Constraining electrification in volcanic plumes through numerical simulation (FlAshPlume)

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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.