Dynamics of single‐particle orbits during substorm expansion phase
Dynamics of single‐particle orbits during substorm expansion phase
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DOI：
10.1029/ja095ia12p20853
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发表时间：
1990-12
影响因子：
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通讯作者：
D. Delcourt;J. Sauvaud;A. Pedersen
中科院分区：
文献类型：
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作者：
D. Delcourt;J. Sauvaud;A. Pedersen
用三维粒子编码的方法研究了离子在“尾巴状”到“偶极状”磁跃迁过程中的轨迹特征。结果表明，由地磁尾“坍缩”引起的大电场导致中尾（~ 10 RE）磁层种群向地球的对流增强。结果表明，粒子运动在很大程度上受稳态漂移的控制，这些漂移在稳态下可以忽略不计，即：(1)平行于磁场方向，与快速E×B输移有关的离心加速度，可以解释新的高空镜像点的产生；(2)垂直于磁场方向，极化漂移可能导致“冻结”破坏和第一个绝热不变量的瞬态破坏。在后一种情况下，模拟强调了引导中心的有效性取决于粒子质量和/或电荷状态，并允许我们根据等离子体片中的注入深度区分三种类型的离子行为（绝热，非绝热和陀螺相依赖，非绝热和陀螺相独立）。此外，系统的轨道计算表明，低纬度人口受地磁尾巴“崩溃”的影响最大，并揭示了粒子可能出现的戏剧性加速（从数百电子伏特到数百千电子伏特）。这些轨迹结果与解释地球同步高度的各种风暴时间特征有关，并为环流区提供了一种人口机制。
Features of ion trajectories during “taillike” to “dipolelike” magnetic transitions are examined by means of three-dimensional particle codes. It is demonstrated that the large electric fields induced by the “collapse” of the geomagnetic tail result in enhanced earthward convection of the midtail (∼10 RE) magnetospheric populations. It is shown that the particle motion is controlled, to a major extent, by drifts that are negligible in steady state, namely, (1) in the direction parallel to the magnetic field, a centrifugal acceleration related to the rapid E×B transport, which can account for creation of new high-altitude mirror points, (2) perpendicularly to the magnetic field, a drift of polarization which possibly yields “frozen-in” violation and transient breaking of the first adiabatic invariant. In this latter case the simulations emphasize that the guiding center validity is at stake depending upon particle mass and/or charge state and allow us to distinguish three types of ion behavior (adiabatic, nonadiabatic and gyrophase dependent, nonadiabatic and gyrophase independent) according to injection depth in the plasma sheet. Also, systematic orbit calculations show that the low-latitude populations are most affected by the “collapse” of the geomagnetic tail and reveal possible dramatic (from hundreds of eV up to hundreds of keV) accelerations of the particles. These trajectory results are of relevance to explain various storm time signatures at geosynchronous altitudes and provide a populating mechanism for the ring current region.