Constraining electrification in volcanic plumes through numerical simulation (FlAshPlume)

全球闪电探测的最新进展表明，上升到10公里或更高高度的火山羽流往往会产生闪电。火山闪电是如此普遍，以至于地球仪各地的火山观测站和气象咨询中心已经开始使用它来近实时地探测火山喷发。就在几个月前，汤加的一座海底火山爆发产生的闪电比迄今为止记录在案的任何单一事件都多，包括地球上最严重的风暴。很明显，火山羽流可以维持极端闪电产生的条件，但对于湍流上升气流、粒子碰撞和水结冰的相对作用，仍有许多未知之处。来自闪电网络的数据也提供了重要的线索，说明羽流中的电荷如何使微小的岩石颗粒（火山灰）粘在一起并形成更大的集群。这种聚集过程对火山灰在空中停留的时间有深远的影响--它威胁到飞机的安全--并且是火山灰危险预测模型和地质记录中喷发沉积物解释的主要不确定性来源。尽管在这一领域的研究兴趣日益活跃，但火山电气化过程从未以一种可以用现在可用的高保真观测进行验证的方式进行过建模。该项目的目标是开发第一个经过实地测试的火山羽流带电数值模型。我们建议整合两个完善的代码从不同的科学应用-火山羽流模型被称为ATHAM，和电气化计划从NOAA的国家严重风暴实验室风暴模块。作为我们正在进行的NERC雷达支持下一代火山灰灾害预测项目的一部分，正在进行补充工作。我们的总体目标是创建一个强大的火山闪电和静电灰聚集的数值模型，可以使用最近火山爆发的观测进行微调。这些努力将揭示在研究爆炸性喷发羽流方面长期存在的科学挑战，更广泛地说，将扩大我们对导致地球上最强大的闪电风暴的大气带电过程的理解。

Recent advances in global lightning detection have revealed that volcanic plumes rising to 10 km altitude and higher tend to generate lightning. Volcanic lightning is so common that volcano observatories and weather advisory centres around the globe have begun using it to detect eruptions in near-real-time. Only a few months ago, the eruption of a submarine volcano in Tonga produced more lightning than any single event yet documented, including the most severe storms on Earth. It is clear that volcanic plumes can sustain the conditions for extreme lightning production, yet much remains unknown about the relative roles of turbulent updrafts, particle collisions, and the freezing of water to ice. Data from lightning networks also hold important clues about how electrical charging in plumes makes the tiny rock particles (volcanic ash) stick together and form larger clusters. This aggregation process has profound effects on how long the ash remains aloft-where it threatens aircraft safety-and represents a major source of uncertainty in models of both ash hazard forecasts, and interpretations of eruption deposits in the geological record. Despite active and growing research interest in this field, the volcanic electrification process has never been modelled in a way that could be validated with the high-fidelity observations now available. The objective of this project is to develop the first field-tested numerical model of volcanic plume electrification. We propose to integrate two well-established codes from different scientific applications-the volcanic plume model known as ATHAM, and the electrification scheme from NOAA's National Severe Storms Laboratory storm module. Complementary work is being conducted as part of our ongoing NERC project on Radar-supported Next-Generation Forecasting of Volcanic Ash Hazard. Our overall aims are to create a robust numerical model of volcanic lightning and electrostatic ash aggregation that can be fine-tuned using observations from recent volcanic eruptions. These efforts will shed light on long-standing scientific challenges in the study of explosive eruption plumes and, more broadly, will expand our understanding of atmospheric electrification processes leading to the most powerful lightning storms on Earth.