The Microphysics of Lightning: Observing the Optical Emission from Downward Terrestrial Gamma-ray Flashes

该奖项全部或部分由2021年美国救援计划法案（公法117-2）资助。地球伽马射线闪光（TGFs）是由闪电产生的亚毫秒持续时间的高能光子爆发。对TGF的研究，包括它们的产生和传播，是闪电研究人员的主要兴趣。望远镜阵列表面探测器（TASD）是位于美国犹他州西部沙漠的一个700平方公里的宇宙射线探测器，是目前世界上研究向下指向的TGF的领先探测器。该项目将允许通过在望远镜阵列站点使用高速摄像机和光度计测量其光学组件来进一步调查向下TGF的初始阶段。 该项目的结果将提高我们对闪电的理解，从而提高减轻其负面影响和相关辐射危害的能力。这项工作的推广部分将使科学家能够通过各种交流场所向公众描述闪电的微观物理学。虽然已知TGFs在雷暴内部产生并与闪电相关，但负责产生TGFs的机制以及云内放电与TGFs的关系仍然未知。有几种主要的可能机制被认为是产生TGF。多项研究得出结论，每种机制的光学特征明显不同。探测到的不同波长的光发射强度将提供有关闪电发展顺序的关键信息。该奖项将允许使用高速摄像机和光度计以及闪电映射阵列（LMA）站、电场变化探测器和高速宽带VHF干涉仪来观察向下指向的TGFs及其光发射之间的关系。这些观测的结果将直接与ASIM卫星上向上的TGF同时观测到的光辐射进行比较。最重要的是，它将提供有关TGF甚至闪电引发过程的关键问题的答案，并将进一步了解闪电研究中的十大问题之一：在我们的大气中产生和传播伽马射线事件的机制是什么？该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估的支持。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Terrestrial Gamma-ray Flashes (TGFs) are bursts of high energy photons of sub millisecond duration that are produced by lightning. The study of TGFs, both their initiation and propagation, is of major interest to lightning researchers. The Telescope Array Surface Detector (TASD), a 700 km2 cosmic ray detector located in the western desert of Utah, U.S.A. is currently the world’s leading detector in the study of downward-directed TGFs. This project will allow further investigation of the initiation phase of downward TGFs by measuring their optical component using a high-speed video camera and a photometer at the Telescope Array site. The results of this project will improve our understanding of lightning, which in turn will improve the ability to mitigate its negative effects and associated radiation hazards. The outreach component of this work will allow scientists to describe the microphysics of lightning to the public at a powerful and impactful level through various communication venues. While it is known that TGFs are produced inside thunderstorms and in correlation with lightning, both the mechanism responsible for producing TGFs and the relation of intra-cloud discharges to TGFs are still unknown. There are several leading possible mechanisms that are believed to produce TGFs. Multiple studies conclude that each mechanism’s optical signature is distinctly different. The intensities at which the optical emission at different wavelengths is detected would provide key information about the lightning development sequence. This award will allow the observation of the relationship between downward-directed TGFs and their optical emissions using a high-speed video camera and a photometer in conjunction with Lightning Mapping Array (LMA) stations, electric field-change detectors, and a high-speed broadband VHF interferometer. Results from these observations will be directly compared to the optical emissions observed simultaneously with the ASIM satellite’s upward-directed TGFs. Most importantly, it will provide answers to critical questions about TGFs and even lightning initiation processes, and will further the understanding regarding one of the top ten questions in lightning research: What are the mechanisms responsible for producing and propagating gamma-ray events in our atmosphere?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.