Understanding the Radio Spectrum of Thunderstorm Narrow Bipolar Events
Understanding the Radio Spectrum of Thunderstorm Narrow Bipolar Events
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DOI：
10.1029/2019jd030439
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发表时间：
2019-09-27
影响因子：
4.4
通讯作者：
Wilson, Jennifer G.
中科院分区：
文献类型：
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作者：
Liu, Ningyu;Dwyer, Joseph R.;Wilson, Jennifer G.
本文报告了一项研究，以了解雷暴窄双极事件（NBE）或紧凑的云内放电，这是高频（HF）和甚高频（VHF）电磁辐射的强大来源的无线电频谱。获得了10 kHz ~ 100 MHz范围内三个NBE的射电谱，其中一个是由快正击穿引起的，两个是由快负击穿引起的。结果表明，快击穿的两个极性具有相似的频谱，在HF和VHF波段具有相对平坦的频谱。在甚低频和HF波段的能谱密度比为（0.9-5）× 10（5）。我们开发了一个统计建模方法来调查，如果一个系统的拖缆可以解释快速击穿的主要特点。假设单个拖缆的电流矩峰值和电荷矩变化分别在5-10 A·m和5-20 μ C·m范围内变化，模拟结果表明，10（7）-10（8）个拖缆的系统可以再现快速击穿的电流矩、电荷转移和无线电频谱。快速击穿产生强HF/VHF发射所需的纳秒时间尺度上的快速电流变化由指数加速和扩展流光提供。因此，我们的研究支持的假设，快速击穿是一个系统的流光。最后，建议有关未来的流光模拟和NBE测量，以进一步发展我们的理解NBE和闪电启动。
This paper reports a study to understand the radio spectrum of thunderstorm narrow bipolar events (NBEs) or compact intracloud discharges, which are powerful sources of high-frequency (HF) and very high frequency (VHF) electromagnetic radiation. The radio spectra from 10 kHz to about 100 MHz are obtained for three NBEs, including one caused by fast positive breakdown and two by fast negative breakdown. The results indicate that the two polarities of fast breakdown have similar spectra, with a relatively flat spectrum in the HF and VHF band. The ratio of energy spectral densities in the very low frequency and HF bands is (0.9-5) x 10(5). We develop a statistical modeling approach to investigate if a system of streamers can explain the main features of fast breakdown. Assuming that the current moment peak and charge moment change of individual streamers vary in the ranges of 5-10 A-m and 5-20 mu C-m, respectively, the modeling results indicate that a system of 10(7)-10(8) streamers can reproduce the current moment, charge transfer, and radio spectrum of fast breakdown. The rapid current variation on a time scale of nanoseconds required for fast breakdown to produce strong HF/VHF emissions is provided by exponentially accelerating and expanding streamers. Our study therefore supports the hypothesis that fast breakdown is a system of streamers. Finally, suggestions are given regarding future streamer simulations and NBE measurements in order to further develop our understanding of NBEs and lightning initiation.