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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/angeo-2020-21
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/angeo-2020-21
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  22 Apr 2020

22 Apr 2020

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A revised version of this preprint was accepted for the journal ANGEO and is expected to appear here in due course.

Induced telluric currents play a major role in the interpretation of geomagnetic variations

Liisa Juusola1, Heikki Vanhamäki2, Ari Viljanen1, and Maxim Smirnov3 Liisa Juusola et al.
  • 1Finnish Meteorological Institute, Helsinki, Finland
  • 2University of Oulu, Oulu, Finland
  • 3Luleå University of Technology, Sweden

Abstract. Geomagnetically induced currents (GIC) are directly described by ground electric fields, but estimating them is time-consuming and requires knowledge of the ionospheric currents as well as the three-dimensional distribution of the electrical conductivity of the Earth. The time derivative of the horizontal component of the ground magnetic field (dH/dt) is closely related to the electric field via Faraday's law, and provides a convenient proxy for the GIC risk. However, forecasting dH/dt still remains a challenge. We use 25 years of 10 s data from the North European International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer network to show that part of this problem stems from the fact that instead of the primary ionospheric currents, the measured dH/dt is dominated by the signature from the secondary induced telluric currents nearly at all IMAGE stations. The largest effects due to telluric currents occur at coastal sites close to highly-conducting ocean water and close to near-surface conductivity anomalies. The secondary magnetic field contribution to the total field is a few tens of percent, in accordance with earlier studies. Our results have been derived using IMAGE data and are thus only valid for the involved stations. However, it is likely that the main principle also applies to other areas. Consequently, it is recommended that the field separation into internal (telluric) and external (ionospheric and magnetospheric) parts is performed whenever feasible, i.e., a dense observation network is available.

Liisa Juusola et al.

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Liisa Juusola et al.

Liisa Juusola et al.

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Latest update: 11 Aug 2020
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Short summary
Rapid variations of the magnetic field measured on the ground can be used to estimate space weather risks to power grids, but forecasting the variations remains a challenge. We show that part of this problem stems from the fact that in addition to electric currents in space, the magnetic field variations are strongly affected by underground electric currents. We suggest that separating the measured field into its space and underground parts could improve our understanding of space weather.
Rapid variations of the magnetic field measured on the ground can be used to estimate space...
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