Remanent magnetization as a fossil of lightning current

Sakai, Hideo; Yonezawa, Kaname

doi:10.2183/pjab.78.1

Cited by 10 publications

(3 citation statements)

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“…These lightning-induced magnetic anomalies have posed problems for those attempting to survey regions for unexploded ordnance 22 or archaeological sites 23 , 24 . These previous studies have shown that CG strikes will impart a lightning-induced remanent magnetization (LIRM), which alters the natural remanent magnetization (NRM), and has been used in some studies to calculate characteristics (e.g., current, polarity) of the discharge 21 , 25 . Using current impulse experiments, one study 26 attributed changes in the magnetic properties of rocks to changes in mineralogy, where existing ferrimagnetic magnetite (Fe 3 O 4 ) transformed to antiferromagnetic hematite (α-Fe 2 O 3 ) through oxidation.…”

Section: Introductionmentioning

confidence: 99%

Effects of Lightning on the Magnetic Properties of Volcanic Ash

Genareau

Hong

Lee

et al. 2019

Sci Rep

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High-current impulse experiments were performed on volcanic ash samples to determine the magnetic effects that may result from the occurrence of volcanic lightning during explosive eruptions. Pseudo-ash was manufactured through milling and sieving of eruptive deposits with different bulk compositions and mineral contents. By comparing pre- and post-experimental samples, it was found that the saturation (i.e., maximum possible) magnetization increased, and coercivity (i.e., ability to withstand demagnetization) decreased. The increase in saturation magnetization was greater for compositionally evolved samples compared to more primitive samples subjected to equivalent currents. Changes in remanent (i.e., residual) magnetization do not correlate with composition, and show wide variability. Variations in magnetic properties were generally more significant when samples were subjected to higher peak currents as higher currents affect a greater proportion of the subjected sample. The electrons introduced by the current impulse cause reduction and devolatilization of the ash grains, changing their structural, mineralogical, and magnetic properties.

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Section: Introductionmentioning

confidence: 99%

Effects of Lightning on the Magnetic Properties of Volcanic Ash

Genareau

Hong

Lee

et al. 2019

Sci Rep

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“…While fulgurites (soils melted by lightning strikes) record magnetic fields associated with the lightning strike itself (> 1 T), through the process known as lightning-induced remanent magnetization (e.g. Sakai et al 1998;Sakai & Yonezawa 2002;Salminen et al 2013), it is not at all clear that the magnetic fields associated with solar nebula lightning currents can be maintained for the hours it took chondrules to cool. As such, chondrules melted by lightning probably would record the background magnetic field, but that is uncertain.…”

Section: Introductionmentioning

confidence: 99%

Magnetic Fields Recorded by Chondrules Formed in Nebular Shocks

Mai

Desch

Boley

et al. 2018

ApJ

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Recent laboratory efforts (Fu et al. 2014) have constrained the remanent magnetizations of chondrules and the magnetic field strengths at which the chondrules were exposed to as they cooled below their Curie points. An outstanding question is whether the inferred paleofields represent the background magnetic field of the solar nebula or were unique to the chondrule-forming environment. We investigate the amplification of the magnetic field above background values for two proposed chondrule formation mechanisms, large-scale nebular shocks and planetary bow shocks. Behind large-scale shocks, the magnetic field parallel to the shock front is amplified by factors ∼ 10 − 30, regardless of the magnetic diffusivity. Therefore, chondrules melted in these shocks probably recorded an amplified magnetic field. Behind planetary bow shocks, the field amplification is sensitive to the magnetic diffusivity. We compute the gas properties behind a bow shock around a 3000 km-radius planetary embryo, with and without atmospheres, using hydrodynamics models. We calculate the ionization state of the hot, shocked gas, including thermionic emission from dust, and thermal ionization of gas-phase potassium atoms, and the magnetic diffusivity due to Ohmic dissipation and ambipolar diffusion. We find that the diffusivity is sufficiently large that magnetic fields have already relaxed to background values in the shock downstream where chondrules acquire magnetizations, and that these locations are sufficiently far from the planetary embryos that chondrules should not have recorded a significant putative dynamo field generated on these bodies. We conclude that, if melted in planetary bow shocks, chondrules probably recorded the background nebular field.

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“…There have been reports of anomalous magnetization of rocks in volcanic terrains attributed to the effects of lightning (e.g., Matsuzaki and colleagues ); Sakai and colleagues examined lightning strokes on steel towers and in flat areas using the magnetic properties of ground surface materials . It was demonstrated that the lightning current polarity, current propagation into steel towers, and other characteristics can be investigated by using remanent magnetization.…”

Section: Introductionmentioning

confidence: 99%

Propagation of IG Current Underground Elucidated by Remanent Magnetization

Sakai

Nagata²,

Masugata

2013

Electrical Engineering Japan

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Summary In our previous studies, we showed that the remanent magnetization of materials could be used to analyze lightning currents at ground level. In this study, using an IG (Impulse Generator) current as a model of lightning, we used remanent magnetization to investigate the underground propagation of IG currents. For this purpose, we dug a square hole with a side length of 80 cm and a depth of 13 cm and placed in it magnetic samples prepared using sea sand. After injecting an IG current of 530 A underground, the magnetization of these samples was measured. The directional distribution of magnetization was successfully used to analyze the circular magnetic field induced by the IG current and its transit point. Then the underground path of the IG current was determined to a depth of 12 cm. The current path was inclined by approximately 9° from the vertical direction, which may be attributed to a ground conductor being located east of the experimental area. To relate the magnetization intensity and the distance from the IG current, an inverse square relation was applied outside the area close to the transit point of the current. From the results obtained in this study, we conclude that the method using the remanent magnetization is useful for elucidating the polarity, intensity, and path of both IG and lightning currents underground. Further, the method of using remanent magnetization as a record of lightning currents may contribute to the development of an effective earth conductor for limiting damage caused by lightning. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 185(4): 1–8, 2013; Published online in Wiley Online Library (http://wileyonlinelibrary.com). DOI 10.1002/eej.22484

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Remanent magnetization as a fossil of lightning current

Cited by 10 publications

References 0 publications

Effects of Lightning on the Magnetic Properties of Volcanic Ash

Effects of Lightning on the Magnetic Properties of Volcanic Ash

Magnetic Fields Recorded by Chondrules Formed in Nebular Shocks

Propagation of IG Current Underground Elucidated by Remanent Magnetization

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