Recovery of streamlines in the flank low‐latitude boundary layer
Recovery of streamlines in the flank low‐latitude boundary layer
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DOI：
10.1029/2006ja012101
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发表时间：
2006-12
影响因子：
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通讯作者：
H. Hasegawa;B. Sonnerup;M. Fujimoto;Yoshifumi Saito;T. Mukai
中科院分区：
文献类型：
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作者：
H. Hasegawa;B. Sonnerup;M. Fujimoto;Yoshifumi Saito;T. Mukai
[1] 我们提出了一种新技术的初步结果，该技术可根据单航天器对整体等离子体参数和磁场的观测来生成速度场的二维 (2-D) 图。对于横向于单向磁场的流，MHD 运动方程可以简化为流函数的 Grad-Shafranov 型（GS 型）方程（Sonnerup 等，2006），前提是等离子体结构是二维的，并且在适当的框架中观察时与时间无关。我们展示了如何使用该方程来恢复航天器路径周围区域的流场，正如 Sonnerup 和Guo (1996) 在磁场的 GS 重建中首次所做的那样。新方法通过使用 GS 型方程的精确解并进一步使用开尔文-亥姆霍兹不稳定性 (KHI) 的二维 MHD 模拟的合成数据来进行基准测试。即使存在预期在侧磁层顶的 KHI 发展过程中的时间演化，也可以生成具有合理精度的流线图。将该技术应用于 Geotail 在低纬度侧翼边界层遇到一系列 KH 波的情况表明，存在一系列涡旋（每个涡旋大小为 ∼3 RE × 1 RE ）并沿着磁层顶向后移动。
[1] We present first results of a novel technique for producing a two-dimensional (2-D) map of the velocity field from single-spacecraft observations of the bulk plasma parameters and magnetic field. For flow transverse to a unidirectional magnetic field, the MHD equations of motion can be reduced to a Grad-Shafranov-type (GS-type) equation for the stream function (Sonnerup et al., 2006), provided that the plasma structure is 2-D and time-independent when seen in its proper frame. We show how this equation can be used to recover the flow field in regions surrounding a spacecraft path, as was first done in the GS reconstruction of the magnetic field by Sonnerup and Guo (1996). The new method is benchmarked by use of an exact solution of the GS-type equation and further by use of synthetic data from 2-D MHD simulations of the Kelvin-Helmholtz instability (KHI). Streamline maps of reasonable accuracy can be generated even when temporal evolution during the KHI development expected at the flank magnetopause is present. Application of the technique to a Geotail encounter with a train of KH waves in the low-latitude flank boundary layer indicates that a chain of vortices (each of size ∼3 R E by 1 R E ) existed and moved tailward along the magnetopause.