Configuration of Magnetotail Current Sheet Prior to Magnetic Reconnection Onset

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.

Statistical Survey of Thin Current Sheets in Earth's Magnetotail: MMS Observations

“…Our observations show that TCSs typically have a strong current density up to 10 nA/m 2 , which would lead to the formation of a very strong magnetic tension force. However, it is unlikely that the plasma pressure gradient is strong enough to balance this force, and it is suggested that the key contribution of ion nongyrotropy ( P xz ) should be considered (An et al., 2022; Arnold & Sitnov, 2023; Artemyev et al., 2021; Artemyev, Angelopoulos, & Runov, 2016; Runov et al., 2021; Sitnov & Arnold, 2022). This nongyrotropy is expected to be contributed by hot ion population, likely outside the FPI energy range (see discussion in Arnold & Sitnov, 2023; Artemyev et al., 2019).…”

Thin Current Sheets in the Magnetotail at Lunar Distances: Statistics of ARTEMIS Observations

“…However, magnetotail models struggle to incorporate such a strong pressure gradient simultaneously across a wide radial range (see discussion in Sitnov, Stephens, et al., 2019; Sitnov et al., 2021). Thus, thin CSs either should form locally, within a radially confined region of strong pressure gradient (Birn et al., 2004; Liu et al., 2014; Schindler & Birn, 2002), or should be balanced by alternative mechanisms that do not involve strong pressure gradients (see discussion in Artemyev et al., 2021; An et al., 2022; Arnold & Sitnov, 2023). Further statistical investigations of the middle and distant magnetotail CSs should shed light on how often thin CSs typically form at these distances.…”

“…(b) To what extent are these characteristics influenced by solar wind conditions? The answer to the first question should provide important data for new CS models (see discussion in Sitnov & Arnold, 2022;Arnold & Sitnov, 2023;An et al, 2022An et al, , 2023). The answer to the second question should reveal if the solar wind is the main driver of thin CS formation in the middle tail.…”

Force‐Free Current Sheets in the Jovian Magnetodisk: The Key Role of Electron Field‐Aligned Anisotropy

“…Instabilities of such current sheets, either internally or externally driven, can result in the magnetic reconnection, a key process during magnetospheric substorms (Sitnov et al., 2019). The current sheet configuration directly controls the magnetic reconnection onset (e.g., An et al., 2022; Y.‐H. Liu et al., 2014; Lu et al., 2020; Sitnov et al., 2021), which further transforms the magnetic energy to the plasma heating and charged particle acceleration (e.g., Birn et al., 2012; Gonzalez & Parker, 2016).…”