The role of oxygen ions in the formation of a bifurcated current sheet in the magnetotail

TL;DR

This study uses numerical simulations to investigate how oxygen ions influence the formation of bifurcated current sheets in the Earth's magnetotail, highlighting the role of magnetic turbulence and ion species.

Contribution

It demonstrates that oxygen ions can support bifurcated current sheet formation regardless of magnetic turbulence levels, providing new insights into magnetotail current sheet structure.

Findings

O$^+$ ions support bifurcated current sheet formation.

Magnetic turbulence influences ion motion but does not prevent bifurcation.

Oxygen ions can sustain double current layers even with high magnetic fluctuations.

Abstract

Cluster observations in the near-Earth magnetotail have shown that sometimes the current sheet is bifurcated, i.e. it is divided in two layers. The influence of magnetic turbulence on ion motion in this region is investigated by numerical simulation, taking into account the presence of both protons and oxygen ions. The magnetotail current sheet is modeled as a magnetic field reversal with a normal magnetic field component $B_n$, plus a three-dimensional spectrum of magnetic fluctuations $\delta {\bf B}$, which represents the observed magnetic turbulence. The dawn-dusk electric field E$_y$ is also included. A test particle simulation is performed using different values of $\delta {\bf B}$, E$_y$ and injecting two different species of particles, O$^+$ ions and protons. O$^+$ ions can support the formation of a double current layer both in the absence and for large values of magnetic fluctuations ($\delta B/B_0 = 0.0$ and $\delta B/B_0 \geq 0.4$, where B$_0$ is the constant magnetic field in the magnetospheric lobes).