地闪先导-回击过程单站多参量同步观测研究

The damage caused by the direct and indirect effect by leader-return stroke process (L-Rs) in cloud-to-ground (CG) lightning is more and more serious. However, insight into L-Rs, especially on the temporal-spatial evolution of electrical parameters in the channel (such as charge density distribution, current waveforms aloft) is apparently hindered by lack of comprehensive observational data and the corresponding data-based inverse model. This project, based on the innovation in comprehensive observation technology, is intended to establish the methodology to retrieve time-resolved electrical parameters distributed along the L-Rs channels, and further reveal the physical mechanism involved in the L-Rs. Specifically, a single-station-based comprehensive observational system would be constructed, which could take the advantages of thunder localization, high-speed optical observation, VHF imaging to provide the three-dimensional spatial and temporal evolution of L-Rs and the synchronized broadband electromagnetic field waveforms. By virtue of this system, a set of high-quality observational data would be accumulated with observation experiments. On the other hand, in order to realize the goal of the 'remote measurement' of the channel parameters, the inverse model based on the transient electromagnetic theory and the optimization principle would be devised and then applied to the observational data. Model results are validated and used to further investigate the relationship between the leader and return stroke process. The physical characteristic and development pattern of the L-Rs determined by this work would provide the ground truths and lay the base for the further research on lightning protection and physics.

地闪先导-回击过程产生的直接和间接效应对人类的生产生活造成的危害日益凸现。由于缺少全面的观测资料和准确的反演模型，对于地闪先导-回击过程仍缺乏深入的理解，特别是对通道电参数（如电荷密度、电流波形）时空演变的认识尚不清晰。本项目拟以综合观测试验技术创新为牵引，重点研究利用观测事实结合模式反演先导-回击通道电参数的方法，深入揭示先导-回击发展的物理过程，准确评估其致灾机制。具体而言，利用单站将闪电声、光、电磁多参量探测手段有机结合，实现单站对闪电先导-回击过程三维时空演变过程和宽带电磁场的同步探测，进而获取和积累一批高质量的观测资料，解决制约闪电先导-回击发展模式和物理机制理解的瓶颈问题；基于同步综合观测资料，依据瞬态电磁场理论和最优化原理，构建反演模型，实现对地闪先导-回击通道电参数时空演变的"遥测"，揭示先导-回击过程的耦合关系和发展特征，为雷电防护和物理机制研究奠定基础。

本项目围绕地闪先导-回击过程的单站探测和建模问题，主要在以下三个方面开展了研究：（1）闪电单站综合探测理论与技术。解决了城市强电磁干扰下宽带VHF定位和可重复触发雷声记录和定位等技术问题；利用高速光电二极管阵列及高速调理电路设计，构建了一套8通道高速光-电阵列探测系统以及一套高速标定光源，试验表明系统的响应上升时间优于40ns，并且能够分辨瞬态发光通道的发展过程；通过系统辨识的方法设计了闪电电场变化传感器的时域标定方案，提出采用快、慢两种激励源联合获取系统传递函数的方法，针对电场时变率标定问题，提出“微分法”和“积分法”两种标定方案。（2）闪电单站综合探测和地闪先导过程分析。利用以上探测技术在南京及苏北开展闪电单站综合探测试验，获取了大量综合探测资料，利用准三维定位、电场和电场时变率等同步观测资料，对闪电先导的发展速度、VHF和电场辐射特性进行了分类分析，研究表明，上述观测特征与先导通道电离特性密切关联，特别是针对“无序先导”的形成机制进行了深入探讨，指出电场无序振荡特征只是由于直窜先导进入电导率较差的通道后产生的辐射增强现象。（3）地闪先导-回击过程的建模分析。基于流注-先导转化理论，在COMSOL中建立了包含上行迎面正先导在内的负极性三维先导发展模型，评估了不同建筑水平尺度与建筑垂直高度等参数对闪击距离的影响；利用时域有限差分法，对有限电导率地面上倾斜先导-回击通道电磁辐射问题进行了建模与仿真，定量评估了有限大地电导率、通道倾斜、有耗传播对先导-回击辐射场的影响，并与观测数据进行了对比。.通过本项目的研究，拓宽了闪电观测手段，加深了对闪电先导-回击过程的认识，可为雷电预警、防护与雷电电磁环境评估提供重要的技术支撑。