Charge mechanism of volcanic lightning revealed during the 2010 eruption of Eyjafjallajökull

Abstract

Volcanic lightning has intrigued observers through the centuries. Several likely processes have been proposed to explain the electrification of volcanic plumes, including quenching magma‐water interactions, the fracturing or internal friction of fine grained ash, and the freezing of plume water at height. Scarce measurements of volcanic lightning have not been able to distinguish between proposed ideas. The Eyjafjallajökull volcanic eruption in Iceland in April–May 2010 may have revealed its charge mechanism. During its 39 days, the eruption went through a few phases while the conditions of the ambient atmosphere also changed, but at different times. The most surprising change in the lightning activity occurred on 11 May, with no obvious change in the physical eruption character or strength. During 3–10 May there was no lightning recorded by long‐range networks, followed by intense activity 11–20 May. The change in lightning activity coincided with a change in the conditions of the ambient atmosphere. At this time the altitude of the isotherms for droplet freezing (about −20°C) dropped drastically below the plume top. Therefore, it appears that the atmospheric conditions around the plume were influencing or even controlling some of the lightning activity. The critical plume top temperature, which appears to have turned on and off the observed lightning activity during the Eyjafjallajökull eruption is estimated to be between −20° and −24°C. We conclude that a significant charge generation process of the observed volcanic lightning is probably analogous to processes in meteorological thunderclouds.

The 2010 eruption of Eyjafjallajökull: Lightning and plume charge structure

“…The second interval, when relatively high rates of lightning were observed, occurred between 11 and 21 May. This distinction was also observed by Bennett et al [] and Arason et al [] in the ATDnet data.…”

“…The figure shows that it was significantly warmer during 5–10 May, when very little lightning was observed, than it was from 11 to 21 May, when high rates of lightning were observed (with the exception of a brief increase in temperature on 12 May). This correlation has already been described by Arason et al [], who compared plume top temperatures (derived by comparing the radar data to the atmospheric data from the UM) to the ATDnet‐detected lightning rates and found that higher rates of lightning occurred with decreasing plume top temperatures. This led Arason et al [] to conclude that plume‐based ice‐contact charging was likely responsible for the lightning detected by ATDnet.…”

Lightning-induced volcanic spherules

“…Lightning was extensively documented during the explosive phase of the Mount Redoubt eruption using the lightningmapping array (Rison et al, 1999;Thomas et al, 2004;Behnke et al, 2013) and throughout the explosive phase of the 2010 Eyjafjallajökull eruption by the UK Met Office (www.metoffice. gov.uk) long-range lightning location network (Bennett et al, 2010;Arason et al, 2011). Two pseudo-ash samples that replicated the chemical, physical, and electrical properties of freshly fallen ash were bulk manufactured using the procedure developed by Wardman et al (2012b) for the flashover experiments (details are pro- vided in Fig.…”

The impact of the atmosphere on the Eyjafjallajökull 2010 eruption plume

“…The purpose of this paper is to present evidence from observations of the impact of the atmosphere on an eruption plume of a medium‐size explosive eruption, from the larger scale features controlling the downstream advection and dispersion of volcanic ash to the small scale features of the convective phase of the plume. Another example of the impact of the ambient atmosphere on the Eyjafjallajökull eruption plume is given by Arason et al [2011b] where it is suggested that the ambient atmospheric temperature had significant impact on lightning activity in the plume. The arrival of the ash from Eyjafjallajökull 2010 over the continental Europe is a subject of numerous papers, based on both observations and model simulations [e.g., Dacre et al , 2011; Devenish et al , 2012; Emeis et al , 2011; Schumann et al , 2011], and is outside the scope of this paper.…”