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| Titel |
New transfer functions for probing 3-D mantle conductivity from ground and sea |
| VerfasserIn |
Christoph Püthe, Alexey Kuvshinov, Nils Olsen |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250097514
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| Publikation (Nr.) |
 EGU/EGU2014-13106.pdf |
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| Zusammenfassung |
| The C-response is a conventional transfer function in global electromagnetic induction
research and is classically determined from local observations of magnetic variations in the
vertical and the horizontal components. Its estimation and interpretation rely on the
assumptions that the source of the considered variations is well approximated by a
large-scale symmetric (magnetospheric) ring current that can be described by a single
spherical harmonic, P10, and that conductivity in the Earth is only a function of
depth.
However, there is growing evidence for a more complex structure of the magnetospheric
source. We investigate the variability of C-responses due to non-P10 contributions to the
source. We show that this variability, which we denote as “source effect” (as opposed to the
well-known ocean effect), is significant and persists at all periods. If inverting estimated
C-responses for mantle conductivity, this source effect will inevitably be mistaken for
conductivity anomalies.
To overcome the problem connected with the assumptions for deriving C-responses, we
introduce new transfer functions that relate the local vertical component of the magnetic
variation to different spherical harmonic coefficients describing the magnetospheric source.
The latter are derived from observations of magnetic variations in the horizontal components.
The new transfer functions are subsequently estimated with a robust multivariate data
analysis tool.
By analyzing 16 years of data, collected at the global network of geomagnetic
observatories, we demonstrate that the new transfer functions exhibit a significant increase in
coherence compared to C-responses, especially at high latitudes. The concept is easily
extended to other data types. For example, by relating the voltage variations in
abandoned submarine telecommunication cables to spherical harmonic coefficients
in the same way as described above, one can define yet another array of transfer
functions.
In spite of the fact that the newly introduced transfer functions allow for a consistent
treatment of a complex spatial structure of the source, the sparse and irregular distribution of
geomagnetic observatories and submarine cables impedes a reliable inversion of these data
for 3-D mantle conductivity on a global scale. However, in combination with matrix
Q-responses estimated from Swarm satellite data, the new transfer functions can be used to
probe the 3-D conductivity structure of Earth’s mantle. |
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