Characteristics of magnetic dipolarizations in the vicinity of the substorm onset region observed by THEMIS  

作　　者：SuPing Duan Chi Wang Weining William Liu ZhaoHai He 

机构地区：[1]State Key Lab of Space Weather,National Space Science Center,Chinese Sciences Academy,Beijing 100190,China [2]University of Chinese Academy of Sciences,Beijing 100049,China

出　　处：《Earth and Planetary Physics》2021年第3期239-250,共12页地球与行星物理（英文版）

基　　金：supported by the National Natural Science Foundation of China(NSFC)under grants 41731070,41674167,41574161;the Strategic Pioneer Program on Space Science,Chinese Academy of Sciences,grants XDA15052500,XDA15350201 and XDA15011401;the Specialized Research Fund for State Key Laboratories of China.

摘　　要：With conjunction observations of electromagnetic fields and plasma from Time History of Events and Macroscale Interactions during Substorm(THEMIS)in the near-Earth magnetotail,we investigate the spatial and temporal properties of substorm dipolarizations in the near-Earth plasma sheet(NEPS)during a substorm at 03:23 UT on 12 February 2008.Substorm dipolarizations with different features are detected by three near-Earth THEMIS probes(THA(P5),THD(P3)and THE(P4))in the magnetotail.In the current sheet with a large plasma beta value(β>2,whereβis the ratio of the plasma thermal pressure to the magnetic pressure),the dipolarization within the substorm onset region,(−10.4,2.8,−2.6)RE_gsm,has a large initial magnetic field elevation angle,θ>60°,θ=arctan(Bz/(Bx2+By2)1/2),and is accompanied by energetic ion(tens to hundred keV)dispersionless injection detected by THD(P3).This substorm onset dipolarization is characterized by Bx and By components around 0 nT with significant fluctuations.The Bz component increases sharply and its subsequent magnitude approaches the total magnetic field,Bt.The maximum value of the elevation angle approaches 85°during the later substorm expansion phase.In the NEPS withβ~1,the dipolarization outside the substorm onset region is characterized by a magnetic elevation angle with a small beginning value ofθ<45°and following multi-step enhancements during the substorm expansion phase.The maximum value of the elevation angle approaches to 70°during the later substorm expansion phase.Our observation results indicate that characteristics of dipolarization with a large beginning elevation angle within the substorm onset region provide a new indicator to identify substorm onset location.

关 键 词：SUBSTORM magnetic dipolarization near-Earth plasma sheet MAGNETOTAIL 

分 类 号：P354[天文地球—空间物理学]