Collaborative Research: Observations of High-energy Radiation Associated with Thunderstorms

该项目将开展一系列实地活动，观察雷暴中产生高能辐射的现象。这些包括地面伽马射线闪光(TGFs)，在雷暴电荷结构的许多部分观察到的长寿命伽马射线发光，以及与闪电先锋台阶相关的X射线。总体战略是将探测传感器放置在这些排放主要产生的高场区域或附近。将使用的传感器包括加州大学圣克鲁斯分校在之前的NSF奖项下开发的两个伽马射线仪器，以及我们的合作者提供的传感器，它们通过静态和动态电场和磁场远程感应闪电。智力价值：所有研究中的现象都是在过去30年左右发现的，研究只是在最近10年才变得普遍。这个项目将解决的许多悬而未决的问题包括：向下的TGFs是否发生在自然闪电中，辉光(相对论电子的雪崩)是否对雷暴的发射有重大贡献，以及正闪电领导者是否像负闪电领导者那样发射X射线和低能量伽马射线。与其他现场测量相比，现场测量具有的主要优势是：1)探测地点靠近要研究的辐射源(雷云电荷中心和闪电领袖)；2)探测器的高时间分辨率和吞吐能力。辐射影响：选定的现场地点(加拿大的一座城市塔楼，日本的一个极低海拔风暴区域，以及墨西哥的一个极高海拔地点)代表了三种情况，在这三种情况下，向下的TGFs可能在地面产生足够高的辐射场，以表示公共安全问题(从太空看到的向上TGFs在10-15公里高度的雷云中产生危险水平的放射性)。因此，这一计划应该会几乎全面地缓解(或证明)对地面辐射的任何担忧。本科生和研究生的大量参与是该计划的一部分，其中包括第一代本科生和其他服务不足的本科生。

The project will conduct a series of field campaigns to observe phenomena producing high-energy radiation in thunderstorms. These include terrestrial gamma-ray flashes (TGFs), long-lived gamma-ray glows observed in many parts of the thunderstorm charge structure, and x-rays associated with the stepping of lightning leaders. The overall strategy is to locate probing sensors in or near the high-field regions where these emissions are primarily generated. The sensors to be used include two gamma-ray instruments developed at the University of California, Santa Cruz, under previous NSF awards, as well as sensors provided by our collaborators that sense lightning remotely via static and dynamic electric and magnetic fields. Intellectual Merit:All the phenomena under study were discovered within the last 30 years or so, with research only becoming widespread in the last decade. Some of the many open questions that will be addressed by this project include: whether downward TGFs occur in natural lightning, whether glows (an avalanche of relativistic electrons) contribute significantly to the discharging of thunderstorms, and whether positive lightning leaders emit x-rays and low-energy gamma rays the way negative leaders do. The primary advantage the field measurements have over others are 1) the proximity of the detection sites to the radiation sources to be studied (thundercloud charge centers and lightning leaders); and 2) the high time resolution and throughput capabilities of the detectors.Broader Impacts:The selected field sites (an urban tower in Canada, a region of very low altitude storms in Japan, and a very high altitude site in Mexico) represent the three situations in which it is at least feasible that downward TGFs might produce high enough radiation fields at the ground to represent a public safety issue (upward TGFs seen from space produce dangerous levels of radioactivity within thunderclouds at 10--15~km altitudes). Thus this program should allay (or justify) any concern about radiation at ground level nearly comprehensively. Significant participation from undergraduate and graduate students, including first-generation and otherwise underserved undergraduates, is part of the program.