Turbulent Cascade in the Magnetosheath Affected by the Solar Wind’s Plasma Turbulence

Abstract

Cosmic plasma represents a natural laboratory for studying turbulence in a wide range of scales. Rapid measurements of the ion flux by the Bright Monitor of the Solar Wind (BMSW) instrument on the Spektr-R satellite make it possible to investigate the characteristics of the plasma turbulence in the solar wind and the magnetosheath at ion and sub-ion scales. This study analyzes the question, in what manner do turbulent cascade characteristics, at these scales in the magnetosheath, depend on the characteristics of the solar wind’s plasma turbulence in front of Earth’s bow shock (BS). Several crosses of Earth’s BS by the Spektr-R satellite are analyzed. A comparison of the shapes of the spectra of ion flux fluctuations and exponents of power-law functions, which describe the spectra at kinetic and magnetohydrodynamic scales in front of and behind Earth’s BS is carried out. It is shown that, directly behind Earth’s BS on magnetohydrodynamic scales, the spectra deviate from the form predicted by the developed turbulence theories and observed in the solar wind. This feature of the spectra indicates the redistribution of energy in the turbulent cascade immediately behind the near-Earth shock wave. At kinetic scales, steeper spectra are usually observed behind the near-Earth shock wave front than in the solar wind, but their slope is determined by the properties of the turbulent cascade in the incident flow. It is shown that the strongest difference between turbulence characteristics in front of and behind Earth’s BS is observed during solar wind flow periods associated with the regions of compression before interplanetary manifestations of coronal mass ejections.