Gyrokinetic theory of magnetic structures in high-beta plasmas of the Earths magnetopause and of the slow solar wind

TL;DR

This paper develops a gyrokinetic theory to explain the formation of magnetic structures like depressions and holes in high-beta space plasmas, revealing their nonlinear origins and characteristics.

Contribution

It introduces a nonlinear gyrokinetic model that accounts for finite Larmor radius effects, explaining the formation of magnetic structures in Earth's magnetopause and solar wind.

Findings

Coherent nonlinear magnetic depressions can form in magnetosheath plasma.

Magnetic holes in solar wind are linked to nonlinear magnetosonic modes.

Structures can be moving, elongated, and supported by trapped particle populations.

Abstract

Nonlinear effects of the trapping of resonant particles by the combined action of the electric field and the magnetic mirror force is studied using a gyrokinetic description that includes the finite Larmor radius effects. A general nonlinear solution is found that is supported by the nonlinearity arising from the resonant particles, trapped by the combined action of the parallel electric field and the magnetic mirror force. Applying these results to the space plasma conditions, we demonstrate that in the magnetosheath plasma, coherent nonlinear magnetic depression may be created associated with the nonlinear mirror mode and supported by the population of trapped ions forming a hump in the distribution function. These objects may appear either isolated or as the train of weakly correlated structures (the cnoidal wave). In the Solar wind and in the Earths magnetopause, characterized with anisotropic electron and ion temperatures that are of the same order of magnitude, we find coherent magnetic holes of the same form that are attributed to the two branches of the nonlinear magnetosonic mode, the electron mirror and the field swelling mode, including also the kinetic Alfven mode, and supported by the population of trapped electrons. The localized magnetic holes may have the form of a moving oblique slab or of an ellipsoid parallel to the magnetic field and strongly elongated along it, that propagates along the magnetic field and may be convected in the perpendicular direction by a plasma flow. While the ion mirror structures are purely compressional magnetic, featuring negligible magnetic torsion and electric field, the magnetosonic and kinetic Alfven structures possess a finite electrostatic potential, magnetic compression, and magnetic torsion, but the ratio of the perpendicular and parallel magnetic fields remains small.