ИСТИНА

One of the main widely discussed unresolved problems of magnetospheric dynamics is the mechanism of formation of magnetospheric substorms, including the localization of the onset of a substorm and the properties of the first brightening of the nearest to the equator auroral arc. We have summarized numerous results from ground-based, lowaltitude and near-equatorial observations. The main attention was focused on the results demonstrating the localization of the onset of an isolated substorm deep inside the ring current region and its connection with the processes of IMF penetration into the magnetosphere modulating magnetospheric current systems. We took into account the results demonstrating the inapplicability of the frozen-in condition for the analysis of substorm dynamics, the high level of turbulence in the plasma sheet, and the inability to explain the absorption of energy within the magnetosphere by a source in the tail. An important part of this problem is the brightening of the aurora arc near to the equator during a substorm onset or the formation of a new arc. We consider that a cold electron beam is formed as a result of the penetration of ionospheric plasma into the region of field-aligned potential drop, and a substorm onset is formed as a result of the development of instability of large-scale field-aligned currents. It is shown that this approach can explain the results of experimental observations without assumptions about reconnection in the tail or disruption of the tail current.