Four‐point Cluster application of magnetic field analysis tools: The discontinuity analyzer
Four‐point Cluster application of magnetic field analysis tools: The discontinuity analyzer
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DOI：
10.1029/2001ja005089
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发表时间：
2002-11
影响因子：
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通讯作者：
M. Dunlop;A. Balogh;K. Glassmeier
中科院分区：
文献类型：
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作者：
M. Dunlop;A. Balogh;K. Glassmeier
[1]星团航天器收集了地球昼侧磁层、磁鞘和近太阳风中小到中等尺度（100-1000公里）磁场结构的三维信息。在这里，我们专注于第一个应用程序的不连续性分析仪分析技术（确定的几何形状和运动的磁不连续性，使用航天器间的定时和方差信息）的情况下，是平面的四个航天器阵列的边界。这种多点技术使用磁场的最小方差来确定每个航天器的边界法线。要确定四个航天器的交叉点，就需要对每个航天器的相遇进行准确的计时，这取决于每个时间序列中的关键特征在边界框架中是静止的。该技术是测试选定的边界交叉事件（磁层顶和弓形激波，和一个TD的磁鞘），其中独立确定的法线是密切（101 -2°）共线。在600-1000公里的空间尺度上，发现大多数研究的交叉点都有紧密排列的法线。对于这样一个平面几何形状，运动可以明确地确定，并表明在航天器上的边界的显着加速度（高达10 km s−2）几乎总是存在的。其后果是，以前根据两个航天器之间的恒定运动对边界尺度的估计可能误差两到三倍，因此，边界厚度的隐含变化可能主要是由于速度的变化。我们评论的错误引入通过假设的恒定运动。
[1] The Cluster spacecraft have collected 3-D information on magnetic field structures at small to medium scales (100–1000 km) in the Earth's dayside magnetosphere, magnetosheath, and near solar wind. We focus here on the first application of the discontinuity analyzer analysis technique (determination of the geometry and motion of magnetic discontinuities, using interspacecraft timing and variance information) for the case of boundaries that are planar over the four-spacecraft array. This multipoint technique uses minimum variance of the magnetic field to determine the boundary normals at each spacecraft. Identification of the four spacecraft crossings requires accurate timing of encounters at each spacecraft, which depends on key features in each time series being stationary in the frame of the boundary. The technique is tested for selected boundary crossing events (magnetopause and bow shock, and one TD in the magnetosheath), for which the independently determined normals are closely (∼1–2°) colinear. Closely aligned normals, on spatial scales of ∼600–1000 km, were found for most crossings studied. For such a planar geometry, the motion can be determined unambiguously and shows that significant acceleration (up to ∼10 km s−2) of the boundary over the spacecraft is nearly always present. This has the consequence that previous estimates of boundary scales, based on constant motion between two spacecraft, may be in error by factors of two or three and that implied variations in boundary thickness could therefore be predominantly due to variations in speed. We comment on the error introduced through assumptions of constant motion.