Summary
GlobalEM-2015-02×02 is a global 3D inverse model of electrical conductivity of the Earth’s mantle based on global ground geomagnetic observatory data from the INTERMAGNET network, obtained using the global electromagnetic inversion technique of Kelbert, Egbert and Schultz (2008) as implemented within the ModEM code (Kelbert et al, 2014). Uses a 2×2 degree grid and a degree and order 40 spherical harmonics parameterization at a discrete set of layers with layer boundaries (km) [12.65 40 250 410 520 670 900 1200 1600 2000 2400 2900 3500]. This model is a successor to GlobalEM-2009-10×10 that provides substantially higher resolution and fits a much larger and better quality data set.
Quicklinks
Description
| Name | GlobalEM-2015-02×02 |
| Title | High resolution global electrical conductivity variations in the Earth’s mantle based on ground observatory data |
| Type | 3-D Electrical Conductivity Model |
| Sub Type | Global |
| Units | Siemens/meter |
| Year | 2015 |
| Short Description | This global electrical conductivity model represents a significant improvement over Kelbert, Schultz and Egbert (2009) in data quality and quantity, source approximation, resolution and period range. It is based on an NLCG inversion (Kelbert, Egbert and Schultz, 2008; Egbert and Kelbert, 2012) of three complex magnetic field components at 207 ground observatory locations. The modern observatories minute values (obtained from INTERMAGNET (www.intermagnet.org), and other sources) were averaged to hourly means; for older data hourly means archived at the National Geophysical Data Center (NGDC) were used. Data were processed using a variant of Smirnov and Egbert (2012) PCA analysis. Source approximation was estimated in quasi-dipole coordinates as described in Sun, Kelbert and Egbert (2015), published in GJR. Sources were created for the 13 periods in the range 1.2 – 102 days using LOOCV best fit. All 13 periods were inverted with a degree 40 spherical harmonic expansion in 9 layers defined by 12.65, 40, 250, 410, 520, 670, 900, 1200, 1600 and 2000 km depths. Three more layers extending to 2400, 2900 and 3500 km used degree and order 3 spherical harmonics. Thinshell was fixed at 0-12.65 km and used Manoj et al (2006) conductance. The parametrization log_l40_crust_tan_l40.prm smoothed both vertically with parameter 0.8 and horizontally with parameters 0.2 at depths 12.65-670, 0.5 at 670-900 and 1.0 at 900-3500. The prior qdsol22_1d_with_crust_pr.prm was obtained using a quick Monte-Carlo 1D + thinsheet inversion in Matlab and used the following 1D structure (in log(10) resistivity): [2.2517 2.2517 2.0192 1.5825 1.1104 1.1104 0.2790 -0.2281 -0.2281 -0.2281 -0.2281 -1 -2]. Initial RMS for the chosen prior, source model and the thinsheet heterogeneities is 2.63. The 3D model improves the data fit to the RMS of 1.71. |
| Authors: | |
| J. Sun | |
| College of Earth, Ocean and Atmospheric Sciences | |
| Oregon State University | |
| Corvallis, Oregon 97331, USA | |
| A. Kelbert | |
| Geomagnetism Program | |
| U.S. Geological Survey | |
| Golden, CO 80401, USA | |
| G. D. Egbert | |
| College of Earth, Ocean and Atmospheric Sciences | |
| Oregon State University | |
| Corvallis, Oregon 97331, USA | |
| Previous Model | GlobalEM-2009-10×10 |
| Reference Model | |
| Prior Model | |
| Inversion Software | ModEM (Egbert & Kelbert 2012; Kelbert et al, 2014) |
| Model Download | GlobalEM-2015-02×02.nc (see metadata), is the netCDF file for the model |
| Model Homepage | |
| Depth Coverage | 0 to 3500 km (can be considered adequately well resolved 250 to 1600 km) |
| Area | latitude: -89° to 89°, longitude: 0° to 360° |
| Data Set Description | Obtained from Egbert220_log_l40_crust_tan_l40_2×2_loocv_selected2_NLCG_046.rho |
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Citations and DOIs
To cite the original work behind this Earth model:
- Sun, J., Kelbert, A. and Egbert, G.D., 2015. Ionospheric current source modeling and global geomagnetic induction using ground geomagnetic observatory data. Journal of Geophysical Research: Solid Earth, 120(10), pp.6771-6796. https://doi.org/10.1002/2015JB012063.
To cite IRIS DMC Data Products effort:
- Trabant, C., A. R. Hutko, M. Bahavar, R. Karstens, T. Ahern, and R. Aster (2012), Data Products at the IRIS DMC: Stepping Stones for Research and Other Applications, Seismological Research Letters, 83(5), 846–854, https://doi.org/10.1785/0220120032.
DOI for this EMC webpage
https://doi.org/10.17611/DP/GLOBALEM201502X02
References:
- Egbert, G.D. and Kelbert, A., 2012. Computational recipes for electromagnetic inverse problems. Geophysical Journal International, 189(1), pp.251-267. https://doi.org/10.1111/j.1365-246X.2011.05347.x.
- Kelbert, A., Egbert, G.D. and Schultz, A., 2008. Non-linear conjugate gradient inversion for global EM induction: resolution studies. Geophysical Journal International, 173(2), pp.365-381.
- Kelbert, A., Meqbel, N., Egbert, G.D. and Tandon, K., 2014. ModEM: A modular system for inversion of electromagnetic geophysical data. Computers & Geosciences, 66, pp.40-53.
- Smirnov, M.Y. and Egbert, G.D., 2012. Robust principal component analysis of electromagnetic arrays with missing data. Geophysical Journal International, 190(3), pp.1423-1438.
Credits
- Anna Kelbert
Timeline
- 2019-05-14
- online
