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Mapping geoelectric fields during magnetic storms: Synthetic analysis of empirical United States impedances
Author(s) -
Bedrosian Paul A.,
Love Jeffrey J.
Publication year - 2015
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2015gl066636
Subject(s) - geomagnetic storm , geophysics , magnetotellurics , amplitude , storm , geology , earth's magnetic field , geomagnetically induced current , magnetic field , seismology , geodesy , electrical resistivity and conductivity , physics , oceanography , quantum mechanics
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 T 0 =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 T 0 =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.