Parametric decay of beam-driven Langmuir wave and enhanced ion-acoustic fluctuations in the ionosphere: a weak turbulence approach
Parametric decay of beam-driven Langmuir wave and enhanced ion-acoustic fluctuations in the ionosphere: a weak turbulence approach
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光束驱动朗缪尔波的参数衰减和电离层中增强的离子声涨落：弱湍流方法
DOI：
10.1007/s00585-999-1172-4
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发表时间：
1999
影响因子：
1.9
通讯作者：
F. Forme
中科院分区：
文献类型：
--
作者：
F. Forme
我们提出了一个描述束流产生的朗缪尔波在电离层上方衰变为离子声波的模型。这种计算是在弱湍流近似的框架内进行的。我们研究了VHF非相干散射雷达所看到的这一过程的光谱特征。非相干散射(IS)谱由两个极大值K雷达和−K雷达组成，分别位于左右两个离子谱线。结果表明，在合理的束流参数下，束流产生的朗缪尔波的参数衰减可以同时增强右束、左束或两束离子线。谱的形状可以在约0.1到1 S的时间尺度上发生很大的变化，还研究了束流参数和电离层参数的作用。对于给定的束流数密度，束流能量或背景密度对触发左或右离子线很重要。束的大能散或低的电子碰撞频率可以解释同时观测到左右两条离子线的原因。电子碰撞频率的重要性可以解释非相干散射雷达观测到的相干回波的高度分布。
We present a model that describes the decay of beam generated Langmuir waves into ion-acoustic waves in the topside ionosphere. This calculation is done within the frame of the weak turbulence approximation. We study the spectral signature of such a process as seen by a VHF incoherent scatter radar. An incoherent scatter (IS) spectrum is characterized by two maxima at kradar and −kradar, the right and left ion lines respectively. It is shown that, for reasonable beam parameters, the parametric decay of beam-generated Langmuir waves can enhance either the right, the left or both ion lines simultaneously. The shape of the spectrum can change drastically on time scale of about 0.1 to 1 s. The role of the beam parameter as well as the ionospheric parameters is also investigated. For a given beam number density, the beam energy or the background density are important to trigger either the left or the right ion line. A large energy spread of the beam or low electron collision frequencies can explain the simultaneous observations of the left and the right ion line. The importance of the electron collision frequency can explain the altitude distribution of the coherent echoes observed by incoherent scatter radars.