Runaway Discharges and Their Roles in Atmospheric Processes

失控排放及其在大气过程中的作用

• 批准号: 0607885
• 负责人: Joseph Dwyer
• 金额: $ 42万
• 依托单位: Florida Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-01-01 至 2011-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0607885&HistoricalAwards=false
• 关键词: Runaway; Discharges; Their; Roles; Atmospheric

Theoretical, observational and experimental investigations are being conducted on runaway breakdown and its role in the initiation and propagation of lightning. Despite the great theoretical progress made in recent years, there remain large disagreements about the runaway breakdown mechanism. Currently the theory is undergoing a period of great flux with many new ideas emerging and a large amount of debate. The intellectual merit of this work is its contributions to this debate.The best observational method for studying runaway breakdown is measuring x-ray emission from electrical discharges, produced by runaway electrons as they collide with neutral molecules in air. The x-ray emissions can travel over much larger distances than the runaway electrons themselves, and allow remote observations of the runaway breakdown process. With funding from a NSF/MRI grant, our group completed the Thunderstorm Energetic Radiation Array (TERA) at the University of Florida/Florida Tech International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, Florida. TERA is designed to make detailed measurements of x-ray and gamma-ray emission from natural and rocket-triggered lightning from thunderstorms. This project supports the analysis of the large sets of x-ray data now being acquired, leveraging the work already done for the MRI award, which is an instrumentation grant that does not fund scientific research. This work keeps the theory well grounded in observations.Observations of X-rays from lightning continue to provide new insight into lightning phenomena. For example, they have already demonstrated a deeper connection between stepped leaders that occur before the first return stroke of a cloud-to-ground lightning flash, and dart leaders that occur prior to subsequent return strokes in the same flash. This advances knowledge previously inferred from optical and field measurements. Using instruments from the ICLRT, our group recently discovered that laboratory sparks also produce x-ray bursts very similar to the x-ray emission observed from natural and triggered lightning. This discovery allows for the first time laboratory study of how x-rays are emitted during the breakdown process. The continuation of this laboratory work as part of this current project is providing important clues about the stepping process that occurs in lightning leaders, since x-rays are found to be produced during the formation of these steps. Monte Carlo simulations and finite difference codes simulating the breakdown process are used to produce simulated x-ray and gamma-ray spectra, which then are compared to x-ray and gamma-ray energy observations. This comparison provides concrete tests of the present runaway breakdown theory. The theory also provides guidance to the experiments, aiding in their interpretation and illuminating the important quantities involved in breakdown. This research has broader impacts through study of previously little-explored properties of lightning, making possible significant advancements in this field. There exists a large amount of confusion and many misconceptions about runaway breakdown in the broader community; with the result that runaway breakdown is frequently being used with little discretion for explaining a number of observations that probably have little to do with the mechanism. This research will provide quantitative measures of runaway breakdown that can be used by the community. This research directly benefits the study of thunderstorms, lightning and laboratory sparks and advances exploration of a new area of plasma physics. By improving our understanding of the physical processes involved in thunderstorms and lightning, such research may eventually result in improved lightning predictions and lightning safety.

目前正在对失控击穿及其在闪电发生和传播中的作用进行理论、观测和实验研究。尽管近年来理论研究取得了很大的进展，但关于失控击穿的机理仍存在很大的分歧。目前，这一理论正处于一个大变革的时期，新的观点层出不穷，争论不断。这项工作的智力价值在于它对这一争论的贡献。研究失控击穿的最佳观测方法是测量失控电子与空气中的中性分子碰撞时放电产生的x射线发射。X射线发射可以比逃逸电子本身传播更远的距离，并允许远程观察逃逸击穿过程。在美国国家科学基金会/磁共振成像基金的资助下，我们小组在佛罗里达布兰丁营的佛罗里达大学/佛罗里达科技国际闪电研究和测试中心（ICLRT）完成了雷暴高能辐射阵列（TERA）。TERA的设计目的是对雷暴中自然闪电和火箭触发闪电的X射线和伽马射线发射进行详细测量。该项目支持对目前正在获取的大量X射线数据进行分析，利用MRI奖已经完成的工作，MRI奖是一项不资助科学研究的仪器拨款。这项工作使理论在观测中有了很好的基础。对闪电X射线的观测继续为闪电现象提供新的见解。例如，他们已经证明了在云对地闪电的第一次回击之前发生的阶梯先导和在同一闪电中随后回击之前发生的飞镖先导之间存在更深层次的联系。这推进了以前从光学和实地测量中推断出的知识。使用ICLRT的仪器，我们的团队最近发现实验室火花也会产生X射线爆发，与从自然闪电和触发闪电中观察到的X射线发射非常相似。这一发现首次允许实验室研究X射线在击穿过程中是如何发射的。作为当前项目的一部分，这项实验室工作的继续提供了有关闪电先导中发生的步进过程的重要线索，因为发现在这些步骤的形成过程中产生了x射线。蒙特卡罗模拟和有限差分代码模拟击穿过程中产生模拟的X射线和伽马射线光谱，然后比较X射线和伽马射线能量观测。这种比较为现行的失控击穿理论提供了具体的检验。该理论还为实验提供了指导，有助于解释实验，并阐明了击穿所涉及的重要量。这项研究通过研究以前很少探索的闪电特性产生了更广泛的影响，使这一领域的重大进展成为可能。在更广泛的社会中，存在着大量的混乱和许多关于失控崩溃的误解;结果是失控崩溃经常被用来解释一些可能与机制无关的观察结果。这项研究将提供可供社区使用的失控故障的量化措施。这一研究直接有利于雷暴、闪电和实验室火花的研究，并推动了等离子体物理新领域的探索。通过提高我们对雷暴和闪电所涉及的物理过程的理解，这种研究可能最终导致改进闪电预测和闪电安全。