Roles of the M‐I Coupling and Plasma Sheet Dissipation on the Growth‐Phase Thinning and Subsequent Transition to the Onset
Roles of the M‐I Coupling and Plasma Sheet Dissipation on the Growth‐Phase Thinning and Subsequent Transition to the Onset
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DOI：
10.1029/2021ja029925
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发表时间：
2021-12
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通讯作者：
T. Tanaka;Y. Ebihara;M. Watanabe;M. Den;S. Fujita;T. Kikuchi;K. Hashimoto;N. Nishitani;R. Kataoka
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文献类型：
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作者：
T. Tanaka;Y. Ebihara;M. Watanabe;M. Den;S. Fujita;T. Kikuchi;K. Hashimoto;N. Nishitani;R. Kataoka
等离子体片动力学导致的亚暴发病进行了分析，从全球模拟。我们计算了三种情况，正常（情况1），减少磁层-电离层（M-I）耦合（情况2）和减少尾部耗散（情况3）。正规解再现了磁层的变薄、重联、尾流和偶极化，以及电离层的Au/AL、初始增亮、串珠、初起弧和向极扩展。情况2表明，M-I耦合通过从等离子体片中抽空磁场来促进减薄。情况3表明，仅用数值耗散来再现膨胀相的Au/AL是不可信的。生长相等离子体片的投影区域非常狭窄，以至于高纬度一侧的安静弧被投影到瓣上。理解这种窄投影的关键点是考虑场向电流（FAC）的起源。FAC的发生是为了传递运动，而颗粒沉降是其结果。平静弧和初始增亮的向上FAC产生亚暴序列，将增强的对流从磁层传递到电离层。亚暴爆发是对流瞬变的传播过程。起始FAC由近地发电机产生。在开始之前，通过撤退零，在中尾（MTNL）和近地（NENL）中性线处发生两阶段重连。伴随的流动解释了假设近地和中尾开始的两个因果区域的模型。
The plasma‐sheet dynamics leading to the substorm onset is analyzed from a global simulation. We calculated three cases, the normal (case 1), reduced magnetosphere‐ionosphere (M‐I) coupling (case 2) and reduced tail dissipation (case 3). The normal solution reproduces the thinning, reconnection, tail flow, and the dipolarization in the magnetosphere, and the AU/AL, the initial brightening, the beads, the pre‐onset arc, and the poleward expansion in the ionosphere. Case 2 shows that the M‐I coupling promotes the thinning by evacuating magnetic field from the plasma sheet. Case 3 shows that it is implausible to reproduce the AU/AL of the expansion phase only with numerical dissipation. The projection area of the growth phase plasma sheet is so narrow that the quiet arcs on the high‐latitude side are projected to the lobe. The key point to understand such narrow projection is to consider the origin of the field‐aligned current (FAC). The FAC occurs to transmit motion, and particle precipitation is the consequence. The upward FACs for the quiet arc and initial brightening, which produce the substorm sequence, are generated to transmit enhanced convection from the magnetosphere to the ionosphere. The substorm onset is the transmission of the convection transient. The onset FAC is generated by the near‐earth dynamo. Before the onset, a two‐stage reconnection occurs at the medium‐tail (MTNL) and the near‐earth (NENL) neutral lines through retreating nulls. The accompanying flow explains the model that assumes two causal areas for the onset in the near‐earth and middle tails.