Two-Dimensional Structure of Flow Channels and Associated Upward Field-Aligned Currents: Model and Observations
Two-Dimensional Structure of Flow Channels and Associated Upward Field-Aligned Currents: Model and Observations
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DOI：
10.3389/fspas.2021.737946
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发表时间：
2021-08
期刊：
影响因子：
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通讯作者：
L. Lyons;Y. Nishimura;Chih‐Ping Wang;Jiang Liu;W. Bristow
中科院分区：
文献类型：
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作者：
L. Lyons;Y. Nishimura;Chih‐Ping Wang;Jiang Liu;W. Bristow
流动爆发是等离子体片和极光椭圆（在这里它们被称为流动通道）内运输的主要组成部分，当它们接近内部等离子体片（极光椭圆的赤道部分）时，会导致各种地磁干扰。然而，当它们接近内部等离子体薄片时，它们的二维结构只受到有限的关注。我们使用Rice对流模式（RCM）和地面雷达和所有天空成像仪观测对这种结构进行了研究。由于能量依赖的磁漂移，流爆发的低熵等离子体在内部等离子体片内以方位角方向扩散，从而产生与流通道相关的场向电流相关的亚极光极化流（SAPS）和黎明极光极化流（DAPS）增强的具体预测。以黎明和黄昏为中心的流动通道对SAPS和DAPS均有显著的增强作用，而进一步靠近黄昏（黎明）对流单元的流动通道对SAPS （DAPS）的增强作用要远远大于对DAPS （SAPS）的增强作用。我们提供了在接近极光椭圆的赤道部分时具有良好流通道覆盖的情况下的观察结果，并发现与上述RCM预测非常好的定性一致，包括关于流爆发位置的预测差异。尽管流动通道的等离子体参数以及背景等离子体片和极光椭圆条件存在无限变化，但观测结果显示了采用理想参数的RCM模拟所预测的总体趋势。这支持了RCM预测低熵等离子体片等离子体的方位角扩散及其相关的FAC和流量响应，给出了等离子体片流爆发（极光椭圆流通道）到达内部等离子体片（接近极光椭圆的赤道边缘）时的真实物理结构描述。
Flow bursts are a major component of transport within the plasma sheet and auroral oval (where they are referred to as flow channels), and lead to a variety of geomagnetic disturbances as they approach the inner plasma sheet (equatorward portion of the auroral oval). However, their two-dimensional structure as they approach the inner plasma sheet has received only limited attention. We have examined this structure using both the Rice Convection Model (RCM) and ground-based radar and all sky imager observations. As a result of the energy dependent magnetic drift, the low entropy plasma of a flow burst spreads azimuthally within the inner plasma sheet yielding specific predictions of subauroral polarization stream (SAPS) and dawnside auroral polarization stream (DAPS) enhancements that are related to the field-aligned currents associated with the flow channel. Flow channels approximately centered between the dawn and dusk large-scale convection cells are predicted to give significant enhancements of both SAPS and DAPS, whereas flow channel further toward the dusk (dawn) convection cell show a far more significant enhancement of SAPS (DAPS) than for DAPS (SAPS). We present observations for cases having good coverage of flow channels as they approach the equatorward portion of the auroral oval and find very good qualitative agreement with the above RCM predictions, including the predicted differences with respect to flow burst location. Despite there being an infinite variety of flow channels’ plasma parameters and of background plasma sheet and auroral oval conditions, the observations show the general trends predicted by the RCM simulations with the idealized parameters. This supports that RCM predictions of the azimuthal spread of a low-entropy plasma sheet plasma and its associated FAC and flow responses give a realistic physical description of the structure of plasma sheet flow bursts (auroral oval flow channels) as they reach the inner plasma sheet (near the equatorward edge of the auroral oval).