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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >An explanation of ground observations of auroral hiss: Role of density depletions and meter-scale irregularities
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An explanation of ground observations of auroral hiss: Role of density depletions and meter-scale irregularities

机译：极光嘶嘶声地面观测的解释：密度耗竭和米级不规则的作用

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Auroral hiss is one of the most intense whistler mode plasma wave phenomena observed both on the ground at high latitudes and on spacecraft in the auroral zone. Propagation of auroral hiss from its source region to the ground is poorly understood. The standard whistler mode propagation in a smooth magnetosphere predicts that auroral hiss generated at large wave-normal angles along the auroral field lines by Cerenkov resonance cannot penetrate to the ground. We show that the presence of density depletions along the field lines in the auroral zone and meter-scale density irregularities at altitudes < 5000 km at high latitude permits the auroral hiss propagation to the ground. In our mechanism the auroral hiss generated at high altitudes (> 5000 - 20,000 km) propagates to lower altitudes (< 3000 - 5000 km) in two modes: (1) a ducted mode guided by field-aligned density depletions and (2) a nonducted mode. The hiss with large wave-normal angle arriving at < 5000 km altitude is scattered by meter-scale irregularities, and about 0.1% to 10% of the scattered hiss has small wave-normal angles which can penetrate to the ground. Our mechanism explains the following features of auroral hiss observed on the ground: (1) the characteristic spectra of continuous and impulsive auroral hiss, (2) the upper and lower frequency cutoffs, (3) the dispersion of impulsive auroral hiss, (4) the location of ionospheric exit points of auroral hiss with respect to visible aurora, and (5) the 2-5 order of magnitude intensity decrease of auroral hiss observed on the ground relative to that observed on spacecraft. Based on the model presented here, we provide methods to infer parameters of density depletions and intensity of lower hybrid waves stimulated by auroral kiss from the ground measurements of auroral hiss together with optical and radar measurements. [References: 68]
机译：极光嘶嘶声是在高纬度地面和极光带中的航天器上观察到的最强烈的啸叫模式等离子波现象之一。极光嘶嘶声从其源区域到地面的传播知之甚少。标准的惠斯勒模式在光滑磁层中的传播预测，由切伦科夫共振沿着极光场线以大波法向角生成的极光嘶嘶声无法穿透地面。我们表明，在高纬度<5000 km的高度上，极光带中沿场线的密度耗尽和米级密度不规则性允许极光嘶嘶声传播到地面。在我们的机制中，高海拔（> 5000-20,000 km）产生的极光嘶嘶声以两种模式传播到低海拔（<3000-5000 km）：（1）场定向密度耗尽引导的管道模式，以及（2）a非导通模式。高度小于5000 km的波法向角发出的嘶嘶声被米级的不规则散射所散射，大约有0.1％到10％的嘶嘶声具有小的波法向角，可以穿透到地面。我们的机制解释了在地面上观测到的极光嘶嘶声的以下特征：（1）连续和冲动极光嘶嘶声的特征谱;（2）上限和下限频率截止;（3）冲动极光嘶嘶声的频散;（4）相对于可见极光的极光嘶嘶电离层出口点的位置，以及（5）在地面上观测到的极光嘶嘶声相对于航天器观测到的强度降低了2-5个数量级。基于此处呈现的模型，我们提供了从极光嘶嘶声的地面测量以及光学和雷达测量值推断极光之吻激发的较低杂波的密度消耗和强度参数的方法。 [参考：68]

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