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Magnetotail current sheet structure and dynamics from multi-point spacecraft measurements.

机译：多点航天器测量的磁尾电流片结构和动力学。

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摘要

We present results of studies examining the structure and dynamics of the magnetotail current sheet with the Cluster spacecraft. After an introduction to the magnetosphere, we present the technique for calculating current densities with Cluster magnetometer data and a comparison of those current densities for different spacecraft separations. We show that current densities inferred for 150 km spacecraft separation tend to be larger than those for 1500 km and 5000 km separations. Fluctuations in the current density are also largest for 150 km spacings, revealing that small spatial scale current structures with large current densities are present in the current sheet. A comparison of integrated current densities to the total change in magnetic field through a plasma sheet crossing is presented to distinguish differences between current densities for the three spacecraft separation distances. We find that integrated current densities sometimes equal the total change in magnetic field but there is no clear dependence on separation distance. The average structure of the current sheet is surveyed through both static and time-varying fits of the Harris current sheet model to Cluster measurements. Current density time series provide a more accurate constraint on such descriptions than was previously available. We find that a time-varying description often provides a reasonable description of current sheet dynamics during the phases of a substorm. Superposed epoch analysis of 21 substorm onsets identified at Cluster further supports the time-varying Harris model. We studied bifurcated current sheets with both an MHD simulation and Cluster measurements. Our MHD simulation, using solar wind conditions present during a previously published event, reveals that current sheet bifurcations are a few RE in scale size, are present over time scales of several minutes, and are magnetically linked to neutral lines in the tail. We developed search criteria to automatically identify bifurcated current sheets in Cluster data for 1500 km and 5000 km spacings using the MHD simulation and previously published events as a guide. We show that bifurcated current sheets are typically ≳ 1 RE in scale size and can often be associated with local neutral lines near Cluster, consistent with our MHD modeling results.
机译：我们提出了研究结果，以研究集群飞船的磁尾电流板的结构和动力学。在介绍了磁层之后，我们介绍了利用簇磁强计数据计算电流密度的技术，并比较了不同航天器分离的那些电流密度。我们表明，推断出的150 km航天器分离的当前密度往往大于1500 km和5000 km分离的密度。在150 km的间隔中，电流密度的波动也最大，这表明电流表中存在具有大电流密度的小空间尺度电流结构。提出了积分电流密度与通过等离子薄片穿越的总磁场变化的比较，以区分三个航天器分离距离的电流密度之间的差异。我们发现，积分电流密度有时等于磁场的总变化，但对分离距离没有明确的依赖性。当前表的平均结构通过Harris当前表模型对Cluster测量的静态和时变拟合进行调查。当前密度时间序列对此类描述的约束比以前更精确。我们发现，随时间变化的描述通常可以在亚暴雨阶段提供当前表层动力学的合理描述。在“星团”处确定的21个亚暴爆发的叠加历时分析进一步支持了时变的哈里斯模型。我们通过MHD模拟和簇测量研究了分叉的电流表。我们的MHD仿真使用先前发布的事件中出现的太阳风条件，揭示了当前的工作表分叉在尺度上只有几个RE，在几分钟的时间尺度上都存在，并且磁链接到尾部的中性线。我们使用MHD模拟和以前发布的事件作为指南，开发了搜索条件以自动识别1500 km和5000 km间距的簇数据中的分叉的当前工作表。我们显示分叉的电流表通常为＆gsim;比例尺大小为1 RE，通常可以与Cluster附近的局部中性线相关联，这与我们的MHD建模结果一致。

著录项

  • 作者

    Thompson, Scott Martin.;

  • 作者单位

    University of California, Los Angeles.;

  • 授予单位 University of California, Los Angeles.;
  • 学科 Geophysics.
  • 学位 Ph.D.
  • 年度 2004
  • 页码 202 p.
  • 总页数 202
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 地球物理学;
  • 关键词

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