Dynamics of Plasma Turbulence at Earth’s Bow Shock and through the Magnetosheath

Abstract

Earth’s magnetosheath can be treated as a natural laboratory to study turbulence development in confined space. The present study focuses on the characteristics of turbulent cascade downstream of the bow shock, where properties of turbulence are known to differ from those in the upstream solar wind. Characteristics of the turbulent spectrum are considered in two distinct points of the magnetosheath for two case studies. The analysis is based on high-resolution measurements of plasma parameters by the Spektr-R spacecraft and magnetic field data by the Themis/Arthemis mission. The measurements are performed for two distinct cases: in the dayside magnetosheath behind the quasi-perpendicular bow shock and in the nightside flank of the magnetosheath behind the quasi-parallel bow shock. The study focuses on the scales at which kinetic effects in plasma become significant and the turbulent spectrum is known to break. The analysis reveals that modification of the fluctuation spectrum at the bow shock is controlled by the distance of the measurement point from the bow shock’s nose. Also, performed statistical results suggest the influence of the large-scale parameters of the upstream solar wind and the type of the bow shock on the turbulent spectrum’s modification in the downstream region.

Plasma and Magnetic Field Turbulence in the Earth’s Magnetosheath at Ion Scales

“…The results of the study are presented in Figure 9. The results are consistent with the results obtained with the help of Cluster data (Sundkvist et al, 2007) and also with the statistical results by Rakhmanova et al (2018b) obtained by plasma measurements on board Spektr-R. Rakhmanova et al (2020b) statistically analyzed the influence of θ BN angle on the power exponents of ion flux fluctuation spectra at MHD and kinetic scales. Crossing of the quasiperpendicular BS was shown to result in flattening of the spectra at MHD scales and their deviation from the Kolmogorov scaling (Figure 10, top).…”

“…Interestingly, behind the quasiperpendicular BS the spectra were characterized by a −1 power exponent while behind the quasi-parallel bow shock, typical Kolmogorov-like scaling was observed. This difference was similar to the results of the statistical and case studies (Rakhmanova et al, 2018b;Rakhmanova et al, 2020b). Note that results of Breuillard et al (2018) were obtained in the dayside MSH.…”

“…Statistical data by Spektr-R measurements in the MSH adjacent to the BS (Rakhmanova et al, 2020b) demonstrated the influence of the large-scale SW type on the modification of the turbulent cascade at MHD scales at the BS. Significant changes at the BS were shown to be most probable during compressed SW flow of type "Sheath," while steady SW flow was typically accompanied by the nearly Kolmogorov scaling of ion flux fluctuation spectra downstream of the BS similar to the results shown in the previous section.…”

“…Recently, Rakhmanova et al (2020b) performed a case study of evolution of compressive turbulence inside the MSH with the help of Spektr-R plasma and Themis magnetic field measurements. For quiet background conditions, the spectra of compressive fluctuations were compared 1) at two points, placed at closely located streamlines at the flank MSH at distances ∼30 R E , and also 2) at two points in the vicinity of the BS, but at different distances from the BS nose.…”

“…During the periods of SW of type "Sheath" behind the BS, the spectra were usually characterized by the plateau (see Figure 3C). (Rakhmanova et al, 2020b)).…”