08 August 2015 2 8K Report

Many years back, I attended a special session on Elves, Sprites and Blue Jets at AGU in San Francisco.

These are typically observed above severe thunderstorm clouds and are observed at something like 100km altitude (magnetosphere).

Explosive volcanic eruptions often occur through a lake or the sea (eg. Rose et al 1995), and can also entrain 100-1000s MTons of water vapour from the boundary layer for atmospheric moisture when extensive pyroclastic density currents are generated and source the ashcloud (eg. 15 June 1991 Pinatubo; Dartevelle et al 2002) .

All such eruptions are rich in water vapour.

Rapidly during ash cloud ascent water vapour condenses on ash particles.

Then freeze over to form snowflakes and ice particles (eg. Rabaul 1937, Surtsey 1963, Pinatubo 1991, Vulcan 1994, Montserrat Boxing Day cloud, Hekla 2000, Eyjafjallajokull 2010...; eg. Durant et al 2008 and refs therein) .

In this way, the eruption cloud turns into some kind of severe thunderstorm or generates one, whichever way one wishes to look at it.

Meteorological severe storms generate electricity.

One can expect that severe storms associated with volcanic explosive eruptions will generate electricty using the same electrification mechanisms as your standard thunderstorm.

In addition to those electrification mechanisms associated with normal thunderstorms, however, when magma is fragmented into ash, additional electrification occurs during explosive volcanic eruptions and especially in phreatomagmatic éruptions as a result of fracto-emission (Gilbert and Lane 1994, etc...). 

Electrification (charge generation, charge separation and "dipole" system development)  from fracto-emission is consistent with field measurements of the electric field during volcanic explosive éruptions (eg. Sakurajima; Gilbert et al 1992) and with lightning detection during explosive eruptions.

Explosive volcanic eruptions commonly reach ascent heights that are similar or higher than severe thunderstorms, exceeding 15-20km elevation above the ground. Indeed numerous VEI 3 eruption clouds are detected by remote sensing colleagues each year (eg. Rose et al 2000).

Hence, with similar thermal energy fluxes (correlated with ascent height) and expected more intense electrification than severe thunderstorms, phreato-subplinian or phreatoplinian explosive eruptions can be expected to generate phenomena such as elves, blue jets and sprites into the magnetosphere directly above the volcanic eruption cloud.

But I am not aware of anyone who would have made any measurements to assess this hypothesis in the atmospheric science community?

I am curious to find out if anyone knows more about this since I first queried atmospheric experts on elves, sprites and blue jets above standard thunderstorms more than 20 years back ?

Cheers,

Gerald

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