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.

The paper is concerned with studying the thickness of fronts of 38 interplanetary shocks detected by the BMSW instrument, which is a part of the scientific payload of the SPEKTR-R spacecraft, which wa

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.

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

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.

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 θ_Bn: the lower the θ_Bn value is, the higher helium abundance decrease behind the front of the interplanetary shock.