On the loss of relativistic electrons at geosynchronous altitude: Its dependence on magnetic configurations and external conditions
On the loss of relativistic electrons at geosynchronous altitude: Its dependence on magnetic configurations and external conditions
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DOI：
10.1029/2008ja013391
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发表时间：
2008-12
影响因子：
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通讯作者：
S. Ohtani;Y. Miyoshi;H. Singer;J. Weygand
中科院分区：
文献类型：
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作者：
S. Ohtani;Y. Miyoshi;H. Singer;J. Weygand
[1]本研究对地球同步轨道磁结构和表征地球同步轨道MeV电子损失的外部条件进行了统计检验。MeV电子的损失通常发生在磁层风暴期间，但它也发生在没有任何明显风暴活动的情况下。结果发现，无论风暴活动如何，地球同步轨道H(南北)磁分量的昼夜不对称性在电子损失事件中表现得非常明显。对于损耗过程，磁失真的大小而不是持续时间似乎很重要，其有效持续时间可短至∼30分钟。在电子损失事件期间，太阳风动压趋于高，行星际磁场Bz趋于南移。在这种外部条件下，日侧磁层顶向地球移动，昼夜磁不对称性增强。结果，封闭漂移轨道的面积缩小了。在电子损失事件中，次太阳磁层顶处的磁场通常比夜间地球同步磁场强，这是根据太阳风动压与力平衡估计的。因此，当地球同步轨道的MeV电子丢失时，夜侧的地球同步轨道上的MeV电子经常处于开放的漂移路径上。虽然目前的结果并不排除被广泛接受的观点，即MeV电子是通过波-粒子相互作用损失到大气中的，但它表明，磁层顶阴影是地球同步轨道MeV电子的另一种看似合理的损失过程。
[1] The present study statistically examines geosynchronous magnetic configurations and external conditions that characterize the loss of geosynchronous MeV electrons. The loss of MeV electrons often takes place during magnetospheric storms, but it also takes place without any clear storm activity. It is found that irrespective of storm activity, the day-night asymmetry of the geosynchronous H (north-south) magnetic component is pronounced during electron loss events. For the loss process, the magnitude, rather than the duration, of the magnetic distortion appears to be important, and its effective duration can be as short as ∼30 min. The solar wind dynamic pressure tends to be high and interplanetary magnetic field BZ tends to be southward during electron loss events. Under such external conditions the dayside magnetopause moves closer to Earth, and the day-night magnetic asymmetry is enhanced. As a consequence the area of closed drift orbits shrinks. The magnetic field at the subsolar magnetopause, which is estimated from force balance with the solar wind dynamic pressure, is usually stronger than the nightside geosynchronous magnetic field during electron loss events. It is therefore suggested that geosynchronous MeV electrons on the night side are very often on open drift paths when geosynchronous MeV electrons are lost. Whereas the present result does not preclude the widely accepted idea that MeV electrons are lost to the atmosphere by wave-particle interaction, it suggests that magnetopause shadowing is another plausible loss process of geosynchronous MeV electrons.