Multi-Frequency Studies of Lightning Initiation and Propagation

闪电是最严重的自然灾害之一，在美国平均造成的死亡人数超过飓风或龙卷风，并对财产和敏感设备造成重大损失。尽管经过了几十年的研究，我们仍然不能确切地理解是什么物理机制导致闪电的第一个火花，火花是如何发展成导电路径（闪电“通道”）的，或者通道是如何在多云和晴朗的空气中移动的。通过使用一组独特的传感器，该项目旨在收集有关闪电产生和传播的新信息，以帮助解释闪电的这两个基本方面是如何工作的。测量将在佛罗里达州的NASA肯尼迪航天中心（KSC）进行。闪电在KSC特别频繁，造成昂贵的操作延误，有时会损坏敏感的火箭和航天飞机车辆和/或设施。智力优势：这个NSF项目是最近完成的NSF探索性研究早期概念资助的延伸-“EAGER闪电起始和传播的多频率研究”-并建立在最初奖励的成功成果之上。已完成的EAGER项目使用五种不同的测量系统进行闪电观测。NSF项目的增强观测方案将扩展EAGER项目，增加八个系统来观测闪电过程：(1)“慢”天线，(2)“快”天线，(3)由七个交叉环路磁传感器组成的网络，(4)KSC电场磨网，(5)KSC雷电探测和测距（LDAR）系统，(6)KSC云对地雷电监视系统（CGLSS），(7)高速摄像机（54,000帧/秒），(8)VHF无线电发射，(9)快速电场变化（dE/dt）。所有九个传感器都在观察闪电加速和移动电荷时引起的电磁变化；传感器的工作范围很宽，部分重叠的电磁频率范围。不同的传感器对闪光的不同部分做出反应：有些部分只有几米长，而另一些则长达几千米。传感器阵列的两个关键特征将在这种新的闪电研究中特别有用。首先，该阵列将能够确定在云中和云对地闪电开始时发生的长而快速的电磁脉冲的未知位置。其次，闪电传播的高速视频图像将为我们提供视觉图像，与其他8个传感器的数据进行组合和比较。总的来说，该项目的智力价值源于将这九个传感器的数据结合起来，为闪电的产生和传播提供了新的见解。更广泛的影响：更好地了解特定危害（在这种情况下是闪电）背后的机制，可以导致新的和改进的方法来保护人民和财产免受这种危害。防雷系统主要以科学为基础，确定闪电如何产生和传播可能会揭示保护地面和空中物体的新方法。该项目对培养和培养几名新科学家也很重要，其中包括一名攻读博士学位的研究生，另外两名刚开始接受训练的研究生，以及两名有意从事科学研究的物理学本科生。培训包括闪电电磁测量的特定技术以及在许多情况下普遍适用的技术（包括计算机编程、仪器的计算机控制、计算机建模等）。该项目的结果也将在同行评议的文献中广泛传播。

Lightning is one of the worst natural hazards, killing more people in the USA on average than hurricanes or tornadoes and causing substantial damage to property and sensitive equipment. In spite of decades of study, we still do not understand exactly what physical mechanism causes the first spark of a lightning flash, how that spark grows into a conducting path (the lightning "channel"), or how the channel moves through cloudy and clear air. By using a unique array of sensors, this project aims to gather new information about lightning initiation and lightning propagation to help explain how these two fundamental aspects of lightning may work. The measurements will be made at the NASA Kennedy Space Center (KSC) in Florida. Lightning is especially frequent at KSC, causes expensive operational delays, and sometimes damages sensitive rocket and shuttle vehicles and/or facilities.Intellectual merits:This NSF project is an extension of a recently completed NSF EArly-concept Grant for Exploratory Research award - "EAGER Multi-Frequency Studies of Lightning Initiation and Propagation" - and builds on the successful results of that initial award. The completed EAGER project used lightning observations with five different measurement systems. The enhanced observational scheme for this NSF project will expand EAGER project with eight systems to observe lightning processes: (1) "slow" antennas, (2) "fast" antennas, (3) a network of seven crossed-loop magnetic sensors, (4) the KSC electric field mill network, (5) the KSC Lightning Detection And Ranging (LDAR) system, (6) the KSC Cloud-to-Ground Lightning Surveillance System (CGLSS), (7) high-speed video cameras (at 54,000 frames/second), (8) VHF radio emissions, and (9) fast electric field changes (dE/dt). All nine sensors look at electromagnetic changes caused by lightning as it accelerates and moves charge; the sensors operate across a wide and partially overlapping range of electromagnetic frequencies. The various sensors respond to different parts of a flash: some parts are only a few meters in length while others are as long as a several thousand meters. There are two key features of the sensor array that will be especially useful in this new lightning investigation. First, the array will be able to determine the previously unknown locations of the long, fast electromagnetic pulses that occur during the initiation of both in-cloud and cloud-to-ground lightning flashes. Second, the high-speed video images of a propagating lightning flash will literally give us visual pictures to combine with and compare with the data from the other 8 sensors. Overall, the intellectual merit of the project stems from combining the data from these nine sensors to provide new insights into how lightning initiation and lightning propagation work.Broader impacts:Developing a better understanding of the mechanisms behind a particular hazard (lightning, in this case) can lead to new and improved ways of protecting people and property from that hazard. Lightning protection systems are primarily based in science, and determining how lightning initiates and propagates may reveal new ways to protect objects on the ground and in the air. This project will also be important for the development and training of several new scientists, including one graduate student pursuing a Ph. D. degree, two other graduate students just beginning their training, and two undergraduate physics students interested in being involved in scientific research. The training involves techniques that are specific to electromagnetic measurements of lightning as well as techniques that are generally applicable in many situations (including computer programming, computer control of instruments, computer modeling, etc.). The results of this project will also be broadly disseminated in the peer-reviewed literature.