Lightning and Thunderstorm Studies

这项研究的重点是加深我们对雷暴中闪电是如何产生的，以及一些闪电如何偶尔产生强烈的伽马射线爆发的理解。伽马射线类似于X射线，但比X射线强得多，研究它们是如何产生的有助于我们更好地了解闪电是如何开始和发展的。这种被称为地面伽马射线闪电(TGFs)的爆发是由卫星首次探测到的，是由云内闪电(IC)引起的向上方向的事件。虽然卫星继续探测到向上的TGFs，但在任何给定位置的探测率都很低，而且没有仔细观察到产生卫星探测到的TGFs的IC闪光。最近，位于犹他州中西部的大面积宇宙线探测望远镜阵列设施的研究表明，云对地(CG)闪电可以产生向下的TGFs。这些研究是与犹他大学的同事合作进行的，提供了关于闪电如何产生TGFs的第一次详细观察，并将在未来的研究中进行扩展。与此同时，类似的研究将在佛罗里达州的肯尼迪航天中心进行，那里更有可能观测到产生卫星探测到的TGFs的IC闪光。这些研究很重要，因为它们不仅促进了我们对TGFs是如何产生的理解，而且还提供了关于闪电放电过程本身的有价值的信息。它们也是跨学科的，在这种情况下，介于传统的闪电研究和高能粒子物理之间，为研究生和本科生提供了极好的学习机会和经验。这些研究利用了从一整套闪电探测技术和系统获得的观测数据，其中包括闪电测绘阵列，该阵列使用闪电产生的甚高频无线电信号的多站到达时间测量来确定闪电的三维结构和发展，以及双宽带甚高频干涉仪系统，该系统以亚微秒级的分辨率连续显示闪电的详细发展。结合对不同放电过程产生的电场变化的高速测量，这些观测提供了闪电在时间和空间上发展的完整图像。望远镜阵列探测伽马射线爆发产生的康普顿电子，不仅具有亚微秒级的分辨率，而且随时间连续，使TGFs能够准确地与闪电数据相关联，而且在数十公里范围内具有1.2公里的网格间距--这是探测效率的主要因素。比较表明，TGFs发生在CG闪电的高能初始击穿脉冲(IBP)期间，对于理解IBP是如何产生的以及它们对闪电如何启动和继续发展的影响起着至关重要的作用。犹他州研究的大面积和连续时间覆盖相结合，使得在一个给定的夏季季风季可以探测到几到十个或更多的TGFs。同样，在肯尼迪航天中心附近的佛罗里达州中东部地区，闪电和雷暴的发生率要高得多，处于轨道上的转化生长因子探测卫星的纬度覆盖范围内。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This research focuses on furthering our understanding of how lightning is produced inside thunderstorms, and how some lightning flashes occasionally produce strong bursts of gamma rays. Gamma rays are similar to but much more powerful than x-rays, and studying how they are produced helps us better understand how lightning begins and develops. The bursts, called terrestrial gamma-ray flashes (TGFs), were first detected by satellites, and are upward-directed events caused by in-cloud (IC) lightning. Although upward TGFs continue to be detected by satellites, the detection rate at any given location is very low, and there have been no close observations of IC flashes that produced satellite-detected TGFs. More recently, studies at the large-area cosmic ray-detecting Telescope Array facility in west-central Utah have shown that cloud-to-ground (CG) lightning can produce downward TGFs. The studies, which are being conducted in collaboration with colleagues at the University of Utah, have provided the first detailed observations of how TGFs are produced by lightning, and are to be expanded upon in the studies going forward. At the same time, similar studies are to be conducted at the Kennedy Space Center in Florida, where there is a greater chance of obtaining observations of IC flashes that produce satellite-detected TGFs. The studies are important because they advance our understanding not only about how TGFs are produced, but also provide valuable information about the lightning discharge processes themselves. They are also cross-disciplinary, in this case between traditional lightning investigations and high-energy particle physics, and provide excellent learning opportunities and experiences for graduate and undergraduate students. The studies utilize observational data obtained from a comprehensive set of lightning detection techniques and systems, including lightning mapping arrays (LMAs) that use multi-station time-of-arrival measurements of the VHF radio signals produced by lightning to determine the 3-D structure and development of flashes, and dual broadband VHF interferometer systems that show the detailed development of flashes continuously in time, with sub-microsecond resolution. Combined with high-speed measurements of the electric field change produced by the different discharge processes, the observations provide complete pictures of the development of lightning flashes both in time and space. The Telescope Array detects Compton electrons produced by the gamma-ray bursts, not only with sub-microsecond resolution and continuously over time, allowing the TGFs to be accurately correlated with the lightning data, but also with 1.2 km grid spacing over tens of kilometers extent – a major factor in detection efficiency. The comparisons show the TGFs occur during energetic initial breakdown pulses (IBPs) of CG flashes, and are playing a crucial role in understanding how IBPs are produced and their effect on how lightning is initiated and continues to develop. The combination of large areal extent and continuous time coverage of the Utah study allows several to ten or more TGFs to be detected in a given summer monsoon season. Similarly continuous coverage of the lightning activity will be obtained in the east central Florida area around Kennedy Space Center, which has a much higher incidence of lightning and thunderstorms, and is within the latitudinal coverage range of the orbiting TGF-detecting satellites.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.