Strong and Fast Variations of Parameters in the Magnetosheath: 1. Variations of Ion Flux and Other Plasma Characteristics

Experimental results on the dynamics of plasma parameters in the magnetosheath obtained aboard the INTERBALL-1 satellite and its subsatellite MAGION-4 are presented. These results are compared with simultaneous measurements of the same parameters in the interplanetary medium (the WIND spacecraft) and expectations from the Spreiter model describing plasma flows in the magnetosheath. It is shown that strong and fast variations of ion flux (really, variations of the plasma density) are permanently observed in the magnetosheath. In most cases these variations are not caused by solar wind fluctuations, they have their own origin, and the above model cannot describe them. It is emphasized that these variations lead to fast oscillations of the plasma pressure on the magnetopause and, therefore, cause different magnetosphere disturbances, which may not be associated with variations of solar wind parameters, such as pressure and direction of the magnetic field.