We have analyzed spectra of fluctuations in the solar wind plasma flux and the magnetic field magnitude near the front of a fast reverse shocks, using data from the BMSW device (Bright Monitor of Solar Wind) operating on the SPEKTR-R satellite. Its time resolution made it possible to study plasma flux fluctuations up to a frequency of 16 Hz. Magnetic field data was taken mainly from the WIND satellite, for which the frequency of the fluctuations considered was up to 5.5 Hz. The slope of the spectra of the solar wind flux fluctuations on MHD scales has been shown to be close to the slope of the spectrum of magnetic field fluctuations in the disturbed region. On kinetic scales, the difference can be significant. For the region ahead of the front, the difference in the slope of the spectrum can be quite large both in the MHD and in the kinetic region. The frequency of the break of the flux spectrum ranges from 0.6 to 1.3 Hz, which corresponds to the scale of the proton inertial length. In a number of events, however, the shape of the spectrum indicates the influence of the proton gyroradius frequency, which is usually 0.05–0.15 Hz. The break in the power spectrum of magnetic field fluctuations also more often ranges from 0.7 to 1.2 Hz. In this case, the slope of the MHD part of the spectrum changes little, but in the kinetic part it increases slightly when moving to the disturbed region.

Magnetosheath is a transition layer between the solar wind and the magnetosphere and may contribute to the geoeffectiveness of various large-scale interplanetary phenomena. In this paper, we examine the dynamics of the turbulent fluctuation spectra behind the bow shock during undisturbed solar wind and when interplanetary coronal mass ejections and corotation interaction regions interact with the magnetosphere. The study is based on statistical analysis of the turbulence features inside the magnetosheath at different distances from the bow shock. We demonstrate that the turbulence features change when plasma crosses the bow shock for the solar wind of all types and they usually recover when plasma moves away from the bow shock. However, peculiarities in the turbulence development occur during interplanetary coronal mass ejections. Moreover, during disturbed solar wind there are relations between the turbulence features at the sub-ion scales and background plasma parameters such as plasma parameter β, the angle θBN between the interplanetary magnetic field and the local bow shock normal, solar wind bulk velocity, and the distance to the magnetosheath boundaries.

The paper investigates the characteristics of the power spectra of fluctuations in the density of protons and α particles near the front of the interplanetary (IP) and Earth’s bow shock (BS). The frequencies of the power spectra break of fluctuations in the density of protons and α particles were calculated before and behind the ramp of the Earth’s bow shock and interplanetary shock. For the disturbed solar wind beyond the IP ramp, the frequency of the spectrum break of proton fluctuations turned out to be noticeably higher (on average 1.3 Hz) than in the undisturbed region (∼0.8–1.0 Hz), which is explained by an increase in both the velocity and the density of particles. In the case of α particles, the frequency of the spectrum break of fluctuations behind the IP front also increased by almost two times (from 0.7 to 0.12 Hz). It is shown that the average value of the frequency of the proton spectra break behind the ramps is less (0.6 Hz) than in the solar wind (1.0 Hz), due to lower velocity. For α particles, this effect was not statistically detected due to an increase in the density (0.11 Hz for both regions) in the case of BS.

Wave trains of magnetic field and ion-flux oscillations generated upstream of the ramp of interplanetary (IP) shock were studied according to BMSW plasma-spectrometer measurements of energy–time spectra of the solar-wind ions supplemented by magnetic-field measurements. It was shown that oscillations of the magnetic field upstream of the ramp of IP shock are accompanied by oscillations of the ion flux. A detailed analysis of two cases is carried out, and the results of statistical study are presented. Right-handed circular or elliptical polarization was observed in all wave trains of magnetic-field oscillations, which is consistent with the characteristics of magnetosonic oscillations corresponding to the low-frequency branch of whistler waves. It was obtained that the mean angles between the propagation direction of whistler waves relative to the magnetic field and shock normal direction were 31° and 40°, respectively. This result suggests that the wave packets upstream of the ramp of IP shock had the properties of propagating whistler waves. It was found that, on average, with an increase in the angle of propagation of whistler waved relative to the shock normal direction θkn, the angle between the wave vector and magnetic-field direction θkB decreases.

Исследуются характеристики спектров мощности флуктуаций плотности протонов и альфа-частиц вблизи фронта межпланетной и околоземной ударной волны. Были посчитаны частоты излома спектров мощности флуктуаций концентрации протонов и альфа-частиц перед и за рампом околоземной ударной волны (ОЗУВ) и межпланетной ударной волны (МУВ). Для возмущенного солнечного ветра за рампом МУВ частота излома спектра флуктуаций протонов оказалась заметно выше (в среднем 1.3 Гц), чем в невозмущенной области (~0.8–1.0 Гц), что объясняется увеличением как скорости, так и концентрации частиц. В случае альфа-частиц частота излома спектра флуктуаций за фронтом МУВ также повышалась – почти в два раза (от 0.7 до 0.12 Гц). Показано, что среднее значение частоты излома спектров протонов за рампом ОЗУВ меньше (0.6 Гц), чем в солнечном ветре (1.0 Гц), ввиду меньшей скорости. Для альфа-частиц этот эффект статистически не был обнаружен из-за увеличения концентрации (0.11 Гц для обеих областей) в случае ОЗУВ.

This article investigates variations in the parameters of the twice ionized helium ions He++ (α-particles) of the solar wind plasma when crossing shock fronts in collisionless plasma, that is, interplanetary (IP) shocks and the Earth’s bow shock. Data from measurements of the BMSW instrument mounted on the SPEKTR-R satellite are used. Using data from this instrument, the parameters of protons and α-particles in the solar wind (velocity, temperature, density, magnitude and direction of the flux, and the relative density of He++ ions) are calculated. It is shown that the absolute density of He++ ions increases behind the shock front (of both the IP and the bow shock), while the relative density of He++ ions decreases behind the IP front and increases behind the bow shock front. A correlation between the change in the relative density of He++ ions and the value of the angle between the magnetic field and shock normal direction f θBn is obtained: the higher the value of θBn is, the larger the value of the relative density of He++ ions is behind the shock front.

The Earth’s magnetosphere is permanently influenced by the solar wind. When supersonic and superalfvenic plasma flow interacts with the magnetosphere, the magnetosheath region is formed, which is filled with shocked turbulent plasma. Varying SW parameters influence the mechanisms of formation of this boundary layer, including the dynamics of turbulence behind the bow shock. The effect of the solar wind on the development of turbulence in the magnetosheath was demonstrated recently based on broad statistics of spacecraft measurements. The present study considers the multipoint observations of turbulent fluctuations in the solar wind, in the dayside magnetosheath and at the flanks, to analyze the evolution of the turbulent cascade while the solar wind plasma enters the magnetosheath. Observations of the magnetosheath behind the quasi-perpendicular bow shock are analyzed to exclude the influence of the bow shock topology from consideration. Three basic types of solar wind flows are considered: slow undisturbed solar wind, compressed regions, and interplanetary manifestations of coronal mass ejections. The results show surviving Kolmogorov scaling behind the bow shock for steady solar wind flow and amplification of the compressive fluctuations at the kinetic scales at the magnetosheath flanks for the solar wind associated with compressed plasma streams. During interplanetary manifestations of the coronal mass ejection, the spectra in the dayside magnetosheath substantially deviate from those observed in the solar wind (including the absence of Kolmogorov scaling and steepening at the kinetic scales) and restore at the flanks.

The structure of the solar wind plasma flow downstream of the ramp of the interplanetary shock is studied based on the BMSW plasma spectrometer installed onboard the SPEKTR-R spacecraft. Particular attention is paid to the overshoot region, where correlated oscillations of the ion flux and magnetic field, which decaying with distance from the ramp, are observed. They are formed by two populations of ions: the inflowing solar wind and the beam of reflected ions. Based on an analysis of 26 crossings of interplanetary shock fronts, in which overshoots were observed in the value of the ion flux and the magnetic field, it is shown that overshoots form not only in supercritical shock, but also in those with Mach numbers that are less than or approach the value of the first critical Mach number. It is found that the formation and value of the overshoot amplitude in the structure of the shock front are significantly influenced by the angle between the normal to the shock front and the magnetic field vector ahead of the front, the Mach number, and the magnetic and plasma compression at the wave front. It is established that the oscillation wavelength determined from the magnetic field measurements onboard the WIND spacecraft, on average, coincides with the oscillation wavelength determined from the ion flux on the SPEKTR-R spacecraft, while the spatial scales of the oscillation-damping regions can greatly differ.

The bow shock crossing by the solar wind can lead in a number of cases to significant changes in the development of the turbulent cascade. Individual cases previously studied on the basis of experimental measurements of the characteristics of turbulence in the magnetosheath have not yet identified the factors that have the greatest influence on the modification of the turbulent cascade behind the bow shock. In this paper, we consider several observation cases of spectra of the compressible component in magnetosheath fluctuations on two satellites separated in space under calm conditions in the solar wind. This makes it possible to estimate the influence of the magnetosheath boundaries and the bow shock topology on the dynamics of a turbulent cascade when the plasma moves behind the bow shock. It is shown that there is a significant redistribution of energy in the turbulent cascade immediately behind the quasi perpendicular bow shock in the daytime part of the magnetosheath. This affects the magnetohydrodynamic scales, and the cascade properties are restored upon further propagation of the plasma towards the flanks. At the same time, behind the quasi parallel bow shock, the characteristics of the turbulent cascade upon the entry of plasma into the magnetosheath change only on subionic scales.

The variations in the parameters of twice ionized helium ions He++ of solar wind plasma during the passage of the front of the interplanetary shock are studied. Data taken from measurements by the Bright Monitor of Solar Wind (BMSW) installed onboard SPEKTR-R satellite were used to calculate the parameters of the He++ ions: the speed, temperature, and absolute and relative density (helium abundance). It was found that the absolute density of He++ ions behind the front of the interplanetary shock increases and that the relative density decreases. The average helium abundance behind the shock front was slightly less (by 9%) than that in the unperturbed region. The change in helium abundance correlated with the parameter θBn: the lower the θBn value is, the higher helium abundance decrease behind the front of the interplanetary shock.

Solar wind — a plasma stream flowing out of the solar corona — is interesting both as a carrier of solar activity and as an example of a collisionless plasma. We present the main results of Russian studies in recent years. The original MHD model allows interpreting the bifurcation of the heliospheric current sheet during maximum activity years as occurring due to the quadrupole component of the heliomagnetic field. On a scale of the order of millions of kilometers, the solar wind consists of transient solar formations. On these scales, one of the basic geomagnetic forecast problems has been solved: it was shown that the interplanetary magnetic field can be assumed stable at times of about three hours. At small scales (hundreds to thousands of kilometers), local structures are formed that can be regarded, both individually and statistically, as turbulent cascades .

The structure of quasiperpendicular interplanetary (IP) shock fronts was studied based on the data from the BMSW plasma spectrometer, installed onboard the SPEKTR-R spacecraft, supplemented by magnetic field measurements on the WIND. Special attention was paid to periodic growths (overshoots) in the value of the ion flux relative to their mean values outside the ramp. A comparison of plasma overshoot was performed with the overshoot in the magnetic field, with the Mach number, and with the β parameter. Based on the analysis of 26 crossings of IP shocks, in which the overshoots in the ion flux and magnetic field value were observed, it was shown that the value of the magnetic field overshoot is, on the average, less than a similar value in the solar wind’s ion flux, which is associated with different time resolution of measurements. The ion flux overshoot value is found to grow with the growth of the Mach number. It is shown that overshoots are formed not only in the supercritical shocks, but also in those with Mach numbers that are less than the value of the first critical Mach number. It is also found that the estimates of the coherent downstream oscillations of the ion flux and magnetic field good correlate with the convected ion gyroradius. This work was supported by the Russian Foundation for Basic Research, grant no. 19-02-00177.

This work is devoted to the study of properties of spectra of turbulent solar wind fluctuations in plasma compression regions, such as CIR (the plasma compression regions in front of high-speed streams from coronal holes) and SHEATH (the compression regions in front of interplanetary manifestations of coronal mass ejections EJECTA and magnetic clouds MC). The spectra of ion flux fluctuations, on both magnetohydrodynamic and ion-kinetic scales, are considered on the basis of data from the BMSW spectrometer on the SPEKTR-R spacecraft with a high (up to 31 ms) time resolution. The comparison of turbulent characteristics in the plasma compression regions and in the undisturbed solar wind is carried out both on a separate example and using extensive statistical material. It is shown in the paper that the turbulent cascade characteristics on the kinetic interval can significantly change in the plasma compression regions, and the signatures of a change in the main processes that determine the energy dissipation are revealed in them, which may cause increased heating in the regions under consideration.