| In this research, some improvements were made to the software and hardware of ourVHF broadband interferometer system. On this basis, a proper observation scheme wasdesigned for some special intracloud lightning events to study the temporal and spatialcharacters of their radiation sources. This dissertation consists of seven chapters.In Chapter1, it gives a brief introduction to the domestic and foreign present situations oflightning locating system and the present studies of some intracloud lightning events such ascompact intracloud discharge events (CIDs), K event, the initial stage of lightning and thepulse trains events in lightning. Finally, the main contents of research are presented.Chapter2introduces the principle and structure of VHF broadband lightninginterferometer in detail. Then, it gives the introductions of the improvements we made to VHFbroadband interferometer and the scheme of experiment.In Chapter3, the distribution of lightning origin height and the speed of lightning initialbreakdown event were studied by using the improved VHF broadband interferometer. For theusing of specifically customized trigger circuit, the improved VHF broadband interferometercould record the lightning radiations almost from the lightning beginning. So, it could give the3D location results of lightning initial stage. In this Chapter,84intracloud lightings and67cloud-to-ground lightings were used for study. Through the statistical analysis, we found thatthe distribution of lightning origin height was bimodal with peaks at5.1km and8.7km abovethe ground level. The origin heights of intracloud flashes were in the range of2.8-11.9km(abg). The origin heights of cloud-to-ground flash were in the range of2.4-9.9km (abg). Thedevelopment speeds of the initial breakdown processes occurred in the height range of4-7kmwere larger than that of the initial breakdown processes occurred above7km. We also foundthat most of the initial breakdown processes of intracloud flash developed upward in verticaldirection and that of the negative cloud-to-ground flash developed downward in verticaldirection.In Chapter4, a high time resolution observation of CIDs obtained by using VHFbroadband interferometers with a scheme customized for CIDs were presented for the firsttime. The characters of fast electric field change waveforms, VHF frequency spectrum, origin heights distribution, channel evolution and the relationships with normal lightning wereanalysed. The amplitudes of-CIDs normalized to100km are tend to larger than that of+CIDs.The VHF radiations of CIDs are more powerful than that of initial breakdown process. Theorigin heights of63CIDs (26–CIDs,37+CIDs) were analyzed.–CIDs mainly occurred above15km (62%), the peak value is about16km.+CIDs mainly occurred below10km (68%), thepeak value is about9km.Analysis of11CIDs showed that the channel of CIDs developedmainly in a vertical direction. The vertical scale of CIDs is in the range of0.4-1.9km. Theaverage apparent speed of CIDs is in the range of0.44-1.01×108m/s, with a mean value of0.65×108m/s. The temporal-spatial evolutions of the radiation sources of the CIDs showed anoscillation pattern, confirming the previous prediction that there is an oscillating current beingreflected at the two ends of the CIDs channel. The estimated speed of the current wave in theCIDs channel was about1.51×108m/s in average. CIDs could be the initial events of normalIC and–CG. There is no evidence that CIDs could be a part of CG.Six IC records which contained K events and could be located in3D were given inChapter5. The relations between K change, VHF radiation of K event and micro second scalepulses occurred in K change waveform were analyzed. The temporal-spatial evolution featuresof K events were also shown in this chapter. The results show that K changes were caused byfast negative breakdowns. The VHF radiations of K events did not occur ahead the K changesand micro second scale pulses obviously. The micro second scale pulses are common events inK change waveforms, they did not only occur in the last phase of K changes but the head of Kchanges. The K events occurred piecemeal in the low level of IC could be the recoil leaderscaused by the forked positive leader. Similarly, the K events developed in retrograde modecould be the recoil leaders caused by the positive leader which developed farther away fromthe origin points. The speeds of9K events were analyzed. The maximum and minimum ofaverage speeds are3.1×107m/s and3.1×106m/s respectively. The mean value is1.6×107m/s.The distribution of the average speeds of K events is similar with dart leaders and differentwith return strokes. Therefore, the K events are more like negative breakdown events thanpositive return stroke.The Chapter6showed the observations of chaotic pulses trains (CPT) and regular pulsestrains (Regular Pulse Bursts) by using VHF broad band interferometer.The spatial and temporal characteristic, power spectral density (PSD) in the30MHz to290MHz band and pulse train structure of10CPT records were analyzed in this chapter. Wefound that the breakdown process associated with CPT were negative and similar with attemptleader or dart leader. The statistical result shows the average progression speeds of10CPTevents are about3.23×106ms-1-1.93×107ms-1with the mean value being1.02×107ms-1. There might be some relationship between the development speed of breakdown events and durationof CPT E-field change waveform. The average PSD of the CPT in the30MHz-290MHz bandis1.8-11.6dB and2.4-12dB larger than that of the step leader and dart leader in the samenegative cloud to ground lightning. The mean value and standard deviation of the pulseseparations in these chaotic pulse trains are5.3-9.0μs and2.7-4.9μs.A regular pulse bursts event which could be located in3D and a regular pulse burstsrecorded in high time resolution mode were analyzed in this chapter. The results show that theradiation sources of regular pulse bursts events have a similar development way with that of Kevents. There is corresponding relationship between VHF radiations and VLF E-field changewaveform of regular pulse bursts events. They showed an intermittent burst developmentmode.At last, Chapter7drew the conclusion on the research and discussed about further study.
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