Ground based observations of low frequency auroral hiss fine structure
Ground based observations of low frequency auroral hiss fine structure
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低频极光嘶嘶精细结构的地面观测
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
J. Labelle
中科院分区：
文献类型：
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作者：
S. Ye;J. Labelle
[1] 2004 年在南极站运行的电场波形接收器记录了许多低频 (LF) 极光嘶嘶声事件，揭示了按发生率排列分为三类的精细结构：斑片/连续特征，具有宽带宽（100 kHz）和缓慢的时间变化（1 秒或更长）；垂直/脉冲特征，具有宽带宽（100s of kHz）和短持续时间（<1 s）；以及离散特征，其具有窄带宽（数百赫兹到几赫兹）和一系列持续时间。我们研究了离散特征的两种可能的生成机制。首先，它们可能源自窄带朗缪尔波的模式转换，其中离散特征频率与极光电离层中的等离子体频率相匹配。事实上，如果朗缪尔波的模式转换解释了这些观测结果中的每一个，那么在最近的探空火箭实验中观察到的窄带离散哨声模式的估计源功率和在南极站观测到的离散特征的估计源功率是按照预期的方式排序的。其次，Sonwalkar 和 Harikumar (2000) 提出，极光嘶嘶声必须在米级密度不规则性上进行模式转换，才能到达地面；我们提出，如果米级不规则性是高度单色的，则到达地面的模式转换哨声模式将由窄带离散特征组成。极光电离层模型中的射线追踪研究表明，10-100 m 不规则性的散射可以解释南极站观测到的 LF 极光嘶嘶声中的精细结构。
[1] An electric field waveform receiver, operated at South Pole Station during 2004, recorded numerous low-frequency (LF) auroral hiss events, revealing fine structures which fall into three categories, in order of occurrence rate: patchy/continuous features, which have wide bandwidth (100s of kHz) and slow time variation (of order 1 s or longer); vertical/impulsive features, which have wide bandwidth (100s of kHz) and short duration (≪1 s); and discrete features, which have narrow bandwidths (100s of Hz to a few kHz) and a range of durations. We investigate two possible generation mechanisms for the discrete features. First, they may arise from mode conversion of narrowband Langmuir waves generated where the discrete feature frequency matches the plasma frequency in the auroral ionosphere. In fact, the estimated source power of narrowband discrete whistler modes observed in recent sounding rocket experiments and the estimated source power of the discrete features observed at South Pole station are ordered in the manner expected if mode conversion of Langmuir waves accounts for each of these observations. Second, Sonwalkar and Harikumar (2000) propose that auroral hiss must mode convert on meter-scale density irregularities in order to gain access to ground level; we put forth that if the meter-scale irregularities are highly monochromatic, the resulting mode-converted whistler modes that reach the ground will be composed of narrow-band discrete features. Ray-tracing studies in a model auroral ionosphere suggest that scattering from 10–100 m irregularities could account for the fine structures in the LF auroral hiss observed at South Pole Station.