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A geomagnetic total intensity anomaly originated from lightning-induced isothermal remanent magnetization: case of the Yatsugatake Magnetic Observatory, central Japan


Magnetic total intensity anomaly maps of the Yatsugatake Magnetic Observatory, central Japan, in 1975, 1982 and 2005 are examined. The magnetic environment seems to be stable during this period except for the appearance of an anomalous thin patch-pair in the middle part of the observatory sometime between 1975 and 1982. The peak-to-peak amplitude of the patch-pair is about 80 nT at 2 m above ground level. The magnetization induced by the horizontal electric current in the ground due to the lightning which hit the observatory area in July 1981 is a probable cause for the patch-pair. Modeling confirmed that the characteristics of the patch-pair are well reproduced by model magnetizations that represent lightning-induced isothermal remanent magnetization acquired from horizontal lightning electric current in the ground. The required maximum magnetization to explain the peak-to-peak amplitude of the patch-pair is estimated to be in the range of 10 to 40 A/m.


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Correspondence to Hisayoshi Shimizu.

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Shimizu, H., Koyama, T., Koyama, S. et al. A geomagnetic total intensity anomaly originated from lightning-induced isothermal remanent magnetization: case of the Yatsugatake Magnetic Observatory, central Japan. Earth Planet Sp 59, 141–149 (2007).

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Key words

  • Magnetic anomaly map
  • lightning-induced isothermal remanent magnetization
  • magnetic environment
  • total intensity