Abstract

The results of the INTERBALL/Tail probe observations which can help to solve the problem of the inner magnetosphere substorm onset and particle acceleration are summarized and compared with the previously obtained results. The observations of the plasma sheet velocity fluctuations support the existence of very high level of the plasma sheet turbulence which produce a real change on the possibility of the development of the spontaneous reconnection as the explanation of substorm expansion phase onset. The role of azimuthal plasma pressure gradients in the destabilization of the plasma distribution near the equatorial edge of the auroral oval is analyzed. The appearance of field-aligned electron beams and rayed auroral arcs is discussed.