Electric current and magnetic field geometry in flapping magnetotail current sheets
Electric current and magnetic field geometry in flapping magnetotail current sheets
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DOI：
10.5194/angeo-23-1391-2005
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发表时间：
2005-06
影响因子：
1.9
通讯作者：
A. Runov;V. Sergeev;Wolfgang Baumjohann;R. Nakamura;S. Apatenkov;Y. Asano;M. Volwerk;Z. Vörös
中科院分区：
文献类型：
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作者：
A. Runov;V. Sergeev;Wolfgang Baumjohann;R. Nakamura;S. Apatenkov;Y. Asano;M. Volwerk;Z. Vörös
利用 Cluster 航天器的四点磁场测量，我们对 2001 年 7 月至 10 月在地心距离 19 RE 处观察到的电流片快速穿越期间的磁场和电流配置进行了统计分析。该数据库包括78个交叉点，专门用于应用多点数据分析技术来计算矢量导数。观察到的 jz 双极变化（通常为 |jz|>jy）表明电流遵循电流片的扭结。电流密度在5-25nA/m 2 之间变化。扑动过程中电流片的半厚度变化范围很广，从 1 到 20 个离子热陀螺半径（Lcp，根据每次交叉的平均温度和波瓣磁场计算）。我们发现当前板材法线的倾斜角和半厚度之间没有关系。在 68 种情况下，磁场曲率矢量具有正（向地）X 分量。在 0<YGSM<7RE 范围内检测到 10 个与重新连接相关的负曲率（尾部）的情况。最小曲率半径主要在 1 到 10Lcp 之间变化，73% 的事件绝热参数为 1。扑动过程中的电流密度通常是偏离中心的，即主电流密度从中性片（|Bx|<5 nT）转移到北半球或南半球。这很可能是与扑动相关的时间效应。分析表明，当前板材的扑动运动与板材表面的扭结状波浪有关。扭结锋面在YZ平面上倾斜，在磁尾的早晨一半向黎明移动，在傍晚一半向黄昏移动。
Using four-point magnetic field measurements by the Cluster spacecraft, we statistically analyze the magnetic field and electric current configurations during rapid cross- ings of the current sheet observed in July-October 2001 at geocentric distances of 19 RE. The database includes 78 crossings, specially selected to apply multi-point data analy- sis techniques to calculate vector derivatives. Observed bipo- lar variations of jz, often with |jz|>jy , indicate that the elec- tric currents follow kinks of the current sheet. The current density varies between 5-25 nA/m 2 . The half-thickness of the current sheet during flapping varies over a wide range, from 1 to 20 ion thermal gyroradii (Lcp, calculated from av- erage temperature and lobe magnetic field for each crossing). We found no relationship between the tilt angle of the cur- rent sheet normal and the half-thickness. In 68 cases the magnetic field curvature vector has a positive (earthward) X-component. Ten cases with a negative (tailward) cur- vature, associated with reconnection, were detected within 0<YGSM<7RE. The minimum curvature radii vary mainly between 1 and 10Lcp, and the adiabaticity parameter 1 for 73% of the events. The electric current density during flapping is often off-central, i.e. the main current density is shifted from the neutral sheet (|Bx|<5 nT) to the Northern or Southern Hemisphere. This is most likely a temporal ef- fect related to the flapping. The analysis shows that the flap- ping motion of the current sheet is associated with kink-like waves on the sheet surface. The kink fronts, tilted in the Y Z plane, moved toward dawn in the morning half and to- ward dusk in the evening half of the magnetotail.