The meeting started at 7.25 pm, following the WG 9 meeting (Anomalies). Chair  Mioara Mandea, cochair  Susan Macmillan (minutes).
1. Achievements since IAGA 2001 (Hanoi)
Meetings: European Repeat Station Workshop, Niemegk, Feb 2003 (organised by Monika
Korte and Mioara Mandea), joint work and involvement with other bodies (SEDI, COSPAR), and other individual contributions to SEDI (
California, July 2002), Ĝrsted International Science Team Meeting (Copenhagen, Sept 2002), First CHAMP Science Meeting (GFZ, Jan 2002).
Publications: Physics of the Earth and Planetary Interiors (Elsevier)  special issue on
Magnetic Field Modelling based on contributions to the IAGA session at IAGA/IASPEI 2001 (Hanoi)
– "Main Magnetic Field and Secular Variations at Earth's Surface and Core–Mantle Boundary".
Editors were Richard Holme and Mioara Mandea and there were five published papers.
2. Data collection
The meeting thanked the Ĝrsted team, the CHAMP team and the organisations around the world
involved in operating geomagnetic observatories, repeat station networks and other magnetic
surveys, for disseminating their data to the wider scientific community. Without these data
global models of the Earth’s magnetic field could not be determined.
3. Determination of 9th generation IGRF
It was agreed at IAGA 2001 to revise the IGRF series of models at IUGG2003, with DGRF1995
(max degree 10, 1 nT/year numerical precision) and DGRF2000 (max degree 13, 0.1 nT/year
numerical precision) mainfield coefficients and secularvariation coefficients for 2000.02005.
0 (max degree 8, 0.1 nT/year numerical precision). Candidate sets of coefficients were called
for in autumn 2002, reminders sent out early 2003 and deadline for submission midMarch 2003.
Some doubts were expressed in the runup to and at this meeting about the Hanoi decision to
have an IGRF revision in 2003. Three options were presented.
 Determine DGRF1995 and DGRF2000 coefficients, but do not publish them until we publish
IGRF2005 and the predictive SV for 2005.02010.0 (presumably in Nov/Dec 2004).
 Determine and publish DGRF1995 and DGRF2000 coefficients but retain existing SV
coefficients for 2000.02005.0.
 Determine and publish DGRF1995, DGRF2000 and SV 2000.02005.0 coefficients.

New coefficients
The following models were evaluated.
ModelAbbreviation 
Authors (countries) 
DGRF1995BGS 
Thomson & Macmillan (UK) 
DGRF1995CM 
Olsen, Lowes, Sabaka (Denmark, UK, USA) 
DGRF1995GFZ 
Maus, Lühr, Rother, Mai, Mandea (Germany, France) 
DGRF1995GFZ2 
Wardinski & Holme (Germany, UK) 
DGRF1995IPGP 
Chambodut, Langlais, Mandea (France, USA) 
DGRF1995IZM 
Bondar & Golovkov (Russia) 
DGRF2000BGS 
Lesur, Thomson & Macmillan (UK) 
DGRF2000CM 
Olsen, Lowes, Sabaka (Denmark, UK, USA) 
DGRF2000OSVM 
Olsen, Lowes, Sabaka (Denmark, UK, USA) 
DGRF2000GFZ 
Maus, Lühr, Rother, Mai, Mandea (Germany, France) 
DGRF2000IPGP 
Chambodut, Langlais, Mandea (France, USA) 
SVBGS 
Lesur, Thomson & Macmillan (UK) 
SVCM 
Olsen, Lowes, Sabaka (Denmark, UK, USA) 
SV–OSVM 
Olsen, Lowes, Sabaka (Denmark, UK, USA) 
SV–GFZ 
Maus, Lühr, Rother, Mai, Mandea (Germany, France) 
SV–IPGP 
Chambodut, Langlais, Mandea (France, USA) 
SV–IZM 
Bondar & Golovkov (Russia) 
SV–IZM2 
Bondar & Golovkov (Russia) 
Evaluations of the models were presented by Frank Lowes, Susan Macmillan and Stefan Maus
(SV only). For each model mean root mean square values of differences in F with all other
models (for particular epoch) at Earth’s spherical surface were computed. Range of these
values for DGRF1995 was 45–63 nT, for DGRF2000 8–10 nT and SV
7–14 nT/year. Discussions and votes were taken whether to take straight means, weighted
means of candidate models and whether to discard particular models. It was decided for DGRF1995
and DGRF2000 to take a straight mean of coefficients and for SV, to discard IZM, ask Olsen,
Lowes, Sabaka to resubmit their coefficients using the correct date and, providing these
revised CM coefficients were satisfactory, take a straight mean of the 6 sets of coefficients.
4. 10th generation IGRF — task force
As the next generation of the IGRF would be required by December 2004, before the next
meeting of IAGA, a Task Force was established to determine the 10^{th} generation IGRF.
Members are Stefan Maus (who subsequently agreed to be leader), Susan Macmillan, Frank Lowes,
Benoit Langlais, Terry Sabaka, Nils Olsen, Susan McLean
5. Change of spheroid from IAU66 to WGS84
The International Astronomical Union 1966 spheroid has been recommended for coordinate
transformations when using the IGRF till now. The parameters of IAU66 are a=6378.160 km,
b=6356.775 km, r=6371.024 km (^{3}√(a^{2}b)) – not 6371.2 km
which is commonly assumed! However the World Geodetic System 1984 datum and spheroid are more
widely recognised as a standard (a=6378.137 km, b=6356.752 km, r=6371.001 km). Presentday
satellite magnetic data are mostly positioned in WGS84 but for other data we are blissfully
unaware which datum is used. Differences in output IGRF magnetic field values at the Earth’s
surface are less than 1 nT when the change of spheroid is made. It is recognised that software
already in circulation uses WGS84. It is therefore recommended that the WGS84 spheroid is used
for coordinate transformations for the IGRF.
However, because the models were derived using the reference radius of 6371.2 km this
must be kept in the forward code used to compute values from the models.
6. IAGA guides – on mainfield modelling
Consideration was given as to whether an IAGA guide on mainfield modelling, similar to
those for observatories and repeat station surveys, would be useful. However the general
consensus was that a guide was not necessary at the moment as the community was small,
everyone already knew what other teams were doing, techniques for selecting data and removing
the rapidly varying external fields were highly dependent on datasets available, and there
were already existing publications which give the latest information about the various
modelling techniques (eg special issues of journals).
7. Symposia for Toulouse and IAGA Resolutions
Preliminary suggestions for symposia titles, convenors, and resolutions were made and
passed onto the Division V chair for further discussion at the Business Meeting.
8. New Div. V WG structure and officers
The proposed restructuring of the Working Groups in Div. V was discussed. The meeting was
generally in agreement that the restructuring should go ahead, with appropriate Task Forces
set up to address particular issues, though concerns were raised as to which Working Group
the Task Force "World Magnetic Anomaly Map" (Korhonen, Reeves, Ravat, Maus) should report.
It was subsequently decided that the Modelling Working Group was the natural "home" for this
Task Force, given the current status of this project. Similarly, the Task Force "External
Field Variations" (Thomson, Stauning) would report to the Modelling Working Group.
It was agreed that the new chair would be Susan Macmillan (UK) and the cochair would
Stefan Maus (Germany). The meeting finished at 9.25 pm.
