Some features of the plasma flow in the magnetosheath behind quasi-parallel and quasi-perpendicular bow shocks

Variations of the ion flux and magnetic field magnitude in the undisturbed solar wind, in the foreshock, and in the magnetosheath have been examined using simultaneous measurements on the INTERBALL-1, IMP 8, WIND and ACE spacecraft. A high-time resolution of INTERBALL-1 measurements has allowed us to observe variations of these parameters in a broad range of frequencies (0.01-1 Hz). In this frequency range, magnetosheath plasma and field parameters fluctuate with very large amplitudes and are subjected to extremely intensive variations even during "quiet" conditions in the solar wind. The dependence of magnetosheath variations on the interplanetary magnetic field (IMF) direction was investigated. It was found that during the quasi-parallel IMF orientation to the bow shock normal (i.e., when theta(Bn) < 45degrees), an increase in the amplitude of variations of the ion flux and magnetic field is observed not only ahead of the bow shock (in the foreshock region) but also behind it, i.e., in the magnetosheath. The OB,, angle turned out to be the parameter, which significantly affects the properties of the turbulent plasma flow. An application of a spectral analysis allowed us to show Substantial differences in the frequency properties of variations of the ion flux and magnetic field magnitude in the undisturbed solar wind, foreshock, and magnetosheath (separately for the quasi-parallel and quasi-perpendicular conditions of the bow shock). (C) 2004 Elsevier Ltd. All rights reserved.