Electromagnetic ion cyclotron rising tone emissions observed by THEMIS probes outside the plasmapause
Electromagnetic ion cyclotron rising tone emissions observed by THEMIS probes outside the plasmapause
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DOI：
10.1002/2013ja019146
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发表时间：
2014-03-01
影响因子：
2.8
通讯作者：
Angelopoulos, Vassilis
中科院分区：
文献类型：
--
作者：
Nakamura, Satoko;Omura, Yoshiharu;Angelopoulos, Vassilis
我们报道了用亚暴期间事件和大尺度相互作用的时间历史(THEMIS)探测器在等离子体层外观测到的电磁离子回旋加速器(EMIC)触发的发射。虽然这些现象最近由于可能与粒子发生强相互作用而受到广泛关注，但在赤道等离子体顶层附近只报道了几个EMIC触发的发射事件。我们对THEMIS探测器的数据进行了调查，发现各种类型的排放主要发生在半径距离为6-10R-E的日侧。我们详细研究了三个不同的事件。第一个是典型事件，午后段有明显的上升基调发射。第二个事件中的发射同时在不同的频段被激发，这些频带由氦离子的回旋频率隔开。在接近当地中午的第三次事件中，由于太阳风对磁层的压缩，在赤道附近的一大片区域激发了不断上升的音调发射，那里的场向B梯度大大减小。我们将这些事件与大村等人发展的非线性波增长理论进行了比较。(2010)。在所有情况下，都发现观测到的发射幅度与频率之间的关系与理论符合得很好。
We report observations of electromagnetic ion cyclotron (EMIC) triggered emissions observed by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes outside the plasmasphere. Although these phenomena have recently received much attention because of the possibility of strong interaction with particles, only a few events of EMIC triggered emissions have been reported near the equatorial plasmapause. We performed a survey of the THEMIS probe data and found various types of emissions mainly on the dayside at radial distances of 6-10 R-E. We study three distinctive events in detail. The first is a typical event with an obvious rising tone emission in the afternoon sector. The emissions in the second event are simultaneously excited in different frequency bands separated by the cyclotron frequency of helium ions. In the third event, which occurred near local noon, rising tone emissions were excited in an extended region near the equator where the field-aligned B gradient was much reduced because of compression of the magnetosphere by the solar wind. We compare these events with the nonlinear wave growth theory developed by Omura et al. (2010). In all events, it is found that the observed relationship between the amplitudes and frequencies of the emissions are in good agreement with the theory.