Ionospheric current source modeling and global geomagnetic induction using ground geomagnetic observatory data

Journal of Geophysical Research
By: , and 

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Abstract

Long-period global-scale electromagnetic induction studies of deep Earth conductivity are based almost exclusively on magnetovariational methods and require accurate models of external source spatial structure. We describe approaches to inverting for both the external sources and three-dimensional (3-D) conductivity variations and apply these methods to long-period (T≥1.2 days) geomagnetic observatory data. Our scheme involves three steps: (1) Observatory data from 60 years (only partly overlapping and with many large gaps) are reduced and merged into dominant spatial modes using a scheme based on frequency domain principal components. (2) Resulting modes are inverted for corresponding external source spatial structure, using a simplified conductivity model with radial variations overlain by a two-dimensional thin sheet. The source inversion is regularized using a physically based source covariance, generated through superposition of correlated tilted zonal (quasi-dipole) current loops, representing ionospheric source complexity smoothed by Earth rotation. Free parameters in the source covariance model are tuned by a leave-one-out cross-validation scheme. (3) The estimated data modes are inverted for 3-D Earth conductivity, assuming the source excitation estimated in step 2. Together, these developments constitute key components in a practical scheme for simultaneous inversion of the catalogue of historical and modern observatory data for external source spatial structure and 3-D Earth conductivity.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Ionospheric current source modeling and global geomagnetic induction using ground geomagnetic observatory data
Series title Journal of Geophysical Research
DOI 10.1002/2015JB012063
Volume 120
Issue 10
Year Published 2015
Language English
Publisher American Geophysical Union
Contributing office(s) Geologic Hazards Science Center
Description 26 p.
First page 6771
Last page 6796