Details of the abstract
| Title of paper | Global induction response to 11 year period and the conductivity of the lower mantle |
| List of authors | Constable, S., Constable, C., Korte, M., Morzfeld, M. |
| Affiliation(s) | Scripps Institution of Oceanography, Scripps Institution of Oceanography, Deutsches GeoForschungsZentrum, Scripps Institution of Oceanography |
| Summary |
The electromagnetic response of Earth at periods longer than one year remains challenging. We adopt a simple approach to extracting the external P_1^0 variations and their inductive response from 117 years of hourly geomagnetic data from 192 observatories. Observatories were selected to be within 65° of the geomagnetic equator, baseline corrections were made, and the time varying IGRF was removed from the data, which were rotated into geomagnetic coordinates year by year to allow for migration of the geomagnetic pole. Data were processed year by year by fitting hourly estimates of the internal and external coefficients of a P_1^0 field to the set of observatories that had no missing data for that year, using one month overlaps between years to remove the small bias from year to year fits. Observatory years with excessive misfit were iteratively removed from the processing. Multi-taper spectral analysis and band averaging was used to estimate the power spectra and transfer functions between the two time series. A clear peak at the 11-year solar cycle appears in the external field spectrum, with a smaller but discernible peak at the first harmonic of 5.5 years, with associated peaks in the coherency spectrum. Error bars on complex admittance were estimated from the statistics of the cross-spectrum and a parametric bootstrap. The data can be fit to RMS 1.0 with a smooth Occam inversion model. A Bayesian inversion approach was also used, generating 10,000 models that fit acceptably well. A conductive core is seen in the models and is required by the data. The well-documented jump in conductivity between the upper and lower mantle is clearly seen, and a second jump in conductivity occurs at depth of 1,800 km. |
| Session Keyword | 7.0 Global and Planetary Studies |
| File upload |
7.0_global_induction_response_constable.pdf
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