Contribution of Anisotropic Electron Current to the Magnetotail Current Sheet as a Function of Location and Plasma Conditions
Contribution of Anisotropic Electron Current to the Magnetotail Current Sheet as a Function of Location and Plasma Conditions
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DOI：
10.1029/2019ja027251
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发表时间：
2020-01
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通讯作者：
A. Artemyev;V. Angelopoulos;I. Vasko;A. Petrukovich;A. Runov;Y. Saito;L. Avanov;B. Giles;C. Russell;R. Strangeway
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作者：
A. Artemyev;V. Angelopoulos;I. Vasko;A. Petrukovich;A. Runov;Y. Saito;L. Avanov;B. Giles;C. Russell;R. Strangeway
磁尾电流片携带的电流负责磁尾中最大比例的能量存储，即叶中的磁能。因此，它与许多磁层现象（如亚暴）的动力学和进化有着千丝万缕的联系。磁尾电流片的结构和稳定性主要取决于填充磁尾的等离子体的动力学特性。这种等离子体最未被充分研究的特性之一是电子温度的各向异性，这可能占总电流的很大一部分。利用磁尾中五个任务的观测结果，我们研究了电子温度各向异性，Te‖/Te⊥，及其对电流密度的潜在贡献，通过y∈[- 20,20]RE和x∈[- 100，- 10]RE上的消防管参数（βe‖- βe⊥）/2来量化。我们发现，所有电流片中有很大一部分（>30%）具有各向异性的电子电流密度>占总电流的10%。这些电流片形成两个不同的组：(1)近地（3nt）和(2)中尾（> 40re），伴随着快速等离子体流（>300km /s）和小赤道磁场（≤1nt）。对于大量的近地电流片，各向异性电子电流可以达到总电流密度的25%。我们的研究结果表明，电子温度各向异性应该包括在描述实际磁尾结构和动力学的当前薄片模型中。
The magnetotail current sheet carries the current responsible for the largest fraction of the energy storage in the magnetotail, the magnetic energy in the lobes. It is thus inextricably linked with the dynamics and evolution of many magnetospheric phenomena, such as substorms. The magnetotail current sheet structure and stability depend mostly on the kinetic properties of the plasma populating the magnetotail. One of the most underinvestigated properties of this plasma is electron temperature anisotropy, which may contribute a large fraction of the total current. Using observations from five missions in the magnetotail, we examine the electron temperature anisotropy, Te‖/Te⊥, and its potential contribution to the current density, quantified by the firehose parameter (βe‖−βe⊥)/2, across y∈[−20,20]RE and x∈[−100,−10]RE. We find that a significant fraction (>30%) of all current sheets have an anisotropic electron current density >10% of the total current. These current sheets form two distinct groups: (1) near‐Earth (3 nT) and (2) middle tail (>40 RE) accompanied by fast plasma flows (>300 km/s) and small equatorial magnetic field (≤1 nT). For a significant number of near‐Earth current sheets, the anisotropic electron current can be >25% of the total current density. Our findings suggest that electron temperature anisotropy should be included in current sheet models describing realistic magnetotail structure and dynamics.