A study of ion injections at the dawn and dusk polar edges of the auroral oval
A study of ion injections at the dawn and dusk polar edges of the auroral oval
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极光椭圆区黎明和黄昏极缘离子注入的研究
DOI：
10.1029/2001ja900060
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发表时间：
2001
影响因子：
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通讯作者：
R. Lepping
中科院分区：
文献类型：
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作者：
H. Stenuit;J. Sauvaud;D. Delcourt;T. Mukai;S. Kokubun;M. Fujimoto;N. Buzulukova;R. Kovrazhkin;R. Lin;R. Lepping
在海拔~ 2-3 R E的极光黎明和黄昏磁层中，在靠近极光椭圆形的极地边缘的Interball 2上，通常可以探测到三个不同的离子和电子沉淀区。从高纬度到低纬度，卫星会遇到(1)类似等离子体的磁鞘/低纬度边界层（LLBL）（1区），(2)介于LLBL和等离子体片之间具有等离子体特征的混合区（2区），以及(3)极光等离子体片降水（3区）。进一步向赤道方向，卫星穿过内部等离子体层，其特征是在早晨扇区的离子间隙。在1区和2区经常检测到脉冲离子注入。它们由重叠的能量分散结构组成，从大约10 keV到几百eV，温度接近磁鞘。利用时间上向后的轨迹计算，这些色散被证明是由靠近赤道磁层顶的遥远源的飞行时间效应引起的。区域1主要位于区域1的极侧（黎明时向下的场向流和黄昏时向上的场向流），而区域2则与区域1基本重合。从局部检测到的弹跳离子簇可以看出，它主要位于封闭的场线上。最后，3区对应向上场向流的2区。对1区进行的统计研究表明，1区出现的概率似乎是由行星际磁场（IMF）控制的。也就是说，当IMF有一个向北的组成部分，并倾向于径向导向时，它就形成了。此外，在太阳风压力增强的时期，它更经常遇到。详细的案例研究揭示了1区内单个注入的开始与磁鞘中压力脉冲的开始之间的显著相关性。两者的特征周期都为~ 200- 250秒，与这些注射相关的Pc5事件相似，并在Interball 2上检测到。总之，这些观察结果表明，注入和相关的阿尔芬波是由与准平行弓形激波相关的磁鞘压力脉冲驱动的。等离子体的穿透机制还有待进一步研究。
In the auroral dawn and dusk magnetosphere at altitudes of ∼2-3 R E , three distinct zones of ion and electron precipitation are commonly detected onboard Interball 2, near the polar edge of the auroral oval. From high to low latitudes the satellite encounters (1) magnetosheath/low-latitude boundary layer (LLBL) like plasma (Zone 1), (2) a mixing region with plasma characteristics between LLBL and plasma sheet (Zone 2), and (3) the auroral plasma sheet precipitation (Zone 3). Further equatorward, the satellite crosses the inner plasma sheet characterized by ion gaps in the morning sector. Inside Zones 1 and 2 impulsive ion injections are often detected. They consist of overlapping energy dispersed structures from about 10 keV down to several hundreds of eV with temperature close to that of the magnetosheath. Using trajectory computations backward in time, these dispersions are shown to be cause by time-of-flight effect from a distant source located close to the equatorial magnetopause. Whereas Zone 1 is located mainly poleward of region 1 (downward field-aligned currents at dawn and upward field-aligned currents at dusk), Zone 2 generally coincides with region 1. It is mainly located on closed field lines, as evidenced from the local detection of bouncing ion clusters. Finally, Zone 3 corresponds with region 2 of upward field-aligned currents. A statistical study of Zone 1 which is present in about 12% of the satellite passes at dawn and dusk reveals that its probability of occurrence seems to be controlled by the interplanetary magnetic field (IMF). That is, it is formed when the IMF has a northward component and tends to be radially directed. Moreover, it is more frequently encountered during periods of enhanced solar wind pressure. Detailed case studies uncover a remarkable correlation between the onsets of individual injections inside Zone 1 and those of pressure pulses in the magnetosheath. Both have a characteristic period of ∼ 200- 250 s, similar to that of Pc5 events associated with these injections and detected on board Interball 2. Altogether, these observations indicate that injections and related Alfven waves are driven by magnetosheath pressure pulses associated with a quasi-parallel bow shock. The plasma penetration mechanism remains to be understood.