A physical explanation for the magnetic decrease ahead of dipolarization fronts
A physical explanation for the magnetic decrease ahead of dipolarization fronts
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DOI：
10.5194/angeo-33-1301-2015
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发表时间：
2015-10
影响因子：
1.9
通讯作者：
Z. Yao;Jiang Liu;C. Owen;C. Forsyth;I. J. Rae;Z. Pu;H. Fu;Xuzhi Zhou;Q. Shi;A. Du
中科院分区：
文献类型：
--
作者：
Z. Yao;Jiang Liu;C. Owen;C. Forsyth;I. J. Rae;Z. Pu;H. Fu;Xuzhi Zhou;Q. Shi;A. Du
抽象的。最近的研究表明，在近地磁尾的环境等离子体可以被压缩的双极化锋（DF）的到来。在本文中，我们研究的变化特征的电流在这个压缩区域流动的DF之前，特别是在交叉尾电流的变化，使用THEMIS卫星的观测。由于我们不知道交叉尾电流的变化是否会导致场向电流的形成，或者只是在磁层中形成电流环，因此我们使用再分布来表示这些局部电流密度的变化。结果表明：（1）交叉尾电流的重新分布是DF前的一个共同特征;（2）交叉尾电流的重新分布是由DF前的等离子体压力梯度引起的;（3）DF引起的净电流重新分布比与中等亚暴电流楔（SCW）相关的典型总电流小一个数量级。此外，我们的研究结果还表明，重新分配的电流前面的DF是封闭的电流DF本身，形成一个封闭的电流回路周围的峰值等离子体压力，这是传统上被称为香蕉电流。
Abstract. Recent studies have shown that the ambient plasma in the near-Earth magnetotail can be compressed by the arrival of a dipolarization front (DF). In this paper we study the variations in the characteristics of currents flowing in this compressed region ahead of the DF, particularly the changes in the cross-tail current, using observations from the THEMIS satellites. Since we do not know whether the changes in the cross-tail current lead to a field-aligned current formation or just form a current loop in the magnetosphere, we thus use redistribution to represent these changes of local current density. We found that (1) the redistribution of the cross-tail current is a common feature preceding DFs; (2) the redistribution of cross-tail current is caused by plasma pressure gradient ahead of the DF and (3) the resultant net current redistributed by a DF is an order of magnitude smaller than the typical total current associated with a moderate substorm current wedge (SCW). Moreover, our results also suggest that the redistributed current ahead of the DF is closed by currents on the DF itself, forming a closed current loop around peaks in plasma pressure, what is traditionally referred to as a banana current.