Fundamental properties of substorm-time energetic electrons in the inner magnetosphere
Fundamental properties of substorm-time energetic electrons in the inner magnetosphere
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内磁层中亚暴时高能电子的基本特性
DOI：
10.1002/jgra.50115
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发表时间：
2013
影响因子：
--
通讯作者：
Y. and T. Tanaka
中科院分区：
文献类型：
--
作者：
Ebihara;Y. and T. Tanaka
用四维漂移动力学模拟方法研究了孤立亚暴期间内磁层(L，≤ 7.4)中高能电子的时空演化特性。当行星际磁场转向南方时，内部磁层中的电势和感应电场都开始增加，导致低能电子(≤51.9 keV)逐渐注入，高能电子(≥114 kev)减速。高能电子的减速导致生长阶段高能电子的相空间密度降低。一段时间后，磁层发生相态突变(亚暴爆发)，从而触发磁层和电离层的突变。AL值迅速下降，磁力线变为偶极子状。由于J×Bforce和GradPforce之间存在明显的力不平衡，磁层内部的偶极过程并不顺利。因此，电场以2-3 分钟的周期振荡，导致低能电子的多次注入。低能电子和高能电子在漂移电子和陀螺电子的强烈影响下加速，因此加速过程本质上是非线性的。我们的模拟结果表明，力诱导的过程在亚暴相关的内磁层高能粒子的重新分布中起着至关重要的作用。
We studied fundamental properties of spatial‐temporal evolution of energetic electrons trapped in the inner magnetosphere (L≤ 7.4) during an isolated substorm by using a four‐dimensional drift kinetic simulation under the time‐dependent electric and magnetic fields provided by a global magnetohydrodynamics (MHD) simulation. When the interplanetary magnetic field turns southward, both the potential and induction electric fields start to increase in the inner magnetosphere, resulting in a gradual injection of low‐energy electrons (≤51.9 keV) and deceleration of high‐energy electrons (≥114 keV). The deceleration of high‐energy electrons results in a decrease in the phase space density of the high‐energy electrons during the growth phase. After a while, an abrupt transition of phase state (a substorm onset) occurs in the magnetosphere, which triggers abrupt changes in the magnetosphere and ionosphere. TheALindex decreases rapidly, and magnetic field lines become dipole‐like. The dipolarization does not proceed smoothly in the inner magnetosphere because of significant force imbalance between theJ×Bforce and the gradPforce. As a consequence, the electric field oscillates with a period of 2–3 min, resulting in multiple injections of the low‐energy electrons. The low‐ and high‐energy electrons are accelerated under the strong influence of the drift betatron and gyro betatron, so that the acceleration process is essentially nonlinear. Our simulation results suggest that the force‐induced processes play an essential role in the substorm‐associated redistribution of energetic particles in the inner magnetosphere.