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Very low frequency radio signatures of transient luminous events above thunderstorms.

机译：雷暴上方瞬时发光事件的极低频无线电信号。

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摘要

Lightning discharges emit intense optical and acoustic energy, in the form of lightning and thunder, respectively, but a large amount of energy is emitted as radio-frequency electromagnetic pulses (EMP). These pulses can be detected thousands of kilometers away, thanks to efficient propagation in the waveguide formed by the conducting Earth and the overlying ionosphere. In addition, intense discharges interact with the overlying ionosphere at 80-100 km altitude. The EMP-ionosphere interaction is directly observed in one manifestation as the bright transient optical emissions known as "elves", but in addition, the interaction can directly modify the free electron density in the nighttime lower ionosphere.;Modifications of the ionospheric electron density can be detected via subionospheric Very Low Frequency (VLF) remote sensing. In this method, coherent signals from powerful VLF transmitters, built for submarine communication and operated by the Navy, are monitored and their amplitude and phase are tracked in time. The variations of these signais are used to sense ionospheric modifications through rapid changes in the received amplitude and/or phase when the transmitted signal propagates through an ionospheric perturbation. When these perturbations are caused by lightning, they are known as "Early VLF" perturbations, due to the negligible delay between the lightning discharge and the appearance of the VLF signal change, whereas lightning-induced electron precipitation (LEP) events have a delay of 1--2 seconds.;In this work, correlations between VLF signatures and optical events are used to show that these Early VLF events may be the signature of ionospheric modification by in-cloud (IC) lightning discharges. While the more impressive cloud-to-ground (CG) lightning discharges are more commonly observed and better understood, they are outnumbered in occurrence 3:1 by IC discharges, whose effects may be relatively stronger in the overlying ionosphere. We use a 3D time-domain model of the lightning EMP-ionosphere interaction to calculate expected ionospheric density changes from IC discharges. We find that bursts of IC-EMPs can significantly modify the lower ionosphere, with both increases and decreases in electron density. We then use a frequency-domain model of the VLF transmitter signal propagation in the Earth-ionosphere waveguide to a receiver to show that these density changes are consistent with measurements. Our results demonstrate that these Early VLF events, which are ubiquitous in VLF data, are signatures of the effects of in-cloud lightning, and that they can be used to quantify the effects of IC lightning on the ionosphere during an intense thunderstorm.
机译：雷电放电分别以雷电和雷声的形式发出强烈的光能和声能，但是大量的能量会作为射频电磁脉冲（EMP）发出。由于在导电地球和上方电离层形成的波导中有效传播，因此可以在数千公里外检测到这些脉冲。此外，在80-100 km的高度，强烈的放电会与上方的电离层相互作用。 EMP-电离层相互作用直接表现为一种明亮的瞬态光发射，称为“精灵”，但除此之外，这种相互作用还可以直接改变夜间较低电离层中的自由电子密度。通过亚电离层甚低频（VLF）遥感进行检测。在这种方法中，来自强大的VLF发射机的相干信号被监测，并由海军操作，该相干信号是为海底通信而建造的，并由海军操作。当发射信号通过电离层扰动传播时，这些信号的变化用于通过接收振幅和/或相位的快速变化来感应电离层的变化。当这些扰动是由雷电引起的时，由于闪电放电和VLF信号变化的出现之间的延迟可以忽略不计，因此它们被称为“早期VLF”扰动，而雷电引起的电子沉淀（LEP）事件的延迟为1--2秒；在这项工作中，VLF信号和光学事件之间的相关性用于显示这些早期VLF事件可能是通过云中（IC）闪电放电对电离层进行修改的信号。虽然更令人印象深刻的云对地（CG）闪电放电得到了更普遍的观察和更好的理解，但在3：1的情况下，IC放电的放电次数却远远超过了闪电放电，其作用在上方的电离层中可能相对较强。我们使用闪电EMP-电离层相互作用的3D时域模型来计算IC放电的预期电离层密度变化。我们发现，IC-EMP的爆发可以显着改变下部电离层，同时电子密度增加和减少。然后，我们使用VLF发射机信号在地球电离层波导中传播到接收机的频域模型，以表明这些密度变化与测量结果一致。我们的结果表明，在VLF数据中无处不在的这些早期VLF事件是云内闪电影响的特征，并且它们可用于量化强雷暴期间IC闪电对电离层的影响。

著录项

  • 作者

    Marshall, Robert Andrew.;

  • 作者单位

    Stanford University.;

  • 授予单位 Stanford University.;
  • 学科 Engineering Electronics and Electrical.;Atmospheric Sciences.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 169 p.
  • 总页数 169
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 无线电电子学、电信技术;
  • 关键词

  • 入库时间 2022-08-17 11:38:28

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