Configuration of magnetotail current sheet prior to magnetic reconnection onset

TL;DR

This study uses particle-in-cell simulations to explore how thin, nongyrotropic current sheets in the Earth's magnetotail transition from 2D to 1D configurations, influencing magnetic reconnection and substorm onset.

Contribution

It reveals the role of plasma pressure nongyrotropy in the transition of current sheet configurations prior to reconnection onset, a novel insight into magnetospheric dynamics.

Findings

Transition from 2D to 1D magnetic field configuration due to nongyrotropy.

Nongyrotropic terms originate from ion distribution properties.

Substorm onset may be driven by instability in nongyrotropic current sheets.

Abstract

The magnetotail current sheet configuration determines magnetic reconnection properties that control the substorm onset, one of the most energetic phenomena in the Earth's magnetosphere. The quiet-time current sheet is often approximated as a two-dimensional (2D) magnetic field configuration balanced by isotropic plasma pressure gradients. However, reconnection onset is preceded by the current sheet thinning and the formation of a nearly one-dimensional (1D) magnetic field configuration. In this study, using particle-in-cell simulations, we investigate the force balance of such thin current sheets when they are driven by plasma inflow. We demonstrate that the magnetic field configuration transitions from 2D to 1D thanks to the formation of plasma pressure nongyrotropy and reveal its origin in the nongyrotropic terms of the ion distributions. We show that substorm onset may be controlled by the instability and dynamics of such nongyrotropic current sheets, having properties much different from the most commonly investigated 2D isotropic configuration.