【作者】 刘恒毅；

【导师】 董万胜；

【作者基本信息】 中国气象科学研究院 ， 气象学， 2012， 博士

【摘要】 本研究的主要目的是在对原有干涉仪的软件、硬件进行改进的基础上，制定合理的观测方案对一些较为特殊的云内闪电放电事件进行定位观测，对其辐射源时空演变特征进行研究。全文共分七章。第一章首先简要介绍了闪电探测系统分类和国内外现状，然后对致密云闪1（CIDs，Compact Intracloud Discharges）、K过程、闪电初始过程以及闪电中的脉冲簇事件这几类有代表意义的闪电云内过程的特点和国内外研究现状进行了介绍。最后阐述了本文的主要研究内容。第二章首先对宽带干涉仪系统的原理和硬件集成方案进行了较为详细的介绍，然后说明了对宽带干涉仪硬件以及定位处理软件作出的改进，最后对双站观测布局以及观测方案的设计进行了介绍。第三章主要利用宽带干涉仪系统对云闪、地闪的起始高度分布特征以及发展速度特征进行了较为详细的观测和分析。改进后的宽带干涉仪系统基本上可以从闪电的起始时刻开始对闪电辐射源进行三维定位，这使得该系统能够对云闪、地闪起始过程的时空发展特征进行研究。文中选择了可从起始阶段进行三维定位的云闪84例、地闪67例。利用这些数据，文章对闪电起始位置的分布特征，以及闪电初始阶段击穿过程的时空发展特征进行了研究。通过统计得出，云闪起始高度（距地面）分布在2.8-11.9km，地闪起始高度分布在2.4-9.9km，总闪起始高度分布会在5.1km和8.7km附近存在两个分布峰值。发生在4-7km范围的闪电初始击穿速度整体上要大于7km以上高度范围发生闪电的初始击穿速度。通过对闪电起始阶段击穿过程发展方向的统计得出，绝大多数云闪的起始阶段在垂直方向上都是向上方发展的，而绝大多数负地闪的起始阶段在垂直方向都是向下发展的。第四章使用专门设计的实验方案对一类特殊的闪电放电事件“致密云闪”（CIDs）进行了高时间分辨率观测，给出了CIDs事件的电场波形时域特征、甚高频辐射频谱特征、发生高度分布特征、通道发展特征以及与其他类型闪电的关系。结果表明-CIDs电场变化波形标准化幅度的集中分布值要大于+CIDs事件标准化幅度的集中分布值，CIDs事件在VHF频段的辐射强于云内初始击穿产生的辐射。对63次CIDs事件发生高度的统计结果表明，-CIDs主要分布在15km以上（约占62%）峰值位于16km，+CIDs主要分布在10km以下（约占68%）峰值位于9km高度。对11次CIDs事件放电通道特征的统计结果表明，致密云闪的垂直放电尺度在0.4-1.9km之间，平均值0.91km，放电通道垂直发展平均速度在0.44-1.01×108m/s之间，平均值为0.65×108m/s，通道电流传输速度在0.56-2.55×108m/s之间，平均值为1.51×108m/s。放电通道虽然倾斜但主要表现为垂直发展，CIDs通道电流的传输存在振荡现象，电流可能在通道两端发生反射。文中还对与CIDs事件存在联系的普通云闪、负地闪个例进行了分析，结果表明CIDs事件可作为普通云闪地闪的起始事件，但没有证据表明CIDs会做为地闪过程的一部分出现。第五章首先给出了6次含有K过程云闪的三维定位结果，然后对这些云闪K过程的K变化、VHF辐射、微秒尺度脉冲三个特征间的关系进行了分析，最后分析了这些K过程的时空发展特征。结果表明，K变化都是由快速发展的负极性击穿引起的，其VHF辐射与K变化和微秒尺度脉冲活动相比没有明显的超前特征。微秒尺度脉冲在K变化中确实是普遍存在的，而且不仅仅出现在K变化后期。发生位置分散在云闪起始区域下方多个方向的K事件可能是正先导多个分叉路径上发生的反冲先导。类似的，表现出的倒退式发展的一系列K事件可能是发展较远的一条正先导引起的反冲先导。9次K事件的平均发展速度最大值为3.1×107m/s，最小值为3.1×106m/s，平均值为1.6×107m/s，其发展速度分布范围与直窜先导类似，但小于回击速度。因此认为K事件是快速发展的负极性击穿与正极性回击不同。第六章分为两个部分，利用宽带干涉仪对闪电中的不规则脉冲簇事件（CPT）和规则脉冲簇事件（Regular Pulse Bursts）进行了定位观测。文中首先对10次不规则脉冲簇事件的三维定位结果进行了分析，给出了CPT辐射源的时空分布特征，计算了辐射源定位结果的发展速度，还给出了CPT事件的时域波形特征和频谱特征。结果表明，不规则脉冲簇事件的击穿过程为负极性击穿，发展特征与直窜先导或企图先导没有明显区别；它们的平均发展速度在3.23×106m/s到1.93×107m/s之间，平均值为1.02×107m/s；平均速度最快的4次CPT事件，是脉冲簇持续时间最短的4次；10次CPT事件在30MHz至290MHz频段的功率谱密度均值比同次地闪中的梯级先导强1.8~11.6dB，比同次地闪中的直窜先导高出2.4~12dB，它们的快电场脉冲间隔的平均值和标准差的统计结果分别为5.3~9.0μs和2.7~4.9μs。第二部分对1次规则脉冲簇的三维定位结果以及1次规则脉冲簇的高时间分辨率二维定位结果进行了分析。结果表明，发生在云闪末期的规则脉冲簇事件与K事件具有相似的发展速度和发展方式。规则脉冲簇事件的VHF辐射信号与快电场脉冲有很好的时间对应性，两者共同呈现出间歇性暴发的发展特征。第七章对全文中的主要研究结果进行总结讨论，并就文中的不足以及今后发展方向进行了讨论。更多还原

【Abstract】 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.更多还原