Space‐Ground Observations of Dynamics of Substorm Onset Beads
Space‐Ground Observations of Dynamics of Substorm Onset Beads
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DOI：
10.1029/2021ja030004
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发表时间：
2022-01
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影响因子：
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通讯作者：
Y. Nishimura;A. Artemyev;L. Lyons;C. Gabrielse;E. Donovan;V. Angelopoulos
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作者：
Y. Nishimura;A. Artemyev;L. Lyons;C. Gabrielse;E. Donovan;V. Angelopoulos
我们在两个亚暴期间使用同步事件时间历史和亚暴卫星和全天空成像仪的大尺度相互作用来确定与亚暴极光开始珠相关的等离子体片动力学。多卫星观测表明，在亚暴极光开始时，交叉尾电流减少，场向电流增加，表明卫星探测到电流开始偏转到电离层。对于向黄昏传播的珠子，电场是尾部的，离子比电子更接近地球。映射的珠传播速度接近高能离子漂移速度。E×B $E\乘以B$和电子漂移速度向黄昏增加，并在开始时减少交叉尾电流。对于朝下传播的珠子，电场是赤道方向/地球方向的，并且推断电子向离子的地球方向积累。绘制的微珠传播速度与朝下的E×B $E\x B$和电子漂移速度相当。黄昏离子漂移和尾电流减小，电子成为主要的载流子。我们建议，负责珠传播的等离子体种类的变化与电场配置和尾电流减少增强E×B $E\倍B$漂移在发病不稳定的等离子体片。离子和电子流出大大增加了低能等离子体密度，并可能增加了E×B $E\times B$漂移的作用。珠波长与离子回旋半径相当，因此离子动力学效应对于确定波长很重要。在朝下传播事件中，等离子体片中的振荡模式被认为是香肠模式拍动振荡。
We present observations during two substorms using simultaneous Time History of Events and Macroscale Interactions During Substorms satellites and all‐sky imagers to determine plasma sheet dynamics associated with substorm auroral onset beads. The multi‐satellite observations showed that the cross‐tail current decreased and the field‐aligned currents increased at the substorm auroral onset, indicating that the satellites detected an initiation of the currents being deflected to the ionosphere. For duskward‐propagating beads, the electric field was tailward, and ions were accumulated closer to the Earth than electrons. The mapped bead propagation speed was close to energetic ion drift speed. The E×B $E\times B$ and electron drift speeds increased duskward and reduced the cross‐tail current at the onset. For dawnward‐propagating beads, the electric field was equatorward/earthward, and electrons were inferred to accumulate earthward of ions. The mapped bead propagation speed was comparable to the dawnward E×B $E\times B$ and electron drift speeds. The duskward ion drift and tail current were reduced, and electrons became the dominant current carrier. We suggest that the plasma species that is responsible for the bead propagation changes with the electric field configuration and that the tail current reduction by the enhanced E×B $E\times B$ drift at onset destabilizes the plasma sheet. Ion and electron outflows substantially increased low‐energy plasma density and may have increased the role of E×B $E\times B$ drifts. The bead wavelength was comparable to ion gyroradius and thus ion kinetic effects are important for determining the wavelength. In the dawnward‐propagating event, the mode of oscillation in the plasma sheet was suggested to be the sausage‐mode flapping oscillations.