Roles of electrons and ions in formation of the current in mirror-mode structures in the terrestrial plasma sheet: Magnetospheric Multiscale observations

Guoqiang Wang,Yufei Hao,Martin Volwerk,Tielong Zhang,Mingyu Wu,Daniel Schmid

doi:10.5194/angeo-38-309-2020

Abstract

Abstract. Mirror-mode structures widely exist in various space plasma environments. Here, we investigate a train of mirror-mode structures in the terrestrial plasma sheet on 11 August 2017 based on the Magnetospheric Multiscale mission. We find that bipolar current densities exist in the cross section of two hole-like mirror-mode structures, referred to as magnetic dips. The bipolar current density in the magnetic dip with a size of ∼2.2 ρi (the ion gyro radius) is mainly contributed by variations of the electron velocity, which is mainly formed by the magnetic gradient–curvature drift. For another magnetic dip with a size of ∼6.6 ρi, the bipolar current density is mainly caused by an ion bipolar velocity, which can be explained by the collective behaviors of the ion drift motions. The current density inside the mirror dip contributes to the maintenance of the hole-like structure's stable. Our observations suggest that the electrons and ions play different roles in the formation of currents in magnetic dips with different sizes.

Highlights

Mirror modes are pressure-balanced and compressional magnetic structures (Hasegawa, 1969; Tsurutani et al, 2011; Wang et al, 2016; Zhang et al, 2018)
We investigate a train of ion-scale mirrormode structures in the terrestrial plasma sheet on 11 August 2017 using the Magnetospheric Multiscale (MMS) mission data
Since mirror-mode structures are stationary in the ambient flow, we can estimate the distance of the structures relative to the Dipolarization fronts (DFs) in the Y direction using the average VY ∼ 30 km s−1 during the structures

Summary

Introduction

Mirror modes are pressure-balanced and compressional magnetic structures (Hasegawa, 1969; Tsurutani et al, 2011; Wang et al, 2016; Zhang et al, 2018) They widely exist in many space plasma regions, such as solar wind (Zhang et al, 2008, 2009; Russell et al, 2009), the planetary magnetosheath (Volwerk et al, 2008; Schmid et al, 2014), the planetary magnetosphere (Vaivads et al, 2001; Rae et al, 2007), and comets (Glassmeier et al, 1993; Volwerk et al, 2016). Our aim is to figure out whether the main contributor to the current density inside the ion-scale mirror-mode structure is the electron or ion

Observation

Overview of a DF event

Plasma properties in MM1

Plasma properties in MM2

Discussion

Summary