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首页> 外文期刊>Annales Geophysicae >Observations of multi-microsecond VHF pulsetrains in energetic intracloud lightning discharges
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Observations of multi-microsecond VHF pulsetrains in energetic intracloud lightning discharges

机译：高能云内闪电放电中多微秒VHF脉冲序列的观测

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摘要

Certain intracloud lightning discharges emit energetic, multi-microsecond pulsetrains of radio noise. Observations of this distinctive form of lightning date from 1980 and have involved both ground-based and satellite-based radio recording systems. The underlying intracloud lightning discharges have been referred to as "Narrow Bipolar Pulses", "Narrow Bipolar Events", and "Compact Intracloud Discharges". An important discriminant for this species of radio emission is that, in the range above ~30MHz, it consists of several microseconds of intense radio noise. When the intracloud emission is viewed from a satellite, each radio pulsetrain is received both from a direct lightning-to-satellite path, and after some delay, from a path via ground. Thus one recording of the radio emission, if of sufficient length, contains the "view" of the intracloud emission from two different angles. One view is of radiation exiting the emitter into the upper hemisphere, the other for radiation exiting into the lower hemisphere. However, the propagation conditions are similar, except that one path includes a ground reflection, while the other does not. One would normally expect a stereoscopic double view of the "same" emission process to provide two almost congruent time series, one delayed from the other, and also differing due to the different propagation effects along the two signal paths, namely, the ground reflection. We present somewhat unexpected results on this matter, using recordings from the FORTE satellite at a passband 118-141 MHz, with simultaneous data at 26-49 MHz. We find that the 118-141 MHz pulsetrain's detailed time-dependence is completely uncor-related between the two views of the process. We examine statistics of the 118-141 MHz pulsetrain's integrated power and show that the power emitted into the lower hemisphere, on average, exceeds the power emitted into the upper hemi- sphere. Finally, we examine statistical measures of the amplitude distribution and show that the 118-141 MHz signal emitted downward is slightly more dominated by discrete, temporally-narrow impulses than is the signal emitted upward.
机译：某些云内闪电放电会发出能量高，数微秒的无线电噪声脉冲序列。这种独特的闪电观测始于1980年，涉及地面和卫星无线电记录系统。底层的云内闪电放电已被称为“窄双极脉冲”，“窄双极事件”和“紧凑型云内放电”。这种无线电发射种类的重要判别是，在〜30MHz以上的范围内，它由几微秒的强烈无线电噪声组成。当从卫星观察云内辐射时，每个无线电脉冲序列都是从直接的闪电到卫星路径以及经过一定延迟后从地面路径接收到的。因此，如果有足够长的无线电发射记录，则从两个不同角度包含云内发射的“视图”。一种观点是辐射从发射器射入上半球，另一种观点是辐射射入下半球。但是，传播条件相似，除了一条路径包括地面反射，而另一条路径没有地面反射。人们通常希望对“相同”发射过程进行立体双重观察，以提供两个几乎一致的时间序列，一个时间序列彼此延迟，并且由于沿两个信号路径的传播效果不同（即地面反射）而有所不同。我们使用来自FORTE卫星在118-141 MHz的通带上的记录以及26-49 MHz的同时数据，就此问题提出了一些出乎意料的结果。我们发现118-141 MHz脉冲序列的详细时间依赖性在该过程的两个视图之间是完全不相关的。我们检查了118-141 MHz脉冲序列的积分功率的统计数据，发现平均而言，发射到下半球的功率超过发射到上半球的功率。最后，我们检查了幅度分布的统计量度，发现向下发射的118-141 MHz信号比向上发射的信号受离散的时间窄脉冲的影响更大。

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