Development of Magnetic Topology During the Growth Phase of the Substorm Inducing the Onset of the Near‐Earth Neutral Line
Development of Magnetic Topology During the Growth Phase of the Substorm Inducing the Onset of the Near‐Earth Neutral Line
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导致近地中性线爆发的亚暴生长阶段磁拓扑的发展
DOI：
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发表时间：
2019
期刊：
影响因子：
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通讯作者：
R. Kataoka
中科院分区：
文献类型：
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作者：
T. Tanaka;Y. Ebihara;M. Watanabe;M. Den;S. Fujita;T. Kikuchi;K. Hashimoto;R. Kataoka
分析了亚暴过程中磁拓扑结构的转变。在极地电离层的生长阶段，磁场由三类组成：封闭磁场、通向北行星际磁场的开放磁场和通向南行星际磁场的开放磁场。当通向南向IMF的开放磁场区域在生长阶段持续扩展时，电离层的起始开始于封闭场线区域内。在电离层中，应该有三种磁场共存的三个点。与三重点相连，复杂的磁拓扑出现在磁层中。全球磁场拓扑发生了明显的变化，如在IMF向北产生的尖点零点退缩，产生具有反曲率的等离子体片磁场，在磁层顶上产生分叉区，形成新的日侧零点，在侧翼发展零点线，在磁层顶上产生分叉区(零点群)。在生长后期，伴随着反曲率的出现，中心等离子体片中激发出发散的VX流。由于发散的VX流导致法向分量BZ的减小，电离层在X=−17.5Re的局域区开始电离层重联前5分钟开始重联。它出现在向北的IMF下形成的剩磁结构中，作为与引导场By的三维重联。由此产生的两圈磁场线圈形成了一个向下喷射的等离子体群。
The transition of magnetic topology is analyzed during the substorm. During the growth phase in the polar ionosphere, magnetic fields consist of three categories: closed magnetic field, open magnetic field leading to the northward interplanetary magnetic field (IMF), and open field leading to the southward IMF. While the open magnetic field region leading to the southward IMF expands consistently during the growth phase, the ionospheric onset starts inside the closed field line region. There should be triple points where three kinds of magnetic field coexist in the ionosphere. Connected to the triple points, complex magnetic topologies appear in the magnetosphere. There occur definitive changes in the global magnetic topology such as retreat of cusp nulls generated under the northward IMF, generation of plasma sheet magnetic fields with reverse curvature, generation of bifurcation areas on the magnetopause, formation of new dayside nulls, development of null lines on the flank, and generation of bifurcation areas (group of nulls) on the magnetopause. During the late growth phase, divergence Vx flow is excited in the central plasma sheet associated with the appearance of reverse curvature. The plasma sheet reconnection starts 5 min before the ionospheric onset from a localized area at X = −17.5 Re due to the reduction of the normal component Bz caused by divergence Vx flow. It occurs in the residual magnetic structure formed under the northward IMF as a three‐dimensional reconnection with a guide field By. The resulting two‐turn coil of magnetic field forms a plasmoid, which is ejected downtail.