Multiparametric observation of volcanic lightning: Sakurajima Volcano, Japan

Abstract

We recorded volcanic lightning generated by Vulcanian explosions at Sakurajima Volcano using a synchronized multiparametric array. Physical properties of lightning are related to plume dynamics, and associated electromagnetic field variations are revealed by video observations (high speed and normal speed) together with infrasound and high sampling rate magnetotelluric signals. Data show that volcanic lightning at Sakurajima mainly occurs in the plume gas thrust region at a few hundred meters above the crater rim, where the overpressure of the turbulent volcanic jets determines the electrification of particles generating a complex charge structure in the growing plume. Organization of charges may be achieved at later stages when the plume transitions from the jet phase to the convective phase. Comparison with atmospheric sounding and maximum plume height data show that the effect of hydrometeors on flash generation at Sakurajima is negligible and can be more prudently considered as an additional factor contributing to the electrification of volcanic plumes.

The Effect of Electrostatic Charge on the Propagation of GPS (L‐band) Signals Through Volcanic Plumes

“…Similarly, at Etna, only the satellite tracks (i.e., the signal paths linking transmitter and receiver) that fell within 3 km of the vent were associated with signal reductions. Additionally, studies at Augustine, Redoubt, and Sakurajima employing LMA sensors and high‐speed cameras indicate that flows exiting the vent may have volumetric charge densities significantly larger than those found in conventional thunderstorms (Aizawa et al, ; Behnke et al, ; Cimarelli et al, ). This combination of high mass loading and elevated charge densities in proximity to the vent likely contributed significantly to the anomalous GPS attenuations observed at Redoubt, Etna, and other volcanoes.…”

“…Instruments like the Lightning Mapping Array (LMA) can provide extremely accurate four‐dimensional maps of discharges in plumes. Processed LMA data have been used to show that charging and discharge processes reflect the kinematics of the associated volcanic atmospheric flow and can be used to obtain information that would otherwise be opaque to observation (Aizawa et al, ; Behnke et al, ; Behnke & Eric, ; Cimarelli et al, ; Méndez Harper et al, ; Thomas et al, ).…”

Compositional and Mineralogical Effects on Ice Nucleation Activity of Volcanic Ash

“…Remote sensing studies of volcanic lightning have determined the altitude of the −20 • C isotherm Heterogeneous ice nucleation will occur on volcanic ash particles between the −10 °C and −20 °C isotherm [8,9], the latter of which is the highest temperature examined in this study using both deposition-mode and immersion-mode experiments. Based upon remote sensing studies of volcanic lightning, the −20 °C isotherm occurs at an altitude ranging from 4 to 10 km [10][11][12][13]. Scale to the left side of the figure does not reflect the true height of the eruption column.…”

First In Situ Observations of Gaseous Volcanic Plume Electrification

“…Understanding of the charging mechanisms above comes from laboratory experiments (Cimarelli et al, 2014;Méndez-Harper et al, 2018) detection of volcanic lightning from (1) lightning mapping arrays (Behnke et al, 2013), (2) global lightning detection networks (Bennett et al, 2010), or (3) high-speed imaging techniques Cimarelli et al, 2016) and measurements of plume charge overhead from ground based electric field mills (James et al, 1998). The only direct measurements of volcanic plume charge have been made by collecting fallout ash particles (Gilbert et al, 1991;Miura et al, 2002) in a Faraday pail situated a few kilometers away from the eruptive vent.…”