Dynamics of plasma, energetic particles, and fields near synchronous orbit in the nighttime sector during magnetospheric substorms
Dynamics of plasma, energetic particles, and fields near synchronous orbit in the nighttime sector during magnetospheric substorms
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DOI：
10.1029/ja085ia05p02043
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发表时间：
1980-05
影响因子：
--
通讯作者：
J. Sauvaud;J. Winckler
中科院分区：
文献类型：
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作者：
J. Sauvaud;J. Winckler
本文从同步轨道上的粒子和场的角度讨论了亚暴磁层动力学的两个阶段。第一阶段对应于高能粒子通量的“减少”，这一现象首先由埃里克森和温克勒（1973）发现，并由步行者等人（1976）和埃里克森等人（1979）讨论。这一阶段开始于亚暴开始前半小时至一小时，其特征是：（1）磁层扭曲成更像尾巴的结构，这是由（2）交叉尾电流及其向地部分（部分环电流）的加强和/或向地球运动引起的，（3）被捕获粒子的轨道沿着常数B的等值线移动到靠近地球的阴面，导致粒子的“减少”，伴随着在地球静止轨道上观测到的俯仰角分布从“饼状”到“蝴蝶状”的变化;（4）极光电喷流（AE）指数响应的开始。高能粒子通量的减少可以对应于McPherron（1970）最初定义的亚暴增长阶段或Erickson等人（1979）定义的增长或前驱阶段。等离子体运动和电流在下降过程中往往是可变的，但上述描述仍然具有大规模趋势的特征。结果表明，地球附近的尾电流增加所产生的电场作用方向与交叉尾对流场相反，可以暂时抑制地球静止轨道附近的对流。第二个阶段是传统的膨胀阶段，从“开始”开始，在我们的研究中，其特征是（1）尾电流突然减少，膨胀的磁层返回到偶极结构，（2）被捕获的高能粒子再次沿着常数B的轮廓突然向尾部移动，与此同时（3）随着感应电场的增加，尾部等离子体向地球涌动，增加了总对流场。因此，单独的影响导致了在亚暴膨胀阶段开始时看到的高能粒子和等离子体粒子的急剧增加，（4）AE指数响应和在当地时间午夜附近的站点出现海湾，伴随着非常活跃的极光以及高能粒子的沉淀。在ATS 1（在磁赤道上）和ATS 6（离开磁赤道）处的响应的不同外观可以通过以上描述很好地解释。粒子群的真正抗磁效应在ATS 6区域是明显的，必须仔细区分远距离电流的影响。在ATS 6上使用相反方向的探测器，可以评估引导中心粒子密度梯度，这在该分析中非常有用。
We discuss two phases of the substorm-associated magnetospheric dynamics in terms of the particles and fields at synchronous orbit. The first phase corresponds to the ‘decreases’ of energetic particle flux first identified by Erickson and Winckler (1973) and discussed by Walker et al. (1976) and Erickson et al. (1979). This phase begins one-half hour to one hour before the substorm onset and is characterized by (1) a distortion of the magnetosphere to a more taillike configuration caused by (2) an intensification and/or motion toward the earth of the cross-tail current and of its earthward part, the partial ring current, (3) a shift of trapped particle trajectories closer to the earth on the nightside following contours of constant B causing the particle ‘decreases,’ accompanied by a change in the pitch angle distributions from ‘pancake’ to ‘butterfly’ as observed at geostationary orbit, (4) an initiation of a response of the auroral electrojet (AE) index. The decreases of energetic particle flux can correspond to the substorm growth phase as defined initially by McPherron (1970) or the growth or precursor phase of Erickson et al. (1979). Plasma motions and currents during decreases tend to be variable, but the description above nevertheless characterizes the large-scale trend. It is suggested that the electric field induced by the increasing tail current near the earth acts opposite to the cross-tail convection field and can temporarily inhibit convection near the geostationary orbit. The second phase is the conventional expansion phase that begins with the ‘onset,’ characterized in our study by (1) a sudden decrease in the tail current and a return of the inflated magnetosphere to a dipolelike configuration, (2) a sudden shift of trapped high-energy particles toward the tail again following contours of constant B, and at the same time (3) a surge of tail plasma toward the earth as the induced electric field now increases the total convection field. Separate effects thus result in the dramatic increases of both high energy and plasma particles seen at substorm expansion phase onset, (4) an AE index response and the appearance of bays at stations near midnight local time accompanied by very active aurora as well as the precipitation of high-energy particles. The different appearance of the responses at ATS 1 (on the magnetic equator) and ATS 6 (off the magnetic equator) can be well explained by the above description. True diamagnetic effects of the particle population are clearly evident at the ATS 6 region and must be carefully distinguished from the effects of distant currents. The use of oppositely directed detectors on ATS 6 that permit the evaluation of the guiding center particle density gradients has been of great use in this analysis.