Modeling Volcanic Shocktube Lightning*

Lightning discharges occur in ash plumes of volcanic eruptions. Identifying their radiofrequency emission may aid in forecasting volcanic ash along aviation routes and characterizing planetary volcanic activity. We propose a model for volcanic lightning in which dust particles accelerate in shocks, separate by their inertia, charge triboelectrically, and spark through streamer breakdown. These processes are strongly affected by the explosive shocks of the volcano eruption. For example, charge magnitude and polarity are sensitive to the shocked drift velocity of small and large particle species. In addition, charge clustering in turbulent eddies creates rapid variations in the Townsend ionization coefficient leading to intermittent breakdown. To validate the model breakdown statistics are compared to measurements from a volcanic shocktube experiment [1] with a well-controlled "dust" consisting of a bimodal distribution of glass beads. 

[1] Cimarelli, C. et al. (2014). Experimental generation of volcanic lightning. Geology, 42(1), 79–82