The effects of dynamics on the triboelectrification of volcanic ash

Harper, Joshua Méndez; Dufek, Josef

doi:10.1002/2015jd024275

Cited by 55 publications

(40 citation statements)

References 102 publications

(176 reference statements)

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“…The percentage increase in total extinction as a function of charge and particle diameter (1 m to 1 cm)-that is, (Q(c) − Q)∕Q × 100-appears in Figures 5a and 5b for L1 and L2, respectively. This computation was done for the charge density ranges described in section 2 ( = 10 −8 -10 −5 C/m 2 ; Gilbert et al, 1991;James et al, 2000;Méndez Harper & Dufek, 2016;. As demonstrated by Figure 5, important increases in attenuation (larger than 10 %) occur when the charge density is above = 10 −7 C/m 2 and the particle size is smaller than 50 m. Up until this point, we have considered the interaction of EM radiation with a single particle.…”

Section: Resultsmentioning

confidence: 99%

“…Volcanic jets can produce a wide range of electrical phenomena (Aizawa et al, ; Behnke & Eric, ; Gilbert et al, ; Hatakeyama, ; Hatakeyama & Uchikawa,1951; Houlié et al, ; James et al, , ; Kikuchi & Endoh, ; McNutt & Williams, 2010; Miura et al, , ; Thomas et al, ). Large eruptions are often accompanied by brilliant displays of lightning, testifying to the high electrical potentials that can be generated by a diverse set of electrification mechanisms (including fractocharging, triboelectrification, and electrification processes similar to those found in thunderstorms; Cimarelli et al, ; Gilbert et al, ; Méndez Harper et al, ; James et al, ; Kikuchi & Endoh, ; Méndez Harper & Dufek, ). Beyond signals at optical wavelengths, volcanic lightning generates a wide array of electromagnetic (EM) signals that can be recorded from afar.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2019

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Recent field studies have shown that the presence of ash in the atmosphere can produce measurable attenuation of Global Positioning System (GPS) signals (Aranzulla et al., 2013, https://doi.org/10.1007/s10291-012-0294-4; Larson, 2013, https://doi.org/10.1002/grl.50556; Larson et al., 2017, https://doi.org/10.1016/j.jvolgeores.2017.04.005). The ability to detect plumes using GPS is appealing because many active volcanoes are already instrumented with high‐quality receivers. However, analyses using a Ralyeigh approximation have shown that the large attenuations cannot be explained by the scattering and absorption associated with ash or hydrometeors alone. Here, we show that the extinction of GPS signals, which fall into the L‐band of the electromagnetic spectrum, may be exacerbated significantly by excess surface charge on pyroclasts. Indeed, volcanic eruptions are often accompanied by a range of electrostatic processes, leading, in some cases, to spectacular lightning storms. We use a modified Mie scattering model to demonstrate that electrostatic effects can increase the extinction of L‐band radiation by up to an order of magnitude, producing attenuations consistent with those observed in the field. Thus, future work involving GPS as a tool to remotely probe plumes must take into account the electrification of ash in radiative transfer models. Additionally, we propose that the sensitivity of GPS to particle charging may catalyze the development of new techniques to explore electrostatic processes in plumes, especially if GPS measurements are complemented with millimeter‐wave RADAR measurements.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2019

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“…Among the noninductive charging mechanisms thought to be operating during volcanic ash emissions, tribo-electrification (Aplin et al, 2016;Cimarelli et al, 2014;Harrison et al, 2010;Houghton et al, 2013;Méndez Harper & Dufek, 2016) and fracto-electrification (Aplin et al, 2016;James et al, 2000;James et al, 2008;Méndez Harper et al, 2015) are considered the most relevant in explosive eruptions where magma fragmentation and consequent production of turbulent particle-laden jets are naturally produced.…”

Section: Introductionmentioning

confidence: 99%

Electrification of Experimental Volcanic Jets with Varying Water Content and Temperature

Stern

Cimarelli

Gaudin

et al. 2019

Geophysical Research Letters

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Volcanic lightning-a near ubiquitous feature of explosive volcanic eruptions-possesses great potential for the analysis of volcanic plume dynamics. To date, the lack of quantitative knowledge on the relationships between plume characteristics hinders efficient data analysis and application of the resulting parameterizations. We use a shock-tube apparatus for rapid decompression experiments to produce particleladen jets. We have systematically and independently varied the water content (0-27 wt%) and the temperature (25-320°C) of the particle-gas mixture. The addition of a few weight percent of water is sufficient to reduce the observed electrification by an order of magnitude. With increasing temperature, a larger number of smaller discharges are observed, with the overall amount of electrification staying similar. Changes in jet dynamics are proposed as the cause of the temperature-dependence, while multiple factors (including the higher conductivity of wet ash) can be seen responsible for the decreased electrification in wet experiments.Plain Language Summary Volcanic explosive eruptions are accompanied by lightning strikes generated from the volcanic dust cloud. Here we have experimentally studied the effects of atmospheric water and plume temperature on the frequency and intensity of the lightning strikes. The results will feed a model for the use of volcanic lightning strikes to estimate plume contents and intensity. Key Points:• Natural observations on the influence of temperature and water content on volcanic lightning have been modelled in laboratory experiments. • The magnitude of electrification and discharging in plumes decreases significantly with added water. • At higher temperatures a decrease in magnitude of individual discharges is observed, while the total neutralized charge stays similar.

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“…The small length scales (likely, centimeters to a few meters) and high rates (up to several dozen events per millisecond) associated with vent discharges hint that the volumetric charge density in proximal volcanic jets may be as much as an order of magnitude larger than that found in thunderclouds or distal plume regions (Aizawa et al, ; McNutt & Williams, ). This is an unsurprising observation given that explosions likely generate large amounts of charge per unit surface area through elevated rates of fractoelectric and triboelectric charging (James et al, ; Méndez Harper et al, ; Méndez Harper & Dufek, ). Indeed, proximal discharges could reflect conventional or dielectric breakdown processes (Aizawa et al, ), rather than the more complex processes thought to operate in thunderclouds (Dwyer, ; Dwyer & Uman, ; Gurevich et al, ).…”

Section: Introductionmentioning

confidence: 99%

Inferring Compressible Fluid Dynamics From Vent Discharges During Volcanic Eruptions

Harper

Cimarelli

Dufek

et al. 2018

Geophysical Research Letters

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Observations at numerous volcanoes reveal that eruptions are often accompanied by continual radio frequency (CRF) emissions. The source of this radiation, however, has remained elusive until now. Through experiments and the analysis of field data, we show that CRF originates from proximal discharges driven by the compressible fluid dynamics associated with individual volcanic explosions. Blasts produce flows that expand supersonically, generating regions of weakened dielectric strength in close proximity to the vent. As erupted material—charged through fragmentation, friction, or other electrification process—transits through such a region, pyroclasts remove charge from their surfaces in the form of small interparticle spark discharges or corona discharge. Discharge is maintained as long as overpressured conditions at the vent remain. Beyond describing the mechanism underlying CRF, we demonstrate that the magnitude of the overpressure at the vent as well as the structure of the supersonic jet can be inferred in real time by detecting and locating CRF sources.

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The effects of dynamics on the triboelectrification of volcanic ash

Cited by 55 publications

References 102 publications

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

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

Electrification of Experimental Volcanic Jets with Varying Water Content and Temperature

Inferring Compressible Fluid Dynamics From Vent Discharges During Volcanic Eruptions

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