Latitudinal structures of nightside field‐aligned currents and their relationships to the plasma sheet regions
Latitudinal structures of nightside field‐aligned currents and their relationships to the plasma sheet regions
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夜侧场对准电流的纬度结构及其与等离子体片区域的关系
DOI：
10.1029/92ja02031
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发表时间：
1993
影响因子：
--
通讯作者：
S. Machida
中科院分区：
文献类型：
--
作者：
H. Fukunishi;Y. Takahashi;T. Nagatsuma;T. Mukai;S. Machida
利用来自曙光（EXOS D）卫星的磁场和低能粒子数据，对20-04 MLT扇区和海拔5000-10,000公里的北半球12个通道的夜侧极光椭圆区的场对准电流和极光粒子的纬度结构进行了详细研究。研究发现，夜侧场对准洋流系统由位于极光椭圆极向边界的窄纬度洋流系统（∼1°）和占据极光椭圆体主要部分的宽纬洋流系统组成。前者被称为“边界流系统”，后者被称为“中心流系统”。建议这两个洋流系统都位于闭合场线区域，因为在边界洋流系统的极地方向观测到极地雨。建议边界电流系统独立于与倒V电子沉淀相关的传统区域1电流系统，因为具有场对准俯仰角分布的超热电子被发现是该电流系统的主要载流子。另一个重要的发现是，能量分散的离子沉淀事件出现在这个边界电流区域，这被解释为离子在等离子体片边界层中向地球流动的E×B漂移的结果。中心电流系统由两个区域组成，极地侧的倒V电子沉淀区和赤道侧的非结构电子和离子沉淀区。因此，建议该中央电流系统对应于夜间区域中的传统区域1和区域2电流系统。进一步发现，等离子体片千伏电子的扩散带从定义为极雨终止区的极冠边界通过倒V电子沉淀区到非结构化沉淀区的赤道边界连续观察到。因此，倒V结构和扩散等离子体片电子沉淀总是共存。根据这些空间关系，强烈建议边界电流系统映射到等离子体片边界层，而中心电流系统映射到主或中央等离子体片。
Using the magnetic field and low-energy particle data from the Akebono (EXOS D) satellite, the latitudinal structures of field-aligned currents and auroral particles in the nightside auroral oval region have been studied in detail for 12 northern hemisphere passes in the 20-04 MLT sector and at altitudes of 5000-10,000 km. It is found that the nightside field-aligned current system consists of the latitudinally narrow (∼1°) current system located at the poleward boundary of the auroral oval and the latitudinally wide current system which occupies the main portion of the oval. The former has been designated as “the boundary current system” and the latter as “the central current system.” Both current systems are suggested to be located in the closed field line region, since the polar rain is observed just poleward of the boundary current system. The boundary current system is suggested to be independent of the traditional region 1 current system associated with inverted V electron precipitation, since suprathermal electrons with field-aligned pitch angle distributions are found to be the main charge carrier of this current system. Another important finding is that energy-dispersed ion precipitation events, which are interpreted to be the result of the E × B drift of ions flowing earthward in the plasma sheet boundary layer, appear in this boundary current region. The central current system consists of the two regions, the inverted V electron precipitation region on the poleward side and the unstructured electron and ion precipitation region on the equatorward side. It is suggested therefore that this central current system corresponds to the traditional region 1 and region 2 current system in the nightside sector. It is further found that the diffuse band of plasma sheet kilovolt electrons is continuously observed form the polar cap boundary defined as the polar rain terminator to the equatorward boundary of the unstructured precipitation region through the inverted V electron precipitation region. Consequently, inverted V structures and diffuse plasma sheet electron precipitation always coexist. From these spatial relationships, it is strongly suggested that the boundary current system is mapped to the plasma sheet boundary layer, while the central current system is mapped to the main or central plasma sheet.