Pressure gradient evolution in the near-Earth magnetotail at the arrival of BBFs  

作　　者：Zhonghua Yao Zuyin Pu Aimin Du Vassilis Angelopoulos Christopher J.Owen Jiang Liu Xiangning Chu Xin Cao Suiyan Fu Qiugang Zong Yuan Wang 

机构地区：[1]Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences [2]Mullard Space Science Laboratory, UCL, Dorking RH5 6NT,UK [3]School of Earth and Space Sciences, Peking University [4]Department of Earth, Planetary and Space Sciences and Institute of Geophysics and Planetary Physics, University of California,Los Angeles, CA 90095-1567, USA

出　　处：《Chinese Science Bulletin》2014年第34期4804-4808,共5页

基　　金：supported by the National Basic Research Program of China(2014CB845903,2012CB825604);the National Natural Science Foundation of China(41211120176,41274167,41031065,41374166,41330104,41374171);the National R&D Projectsfor Key Scientific Instruments(ZDYZ2012-1-01);UK Science and Technology Facilities Council grant(ST/L005638/1)at UCL/MSSL;China Postdoctoral Science Foundation(2014M550826)

摘　　要：Using in situ observations from THEMIS A, D and E during the 2008–2011 tail season, we present a statistical study of the evolution of pressure gradients in the near-Earth tail during bursty bulk flow(BBF) convection.We identified 138 substorm BBFs and 2,197 non-substorm BBFs for this study. We found that both the pressure and the BZcomponent of the magnetic field were enhanced at the arrival of BBFs at the spacecraft locations. We suggest that the increase of BZduring non-substorm BBFs is associated with flux pile-up. However, the much stronger enhancement of BZduring substorm BBFs implies the occurrence of magnetic field dipolarization which is caused by both the flux pile-up process and near-Earth current disruption. Furthermore, a bow-wave-like high pressure appears to be formed at the arrival of substorm BBFs,which is responsible for the formation of region-1-sense FACs. The azimuthal pressure gradient associated with the arrival of substorm BBFs lasts for about 5 min. The enhanced pressure gradient associated with the bow waveis caused by the braking and diversion of the Earthward flow in the inner plasma sheet. The results from this statistical study suggest that the braking and azimuthal diversion of BBFs may commonly create azimuthal pressure gradients, which are related to the formation of the FAC of the substorm current wedge.Using in situ observations from THEMIS A, D and E during the 2008-2011 tail season, we present a statistical study of the evolution of pressure gradients in the near-Earth tail during bursty bulk flow （BBF） convection. We identified 138 substorm BBFs and 2,197 non-substorm BBFs for this study. We found that both the pressure and the Bz component of the magnetic field were enhanced at the arrival of BBFs at the spacecraft locations. We suggest that the increase of Bz during non-substorm BBFs is associated with flux pile-up. However, the much stronger enhancement of Bz during substorm BBFs implies the occurrence of magnetic field dipolarization which is caused by both the flux pile-up process and near-Earth current disruption. Furthermore, a bow-wave-like high pressure appears to be formed at the arrival of substorm BBFs, which is responsible for the formation of region-1-sense FACs. The azimuthal pressure gradient associated with the arrival of substorm BBFs lasts for about 5 min. The enhanced pressure gradient associated with the bow wave is caused by the braking and diversion of the Earthward flow in the inner plasma sheet. The results from this statistical study suggest that the braking and azimuthal diversion of BBFs may commonly create azimuthal pressure gradients, which are related to the forrnation of the FAC of the substorm current wedge.

关 键 词：压力梯度 地球磁尾 亚暴电流楔 演进 堆积过程 等离子体片 方位角 FAC 

分 类 号：P318[天文地球—固体地球物理学]