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 study estimates the contribution of middle-scale solar wind structures (variations recorded by a spacecraft during 10 min intervals) in turbulence development in the transition region behind the bow shock. The analysis is based on simultaneous measurements of plasma and/or magnetic field parameters in the solar wind, in the dayside magnetosheath, and on the flanks. The study adopts measurements by Wind, THEMIS, and Spektr-R spacecraft. The properties of the magnetic field and ion flux fluctuation spectra are analyzed in the 0.01–4 Hz frequency range, which corresponds to the transition from MHD to kinetic scales. The dynamics of turbulence properties in the magnetosheath is governed by large-scale disturbances, while structures with smaller scales have an effect in the absence of large-scale structures.

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

In this work, we discuss the problems associated with the formation of the outer radiation belt (ORB) taking into account previous results, including the recent ones. In our opinion, the traditional approaches to the dynamics of the ORB have the following problems: • inconsistency between the times provided by the popular “quasilinear” approach to the ORB description and the observed electron acceleration times; • impossibility to describe ORB dynamics during magnetospheric storms using the “quasilinear” approach when the particle fluxes after storm restore to their pre-storm values, i.e., belong to the storms of the third type according to Reeves et al. (2003, https://doi.org/10.1029/2002GL016513 ) classification; • impossibility of explaining the Tverskaya’s relation, which connects the position of the maximum of the relativistic flux formed after storm with the minimum value of the Dst/SYM-H variation, as well as the acceleration of relativistic electrons during magnetospheric substorms even in the absence of storms. We show that such difficulties do not appear if we take into account the large- scale magnetospheric dynamics, including auroral oval shift toward low latitudes during storms, substorm injections into the region of depressed magnetic field during storm recovery phase and the action of the adiabatic mechanism of electron deceleration and acceleration. The action of stochastic mechanisms of ORB acceleration is also discussed.

Based on the OMNI2 database for the period from 1976 to 2019, the behavior of the relative abundance of helium ions Nα/Np is investigated inside interplanetary coronal mass ejections (ICMEs). It is shown that the previously discovered anticorrelation between Nα/Np and the parameter β inside ICMEs is due to the dependence on magnetic pressure (or the magnitude of the interplanetary magnetic field), while the dependence of Nα/Np on the magnitude of the thermal pressure weakly falling in a magnetic cloud and increases in EJECTA. The data obtained are consistent with the previously suggested hypothesis that an electric current enriched with helium ions flows inside an ICME [1–3].

This study is concerned with the relative helium abundance variations, as well as other solar wind plasma and interplanetary magnetic field parameters, inside interplanetary coronal mass ejections on medium spatial scales (10 5 –10 6 km). The analysis is based on long-term WIND spacecraft measurements. It is shown that those scales lack an unambiguous anticorrelation between the helium abundance and plasma parameter β that was revealed on spatial scales greater than 10 6 km. Events with significant positive and negative correlations are observed with the same probability. In this case, both types of structures can be observed: structures in which the helium abundance grows simultaneously with an increase in the interplanetary magnetic field that are similar to those observed on large scales, as well as structures in which the helium abundance increases with a decline in the interplanetary magnetic field.

Studying the direction of the solar wind flow is a topical problem of space weather forecasting. As a rule, the quiet and uniform solar wind propagates radially, but significant changes in the solar wind flow direction can be observed, for example, in compression regions before the interplanetary coronal mass ejections (Sheath) and Corotating Interaction Regions (CIR) that precede high-speed streams from coronal holes. In this study, we perform a statistical analysis of the longitude (φ) and latitude (θ) flow direction angles and their variations on different time scales (30 s and 3600 s) in solar wind large-scale streams of different types, using WIND spacecraft data. We also examine the relationships of the value and standard deviations SD of the flow direction angles with various solar wind parameters, regardless of the solar wind type. We have established that maximum values of longitude and latitude angle modulus, as well as their variations, are observed for Sheath, CIR, and Rare, with the probability of large deviations from the radial direction (>5°) increasing. The dependence on the solar wind type is shown to decrease with scale. We have also found that the probability of large values of SD(θ) and SD(φ) increases with increasing proton temperature (Tp) in the range 5–10 eV and with increasing proton velocity (Vp) in the range 400–500 km/s.

We investigated variations on scales of 10 4 –10 5 km and local spatial inhomogeneities in the density of protons N p , doubly ionized helium ions (α-particles) N α , and the relative abundance of helium N α / N p in the solar wind. Measurements taken by two spacecraft, SPEKTR-R and WIND , separated in space by a distance of more than 1 million km, are analyzed, and the correlation coefficient between measurements of the corresponding parameters at different time intervals is determined. For intervals with a generally high level of correlation of plasma parameters, variations in the level of local (over shorter subintervals) correlation were analyzed. We showed that a low level of local correlation of all studied parameters is relatively common. The level of local correlation depends on the type of large-scale solar wind stream, as well as on the bulk velocity of the flow and the degree of flux variability. In addition, a low level of local correlation is often characterized by a negative component B x of the interplanetary magnetic field. The regions of local spatial inhomogeneities in the densities of protons and helium and the relative abundance of helium are identified and their size is estimated.

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.

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 .

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.

This work is a continuation of our previous articles (Yermolaev et al., 2015, ; 2017, ; 2018, ), which describe the average temporal profiles of interplanetary plasma and field parameters in large-scale solar-wind (SW) streams: corotating interaction regions (CIRs), interplanetary coronal mass ejections (ICMEs including both magnetic clouds (MCs), and ejecta), and sheaths as well as interplanetary shocks (ISs). In this work, we analyze the average profile of helium abundance,N-alpha/N-p, for 1976-2016. Our results confirm the main results that were obtained in earlier studies:N-alpha/N(p)is higher in quasi-stationary fast streams than in slow ones; it slowly changes in compression regions CIRs and sheaths from values in undisturbed SW to values in the corresponding fast stream type pushing like a piston, in high-speed stream (HSS) flow for CIRs, or in ICME for sheaths; in ejecta, it is close to the abundance observed in undisturbed streams, and it is maximal in MCs. For the first time, the results show thatN(alpha)/N(p)correlates with the proton beta-parameter in compression regions CIRs and sheath and anticorrelates in ICMEs. TheN(alpha)/N(p)versus beta dependence is stronger in MCs than in ejecta and may be used as an indicator of conditions at the place on the Sun where CMEs are formed.

The magnetosheath is an integral element of solar–terrestrial relations. The paper analyzes the influence of the solar wind parameters and their variability, as well as the topology of the bow shock on the characteristics of plasma turbulence in the magnetosheath on scales corresponding to the transition from the inertial region of a turbulent cascade to the dissipative one. The analysis is based on extensive statistics of measurements of the BMSW instrument with high time resolution on board the Spektr-R satellite in the magnetosheath in 2011–2018. It is shown that the variability of the solar wind plasma density and the interplanetary magnetic field magnitude, as well as the angle between the normal to the bow shock and the interplanetary magnetic field has the greatest influence on the form of the turbulent cascade directly behind the bow shock.