ELF/VLF waves correlated with transversely accelerated ions in the auroral region observed by Akebono
ELF/VLF waves correlated with transversely accelerated ions in the auroral region observed by Akebono
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ELF/VLF波与Akebono观测到的极光区横向加速离子相关
DOI：
10.1029/2000ja000318
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发表时间：
2001
影响因子：
--
通讯作者：
Ryotaro Niitsu
中科院分区：
文献类型：
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作者：
Y. Kasahara;T. Hosoda;T. Mukai;S. Watanabe;I. Kimura;H. Kojima;Ryotaro Niitsu
本文研究了Akebono卫星在横向于地磁场线的离子加热/加速区观测到的等离子体波。特别是，静电，宽带低频噪声是密切相关的横向加速离子。同时电子沉淀的能量范围从几十到几百eV也通常观察到。我们的波形分析表明，静电宽带噪声分为两种类型的噪声：一种是连续的噪声，其上限约为几千赫兹，另一种是间歇脉冲波形扩展超过10 kHz。对连续宽带噪声的主要部分的可能解释是，它们是由沉淀电子（大约几百eV）产生的离子声波，并且该波是离子加热/加速的可能的主要能量源。然而，其他机制有时对于产生宽带噪声可能是重要的。利用在270至10，000公里高度范围内轨道运行的Akebono的长期观测数据集，对连续宽带噪声的空间和时间分布进行了统计研究。阐明了几种统计特征：（1）发生区分布在尖点和沿着极光椭圆分布;（2）发生区向低纬延伸，而地磁活动较高;（3）尖点强度大于夜面;（4）冬季最大，夏季最弱。
Plasma waves observed by the Akebono satellite in the region of ion heating/acceleration transverse to the geomagnetic field line are studied. Especially, electrostatic, broadband low-frequency noise is closely correlated with transversely accelerated ions. Simultaneous electron precipitation in the energy ranges from a few tens to hundreds eV is also usually observed. Our waveform analysis revealed that the electrostatic broadband noise is classified into two types of noise: one is continuous noise with upper cutoff around a few kilohertz, and the other is an intermittent impulsive waveform extended more than 10 kHz. A possible explanation to the dominant part of continuous broadband noise is that they are ion acoustic waves generated by precipitating electrons (approximately a few hundreds eV) and that the wave is the possible main energy source of ion heating/acceleration. The other mechanisms may, however, be sometimes important for generating the broadband noise. Using long-period observation data sets of Akebono, which is orbiting in the altitude range between 270 and 10,000 km, statistical studies on the spatial and temporal distribution of the continuous broadband noise are made. Several kinds of statistical features are clarified: (1) The occurrence region is distributed in the cusp and along the auroral oval, (2) the region is extended toward the lower latitude while the geomagnetic activity is higher, (3) the intensity is larger in the cusp than it is in the nightside, and (4) it is largest in winter and weakest in summer.