Low-frequency fluctuations in the magnetosheath near the magnetopause
Low-frequency fluctuations in the magnetosheath near the magnetopause
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DOI：
10.1029/94ja03024
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发表时间：
1995-04
影响因子：
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通讯作者：
R. Denton;S. Gary;Xinlin Li;B. Anderson;J. Labelle;M. Lessard
中科院分区：
文献类型：
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作者：
R. Denton;S. Gary;Xinlin Li;B. Anderson;J. Labelle;M. Lessard
在近乎双麦克斯韦的高β等离子体中，有四种低频模式可以传播。它们是磁声、阿尔芬、离子声学和镜像模式。这份手稿定义了一个基于线性Vlasov理论的程序，通过使用输运比、脉动场和等离子体数量的无量纲比来唯一地识别这些模式。定义了一个单独的参数，即模式偏差，它表征了特定模式的理论输运比与观测比之间的差异。使用主动磁层粒子示踪器探测器/离子释放模块航天器收集的等离子体和磁场数据来计算模式偏差，以确定在磁层顶附近的地球磁鞘中观察到的模式。除了确定最好地描述观察到的波动的模式之外，它还给我们提供了一个衡量结果识别是否唯一的衡量标准。使用时间上接近磁层顶交叉点的17个时间周期，并将我们的研究限制在0.01-0.04赫兹的频率范围内，我们发现在这个频率范围内唯一明确识别的模式是镜面模式。最常见的是观察到准垂直镜模(波矢k大致垂直于背景磁场B0)。在两个事件中发现了准平行镜面模(k∥B0)。
There are four low-frequency modes which may propagate in a high-beta nearly bi-Maxwellian plasma. These are the magnetosonic, Alfven, ion acoustic, and mirror modes. This manuscript defines a procedure based on linear Vlasov theory for the unique identification of these modes by use of transport ratios, dimensionless ratios of the fluctuating field and plasma quantities. A single parameter, the mode deviation, is defined which characterizes the difference between the theoretical transport ratios of a particular mode and the observed ratios. The mode deviation is calculated using the plasma and magnetic field data gathered by the Active Magnetospheric Particle Tracer Explorers/Ion Release Module spacecraft to identify the modes observed in the terrestrial magnetosheath near the magnetopause. As well as determining the mode which best describes the observed fluctuations, it gives us a measure of whether or not the resulting identification is unique. Using 17 time periods temporally close to a magnetopause crossing, and confining our study to the frequency range from 0.01 to 0.04 Hz, we find that the only clearly identified mode in this frequency range is the mirror mode. Most commonly, the quasi-perpendicular mirror mode (with wave vector k roughly perpendicular to the background magnetic field B0) is observed. In two events the quasi-parallel mirror mode (k ∥ B0) was identified.