A preliminary exploration of the mechanism for the occurrence of two types of various magnetic structures in the magnetotail

As well known, the magnetic cross-tail component By in the magnetotail is in direct proportion to the in-terplanetary magnetic field (IMF) By component. And the polarity of IMF and plasmoid / flux rope By components do indeed agree. This results indicate that the IMF By penetrates plasmoids and the magnetic structures must therefore be three-dimensional. In this note, the dynamical processes of magnetotail in the course of a substorm are studied using a MHD code with two-dimensions and three components on the basis of two types of initial equilibrium solutions of the quiet magnetotail. The numerical results of two cases illustrate various features of time evolution of By component that correspond to two kinds of plasmoid-like structures: one is associated with a flux rope core and the other resembles a 'closed loop' plamoid. Therefore, the occurrence of various magnetic structures in the magnetotail might be related to nonsteady driven reconnection with different distributions of the By component.

磁尾地向传播等离子体团的模拟研究

卫星观测证实了磁尾等离子体团与亚暴活动的相关性 ,除了具有北—南双极特征的尾向传播等离子体团外 ,还发现地向传播等离子体团 ,它们表现为南—北双极中性片事件和南—北双极瓣区讯号 .资料分析表明 :南—北双极讯号的出现几率远低于北—南双极讯号 ,并且南—北双极事件主要发生于行星际磁场北向和地磁宁静条件 ,它们往往与小的孤立的地磁亚暴相关 .本文根据地磁宁静时期 (IMFBz 北向且 By ≥Bz)越尾电场Ey 分量的分布特点 ,对地向传播等离子体团作模拟研究 .两类算例的数值结果展示了通量绳磁结构及具有复杂闭合磁力线位形的等离子体团的基本特征 ,上述特征与尾向传播的等离子体团类似 ,与IMP 8卫星关于地向传播南—北中性片事件的观测特征大致相符 .数值结果还展示了与Schindler示意图相类似的磁力线拓扑位形 ,在一定程度上为南—北事件出现几率低作出了解释 ;并且揭示了磁尾中性片内越尾磁场分量By 对磁重联发展的抑制作用 .本文的模拟研究说明 :无论磁尾处于活动时期 (IMFBz 为南向 ) ,还是宁静时期 (IMFBz 为北向且 By ≥Bz) 。