基于光辐射强度测量的闪电通道电流空间分布和时间演化研究

As the lightning current propagates along the lightning channel, its waveform will change with altitudes and also with time. This spatial distribution and temporal evolution is essential to correctly understand the characteristics of lightning electromagnetic fields radiated by lightning channel. However, it is very difficult to directly measure the current at different altitudes of the lightning channel. Using the rocket-triggered lightning and the natural cloud-to-ground lightning, we are going to acquire the synchronous data of the channel-base current and the channel light intensities, and the characteristics of light intensity in different processes and different altitudes are further analyzed. Moreover, to analyze the influence of the current waveform, the atmospheric pressure, the distance and the observation position on the channel light intensity, the laboratory-generated arcs, produced between the air gap, whose waveshapes of current flow are similar to those of the return strokes, M-components and continuing current of the natural lightning, will be conducted in the high voltage laboratory. The correlation analysis between the current and the light intensity of the channel will be carried out via the comprehensive results of the natural observation and laboratory experiments. Furthermore, the method to reconstruct the lightning current through the corresponding light signal can be established. Based on the light intensity variation measured in the lightning channel, and on the established correlation between current and light intensity, we can obtain the spatial distribution and temporal evolution of lightning current along the channel, from which, the return stroke model calculating and interpreting the radiated electromagnetic fields will be developed. This research will enhance the understanding of the current spatial development in different processes of lightning, and promote the development of lightning protection technology.

雷电流沿闪电通道的时空分布是正确认识雷电电磁辐射特性的基础，现有技术手段尚不能对闪电通道各高度的电流进行直接测量。本项目针对人工触发闪电及自然下行地闪，获取闪电通道底部电流和通道光辐射强度同步观测资料，分析闪电不同过程、不同通道高度光辐射强度特征。同时，在高电压实验室内针对短空气间隙放电形成电弧，产生类似自然雷电回击、M分量、连续电流等不同阶段波形特征的冲击电流，分析电流波形变化、气压变化、观测距离、观测方位等对电弧通道光辐射强度影响。综合自然观测与实验室模拟试验结果，研究通道电流与光辐射强度关系，实现雷电电流波形的光学反演。基于实测闪电通道光辐射强度变化，揭示闪电通道电流空间分布和时间演化特征，并进一步发展回击模型，计算并阐释不同距离的地表电磁场变化观测事实。本研究将提升我们在闪电不同过程中电流空间发展特征的科学认识，为雷电防护设计和技术发展提供科学理论与关键支撑。

本项目针对人工触发闪电及自然下行地闪，获取闪电通道底部电流和通道光辐射强度同步观测资料，对比了13次触发闪电（传统火箭-导线人工引雷）通道底部电流和对应光辐射强度同步数据，共包括104个初始连续电流脉冲（Initial Continuous Current Pulses, ICC脉冲）、67次回击和148个M分量，各脉冲电流分量的峰值范围为70 A~38.09 kA，10-90%上升时间0.16 us~14.82 ms，半峰宽度5.62 us~26.14 ms。开展了闪电通道电流与光辐射强度关系研究。在高压实验室，模拟产生了与自然界雷电流分量波形特征类似的电弧通道电流，搭建了放电通道电流与光辐射强度同步观测平台，探究了电弧通道光辐射强度测量的影响因素，分析了实验室电弧通道放电电流与光强度的关系，对比了实验室电弧放电与自然界雷电放电之间的内在联系及差异。利用通道光强度波形反演得到了模拟雷电流全过程的波形和电流转移电荷量，所得结果与实测电流波形及转移电荷量对比显示出了较高的拟合度，其中反演电荷量的相对误差平均值不超过7%。基于实测闪电通道光辐射强度变化，揭示了闪电通道电流空间分布和时间演化特征，并进一步发展回击模型，计算并阐释不同距离的地表电磁场变化观测事实。结合最新闪电连接过程与发展的观测结果，提出了计及闪电连接高度的回击发展模型，并开展了回击电磁场波形特征研究。基于最新闪电通道底部回击的衰变观测结果，提出相应通道衰变回击模型，分析了回击速度对电流及其引发电场的影响，发现考虑回击电流发展速度快于光强速度以及考虑通道底部回击电流衰变时，计算得到的地面电场波形与实测的电场波形一致，研究结果阐释了传统模型与最新实测通道底部回击衰变不符但电场峰值计算结果仍与实测结果吻合的原因。本研究将提升我们在闪电不同过程中电流空间发展特征的科学认识，为雷电防护设计和技术发展提供科学理论与关键支撑。