Spatial relationships between field‐aligned currents and suprathermal electron beams observed at the poleward boundary of the nightside auroral oval
Spatial relationships between field‐aligned currents and suprathermal electron beams observed at the poleward boundary of the nightside auroral oval
复制标题
在夜侧极光椭圆形极向边界观察到的场对准电流和超热电子束之间的空间关系
DOI：
10.1029/94ja02440
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发表时间：
1995
影响因子：
--
通讯作者：
T. Mukai
中科院分区：
文献类型：
--
作者：
T. Nagatsuma;H. Fukunishi;T. Mukai
本文利用1989年12月至1990年2月期间Akebono卫星的磁场和粒子数据，研究了极光椭圆的极向边界区电子数与场向电流之间的关系。研究发现，在极光椭圆区的极向边界上经常观测到的超热电子束与极向边缘的纬向窄场（0.11 °）电流系统有关，这种电流系统被西等人（1993，p.11，250）命名为“边界电流系统”。此外，一个非结构化的等离子体片状电子带与各向同性的俯仰角分布，除了损失锥出现通过极光椭圆包括边界电流区。因此，在极向边界处的电子能谱的特征在于由两个麦克斯韦函数的叠加：各向同性的高温分量和场对准的低温分量。根据麦克斯韦拟合方法，高温成分的温度和密度分别估计为0.3 - 1.7 keV和≤ 1.0 cm−3，低温成分的温度和密度分别估计为10 - 80 eV和2 - 16 cm−3。一个重要的发现是，温度和密度的低温成分和密度的高温成分的密度显着增强，在向上的电流区域占据边界流系统的赤道部分，而高温成分的温度几乎是恒定的整个区域。这些特征强烈地表明，高温成分来源于等离子体片电子，而低温成分来源于电离层电子。电离层热电子在E × B漂移的作用下，可能从极向下方的电流区向磁层内运动，并受到波粒相互作用的加速和加热。
Magnetic field and particle data obtained from the Akebono satellite in the period from December 1989 to February 1990 are used for examining the relationships between electron populations and field-aligned currents in the poleward boundary region of the nightside auroral oval. It is found that suprathermal electron beams frequently observed at the poleward boundary of the auroral oval associated with a latitudinally narrow (∼ 1°) field-aligned current system located at the poleward edge, which has been designated as “the boundary current system” by Fukunishi et al. (1993, p. 11,250). In addition, an unstructured band of plasma-sheet-like electrons with isotropic pitch angle distributions except for loss cone appears through the auroral oval including the boundary current region. As a result, the electron energy spectra at the poleward boundary are characterized by a superposition of two Maxwellian functions: the isotropic high-temperature component and the field-aligned low-temperature component. From the Maxwellian fitting procedure, the temperature and the density of the high-temperature component are estimated to be 0.3 - 1.7 keV and ≤ 1.0 cm−3, respectively, and those of the low-temperature component are estimated to be 10 - 80 eV and 2 - 16 cm−3, respectively. An important finding is that the temperature and the density of the low-temperature component and the density of the high-temperature component are significantly enhanced in the upward current region occupying the equatorward portion of the boundary current system, while the temperature of the high-temperature component is nearly constant throughout this region. These characteristics strongly suggest that the high-temperature component originates from plasma sheet electrons, while the low-temperature component originates from ionospheric electrons. It is likely that ionospheric thermal electrons flow away from the polewardmost downward current region into the magnetosphere and are accelerated and heated by some wave-particle interaction process during their inward motion due to E × B drift.