闪电VLF/VHF信号大容量采集系统及其现场实验

A Bulky Acquisition System of Lightning VLF/VHF Signals and Its Situ Experiments

简要描述了闪电ＶＬＦ／ ＶＨＦ信号大容量采集系统的硬件构成、 软件设计以及现场实验等情况， 并对系统观测到的一次云地闪电和一次云内闪电的过程ＶＬＦ／ＶＨＦ辐射特征进行了个例分析， 初步分析结果揭示了以下一些有趣的新现象： （１）无论云闪还是地闪都以一个间歇性的大双极性脉冲列为启动标志， 并伴随强烈的ＶＨＦ辐射。云闪和地闪初始击穿大脉冲序列波形特征明显不同。（２）地闪的云内放电以及云闪放电都产生一类特征性的ＶＬＦ辐射， 该辐射表现为一个脉冲半宽３～４ μｓ、 出现频率１０５个·ｓ－１的快脉冲列。该过程同时伴随明显的ＶＨＦ辐射。（３）回击主峰期间ＶＨＦ辐射相当微弱。闪电过程中最强的ＶＨＦ辐射起源于以下云内放电过程： （ａ） 云闪和地闪的初始击穿过程； （ｂ） 云内Ｋ过程和ｃ回击主峰后１００～２５０ μｓ期间的云内放电。上述初步分析结果显示了本系统在闪电放电物理研究方面的应用潜力。

In this paper a multi－channel bulky acquiring system is described which is designed to record synchronouslyVLF/VHF signals radiated duringlightning discharges, In summer of 1999,several system－performance tests areconducted in Hefei and a lot of lightning data with VLF radiation as well as associated VHF radiation are obtained. The case studies on one cloud－to－ground and one incloud flash reveal some interesting respect of lightning discharges: (1) Both the ground flash and the incloud flash are initiated by a initial breakdown process which is characterized by a sequence of large bipolar pulses. However, large bipolar pulses in cloud－to－ground flashes occur in quite a different manner from those of incloud flashes. (2) In the stage after the initial breakdown of a cloud flash or the intermission between return strokes of a cloud－to－ground flash, there occurs a typical type of VLF radiation waveform: It consists of a train of narrow pulses with 3－4 μs in half width and a pulse rate of about 105·s-1. Sometimes there also occur several larger bipolar pulses alongthe train.(3)Return strokes produce quite weak VHF radiation and the strongest VHF radiation always originate from in the following incloud discharges: The initial breakdown of both cloud and cloud－to－ground flashes, K events and incloud discharges during 100~250 μs after the return stroke peak. The result indicatesthat the VLF/VHF radiationrecording system is useful and promising for future analysis of lightning discharges.