Mapping geoelectric fields during magnetic storms: Synthetic analysis of empirical United States impedances

Geophysical Research Letters
By:  and 



Empirical impedance tensors obtained from EarthScope magnetotelluric data at sites distributed across the midwestern United States are used to examine the feasibility of mapping magnetic storm induction of geoelectric fields. With these tensors, in order to isolate the effects of Earth conductivity structure, we perform a synthetic analysis—calculating geoelectric field variations induced by a geomagnetic field that is geographically uniform but varying sinusoidally with a chosen set of oscillation frequencies that are characteristic of magnetic storm variations. For north-south oriented geomagnetic oscillations at a period of T0=100 s, induced geoelectric field vectors show substantial geographically distributed differences in amplitude (approximately a factor of 100), direction (up to 130), and phase (over a quarter wavelength). These differences are the result of three-dimensional Earth conductivity structure, and they highlight a shortcoming of one-dimensional conductivity models (and other synthetic models not derived from direct geophysical measurement) that are used in the evaluation of storm time geoelectric hazards for the electric power grid industry. A hypothetical extremely intense magnetic storm having 500 nT amplitude at T0=100 s would induce geoelectric fields with an average amplitude across the midwestern United States of about 2.71 V/km, but with a representative site-to-site range of 0.15 V/km to 16.77 V/km. Significant improvement in the evaluation of such hazards will require detailed knowledge of the Earth's interior three-dimensional conductivity structure.


Publication type Article
Publication Subtype Journal Article
Title Mapping geoelectric fields during magnetic storms: Synthetic analysis of empirical United States impedances
Series title Geophysical Research Letters
DOI 10.1002/2015GL066636
Volume 42
Issue 23
Year Published 2015
Language English
Publisher American Geophysical Union
Contributing office(s) Geologic Hazards Science Center
Description 11 p.
First page 10160
Last page 10170
Online Only (Y/N) N
Additional Online Files (Y/N) N
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