[1] A self-consistent theory of relatively thin anisotropic current sheets (TCS) in collisionless plasma is developed, taking into account the presence of a guiding field B y (all notations are used in the GSM coordinate system). TCS configurations with a finite value of guiding field B y are often observed in Earth's magnetotail and are typical for Earth's magnetopause. A characteristic signature of such configurations is the existence of a magnetic field component along the direction of TCS current. A general case is considered in this paper with global sheared magnetic field B y = const. Analytical and numerical (particle-in-cell) models for such plasma equilibria are analyzed and compared with each other as well as with Cluster observations. It is shown that, in contrast to the case with B y = 0, the character of "particle-current sheet" interaction is drastically changed in the case of a global magnetic shear. Specifically, serpentine-like parts of ion trajectories in the neutral plane become more tortuous, leading to a thicker current sheet. The reflection coefficient of particles coming from northern and southern sources also becomes asymmetric and depends upon the value of the B y component. As a result, the degree of asymmetry of magnetic field, plasma, and current density profiles appears characteristic of current sheets with a constant B y . In addition, in the presence of nonzero guiding field, the curvature current of electrons in the center of the current sheet decreases, yielding an effective thickening of the sheet. Implications of these results for current sheets in Earth's magnetosphere are discussed.

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Abstract.We examine the effectiveness of nonuniform, quasistatic, transverse electric fields that are often observed in the auroral region in destabilization of inhomogeneous energy-density-driven (IEDD) waves. Specifically, the IEDD dispersion relation of Ganguli et al. (1985a, b) is evaluated for an electric field structure observed by the FAST satellite in the auroral ionosphere at 1000 km altitude. The background field-aligned current, plasma density and ion composition are derived from FAST observations. Other input parameters adopted in the calculations are varied in pertinent ranges. Unstable solutions are obtained that indicate a variety of frequencies and perpendicular wavelengths. These can manifest as a broadband spectrum of IEDD waves.

Magnetic perturbations in the topside auroral ionosphere observed by the FAST satellite in the events of broadband extra low frequency (BB ELF) turbulence are investigated at frequencies 0.5–8 Hz (scales from 14 km down to 0.9 km). The power‐law scaling and peculiar polarization patterns of the perturbations are highlighted. By comparing with the magnetic fields simulated according to the Chang et al. (2004) scenario of coarse‐graining process development, we demonstrate that the magnetic perturbations observed in the events of the BB ELF turbulence can be reasonably understood in terms of non‐linearly interacting multiscale field‐aligned currents traversed by the spacecraft.

Dynamics of magnetic field-aligned small-scale irregularities in the electron concentration, existing in the F-layer ionospheric plasma, is investigated with the help of a mathematical model. The plasma is assumed to be a rarefied compound consisting of electrons and positive ions and being in a strong, external magnetic field. In the applied model, kinetic processes in the plasma are simulated by using the Vlasov-Poisson system of equations. The system of equations is numerically solved applying a macroparticle method. The time evolution of a plasma irregularity, having initial cross-section dimension commensurable with a Debye length, is simulated during the period sufficient for the irregularity to decay completely. The results of simulation indicate that the small-scale irregularity, created initially in the F-region ionosphere, decays accomplishing periodic damped vibrations, with the process being collisionless.

In this paper, we derive a divergent form of the force balance equation for collisionless plasma in the quasineutrality approximation, in which the electric field and current density are excluded. For a stationary spatially one-dimensional current sheet with a constant normal component of the magnetic field and magnetized electrons, the general form of the force balance equation has been obtained for the first time in the form of a conservation law. An equation in this form is necessary for the correct formulation of boundary conditions when modeling asymmetric current sheets, as well as for the control of the stationarity of the numerical solution obtained in the model. Furthermore, the fulfillment of this equation is considered for two types of stationary configurations of a thin current sheet, which are obtained using a numerical model. The derived equation makes it possible to develop models of asymmetric current sheets, in particular current sheets on the magnetopause flanks in the magnetotail.

Self-consistent kinetic (particle-in-cell) model of magnetotail thin current sheet (TCS) is used to understand the formation of self-consistent sheared magnetic structures. It is shown that shear configurations appear in TCS as a result of self-consistent evolution of some initial magnetic perturbation at the current sheet center. Two general shapes of shear TCS components are found as a function of the transverse coordinate: symmetric and antisymmetric. We show that TCS formation goes together with the emergence of field-aligned currents in the center of the current sheet, as a result of north-south asymmetry of quasi-adiabatic ion motions. Ion drift currents can also contribute to the magnetic shear evolution, but their role is much less significant, their contribution depending upon the normal component B z and the amplitude of the initial perturbation in TCS. Parametric maps illustrating different types of TCS equilibria are presented that show a higher probability of formation of symmetric shear TCS configuration at lower values of the normal magnetic component.