Identification of low‐frequency magnetosheath waves
Identification of low‐frequency magnetosheath waves
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DOI：
10.1029/98ja02196
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发表时间：
1998-10
影响因子：
--
通讯作者：
R. Denton;M. Lessard;J. Labelle;S. Gary
中科院分区：
文献类型：
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作者：
R. Denton;M. Lessard;J. Labelle;S. Gary
四个低频模式可以在高β，近双麦克斯韦等离子体中传播，磁声，Alfv {acute e} n，离子声和镜像模式。本研究使用的程序的基础上的线性弗拉索夫理论的识别这些模式的传输比，无量纲比的波动场和等离子体量。一个单一的参数，模式偏差，计算其特征之间的差异，一个特定的模式和观察到的比率的理论传输比。除了确定最能描述观测到的波动的模式外，它还为我们提供了一个衡量结果是否唯一的标准。不幸的是，由于这里讨论的问题，唯一标识并不总是可能的。一个问题是平行相位比（与密度和平行磁波动之间的相位角有关）通常没有很好地定义。使用等离子体和磁场数据收集的主动磁层粒子示踪剂探测器/离子释放模块航天器，我们计算的模式偏差，并确定在磁鞘中观察到的模式。准垂直（与波矢量在一个大角度的背景磁场）镜像模式被清楚地确定在内（接近磁层顶）和中间磁鞘。在内磁鞘中可以观察到准平行镜模式，但这种识别并不确定。在外磁鞘（弓激波附近）的一个事件中观察到的Alfv {acute e} n-样模式，并可能观察到在其他两个。{copyright} 1998美国地球物理联合会« less
Four low-frequency modes may propagate in a high-beta, nearly bi-Maxwellian plasma, the magnetosonic, Alfv{acute e}n, ion acoustic, and mirror modes. This study uses a procedure based on linear Vlasov theory for the 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 calculated which characterizes the difference between the theoretical transport ratios of a particular mode and the observed ratios. As well as determining the mode that best describes the observed fluctuations, it gives us a measure of whether or not the resulting identification is unique. Unfortunately, a unique identification is not always possible because of problems discussed herein. One problem is that the parallel phase ratio (related to the phase angle between density and parallel magnetic fluctuations) is often not well defined. Using the plasma and magnetic field data gathered by the Active Magnetospheric Particle Tracer Explorers/Ion Release Module spacecraft, we calculate the mode deviations and identify the modes observed in the magnetosheath. The quasi-perpendicular (with wave vector at a large angle to the background magnetic field) mirror mode is clearly identified in the inner (close to the magnetopause) and middle magnetosheath. The quasi-parallelmore » mirror mode may be observed in the inner magnetosheath, but that identification is not certain. Alfv{acute e}n-like modes are observed for one event in the outer magnetosheath (near the bow shock) and are probably observed in two others. {copyright} 1998 American Geophysical Union« less