GUFM1 FIELD MODEL AND FORMAT OF GAUSS COEFFICIENTS IN FILES
GENERAL INFORMATION
gufm1 is available for general use by the community.
When used, the following reference should be cited:
Four centuries of geomagnetic secular variation from historical records
Jackson, A., Jonkers, A. R. T. and Walker, M. R.
Phil. Trans. Roy. Soc. A (2000) Vol. 358, pp957-990
Some of the data and modelling procedures were also described in the
earlier papers:
Time-dependent mapping of the magnetic field at the core-mantle boundary
Bloxham, J. and Jackson, A.
Journal of Geophysical Research Vol. 97, B13, pp.19537-19563
Geomagnetic Secular Variation
Bloxham, J., Gubbins, D. and Jackson, A.
Phil. Trans. Roy. Soc. A (1989) Vol. 329 pp415-502
Animations of various field components derived from gufm1 at both the core
surface and the Earth's surface can be found at the webpage:
http://www.epm.geophys.ethz.ch/gufm1.html
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FORMAT OF FIELD MODEL FILES
The single epoch field models can be found online at
http://www.epm.geophys.ethz.ch/gufm1/model/****.00
where **** is the year of interest eg.1990.00 for 1990.
The file 'gufm1' contains the full time-dependent field model:
First Line: Header describing model
Followed by:
Spherical Harmonic Order of model, No. splines in model, Spline knot points in order
Followed by:
Schmidt-quasi normalised Gauss coeffients (units=nT) 4 per line in order eg.
g(t=1st_knot,l=1,m=0), g(t=1st_knot,l=1,m=1),h(t=1st_knot,l=1,m=1),g(l=2,m=0,t=t=1st_knot)...
so g, h are listed for each m (for m=0 no h), then for all l with such listings
made for each knot point in the time sequence.
Single epoch field models derived from the time-dependent model at each year
from 1590 to 1900 are also found in files eg. 1990.00. These have a similar
format:
1st line : header with information (mf=main field)
2nd line : l, -4= single epoch model, time of model in year
Then gauss coefficents in same order listing g, h for all m and for each l up to 14.
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eval_field.f
This fortran program originally written by Jeremy Bloxham can be used to
evaluate the time dependent field model gufm1 at the latitude, longitude,
altitude and time of interest. Instructions are given in the program's comments.
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