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首页> 外文期刊>Journal of Geophysical Research, A. Space Physics: JGR >The force-free configuration of flux ropes in geomagnetotail: Cluster observations
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The force-free configuration of flux ropes in geomagnetotail: Cluster observations

机译：自由配置的通量绳geomagnetotail:集群的观察

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摘要

Unambiguous knowledge of magnetic field structure and the electric current distribution is critical for understanding the origin, evolution, and related dynamic properties of magnetic flux ropes (MFRs). In this paper, a survey of 13 MFRs in the Earth’s magnetotail are conducted by Cluster multipoint analysis, so that their force-free feature, i.e., the kind of magnetic field structure satisfying J × B = 0, can be probed directly. It is showed that the selected flux ropes with the bipolar signature of the south-north magnetic field component generally lie near the equatorial plane, as expected, and that the magnetic field gradient is rather weak near the axis center, where the curvature radius is large. The current density (up to several tens of nA/m~2) reaches their maximum values as the center is approached. It is found that the stronger the current density, the smaller the angles between the magnetic field and current in MFRs. The direct observations show that only quasi force-free structure is observed, and it tends to appear in the low plasma beta regime (in agreement with the theoretic results). The quasi force-free region is generally found to be embedded in the central portion of the MFRs, where the current is approximately field aligned and proportional to the strength of core field. It is shown that ~60% of surveyed MFRs can be globally approximated as force free. The force-free factor α is found to be nonconstantly varied through the quasi force-free MFR, suggesting that the force-free structure is nonlinear.
机译：明确的磁场结构的知识和电流分布是至关重要的理解起源、进化和动态属性相关的磁通绳索(生产商)。地球磁尾是由集群多点分析,所以他们的自由功能,即磁场结构满足J×B = 0,可以探测直接。绳子的双签名南北磁场分量躺在赤道平面附近,正如所料,和的磁场梯度相当薄弱轴中心附近的曲率半径很大。nA / m ~ 2)达到其最大值中心是靠近。电流密度越大,越小磁场和电流之间的角度生产商。准自由结构观察,它往往出现在低血浆β政权(在与理论结果协议)。自由地区通常被发现嵌入在中央部分的生产商,目前大约是字段一致和核心领域的强度成正比。结果表明,~ 60%的受访生产商在全球范围内近似为自由的力量。自由因子α非常数的通过准自由生产商不同,这表明自由结构非线性。

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