Simulations and Theory of Streamer Discharges in Transient Luminous Events

本课题是对瞬态发光事件中流光放电基本特性的理论研究。瞬变发光事件是最近发现的发生在地球大气平流层和中间层/电离层较低高度的大尺度光学现象，它与潜在雷暴的电活动直接相关。虽然一个典型的瞬态发光事件可能会占据高层大气的很大体积，但这些事件的高空间分辨率图像揭示了许多内部和尚未完全理解的小尺度特征，包括明亮的离子化丝状通道，或流光，其横向空间尺度从几十米到几百米不等。这些流带是等离子体结构，可以在接近地面压力的空气中相对较小的间隙中引发火花放电。流光体通常具有分支结构，但在瞬态发光事件和高压应用中分支机制的实验和理论研究仍处于初级阶段。作为这个项目的一部分，将探索和量化流光分支的确切机制，以及流光和瞬态发光事件的微物理学及其对地球大气的影响。本项目进行了集中的努力，包括数值模拟和建模，这将解决当前关于瞬态发光事件中流光放电基本特性的有限问题。需要研究的具体科学问题有：(1)在低外加电场条件下，拖缆的起始机制是什么？(2)在不同压力下，流光在空气中传播所需的最小场是什么？(3)流光分支的机制是什么？回答这些问题将更准确地量化受瞬态发光事件影响的大气总量，以及这些事件在对流层和中间层/较低电离层区域之间建立电接触直接路径的能力。拟议活动的更广泛影响包括研究生的教育和培训，博士后学者的支持和进一步培训，本科REU学生在夏季期间参与与该项目相关的研究活动。

This project is a theoretical investigation of the fundamental properties of streamer discharges in transient luminous events. Transient luminous events are recently discovered large scale optical phenomena occurring at stratospheric and mesospheric/lower ionospheric altitudes in the Earth's atmosphere, which are directly related to electrical activity in underlying thunderstorms. Although a typical transient luminous event may occupy a large overall volume of the upper atmosphere, high spatial resolution imagery of these events reveals many internal and not yet fully understood small scale features, including bright filamentary channels of ionization, or streamers, with transverse spatial scales ranging from tens to hundreds of meters. These streamers are plasma structures which can initiate spark discharges in relatively small gaps in air which is near ground pressures. Streamers are commonly observed with branching structures, but the experimental and theoretical work on understanding the branching mechanism in both transient luminous events and in high pressure applications is still in the preliminary stage. The exact mechanism of streamer branching will be explored and quantified as part of this project, as well as the microphysics of streamers and transient luminous events and their effects on the Earth's atmosphere. This project undertakes a focused effort, including numerical simulations and modeling, which will attack a limited set of current outstanding questions on the fundamental properties of streamer discharges in transient luminous events. The specific scientific questions to be investigated are: (1) What is the initiation mechanism for streamers in low applied electric fields? (2) What are the minimum fields required for the propagation of streamers in air at different pressures? (3) What is the mechanism or mechanisms involved in streamer branching? Answering these questions will quantify more accurately the total volume of atmosphere affected by transient luminous events and the ability of these events to establish a direct path of electrical contact between the troposphere and the mesosphere/lower ionosphere regions. The broader impacts of the proposed activity include the education and training of a graduate student, the support and further training of a post-doctoral scholar, the involvement of undergraduate REU students in research activities related to this project during summer time periods.