University of Oulu

Juusola, L., Vanhamäki, H., Viljanen, A., and Smirnov, M.: Induced currents due to 3D ground conductivity play a major role in the interpretation of geomagnetic variations, Ann. Geophys., 38, 983–998, https://doi.org/10.5194/angeo-38-983-2020, 2020.

Induced currents due to 3D ground conductivity play a major role in the interpretation of geomagnetic variations

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Author: Juusola, Liisa1; Vanhamäki, Heikki2; Viljanen, Ari1;
Organizations: 1Finnish Meteorological Institute, Helsinki, Finland
2Space Physics and Astronomy Research Unit, University of Oulu, Oulu, Finland
3Department of Civil, Environmental and Natural Resources Engineering, Luleå University of Technology, Luleå, Sweden
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 14.1 MB)
Persistent link: http://urn.fi/urn:nbn:fi-fe2020102287387
Language: English
Published: Copernicus Publications, 2020
Publish Date: 2020-10-22
Description:

Abstract

Geomagnetically induced currents (GICs) are directly described by ground electric fields, but estimating them is time-consuming and requires knowledge of the ionospheric currents and the three-dimensional (3D) 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 northern 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 at nearly all IMAGE stations. The largest effects due to telluric currents occur at coastal sites close to high-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 stations involved. 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).

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Series: Annales geophysicae
ISSN: 0992-7689
ISSN-E: 1432-0576
ISSN-L: 0992-7689
Volume: 38
Pages: 983 - 998
DOI: 10.5194/angeo-38-983-2020
OADOI: https://oadoi.org/10.5194/angeo-38-983-2020
Type of Publication: A1 Journal article – refereed
Field of Science: 1171 Geosciences
Subjects:
Funding: This research has been supported by the Academy of Finland, Luonnontieteiden ja Tekniikan Tutkimuksen Toimikunta (grant no. 314670).
Copyright information: © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License.
  https://creativecommons.org/licenses/by/4.0/