doi:10.1016/j.pepi.2003.07.013
Copyright © 2003 Elsevier B.V. All rights reserved.
Continuous global geomagnetic field models for the past 3000 years
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Monika Korte
, a, b and Catherine Constable, b
a GeoForschungsZentrum Potsdam, Telegrafenberg, 14473, Potsdam, Germany
b Institute for Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0225, USA
Accepted 11 July 2003. ;
Available online 4 November 2003.
Abstract
Several global geomagnetic field models exist for recent decades, but due to limited data availability models for several centuries to millennia are rare. We present a continuous spherical harmonic model for almost 3 millennia from 1000 
to 1800 
, based on a dataset of directional archaeo- and paleomagnetic data and axial dipole constraints. The model, named Continuous Archaeomagnetic and Lake Sediment Geomagnetic Model for the last 3k years (CALS3K.1), can be used to predict both the field and secular variation. Comparisons and tests with synthetic data lead to the conclusion that CALS3K.1 gives a good general, large-scale representation of the geomagnetic field, but lacks small-scale structure due to the limited resolution of the sparse dataset. In future applications the model can be used for comparisons with additional, new data for that time span. For better resolved regions, the agreement of data with CALS3K.1 will provide an idea about the general compatibility of the data with the field and secular variation in that region of the world. For poorly covered regions and time intervals we hope to iteratively improve the model by comparisons with and inclusion of new data. Animations and additional snapshot plots of model predictions as well as the model coefficients and a FORTRAN code to evaluate them for any time can be accessed under http://www.mahi.ucsd.edu/cathy/Holocene/holocene.html. The whole package is also stored in the Earthref digital archive at http://www.earthref.org/…
Author Keywords: Geomagnetic field modelling; Secular variation; Archaeomagnetism; Paleomagnetism; Geodynamo
Fig. 1. PSVMOD1.0 sites. Dots have lake sediment data, diamonds archaeomagnetic. Archaeomagnetic site AUS and Lake Keilambete (KEI) in southern Australia are closely adjacent.
Fig. 2. GUFM [
Jackson et al. , 2000] (a) and model from GUFM predictions at the 24 sites of
Fig. 1 with normally distributed errors added (b). Radial component
Br and non-axial-dipole contribution
BrNAD at the CMB; inclination anomaly and declination at the Earth’s surface with equal colour scheme.
Fig. 3. Inclination data (thin black line) and model predictions (thick grey line) for Hawaii. Models with RMS-misfit (a) 1.61, (b) 1.30 and (c) 0.99.
Fig. 4. Inclination (a) and declination (b) data (black) and model predictions (grey) for site WUR. Model with RMS misfit 1.30.
Fig. 5. Comparison of different geomagnetic field models for epoch 1800 Radial component
Br and non-axial-dipole part B
rNAD of radial component at the CMB, inclination anomaly and declination at the Earth’s surface. (a) Snapshot model of [
Constable et al. , 2000], (b) continuous model with normalised RMS misfit of 1.30, (c) continuous model with misfit 0.99, (d) GUFM [
Jackson et al. , 2000].
Fig. 6. Dipole coefficients of continuous model with misfit 1.30. For the axial dipole coefficient the dots are the preset values of the modelling constraint at the knotpoints of the spline basis.
Fig. 7. Snapshots from the continuous model CALS3K.1. Columns show (1)
Br and (2)
BrNAD at the CMB, (3) inclination anomaly and (4) declination at the Earth’s surface. Unequal time intervals were chosen to highlight some of the features described in the text. Inclination anomaly and declination have the same colour scale.Small black dots are the actual data sites available for each 100 year interval.
Fig. 8. Averages for
Br and
BrNAD at the CMB and declination and inclination anomaly at the Earth’s surface.
Fig. 9. Snapshots of secular variation of the radial component at the CMB for the same epochs as shown in
Fig. 7. The
Br plots from that figure are repeated on the right for comparison.
Fig. 10. Comparison of secular variation from CALS3K.1 (left) and GUFM (right) for three epochs. GUFM shows significantly more small-scale structure.
Fig. 11. Power spectra of 100 year averages of secular variation at the CMB. Examples from early and recent time intervals of the GUFM and CALS3K.1 models.
Fig. 12. Averaged secular variation for the time intervals 500 –0 (a), 1300 –1800 (b) and the whole 3 millennia (c). Radial component , non-axial-dipole radial component and non-dipole component at the CMB.
Table 1. Normalised RMS misfit between 100-year data and different models
Table 2. Parmaters and norms of three models with different rms-misfits
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