A numerical model is used to study the possibility of a thin current sheet formation in the near-Earth magnetotail in the growth phase of a substorm for a wide range of parameters of longitudinal countermoving ion flows that create current sheet. The simulation results make it possible to conclude that the current sheet can be formed by oxygen ion flows of ionospheric origin in cases where the proton fluxes can be neglected or they are rather weak. Such conditions are realized in the Earth’s magnetosphere during periods of increased geomagnetic activity. In addition, the influence of electron pressure anisotropy on the steady-state configuration of the considered current sheet is investigated.

Crossings of the heliospheric current sheet (HCS) at the Earth’s orbit are often associated with observations of anisotropic beams of energetic protons accelerated to energies from hundreds of keV to several MeV and above. A connection between this phenomenon and the occurrence of small-scale magnetic islands (SMIs) near reconnecting current sheets has recently been found. This study shows how pre-accelerated protons can be energized additionally due to oscillations of multiple SMIs inside the ripple of the reconnecting HCS. A model of the electromagnetic field of an oscillating 3D SMI with a characteristic size of ~0.001 AU is developed. A SMI is supposed to be bombarded by protons accelerated by magnetic reconnection at the HCS to energies from ~1keV to tens of keV. Numerical simulations have demonstrated that the resulting longitudinal inductive electric fields can additionally reaccelerate protons injected into a SMI. It is shown that there is a local “acceleration” region within the island in which particles gain energy most effectively. As a result, their average escape energies range from hundreds of keV to 2 MeV and above. There is almost no particle acceleration outside the region. It is shown that energies gained by protons significantly depend on the initial phase and the place of their entry into a SMI but weakly depend on the initial energy. Therefore, low-energy particles can be accelerated more efficiently than high-energy particles, and all particles can reach the total energy limit upon their escape from a SMI. It is also found that the escape velocity possesses a strong directional anisotropy. The results are consistent with observations in the solar wind plasma.

The dissipation processes which transform electromagnetic energy into kinetic particle energy in space plasmas are still not fully understood. Of particular interest is the distribution of the dissipated energy among different species of charged particles. The Jovian magnetosphere is a unique laboratory to study this question because outflowing ions from the moon Io create a high diversity in ion species. In this work, we use multispecies ion observations and magnetic field measurements by the Galileo spacecraft. We limit our study to observations of plasmoids in the Jovian magnetotail, because there is strong ion acceleration in these structures. Our model predicts that electromagnetic turbulence in plasmoids plays an essential role in the acceleration of oxygen, sulfur, and hydrogen ions. The observations show a decrease of the oxygen and sulfur energy spectral index γ at ∼30 to ∼400 keV/nuc with the wave power indicating an energy transfer from electromagnetic waves to particles, in agreement with the model. The wave power threshold for effective acceleration is of the order of 10 nT 2 Hz −1 , as in terrestrial plasmoids. However, this is not observed for hydrogen ions, implying that processes other than wave‐particle interaction are more important for the acceleration of these ions or that the time and energy resolution of the observations is too coarse. The results are expected to be confirmed by improved plasma measurements by the Juno spacecraft.

Within the self-consistent hybrid model based on the quasi-adiabatic approximation of the proton dynamics, a fine structure of strong current sheets (SCSs) in the solar wind has been investigated, including the heliospheric current sheet. The motion of electrons is fast and considered in the Boltzmann approximation. The simulation results have been shown that the SCS profiles have a multiscale enclosed structure with a narrow central current sheet that is enclosed in a wider sheet, similar to the heliospheric current sheet surrounded by the plasma sheet. The features of the SCS structure are determined by the relative contributions of the current of demagnetized protons in serpentine orbits and drift currents of electrons. The model predicts and describes the properties of SCSs observed by spacecraft. It has been shown that the multiscale structure of current sheets is an inherent intrinsic property of current sheets in the solar wind.

Within the axisymmetric MHD model of the solar wind, the magnetic field of the Sun has been analyzed in two phases of the solar cycle: the minimum activity, when the dipole magnetic field dominates and the maximum activity, when the quadrupole field predominates. It has been shown that during the period of maximum solar activity, the heliospheric current sheet acquires a conical shape and shifts to high latitudes up to 30° above the ecliptic plane. In the opposite hemisphere, at the same latitudes, a second current sheet of conical shape with an azimuth current of the opposite direction is established. It has been shown that the profiles of the main characteristics of the solar wind become steeper with distance from the Sun, and their amplitudes decrease, in this case, for the quadrupole field, the dependences of the main characteristics of the solar wind are more complex. A comparison of the results of the model with averaged characteristics of the solar wind shows a good match between the observed values and model parameters.