Positive and negative feedbacks in the magnetosphere-ionosphere coupling

We study dynamics of field-aligned currents (FACs) during the expansion phase (EP) of two selected summer and winter substorms, by applying the magnetogram inversion technique (MIT) to the data of the world network of ground-based stations. The empirical MIT data and the modified Iijima and Potemra (I-P) model are presented. It is supposed a sharp increase in the upward FAC in I-P Region 1 and associated upward inter-hemispheric current in the dusk sector of the summer hemisphere during EP – in correspondence with theoretical models. Simultaneously (relative to the substorm onset time), and with the same value range, the downward inter-hemispheric current should enhance in the conjugate sector of the winter hemisphere. This FACs restructuring scenario in two hemispheres may clarify some of the unresolved issues in substorm physics. E.g., we describe the strong seasonal variation in the magnetic and auroral activity that is practically absent or unknown in literature even for the Northern hemisphere. Trying to answer this and other questions debated in literature, we study and describe strong feedbacks between the intensity of night FACs flowing in/out of each hemisphere, on the one hand, and the ionosphere conductivity or electric field, on the other. These magnetosphere-ionosphere feedbacks cause, in particular, the above inter-hemispheric currents and consequences prior and during the EP of the addressed substorms.