Statistics of low-frequency variations in solar wind, foreshock and magnetosheath: INTERBALL-1 and CLUSTER data

The properties of small-scale ion flux and magnetic field fluctuations in the regions of undisturbed solar wind, foreshock and magnetosheath have been investigated. The systematic measurements of these parameters with very high time resolution, which were obtained onboard INTERBALL-1 spacecraft during 1996–2000, make it possible to examine their variations in a broad range of timescales (1–1800 s). The results from similar analysis of CLUSTER data are then compared with those from INTERBALL-1 data. The magnetic field variations from these two different satellites data are consistent not only in quality but also in quantity. Statistical results show that the level of the relative variations of parameters in magnetosheath and foreshock is about 3 times larger than those in undisturbed solar wind. Very intensive fluctuations in the magnetosheath are observed even under the “quiet” conditions of upstream solar wind. Properties of the small-scale fluctuations in the magnetosheath are strongly controlled by the angle Θ Bn between the interplanetary magnetic field vector and the bow shock normal, i.e. the level of fluctuations grows while the angle Θ Bn decreases. Wave properties of the plasma and magnetic field fluctuations are also very different in undisturbed solar wind, foreshock, quasi-parallel and quasi-perpendicular magnetosheath.