Modeling the properties of plasmaspheric hiss: 1. Dependence on chorus wave emission
Modeling the properties of plasmaspheric hiss: 1. Dependence on chorus wave emission
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DOI：
10.1029/2011ja017201
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发表时间：
2012-05
影响因子：
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通讯作者：
Lunjin Chen;J. Bortnik;Wen Li;R. Thorne;R. Horne
中科院分区：
文献类型：
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作者：
Lunjin Chen;J. Bortnik;Wen Li;R. Thorne;R. Horne
[1]越来越多的证据表明，等离子体层嘶嘶声是由一部分合唱波的演化形成的，这些合唱波在等离子体层中被激发并传播到等离子体层中。通过比较THEMIS数据1993年以来活动时段早晨时段两种辐射的统计空间分布，发现两种辐射的峰值强度相当，但空间分布不同。我们提出了一个建模研究的嘶嘶声频谱，射线追踪的基础上，通过观察合唱源区作为一个输入的磁层，其中包含冷和超热电子。模拟结果表明，我们能够再现典型嘶嘶声的主要特征，包括频谱、波法线角和空间分布。然而，模拟的嘶嘶声强度比观察到的强度弱（小105 dB），这表明等离子体内部存在一些适度的内部放大。的嘶嘶声的空间分布，波法线角分布和频率分布的源合唱的变化的响应进行了检查。我们发现，大部分嘶嘶声的形成是由于等离子体层顶103 RE内的一小部分合唱发射，其波的法线方向指向地球，与地球成30°-60°角，频率范围为0.1- 0.3fce。如果使合唱功率增加到更接近等离子体层顶，嘶嘶声的强度和峰值频率也会增加，这大致模拟了活跃的地磁条件。合唱源分布的变化不会显著影响嘘声的波法线角分布和频率分布，但会影响所产生的嘘声的绝对强度。
[1] There is increasing evidence that plasmaspheric hiss is formed by the evolution of a portion of chorus waves that are excited in the plasmatrough and propagate into the plasmasphere. Comparison between the statistical spatial distributions of these two emissions in the morning sector during active times from THEMIS over ∼3 years shows that the two emissions have comparable peak intensities but are distinct in their spatial distributions. We present a modeling study of the hiss spectrum, based on ray tracing, by taking the observed chorus source region as an input in the magnetosphere, which contains cold and suprathermal electrons. Our modeling results show that we are able to reproduce the main features of typical hiss, including the frequency spectrum, wave normal angle and spatial distribution. However, the simulated hiss intensity is weaker (∼15 dB less) than the observed intensity, which suggests some modest internal amplification inside the plasmasphere. The responses of hiss to variations in the spatial distribution, wave normal angle distribution and frequency distribution of the source chorus are examined. We find that the majority of hiss formation is due to a small portion of chorus emission originating within ∼3 RE from the plasmapause, with wave normal directions pointing toward the Earth at an angle of 30°–60°, and over a frequency range of 0.1–0.3 fce. If the chorus power is made to increase closer to the plasmapause, the hiss intensity and the peak frequency also increases, which roughly mimics active geomagnetic conditions. Variations of the chorus source distribution do not significantly affect the wave normal angle distribution and frequency distribution of hiss, but does impact the absolute intensity of the resulting hiss.