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Spectral and spatial decomposition of lithospheric magnetic field models using spherical Slepian functions

Author(s): Beggan, Ciarán D; Saarimäki, Jarno; Whaler, Kathryn A; Simons, Frederik J

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Abstract: Global magnetic field models are typically expressed as spherical-harmonic expansion coefficients. Slepian functions are linear combinations of spherical harmonics that produce new basis functions, which vanish approximately outside chosen geographical boundaries but also remain orthogonal within the spatial region of interest. Hence, they are suitable for decomposing spherical-harmonic models into portions that have significant magnetic field strength only in selected areas. Slepian functions are spatio-spectrally concentrated, balancing spatial bias and spectral leakage. Here, we employ them as a basis to decompose the global lithospheric magnetic field model MF7 up to degree and order 72, into two distinct regions. One of the resultant fields is concentrated within the ensemble of continental domains, and the other is localized over its complement, the oceans. Our procedure neatly divides the spectral power at each harmonic degree into two parts. The field over the continents dominates the overall crustal magnetic field, and each region has a distinct power-spectral signature. The oceanic power spectrum is approximately flat, while that of the continental region shows increasing power as the spherical-harmonic degree increases. We provide a further breakdown of the field into smaller, non-overlapping continental and oceanic regions, and speculate on the source of the variability in their spectral signatures.
Publication Date: 15-Feb-2013
Citation: Beggan, Ciarán D., Jarno Saarimäki, Kathryn A. Whaler, and Frederik J. Simons. "Spectral and spatial decomposition of lithospheric magnetic field models using spherical Slepian functions." Geophysical Journal International 193, no. 1 (2013): 136-148. doi:10.1093/gji/ggs122.
DOI: doi:10.1093/gji/ggs122
ISSN: 0956-540X
EISSN: 1365-246X
Pages: 136 - 148
Type of Material: Journal Article
Journal/Proceeding Title: Geophysical Journal International
Version: Final published version. Article is made available in OAR by the publisher's permission or policy.

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