Observations Of The Magnetotail Field-aligned Current During Substorm Time

In this paper,we have analyzed the Field-Aligned Currents(FACs)in the auroral and magnetotail areas based on multiple spacecraft measurements during substorm time,and this master's dissertation consists of three parts.The first section includes the first two chapters,in the first chapter,phenomena and physical processes of substorm are introduced,and the background of auroral FACs,cross-tail currents and substorm current wedge are also presented.The second chapter gives brief introductions to MMS and Swarm satellite programs and related data,and covers the multiple spacecraft measurements.In the second part,a moderate intense substorm event on 1 July 2016 07:00UT to10:00 UT was analyzed.In the event,the four MMS satellites were formed a tetrahedral configuration in the midnight region,at?11 R_E tailward from Earth.The three Swarm spacecraft were running at the circular,low-Earth polar orbits with an orbital period of~90 minutes.After the substorm onset,theincrease of auroral FACs were observed by Swarm probes,the value in the summer hemisphere is much larger than in the winter hemisphere,and the results detected by single or double star are almost uniform,because the auroral current sheet moves along the polar axis primarily with a small amplitude and the speed of spacecraft larger than the speed of the current sheet,so a single satellite can measure the direction and size of the FACs.During the expansion phase,MMS satellites observed magnetic field disturbance and sharp increase of magnetic field gradient and FACs in the magnetotail.The magnetotail FACs in unit flux are much larger than auroral FACs in unit flux,the magnetotail FACs are enough to drive the R1 type FACs.The third section analyzed the relationship between vortex-like motions and the magnetotail FACs and vortex can drive the formation of inertial currents of the substorm current wedge theoretically.We calculated the vorticity at the center of MMS via MRA method with electric drift velocity.The results show that particles are transferred heading towards the Earth during the expansion phase of substorm event,the azimuthal flow at stopping point form clockwise(counter-clockwise)vortex-like motion,and then generate downward(upward)FACs on the tailward/poleward side of the distorted field with opposite vorticity on their earthward/equatorward side,however not obviously in numerical.On the event of 16 June 2017,vorticity calculated with electric drift,electron and ion velocities,and distinguished vortex using electric drift data however cannot distinguish vortex motion with other velocities.In this paper,we tried to analyze the relationship of the FACs in different areas and the driving mechanism,our work can provide new clues and ideas to the origin and characteristics of the substorm current wedge.