TY - JOUR
T1 - Physical properties of volcanic lightning
T2 - Constraints from magnetotelluric and video observations at Sakurajima volcano, Japan
AU - Aizawa, Koki
AU - Cimarelli, Corrado
AU - Alatorre-Ibargüengoitia, Miguel A.
AU - Yokoo, Akihiko
AU - Dingwell, Donald B.
AU - Iguchi, Masato
N1 - Funding Information:
We are greatly indebted to land owners for the prolonged hosting of MT stations. We thank the Earthquake Research Institute of the University of Tokyo for the loan of two sets of MT apparatuses (KYODO-RIYO CODE 2013-F-07), and the staff of Sakurajima Volcano Observatory, Kyoto University, Japan, for valuable assistance during fieldwork. Bettina Scheu and Sebastian Mueller are acknowledged for their contribution to HS video observations. Constructive suggestions and comments from two anonymous reviewers and from the editor, Tamsin Mather, greatly improved the manuscript. Plume height data were obtained from the Japan Meteorological Agency (JMA). This work was supported by MEXT KAKENHI Grant Number 23740332 . CC and MA were supported by the AXA Research Fund “Risk from volcanic ash in the Earth System”. DBD acknowledges the support of ERC Advanced Grant No. 247076 : (EVOKES – Explosive Volcanism in the Earth System).
Publisher Copyright:
© 2016 The Authors.
PY - 2016/6/15
Y1 - 2016/6/15
N2 - The lightning generated by explosive volcanic eruptions is of interest not only as a promising technique for monitoring volcanic activity, but also for its broader implications and possible role in the origin of life on Earth, and its impact on the atmosphere and biosphere of the planet. However, at present the genetic mechanisms and physical properties of volcanic lightning remain poorly understood, as compared to our understanding of thundercloud lightning. Here, we present joint magnetotelluric (MT) data and video imagery that were used to investigate the physical properties of electrical discharges generated during explosive activity at Sakurajima volcano, Japan, and we compare these data with the characteristics of thundercloud lightning. Using two weeks of high-sensitivity, high-sample-rate MT data recorded in 2013, we detected weak electromagnetic signals radiated by volcanic lightning close to the crater. By carefully inspecting all MT waveforms that synchronized with visible flashes, and comparing with high-speed (3000 frame/s) and normal-speed (30 frame/s) videos, we identified two types of discharges. The first type consists of impulses (Type A) and is interpreted as cloud-to-ground (CG) lightning. The second type is characterized by weak electromagnetic variations with multiple peaks (Type B), and is interpreted as intra-cloud (IC) lightning. In addition, we observed a hybrid MT event wherein a continuous weak current accompanied Type A discharge. The observed features of volcanic lightning are similar to thunderstorm lightning, and the physical characteristics show that volcanic lightning can be treated as a miniature version of thunderstorm lightning in many respects. The overall duration, length, inter-stroke interval, peak current, and charge transfer all exhibit values 1-2 orders of magnitude smaller than those of thunderstorm lightning, thus suggesting a scaling relation between volcanic and thunderstorm lightning parameters that is independent of the type of charged particles. On the other hand, the polarities, which are estimated by long-time (3.4 yrs) MT (32 samples/s) and video (30 frame/s) observations, are different than those of normal thunderstorm lightning. These observations are consistent with the notion that charge structures in volcanic ash plumes are highly disordered and are characterized by numerous small charged regions with high charge density.
AB - The lightning generated by explosive volcanic eruptions is of interest not only as a promising technique for monitoring volcanic activity, but also for its broader implications and possible role in the origin of life on Earth, and its impact on the atmosphere and biosphere of the planet. However, at present the genetic mechanisms and physical properties of volcanic lightning remain poorly understood, as compared to our understanding of thundercloud lightning. Here, we present joint magnetotelluric (MT) data and video imagery that were used to investigate the physical properties of electrical discharges generated during explosive activity at Sakurajima volcano, Japan, and we compare these data with the characteristics of thundercloud lightning. Using two weeks of high-sensitivity, high-sample-rate MT data recorded in 2013, we detected weak electromagnetic signals radiated by volcanic lightning close to the crater. By carefully inspecting all MT waveforms that synchronized with visible flashes, and comparing with high-speed (3000 frame/s) and normal-speed (30 frame/s) videos, we identified two types of discharges. The first type consists of impulses (Type A) and is interpreted as cloud-to-ground (CG) lightning. The second type is characterized by weak electromagnetic variations with multiple peaks (Type B), and is interpreted as intra-cloud (IC) lightning. In addition, we observed a hybrid MT event wherein a continuous weak current accompanied Type A discharge. The observed features of volcanic lightning are similar to thunderstorm lightning, and the physical characteristics show that volcanic lightning can be treated as a miniature version of thunderstorm lightning in many respects. The overall duration, length, inter-stroke interval, peak current, and charge transfer all exhibit values 1-2 orders of magnitude smaller than those of thunderstorm lightning, thus suggesting a scaling relation between volcanic and thunderstorm lightning parameters that is independent of the type of charged particles. On the other hand, the polarities, which are estimated by long-time (3.4 yrs) MT (32 samples/s) and video (30 frame/s) observations, are different than those of normal thunderstorm lightning. These observations are consistent with the notion that charge structures in volcanic ash plumes are highly disordered and are characterized by numerous small charged regions with high charge density.
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U2 - 10.1016/j.epsl.2016.03.024
DO - 10.1016/j.epsl.2016.03.024
M3 - Article
AN - SCOPUS:84962439227
VL - 444
SP - 45
EP - 55
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
SN - 0012-821X
ER -