Collaborative Research: Characterizing Small-scale Lightning Discharges Associated with Explosive Volcanic Activity at Sakurajima Volcano

火山闪电放电的长度范围从几十米到几十公里不等。大多数小规模的喷发发生在火山喷口附近，同时发生或在火山爆发后几分钟内发生。大规模喷发通常发生在爆炸性喷发后5分钟或更长时间形成的成熟羽流中。这项研究工作的重点是研究与火山爆发同时发生的小规模、近端的排放。主要目标是在喷发活动的背景下更好地描述近端电活动的特征，以便更好地了解产生不同类型小规模放电所需的喷发条件。这一特征将通过对位于日本西南部九州地区的樱岛火山小型爆炸性喷发期间的闪电放电进行高分辨率3-D闪电测绘观测来实现。其他仪器(次声、摄像机和电场变化传感器)将用于监测雷击引起的爆炸活动、羽流发展和电场变化。这些数据将被用来确定与爆炸性喷发的开始和火山喷发的上升有关的不同类型的电放电发生的时间。电放电的特征将是确定放电的长度、规模、速度和极性，以及确定放电的起始位置。智力优势：这项研究将是迄今为止对火山闪电最详细的研究，将火山次声、电场变化和羽流发展的测量与高分辨率闪电测绘阵列(LMA)数据和火山闪电的高速视频观测相结合。电场变化测量、高速视频和可见光羽流观测的加入，使该项目有别于以前的研究。这项研究将增加对火山爆发直接导致的电活动的了解。这将有助于我们理解在火山喷口附近产生电活动的喷发过程。更广泛的影响：由于小范围的放电经常伴随着大范围的火山喷发，研究结果将适用于开发利用甚高频闪电和电活动观测的喷发监测系统。此外，这项研究的结果将被用来确定是否可以根据对电活动的观察来预测喷发的强度或火山灰羽流的高度。这项研究还将为来自代表性不足群体的一名早期职业研究人员和三名研究生提供培训。他们将参与收集、组织、归档和分析数据。

Volcanic lightning discharges have length scales ranging from tens of meters to tens of kilometers. Most small discharges occur proximally to a volcanic vent concurrent or within a few minutes of an explosive volcanic eruption. Large scale discharges typically occur throughout a mature plume formed 5 or more minutes subsequent to an explosive eruption. This research work focuses on studying the small, proximal discharges that occur concurrent with explosive volcanic eruptions. The main goal is to better characterize the proximal electrical activity within the context of the eruptive activity to gain a better understanding of the eruptive conditions that are required to produce different types of small-scale discharges. This characterization will be accomplished by making high-resolution 3-D lightning mapping observations of lighting discharges during small explosive eruptions of Sakurajima Volcano located in the Kyushu region of southwestern Japan. Other instrumentation (infrasound, video cameras, and electric field change sensors) will be used to monitor the explosive activity, plume development, and changes in electric field caused by lightning. The data will be used to determine when different types of electrical discharges occur relative to the onset of an explosive eruption and in relation to the ascent of volcanic ejecta. Electrical discharges will be characterized by determining the length scales, speeds, and polarities of the discharges, as well as by locating where the discharges initiate.Intellectual Merit: The research would be the most detailed study of volcanic lightning to date, combining measurements of volcano infrasound, electric field changes, and plume development with high-resolution Lightning Mapping Array (LMA) data and high-speed video observations of volcanic lighting. The inclusion of electric field change measurements, high-speed video, and visual plume observations distinguishes this project from previous research. The research will increase knowledge of electrical activity that occurs as a direct result of an explosive volcanic eruption. This will contribute to our understanding of the eruption processes that are responsible for producing electrical activity proximally to a volcanic vent.Broader Impacts: Because small-scale discharges frequently accompany volcanic eruptions of a large range of sizes, the results of the research will be applicable to developing an eruption monitoring system that utilizes VHF observations of lightning and electrical activity. In addition, the results of the research will be used to determine if one can predict eruption magnitudes or ash plume heights based on observations of electrical activity. The research will also provide training for an early career researcher from an underrepresented group and three graduate students. They will participate in gathering, organizing, archiving, and analyzing the data.