Transient, small-scale field-aligned currents in the plasma sheet boundary layer during storm time substorms.

R Nakamura,H K Leinweber,B H Mauk,B L Giles,C T Russell,A N Jaynes,I J Cohen,E L Kepko,Y Saito,S A Fuselier,W Magnes,H J Singer,D Fischer,D N Baker,M R Argall,T E Moore,W Baumjohann,B J Anderson,D J Gershman,R E Ergun,R J Strangeway,J L Burch,B Lavraud,C J Pollock,G Le,A Varsani,R B Torbert,M Chutter,L A Avanov,K R Bromund,V N Coffey ,Takuma Nakamura ,Yuri V Khotyaintsev ,В А Сергеев ,Per‐Arne Lindqvist ,W R Paterson ,K J Genestreti ,Ferdinand Plaschke ,J A Slavin ,Daniel Schmid ,Göran Marklund ,J Dorelli

doi:10.1002/2016gl068768

Abstract

We report on field‐aligned current observations by the four Magnetospheric Multiscale (MMS) spacecraft near the plasma sheet boundary layer (PSBL) during two major substorms on 23 June 2015. Small‐scale field‐aligned currents were found embedded in fluctuating PSBL flux tubes near the separatrix region. We resolve, for the first time, short‐lived earthward (downward) intense field‐aligned current sheets with thicknesses of a few tens of kilometers, which are well below the ion scale, on flux tubes moving equatorward/earthward during outward plasma sheet expansion. They coincide with upward field‐aligned electron beams with energies of a few hundred eV. These electrons are most likely due to acceleration associated with a reconnection jet or high‐energy ion beam‐produced disturbances. The observations highlight coupling of multiscale processes in PSBL as a consequence of magnetotail reconnection.

Highlights

In the Earth’s magnetotail the most dynamic energy conversion takes place during substorms
We report on field-aligned current observations by the four Magnetospheric Multiscale (MMS)
In this paper we report on the evolution of the field-aligned currents (FACs) during a storm time substorm interval on 23 June 2015, when the four Magnetospheric Multiscale (MMS) [Burch et al, 2015] satellites were located near the southern edge of the near-Earth plasma sheet

Summary

Introduction

In the Earth’s magnetotail the most dynamic energy conversion takes place during substorms. A spacecraft located near the PSBL usually experiences a sudden dropout of hot plasma sheet plasma, entering the lobe due to thinning of the plasma sheet. Hones et al [1984] considered that this fast thinning at substorm onset was due to the formation of a reconnection region earthward of the spacecraft, whereas the subsequent plasma sheet expansion was due to its tailward retreat. Sergeev et al [2008], reported that both the thinning of the plasma sheet and dipolarization can take place earthward of a near-Earth closed-field line reconnection region. In this paper we report on the evolution of the FACs during a storm time substorm interval on 23 June 2015, when the four Magnetospheric Multiscale (MMS) [Burch et al, 2015] satellites were located near the southern edge of the near-Earth plasma sheet. Using the high time resolution measurements from MMS, we resolve, for the first time, intriguingly detailed properties of small-scale FACs in the PSBL

Storm Time Substorms

Plasma Sheet Boundary Layer Crossings

Discussion

Conclusions