摘要：Volcanic plumes generate lightning from the electrification of plume particles. Volcanic
plume charging at over 1200 km from its source was observed from in situ balloon sampling
of the April 2010 Eyjafjallajökull plume over Scotland. Whilst upper and lower edge
charging of a horizontal plume is expected from fair weather atmospheric electricity, the
plume over Scotland showed sustained positive charge well beneath the upper plume edge.
At these distances from the source, the charging cannot be a remnant of the eruption
itself because of charge relaxation in the finite conductivity of atmospheric air.
