Towards probing Earth’s upper mantle with daily magnetic field variations: exploring a physics-based parametrization of the source

Open access
Date
2021Type
- Journal Article
Abstract
The electromagnetic (EM) field variations capable of probing the electrical conductivity of the upper mantle and mantle transition zone have a period range between a few hours and 1 day. At these periods, the dominant source of the EM signals is the ionospheric current system, which has a complex spatial and temporal structure. A concept of global-to-local (G2L) transfer functions can handle spatially complex source by relating global source expansion coefficients with locally measured magnetic (or/and electric) fields. When estimating the G2L transfer functions, the source is commonly expanded into spherical harmonics (SH). In this paper, we explore an alternative parametrization of the source based on a principal component analysis (PCA) of the Fourier transformed output from the physics-based Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE-GCM). Specifically, we investigate whether magnetic fields computed in the realistic three-dimensional conductivity model of Earth excited by the PCA-based source agree better with observatory data than those computed in the same model but induced by the SH-based source. Using PCA to capture the source current compared to SH parametrization, we find that agreement with the observatory data is better during magnetically disturbed times and at shorter periods. Vice versa, it is poorer during magnetically quiet times and at longer periods. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000492892Publication status
publishedExternal links
Journal / series
Earth, Planets and SpaceVolume
Pages / Article No.
Publisher
SpringerSubject
Electromagnetic induction; Ionospheric current systems; Magnetic field variations; Principal component analysisOrganisational unit
03476 - Giardini, Domenico / Giardini, Domenico
03734 - Jackson, Andrew / Jackson, Andrew
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