太阳风中重联喷流厚度的四航天器直接测量
Direct Four-Spacecraft Measurement of Reconnection Exhaust Thickness in the Solar Wind
- Sikkim University（锡金大学）
- Netaji Subhas University of Technology（内塔吉·苏巴斯技术大学）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本研究利用磁层多尺度任务的四航天器测量，直接测定太阳风重联喷流厚度为29-31离子惯性长度，验证了单航天器厚度估计的精度并揭示了喷流的非平行几何结构。
AI中文摘要：
重联太阳风电流片的厚度通常由单个航天器通过边界法向速度与穿越持续时间的乘积来推断。多点测量已针对一般太阳风电流片测试了该方法，并约束了重联喷流的几何结构，但仍缺乏对同一重联相关穿越事件与单航天器厚度估计值的直接对比。我们分析了磁层多尺度任务（MMS）于2017年11月10日在宁静太阳风中观测到的四次电流片穿越事件：一次已确认重联喷流的两个边界，以及两个邻近的电流片。四面体间距约为16 km。磁场斜坡的互相关给出了毫秒级的延迟不确定度，边界法向的不确定度为4°-8°，速度不确定度为5%-8%，而在该间距下的单阈值计时受噪声主导。喷流边缘的厚度为29-31个离子惯性长度（di）。两个边缘法向相差22°（68%置信区间为[19°,26°]），这一结果明确了非平行的喷流几何结构。在喷流边缘，测得的边界速度与三种标准单航天器估计值的偏差为4%-15%，且始终保持在等离子体运动的约1个阿尔文速度范围内。从单个航天器估计法向是更大的误差来源，不过当排除简并的最小方差解时，厚度仍可恢复至百分之几十以内。在主动重联的电流片处，边界速度沿法向超出局部等离子体速度29%±10%。
英文摘要：
The thickness of a reconnecting solar wind current sheet is normally inferred from a single spacecraft as the product of the boundary-normal speed and the crossing duration. Multipoint measurements have tested this method for generic solar wind current sheets and constrained the geometry of reconnection exhausts, but a direct comparison with single-spacecraft thickness estimates for the same reconnection-associated crossings is still lacking. We analyze four current-sheet crossings observed by Magnetospheric Multiscale in the pristine solar wind on 2017 November 10 the two boundaries of a confirmed reconnection exhaust and two nearby current sheets. The tetrahedron separation was $\approx 16$ km. Cross-correlation of the magnetic-field ramps gives millisecond-level lag uncertainties, boundary normals to $4^\circ-8^\circ$ and speeds to $5\%-8\%$, while single-threshold timing at these separations is noise dominated. The exhaust edges are 29-31 ion inertial lengths ($d_i$) thick. The two edge normals differ by $22^\circ$ (68% interval [$19^\circ,26^\circ$]), resolving a nonparallel exhaust geometry. At the exhaust edges, the measured boundary speeds agree with three standard single-spacecraft estimates to 4%-15% and remain within about one Alfvén speed of the plasma motion. Estimating the normal from one spacecraft is the larger source of error, though the thickness is still recovered to within tens of percent when a degenerate minimum-variance solution is rejected. At the actively reconnecting sheet, the boundary speed exceeds the local plasma speed along the normal by $29\% \pm 10\%$.
