V028-0013
Exploring of the conditions leading to volcanic lightning: Results of a field study at Sakurajima volcano, Japan

Friday, 11 December 2020
Poster
Andre Geisler1, Matthias KG Hort1, Joachim Bülow1, Lea Scharff2,3, Masato Iguchi4 and Daisuke Miki4, (1)University of Hamburg, Institute of Geophysics, Hamburg, Germany, (2)Universitaet Hamburg, Hamburg, Germany, (3)University of Hamburg, CEN, Institut of Geophysics, Hamburg, Germany, (4)Kyoto University, Sakurajima Volcano Research Center, Disaster Prevention Research Institute, Kyoto, Japan
Abstract:
Volcanic plumes are known to exhibit electrical phenomena. Highly electrified plumes can be detected via their electrical properties (including discharges) using e.g. lightning location networks (LLN). However, not every eruption produces strong enough electrification/discharges that can be measured several tenth of kilometres away from the volcano. But importantly even in smaller eruptions that are not detected by LLNs, electrical phenomena occur and are related to the dynamics of the eruption. To investigate the conditions under which electrical phenomena and lightning occur within a volcanic plume, we installed a geophysical network at Sakurajima Volcano, Japan, in February 2019. The network includes two Doppler radar systems, three electric field mills, a thunderstorm detector, a weather station, an absolute barometer for acoustic pressure measurements, a broadband seismometer, as well as a camera. Our data are complemented by data from the Sakurajima volcano observatory network.

For our systematic analysis of electrical phenomena recorded between May 15th and Dec 15th we first generate a most complete eruption catalogue using the acoustic and radar data. The main reason for doing this is the fact that the Japanese Meteorological Agency (JMA, responsible for monitoring) only reports eruptions higher than 1000 m above the vent, but there are certainly more, smaller eruptions including ash venting that are of interest. The electrical properties and discharges within the plumes are identified using our field mill (directly measuring the electrical field) and the lightning detector (measuring the change of electrical field) data. This allows us to determine plume electrification, the number of discharges, the discharge rate and the time lag between the beginning of the eruption (determined by the acoustic network) and the first appearance of the electrical discharges for each eruption. The plume properties/eruption dynamics are quantified using the Doppler radar and acoustic data as well as our 1 min photographic images. In our presentation we explore correlations between the electrification of the volcanic plume and the dynamics driving the eruptions in order to explore a correlation between mass flux and electrification phenomena in the plume.

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