current paths are compared. For the single path case, it was found that an arch-shape electric current is sheared with the increasing current intensity, then screwed into a current loop with the helical structure and when the electric current generates a magnetic field greater than the initial dipole magnetic field the current path becomes unstable. During all this process the current path moves upwards. Although the multiple current paths show more complex internal structures of electric currents, the global aspect of these processes remains the same. The relevance of this modelling for processes in the solar atmosphere is discussed.