Flow Vortex‐Associated Downward Field‐Aligned Current Retreating in the Near‐Earth Plasma Sheet

Earth and Space Science

Ming Wang¹  Huanzhi Yuan¹  Jianyong Lu¹  Hui Zhang²  Changbo Zhu³ 

[1] Institute of Space Weather, College of Math & Statistics Nanjing University of Information Science & Technology Nanjing China;Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics Chinese Academy of Sciences Beijing China;National Space Science Center Chinese Academy of Sciences Beijing China;

关键词: field‐aligned current;    vortex;    substorm;   

DOI  :  10.1029/2019EA000916

来源: DOAJ

【 摘 要 】

Abstract The formation of field‐aligned currents (FACs) of a substorm current wedge is a key element of substorms. Conjunctive observations of a downward FAC during a substorm on 20 December 2007 were made in space by THEMIS satellites and on the ground by geomagnetic field and aurora stations, which provides a unique opportunity to investigate the generation of downward FAC. On the ground, AL index decreased significantly at 04:17:00 UT, denoting the onset of the substorm. The geomagnetic perturbations observed at the postmidnight station KUUJ show that the FAC of the substorm current wedge flowed into the ionosphere. Meanwhile, in space, two THEMIS satellites, THC and THB, the magnetic footprints of which were close to the postmidnight station KUUJ, were located in the near‐Earth magnetotail and recorded the outside‐in signatures of the plasma sheet thinning first and then the large‐scale inside‐out propagating plasma flow vortex inferred from the rotation of the flow vector. The magnitude of the FAC was estimated by using the bipolar BY perturbations associated with the flow vortex. It is found that this FAC was so strong that it cannot be produced by the time derivative of the vorticity and that the pressure gradient may act in this event. The upward flowing low‐energy electrons are the possible carriers for this FAC.

【 授权许可】

Unknown