Effect of the Magnetopause and Bow Shock on Characteristics of Plasma Turbulence in the Earth’s Magnetosheath

Resumo

The magnetosheath is a natural laboratory for the study of plasma turbulence. The magnetopause and the bow shock prevent freely development of turbulence and modify turbulent cascade. In this paper, the effect of the magnetosheath boundaries on the forms of frequency spectra of ion flux fluctuations is analyzed based on statistics. In addition, variance in the spectrum characteristics are considered, such as spectral slope at the magnetohydrodynamic (MHD) and kinetic scales, as well as the frequency of transition between these scales when the satellite crosses the magnetosheath. The analysis is based on measurement of the ion flux by the Fast Solar Wind Monitor (BMSW) onboard the Spektr-R satellite with a time resolution of 31 ms. It is shown that the probability of observing spectra of the particular type greatly varies upon crossing of the magnetosheath: standard spectra with two slopes and a distinct breakpoint are observed in most cases in all parts of the magnetosheath, and the probability of their observation is slightly higher upon the approach to the magnetopause; spectra with a peak in the region of transition between the scales (MHD and kinetic) are more often observed closer to the bow shock, and spectra with a plateau in the region of transition between the scales are usually observed closer to the magnetopause. It is revealed that the spectra at the MHD scales immediately behind the bow shock are described by a power function with index –1.3 on average, which noticeably differs from the index of –5/3 predicted by the classical theories. The spectra at the kinetic scales immediately behind the shock wave become steeper than in the solar wind and slightly flatten on the approach to the magnetopause.