Development of Efficient Three-Dimensional Models of Lightning Discharges

一项为期五年的工作将发展一套有效的三维闪电模型，并应用这些模型从理论上研究一系列与雷暴电气化和不同形式闪电放电发展有关的突出科学问题。本研究将寻求回答的突出问题是：(1)基于分形方法的闪电模型能否提供不同类型闪电放电的现实描述？这些模型在描述整个闪电-雷云电力系统的电荷、电位和电场方面有什么具体的局限性？是否可以对这些模型进行修改，以提供一个计算效率高的参数化正负雷锋的飘带区？(2)随气压变化，空气中从流线到领先者的有效时间尺度是什么？在什么高度范围和其他相关的物理条件下，在地球大气中不可能形成先导通道？(3)雷云电荷的具体配置是什么，使得雷云顶部的闪电先导向上延伸，导致最近发现的蓝色射流和巨大射流现象？正、负闪电引线飘带区的压力比例分形模型是否能够描述实验观察到的蓝色喷流和巨大喷流的特征？针对回答这些问题的具体活动将包括基于闪电建模的概率方法的三维数值模型的发展。这些模型将考虑到目前在三维计算领域有效表示先导树的最佳知识，并将包括开放边界条件、在模拟过程中任何点保留先导树的完全电荷中性以及具有有限电阻率的闪电通道的准确建模等特征。模型的开发将协同补充新墨西哥矿业和技术研究所现有的基于观测的研究工作，这些研究旨在调查雷暴的电结构，包括反极性电结构的研究，闪电起始的研究，以及不同和新发现的闪电放电类型的研究。拟议活动的更广泛影响包括学生培训和教育，理论建模者和实验者之间的协同合作，以及以与社区共享的模型形式和以总结新结果的出版物形式传播结果。

A five-year effort will develop a set of efficient three-dimensional lightning models and apply these models to theoretically investigate a range of outstanding science questions related to thunderstorm electrification and development of different forms of lightning discharges. The outstanding questions which the research will seek to answer are:(1) Can lightning models based on a fractal approach provide realistic descriptions of different types of lightning discharges? What are the specific limitations of these models in terms of description of charges, potentials and electric fields of the overall lightning-thundercloud electric system? Can these models be modified to provide a computationally efficient parameterization of the streamer zones of both positive and negative lightning leaders? (2) What are the effective time scales of streamer-to-leader transition in air as a function of air pressure? What are the altitude range and other relevant physical conditions for which formation of leader channels is not possible in the Earth's atmosphere?(3) What are the specific thundercloud charge configurations which allow upward extensions of lightning leaders above thundercloud tops leading to recently discovered blue jet and gigantic jet phenomena? Are pressure scaled fractal models of streamer zones of positive and negative lightning leaders capable of describing experimentally observed features of blue jets and gigantic jets?The specific activities directed toward answering these questions will include development of three-dimensional numerical models based on a probabilistic approach to lightning modeling. These models will account for the best currently available knowledge for efficient representation of leader trees in the three dimensional computation domain and will include such features as open boundary conditions, preservation of full charge neutrality of leader trees at any point during simulations, and accurate modeling of lightning channels with finite resistivity. Model development will synergistically complement existing observationally-based research efforts at the New Mexico Institute of Mining and Technology directed toward investigation of electrical structure of thunderstorms, including studies of inverted-polarity electrical structures, lightning initiation studies, and studies of different and newly discovered types of lightning discharges.Broader impacts of the proposed activity include student training and education, synergistic collaboration between theoretical modelers and experimentalists, and the dissemination of results in the form of models to be shared with the community and in the form of publications summarizing new results.