Natalia Borodkova

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.

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.

Solar activity and solar wind parameters decreased significantly in solar cycles (SCs) 23–24. In this paper, we analyze solar wind measurements at the rising phase of SC 25 and compare them with similar data from the previous cycles. For this purpose, we simultaneously selected the OMNI database data for 1976–2022, both by phases of the 11-year solar cycle and by large-scale solar wind types (in accordance with catalog [http://www.iki.rssi.ru/pub/omni]), and calculated the mean values of the plasma and magnetic field parameters for the selected datasets. The obtained results support the hypothesis that the continuation of this cycle will be similar to that of cycle 24, i.e. SC 25 will be weaker than SCs 21 and 22

Experimental investigations of the fine plasma structure of interplanetary shocks are extremely difficult to conduct due to their small thickness and high speed relative to the spacecraft. We studied the variations in the parameters of twice-ionized helium ions (4He⁺⁺ ions or α-particles) in the solar wind plasma during the passage of interplanetary shocks and Earth’s bow shock. We used data with high time resolution gathered by the BMSW (Bright Monitor of Solar Wind) instrument installed on the SPEKTR-R satellite, which operated between August 2011 and 2019. The MHD parameters of He⁺⁺ ions (the bulk velocity Vα, temperature Tα, absolute density Nα, and helium abundance Nα/Np) are analyzed for 20 interplanetary shocks and compared with similar parameters for 25 Earth bow shock crossings. Measurements from the WIND, Cluster, and THEMIS satellites were also analyzed. The correlations in the changes in helium abundance Nα/Np with the parameters β_i, θ_Bn, and M_MS were investigated. The following correlation between Nα/Np and the angle θ_Bn was found: the lower the value of θ_Bn, the greater the drop in helium abundance (Nα/Np) falls behind the IP shock front. For Earth’s bow shock crossings, we found a significant increase in the helium abundance (Nα/Np) in quasi-perpendicular events.

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 θ_Bn is obtained: the higher the value of θ_Bn is, the larger the value of the relative density of He⁺⁺ ions is behind the shock front.

In solar cycles 23–24, solar activity noticeably decreased and, as a result, solar wind parameters decreased. Based on the measurements of the OMNI base for the period 1976–2019, the time profiles of the main solar wind parameters and magnetospheric indices for the main interplanetary drivers of magnetospheric disturbances (solar wind types CIR. Sheath, ejecta and MC) are studied using the double superposed epoch method. The main task of the research is to compare time profiles for the epoch of high solar activity at 21–22 SC and the epoch of low activity at 23–24 SC. The following results were obtained. (1) The analysis did not show a statistically significant change in driver durations during the epoch of minimum. (2) The time profiles of all parameters for all types of SW in the epoch of low activity have the same shape as in the epoch of high activity, but locate at lower values of the parameters. (3) In CIR events, the longitude angle of the solar wind flow has a characteristic S shape; but in the epoch of low activity, it varies in a larger range than in the previous epoch.

Experimental investigations of the fine plasma structure of interplanetary shocks are extremely difficult to conduct due to their small thickness and high speed relative to the spacecraft. We study the variations in the parameters of twice-ionized helium ions (4He++ ions or {\alpha}-particles) in the solar wind plasma during the passage of interplanetary shocks and Earth's bow shock. We use data with high time resolution gathered by the BMSW (Bright Monitor of Solar Wind) instrument installed on the SPEKTR-R satellite, which operated between August 2011 and 2019. The MHD parameters of He++ ions (the bulk velocity Va, temperature Ta, absolute density Na, and helium abundance Na/Np) are analyzed for 20 interplanetary shocks and compared with similar parameters for 25 Earth's bow shock crossings. Measurements from the WIND, Cluster and THEMIS satellites were also analyzed. The correlations in the changes in helium abundance Na/Np with the parameters {\beta}_{i}, {\theta}_{Bn} and M_{ms} were investigated. A correlation between Na/Np and the angle {\theta}_{Bn} was found: the lower the value of {\theta}_{Bn}, the greater the drop in helium abundance Na/Np falls behind the IP shock front. For Earth's bow shock crossings, we found a significant increase in the helium abundance Na/Np in quasi-perpendicular events.

The structure of the solar wind plasma flow downstream of the ramp of the interplanetary and bow shocks was studied based on the BMSW plasma spectrometer installed onboard the SPEKTR-R spacecraft. Particular attention was paid to the overshoot region, where correlated oscillations of the ion flux and magnetic field are observed. They are formed by two populations of ions: the inflowing solar wind and the beam of coherent gyrating ions. Based on the statistical analysis it was shown that overshoots form both in supercritical and subcritical shocks. It is found that maximum values of the overshoot amplitudes are significantly influenced by the angle between the shock normal and magnetic field vectors, Mach number, plasma and magnetic compression at the shock front. It was 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, while the rates of relaxation of these oscillations can greatly differ. It was also shown that the estimates of the overshoot wavelength good correlate with the convected ion gyroradius.

Variations in the solar wind (SW) parameters with scales of several years are an important characteristic of solar activity and the basis for a long‐term space weather forecast. We examine the behavior of interplanetary parameters over 21–24 solar cycles (SCs) on the basis of the OMNI database (https://spdf.gsfc.nasa.gov/pub/data/omni). Since changes in the parameters can be associated with both changes in the number of different large‐scale types of SW and with variations in the values of these parameters at different phases of the solar cycle and during the transition from one cycle to another, we select the entire study period in accordance with the Catalog of large‐scale SW types for 1976–2019 (see the site http://www.iki.rssi.ru/pub/omni, [Yermolaev, Nikolaeva, et al., 2009, https://doi.org/10.1134/s0010952509020014], which covers the period from 21 to 24 SCs) and in accordance with the phases of the cycles, and average the parameters at selected intervals. In addition to a sharp drop in the number of interplanetary coronal mass ejections and associated sheath types, there is a noticeable drop in the value (by 20%–40%) of plasma parameters and magnetic field in different types of solar wind at the end of the 20th century and a continuation of the fall or persistence at a low level in the 23–24 cycles. Such a drop in the solar wind is apparently associated with a decrease in solar activity and manifests itself in a noticeable decrease in space weather factors.